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A Caltech Library Repository Feedhttp://www.rssboard.org/rss-specificationpython-feedgenenTue, 16 Apr 2024 01:31:35 +0000Decay of Turbulence Behind Three Similar Grids
https://resolver.caltech.edu/CaltechETD:etd-04062006-141720
Authors: {'items': [{'id': 'Corrsin-Stanley', 'name': {'family': 'Corrsin', 'given': 'Stanley'}, 'show_email': 'NO'}]}
Year: 1942
DOI: 10.7907/GXRW-6609
u’ and v’ decay measurements were made behind three similar girds. The u’ readings were corrected for wire length and the v’ readings were corrected for the sensitivity of the v’-meter to u’. These corrected values were plotted against x/M on logarithmic cross-section paper. The slope of these lines gave the exponent in the theoretical law for the decay of isotropic turbulence.
A consistent deviation was found between the average u’ and v’ values. A suitable length correction applied to the v’ values would increase them somewhat, lessening the discrepancy, and giving a true comparison between the two components of the turbulent energy.
From a comparison of the present u’ values behind the 1” grid with the u’ values measured with a free stream turbulence level 10 times as great as the present one, it is concluded that the change in initial turbulence has no appreciable effect on the u’ behind a grid.https://thesis.library.caltech.edu/id/eprint/1279Technique of Measuring Transverse Components of Velocity Fluctuations in Turbulent Flow
https://resolver.caltech.edu/CaltechETD:etd-11242008-111753
Authors: {'items': [{'id': 'Zebb-George-Keirn', 'name': {'family': 'Zebb', 'given': 'George Keirn'}, 'show_email': 'NO'}]}
Year: 1943
DOI: 10.7907/H56H-BX29
<p>The mean speed characteristics of several X-type v'/U-meters having widely varied dimensions were measured in order to verify assumptions usually made regarding the range of linear characteristics for meters of this type.</p>
<p>Using the same meters, and other meters with intermediate sizes, values of v'/U were measured in the turbulent fields behind three grids. Comparison of the results gave a qualitative indication of the effect of meter size on turbulence measurements.</p>
<p>A length correction for the X-type meters used was derived and the turbulence values corrected, with the result that all meters gave approximately the same answers.</p>
<p>However, even after application of the length correction, it was found that in the turbulent field behind grids (generally assumed to be isotropic) v'/U was consistently lower than u'/U at a given distance behind the grid. This result is the same as that described by Corrsin in ref. (4) where no length correction was applied.</p>https://thesis.library.caltech.edu/id/eprint/4655An Investigation of Wind Tunnel Wall Effects at High Mach Numbers
https://resolver.caltech.edu/CaltechTHESIS:10162015-093151774
Authors: {'items': [{'id': 'Leydon-John-Koebig', 'name': {'family': 'Leydon', 'given': 'John Koebig'}, 'show_email': 'NO'}, {'id': 'Miller-Walter-Bernard', 'name': {'family': 'Miller', 'given': 'Walter Bernard'}, 'show_email': 'NO'}]}
Year: 1945
DOI: 10.7907/HNBB-CK44
<p>This paper presents the results of an investigation of
wind tunnel wall interference in a two-dimensional wind tunnel
at high Mach numbers. The results are presented in the form of
curves of lift coefficient versus the ratio of model chord to
tunnel height, as functions of Mach number and angle of attack.
The investigation was carried out by the authors at the
Guggenheim Aeronautical Laboratory of the California Institute
of Technology during the school year 1944-45.</p>
<p>Tests were carried out on the NACA low drag airfoil
section 65,1-012 at Mach numbers from .60 to .80, and angles of
attack of from 1 to 3 degrees. Models were 1", 2", 4" and 6"
chord, giving values of the chord to tunnel height ration of .1
to .6. Schlieren photographs were made of shock waves where they
occurred.</p>https://thesis.library.caltech.edu/id/eprint/9223The Effect of Dive Recovery Flaps on the Lift of a Two Dimensional Symmetrical Airfoil with Changes in Chordwise Location of the Flaps
https://resolver.caltech.edu/CaltechETD:etd-11262008-112929
Authors: {'items': [{'id': 'Weitzenfeld-Daniel-Kehr', 'name': {'family': 'Weitzenfeld', 'given': 'Daniel Kehr'}, 'show_email': 'NO'}, {'id': 'Trauger-Robert-James', 'name': {'family': 'Trauger', 'given': 'Robert James'}, 'show_email': 'NO'}, {'id': 'Kronmiller-George-Hannibal', 'name': {'family': 'Kronmiller', 'given': 'George Hannibal'}, 'show_email': 'NO'}]}
Year: 1946
DOI: 10.7907/CV3E-KC83
NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.
<p>It was desired in this investigation to determine the effect of the chordwise position of dive recovery flaps on the lift of a laminar flow, low drag, two-dimensional airfoil at high subsonic Mach numbers. Schlieren pictures were taken to relate the formation, extension and strength of shock waves to the measured lift. Tests were made on a four inch chord airfoil of section 65,1-012 at Mach numbers from .50 to .83, a Reynolds number of 1,600,000 at M[subscript o] = 0.7, angles of attack from 1 to 3 degrees, and flap locations at 15%, 30%, and 45% chord; the flap is 10% of the chord.</p>
<p>The investigation was carried out by the authors at the Guggenheim Aeronautical Laboratory of the California Institute of Technology during the school year 1945-1946.</p>
<p>It was concluded that dive recovery flaps materially increase the lift of an airfoil, and there is an optimum flap location for maximum lift and one for maximum […]. Moreover, it was concluded that the formation and development of shock waves is directly related to the lift, but that the successive development of the shock wave pattern as a function of Mach number is independent of angle of attack or flap location; the Mach number for initial shock formation varies. Finally, in this tunnel where the thickness of the boundary layer is a large percent of the tunnel width the correction for non-uniform spanwise lift distribution must be investigated more carefully before absolute lift values can be computed.</p>https://thesis.library.caltech.edu/id/eprint/4673An Investigation of the Effects of the Sudden Extension of a Dive-Recovery Flap on the Aerodynamic Characteristics of a Symmetrical Airfoil in Two Dimensional Flow
https://resolver.caltech.edu/CaltechETD:etd-12022008-102010
Authors: {'items': [{'id': 'Parker-James-Frederick', 'name': {'family': 'Parker', 'given': 'James Frederick'}, 'show_email': 'NO'}, {'id': 'Anderson-John-Berwick', 'name': {'family': 'Anderson', 'given': 'John Berwick'}, 'show_email': 'NO'}, {'id': 'Tunnell-Richard-McClellan', 'name': {'family': 'Tunnell', 'given': 'Richard McClellan'}, 'show_email': 'NO'}, {'id': 'Vincent-Harry-Lansing', 'name': {'family': 'Vincent', 'given': 'Harry Lansing'}, 'show_email': 'NO'}]}
Year: 1946
DOI: 10.7907/DJD3-KV06
<p>This report presents the results of an investigation of the aerodynamic characteristics of the NACA symmetrical laminar flow 65,1-012 airfoil. The model was tested with and without a dive recovery flap. The effects obtained by suddenly extending the flap are compared to those obtained with the flap set down in position. The tests cover a range of angle of attack from zero to plus three degrees while the Mach number was varied from 0.5 to 0.8.</p>
<p>The following conclusions were reached:<br />
1. The lift curve for the airfoil with no flap is essentially a straight line.<br />
2. A flap suddenly extended produces aerodynamic effects which are different from those produced by a flap which is set. Whenever model test results are to be used to produce design information to be incorporated in full scale aircraft, the dive recovery flaps on the model should be equivalent to those on the full scale airplane in regard to dimensional proportions and to the method and timing of operation, if a high degree of accuracy is desired.</p>
<p>This investigation was carried out by the authors at the Guggenheim Aeronautical Laboratory of the California Institute of Technology during the school year 1945-46.</p>https://thesis.library.caltech.edu/id/eprint/4723I. Extended Applications of the Hotwire Anemometer. II. Investigations of the Flow in Round, Turbulent Jets
https://resolver.caltech.edu/CaltechETD:etd-12092008-105044
Authors: {'items': [{'id': 'Corrsin-Stanley', 'name': {'family': 'Corrsin', 'given': 'Stanley'}, 'show_email': 'NO'}]}
Year: 1947
DOI: 10.7907/NB53-K411
Part 1:
Two new fields of application of the hot-wire anemometer are proposed, and the appropriate response equations and measuring procedures are developed.
The first analysis leads to a method for the measurement of physically significant statistical quantities in a turbulent flow with heat transfer: for example the turbulence levels, the temperature fluctuation level, the turbulent heat transfer coefficient, the velocity scale, the temperature scale and some spectra.
The second analysis involves the use of the hot-wire in the turbulent isothermal mixing of two appropriately different gases. If the thermal conductivity of the mixture is known and is a monotonic function of the relative concentration, it is possible to measure the mean velocity and mean concentration at any point. If no data are available on the thermal conductivity of the mixture, this additional unknown can be determined by an additional measurement. Furthermore, it is also possible to measure the various statistical functions of the fluctuating velocities and the local concentration fluctuation, provided, again, that the thermal conductivity is a known monotonic function of the concentration.
Although the details of the present analysis are dependent upon the accuracy of King's equation for the rate of heat loss from fine wires, the general approach is equally valid for any (possibly more accurate) equation that may be deduced.
Part 2:
A detailed investigation has been made of the flow in a round turbulent air jet, heated slightly to permit measurement of mean temperature.
Oscillograms of the velocity fluctuation plus direct measurement of the turbulent shear both show that the flow in a fully developed "turbulent" jet is completely turbulent only out to approximately the radius at which the extreme outer edge is in the nature of a "laminar collar", with predominantly radial (inward) mean velocity, and in between the turbulent core and the laminar collar is a rather wide annular transition region.
A study of the downstream history of the radial distribution of turbulent velocity shows that the fully developed state of this round jet is reached between 15 and 20 diameters. This conclusion is corroborated by examination of the partition between turbulent motion and mean motion, of total kinetic energy crossing planes perpendicular to the axis in unit time.
The directly measured shear distribution is checked roughly by a computation of the same quantity from the mean velocity distribution.
A measurement of the double correlation function between points symmetrical about the jet axis shows considerable similarity to the corresponding function in isotropic turbulence, and permits calculation of scale and microscale.
With the assumption of constant microscale across a section, a rough estimate is made of the energy balance distribution of production, dissipation and diffusion of turbulent energy.
A comparison with momentum transfer, modified vorticity transfer and constant exchange coefficient theories show that none of them is satisfactory.
A comparison of mean velocity and temperature distributions verifies Ruden's result that the lateral rate of heat transfer in turbulent shear flow is appreciably greater that the lateral rate of momentum transfer.
The use of considerably increased heating, in a second jet unit, has permitted direct measurement of the temperature fluctuation level. Velocity fluctuations were also measured in this case for comparison, and they were found to be the same order of magnitude.
The final result is the direct measurement of temperature-velocity correlation and of velocity correlation in the hot jet. This gives a direct measure of the turbulent heat transfer and momentum transfer in the jet, and directly verifies the fact that the former is appreciably greater than the latter.
https://thesis.library.caltech.edu/id/eprint/4912The Rotational Motion of an Ideal Fluid and Application to the Three-Dimensional Flow Through Axial Turbomachinery
https://resolver.caltech.edu/CaltechETD:etd-11122003-141530
Authors: {'items': [{'id': 'Marble-Frank-Earl', 'name': {'family': 'Marble', 'given': 'Frank Earl'}, 'show_email': 'NO'}]}
Year: 1947
DOI: 10.7907/CJJR-H730
The present paper discusses the principles and applications of an iteration method for solving certain problems involving rotational motion of an ideal fluid, such as occur in the presence of heat transfer, combustion, mechanical work processes, and non-uniform shock waves. The iteration process linearizes the essentially non-linear equations for rotational fluid motion by assuming a process for the vorticity transport, namely: the nth approximation is linearized by assuming the vorticity to be transported by the n-1th velocity field. In some important cases, the first order solutions seem to offer considerable accuracy.
Two applications of the procedure are discussed in some detail, namely: 1) The process of straightening a non-uniform flow in a two-dimensional parallel-wall channel by means of a screen and 2) The three-dimensional flow in a multistage axial turbomachine having an infinite number of blades in each blade row. The second of these, the three-dimensional flow through a turbomachine, is given detailed analysis bearing some analogy to the Prandtl theory of finite wings. The results for the first order solution of velocity and enthalpy distributions are given explicitly and are shown to be defined by four relatively simple integrals. The cases of rotating and stationary single blade rows are evaluated completely. The general iteration process for obtaining higher approximations, utilizing the method of Green's functions, is given in some detail.
The calculations of the flow field generated by a blade row of given geometry is illustrated by the problem of a "vortex" turbomachine operating off the design condition. The problem is found to be essentially non-linear in some respects, especially as to the approach to periodic solutions for a succession of similar stages.https://thesis.library.caltech.edu/id/eprint/4519On the Transonic Flow Past Thin Airfoils
https://resolver.caltech.edu/CaltechETD:etd-04202004-105048
Authors: {'items': [{'id': 'Cole-Julian-David', 'name': {'family': 'Cole', 'given': 'Julian David'}, 'show_email': 'NO'}]}
Year: 1947
DOI: 10.7907/7YQN-9C32
No Abstract Submittedhttps://thesis.library.caltech.edu/id/eprint/1419Investigation of Turbulent Flow in a Two-Dimensional Channel
https://resolver.caltech.edu/CaltechETD:etd-09152005-133021
Authors: {'items': [{'id': 'Laufer-John', 'name': {'family': 'Laufer', 'given': 'John'}, 'show_email': 'NO'}]}
Year: 1948
DOI: 10.7907/6ZYC-HJ88
NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.
<p>A detailed exploration of the field of mean and fluctuating quantities in a two-dimensional turbulent channel flow is presented. The measurements were repeated at three Reynolds numbers, 1.23 x 10⁵, 3.08 x 10⁵ and 6.16 x 10⁵, based on the half width of the channel and the maximum velocity. A channel of 5" width and 12:1 aspect ratio was used for the investigation.</p>
<p>Mean speed and axial fluctuation measurements were made well within the laminar sublayer. The semi-theoretical predictions concerning the extent of the laminar sublayer were confirmed. It was found that the viscosity has a more profound influence on the fluctuations than on the mean velocity, the region of influence being approximately four times as wide.</p>
<p>Fluctuations perpendicular to the flow direction v', w' and the correlation coefficient [...] were measured, and the turbulent shear distribution calculated. Shear calculations from independent methods using the measured velocity gradient at the wall and pressure gradient along the channel furnished a good check on the values of the shearing stress in all cases with the exception of the highest Reynolds number where Τ obtained from the fluctuation measurements is approximately 25% lower. All mean fluctuating quantities were found to decrease with increasing Reynolds number. Measurements of the scales Ly, Lz and micro-scales of turbulence λy, λz across the channel are presented and their variation with Reynolds number is discussed. Using a new technique, values for λx were obtained; a method for estimating Lx is also given.</p>
<p>The energy balance in the turbulent flow field was calculated from the measured quantities. From this calculation it is possible to give a descriptive picture of turbulent energy diffusion in the center portion of the channel cross-section.</p>https://thesis.library.caltech.edu/id/eprint/3549Some Problems Concerning the Rotational Motion of a Perfect Fluid
https://resolver.caltech.edu/CaltechETD:etd-11122003-104144
Authors: {'items': [{'id': 'Marble-Frank-Earl', 'name': {'family': 'Marble', 'given': 'Frank Earl'}, 'show_email': 'NO'}]}
Year: 1948
DOI: 10.7907/2JGF-0Z67
In an effort to obtain some understanding of the processes involved in the rotational motion of a perfect fluid several particular linearized examples of rotational flow are solved in detail. The first part discusses some types of boundary value problem which arise. The solution of the non-linear partial differential equation by a particular iteration process is considered and the process is shown to converge for an extended version of the problem when the vorticity distribution is sufficiently smooth. The first step of the iteration process may constitute a good approximation in these cases and is taken as the basis of linearized solutions studied in the remainder of the work.
The process of straightening a non-uniform velocity profile by means of an idealized screen is considered in Part II as a problem in rotational motion of an ideal fluid with the screen replaced by an appropriate non-conservative force field. The detailed solution is given for both the linearized problem and the second approximation, The complete second order correction is less than 6 percent of the local velocity given by the linear solution for a rather severe case, The corrections arising from the various physical processes involved are analyzed and found to exceed 6 percent in same cases but are inherently compensating.
The two-dimensional rotational flow about a closed body is obtained in Part III by utilizing the Green's function method of solving the inhomogeneous differential equation involved. The conformal transformation which maps the given contour into a circle is used to find the appropriate Green's function for the contour. Solutions are then written down for any body, the Riemann mapping function of which is known, The Blasius force and moment formula are extended to include the case of general rotational motion, the relations of Kuo appearing as special forms where the vorticity distribution is uniform.
In the final part the theory of the three-dimensional. flow through an axial turbomachine, associated with variation of circulation along the blade length, is described as an extension of the classical theory of finite wings and is simplified to a problem in axially symmetric rotational fluid motion by considering an infinite number of blades in each row. The linearized problem is solved for the radial, tangential, and axial velocity components induced by a single row of stationary or rotating blades with finite chord and prescribed loading. The particular case for which the blade chord approaches zero, and the tangential velocity changes discontinuously, is associated with the theory of the Prandtl lifting line for finite wings, The complete solution is given for a single stationary or rotating blade row of given loading with a hub/tip ratio of 0.6 and blade aspect ratio of 2. The corresponding discontinuous approximation is compared with the more nearly exact solution and is shown to constitute a useful approximation to the solution for a finite blade chord when the discontinuity is located appropriately. An exponential approximation for the velocity components, deduced from the analysis, allows rapid estimation of the rate at which the equilibrium velocity profiles develop ahead of and behind a blade row and, using the superposition principle, provides a simple means or approximating the velocity distribution in a multistage turbomachine and of discussing mutual interference of blade rows.https://thesis.library.caltech.edu/id/eprint/4518Base Pressure at Supersonic Velocities
https://resolver.caltech.edu/CaltechETD:etd-12122008-143236
Authors: {'items': [{'id': 'Chapman-Dean-Roden', 'name': {'family': 'Chapman', 'given': 'Dean Roden'}, 'show_email': 'NO'}]}
Year: 1948
DOI: 10.7907/F2ZC-4B47
The existing theories of base pressure are described in detail and are shown to be unsatisfactory. An "exact" analysis is then made of the base pressure in an inviscid fluid, both for two-dimensional and axially-symmetric flow. It is shown that for a given body there are, in general, an infinite number of possible solutions satisfying all necessary boundary conditions. For the particular case of inviscid flow about projectile-shaped bodies only one solution is possible, but it corresponds to zero base drag. This latter result is generalized and the following conjecture made: it is impossible for a steady axially-symmetric inviscid supersonic flow to converge toward, and to meet the axis at a finite (non-zero) angle.
Since the inviscid-fluid theory does not adequately describe the conditions in a real fluid, an approximate theory for base pressure in a viscous fluid is developed. This latter theory is based in part on the inviscid-flow calculations and in part on dimensional analysis. It includes the effects of Mach number, Reynolds number, body shape, and type of boundary-layer flow. A comparison of the theory with the available experimental data indicates satisfactory agreement.
It is shown that under certain conditions the airfoil contour for minimum profile drag in a viscous fluid necessarily has a blunt trailing edge. Approximate calculations indicate that very substantial reductions in profile drag are possible by designing airfoils with blunt trailing edges. Consideration is briefly given to the interference of a support rod on base pressure measurements in a supersonic wind tunnel.
https://thesis.library.caltech.edu/id/eprint/4979Higher Order Approximations for Transonic Flow Over Slender Bodies
https://resolver.caltech.edu/CaltechTHESIS:05252011-132758648
Authors: {'items': [{'id': 'Srinivasan-Natesan', 'name': {'family': 'Srinivasan', 'given': 'Natesan'}, 'show_email': 'NO'}]}
Year: 1948
DOI: 10.7907/8HMA-7V02
No abstract.https://thesis.library.caltech.edu/id/eprint/6436Investigations of Spontaneous Condensation Phenomena
https://resolver.caltech.edu/CaltechTHESIS:04212011-134533762
Authors: {'items': [{'id': 'Head-Richard-Moore', 'name': {'family': 'Head', 'given': 'Richard Moore'}, 'show_email': 'NO'}]}
Year: 1949
DOI: 10.7907/06R8-C778
The results of a systematic wind tunnel investigation into the attainment and ultimate collapse of the supersaturated state of water vapor are presented. These results, together with those of other recent investigations, are collected and compared with the theory. It is found that the deviations from the quasi-stationary conditions upon which the theory is based are very pronounced in the supersonic wind tunnel. A much higher degree of supersaturation can, therefore, be attained before condensation occurs than is predicted theoretically.
Measurements at low temperatures indicate that if the water vapor reaches a temperature of about 153 °K, without the occurrence of condensation, the vapor will not condense upon further expansion, regardless of how highly supersaturated it becomes. This observation is in agreement with some recent Wilson Cloud Chamber investigations.
The shock relations for flow-involving condensation are discussed. It is shown that two types of discontinuities can occur; the condensation shock and the shock with condensation (or vaporization). The latter solution has been disregarded in the past, but it is shown that the shock with vaporization is of importance and can result in appreciable errors in Mach number determination when droplets are present in the flow.
Various techniques of measurement of the condensation processes in supersonic flow are considered.
https://thesis.library.caltech.edu/id/eprint/6346On the Design and Use of a Flexible Nozzle for the GALCIT Transonic Wind Tunnel
https://resolver.caltech.edu/CaltechETD:etd-04202004-110634
Authors: {'items': [{'id': 'Dhawan-Satish', 'name': {'family': 'Dhawan', 'given': 'Satish'}, 'show_email': 'NO'}]}
Year: 1949
DOI: 10.7907/ESYY-5P20
Some aspects concerning the design of flexible nozzles for use in supersonic wind tunnels are discussed. Methods are investigated for matching the deflection patterns of nozzle plates and the theoretical aerodynamic shapes required for uniform, parallel, shockfree flow. Application of the design procedures to the Galcit 4" x 10", transonic wind tunnel is detailed. As a demonstration of a use of the tunnel, the Mach number of shock detachment from a 10° wedge (half angle) is experimentally investigated.https://thesis.library.caltech.edu/id/eprint/1422The Anemometric Application of an Electrical Glow Discharge in Transverse Air Streams
https://resolver.caltech.edu/CaltechETD:etd-11032003-110318
Authors: {'items': [{'id': 'Mettler-Ruben-Fred', 'name': {'family': 'Mettler', 'given': 'Ruben Fred'}, 'show_email': 'NO'}]}
Year: 1949
DOI: 10.7907/RTBA-4692
The possibility of using an electrical glow discharge for quantitative turbulence measurements is experimentally investigated. It is found that a glow discharge is stable in a transverse air stream throughout the subsonic velocity range, and at supersonic air velocities up to a Mach number of 1.5, with no indication that this Mach number represents an upper velocity limit. A calibration procedure is developed and used in measuring the decay of turbulence behind a grid at low subsonic velocities. Comparison with decay measurements made independently with a hot wire anemometer under similar flow conditions shows that the glow discharge data is as yet quite badly scattered and somewhat inconsistent.
A quantitative theory of the dark current anemometer is presented and gives results which agree in form with reported experimental results. A qualitative theory of the mechanism of the glow discharge anemometer and the first steps of the corresponding quantitative analysis are also presented.https://thesis.library.caltech.edu/id/eprint/4383The Design and Construction of a Mach-Zehnder Interferometer for Use with the GALCIT Transonic Wind Tunnel
https://resolver.caltech.edu/CaltechETD:etd-04232008-154118
Authors: {'items': [{'id': 'Ashkenas-Harry-Israel', 'name': {'family': 'Ashkenas', 'given': 'Harry Israel'}, 'show_email': 'NO'}]}
Year: 1950
DOI: 10.7907/D0V1-MJ80
A Mach-Zehnder Interferometer has been designed and constructed for use in conjunction with the GALCIT Transonic Wind Tunnel. The instrument is to be utilized in making detailed density measurements of supersonic air streams. The design of the instrument is such that, contrary to general wind tunnel practice, both light beams of the interferometer traverse the test section of the wind tunnel in an effort to minimize boundary layer corrections. A detailed description of the instrument is presented, as well as a “cook-book” adjustment procedure. A discussion of the limitations of the instrument is included.https://thesis.library.caltech.edu/id/eprint/1483Acoustical Airspeed Indicators
https://resolver.caltech.edu/CaltechETD:etd-02022009-083911
Authors: {'items': [{'id': 'Barish-David-Theodore', 'name': {'family': 'Barish', 'given': 'David Theodore'}, 'show_email': 'NO'}]}
Year: 1950
DOI: 10.7907/FR7P-K372
Some of the problems associated with the applications of acoustical devices for the determination of airstream characteristics are considered in this study. The velocity and pressure fields for both point sound sources and finite sound sources in both subsonic and supersonic flow are discussed, with a view toward using sound waves for the determination of velocity, Mach number , temperature, and other properties of a flow.
The experimental investigations included the measurement of the spectra of ultra-audio-pressure pulsations, both static and total, in the small C.I.T. supersonic tunnel and also in the C.I.T. hypersonic tunnel. A broad range of Mach numbers and a variety of operating conditions were covered. The development of a modified Hartmann sound generator is described, and measurements of the sound field from this device in supersonic flow are included.https://thesis.library.caltech.edu/id/eprint/472On the Statistical Theory of Turbulence
https://resolver.caltech.edu/CaltechETD:etd-10302003-154021
Authors: {'items': [{'id': 'Chuang-Feng-Kan', 'name': {'family': 'Chuang', 'given': 'Feng-Kan'}, 'show_email': 'NO'}]}
Year: 1950
DOI: 10.7907/2TJM-BK44
The present work starts with a study of isotropic turbulence which was introduced by G. I. Taylor in 1935. The different notions of averages are critically examined. The notion of stochastic average is then introduced and the general transport equation is developed. After a detailed study of kinematics of turbulence, the concept of correlation and spectrum, the correspondence between the Karman-Howarth equation and the spectrum equation is made. The turbulence decay is studied. A theory for turbulence decay at large Reynolds number is proposed. In the study of turbulence spectrum, different assumptions on the transfer function are critically discussed and the solution using Heisenberg's assumption is obtained explicitly. The spectrum is further studied by trying to fit the turbulence phenomenon into a general scheme of stochastic processes. In the second part of the work, an entirely different approach to the statistical theory is made. Linearized vorticity transport theory is developed and finally the non-linear effects in turbulence are studied.https://thesis.library.caltech.edu/id/eprint/4323Spectra of the Velocity Fluctuations in the Wake of Stalled Airfoils
https://resolver.caltech.edu/CaltechETD:etd-03192009-115101
Authors: {'items': [{'id': 'Stuart-Jay-William', 'name': {'family': 'Stuart', 'given': 'Jay William'}, 'show_email': 'NO'}]}
Year: 1951
DOI: 10.7907/0DKR-ZG89
During the last twenty years a considerable amount of work has been done in order to understand buffeting and the mechanism of the separated flow that causes it. In these investigations the results have either not been clear or they contain some unknown interaction between the indicating apparatus and the flow in the wake. In the present paper one type of the formerly observed flow configurations is investigated by using a properly compensated hot wire anemometer. This technique exhibits some of the results previously obtained but with greater significance and some added phenomena.https://thesis.library.caltech.edu/id/eprint/1028Direct Measurements of Skin Friction
https://resolver.caltech.edu/CaltechETD:etd-09262002-155504
Authors: {'items': [{'id': 'Dhawan-Satish', 'name': {'family': 'Dhawan', 'given': 'Satish'}, 'show_email': 'NO'}]}
Year: 1951
DOI: 10.7907/1S03-8631
<p>A device has been developed to measure local skin friction on a flat plate by measuring the force exerted upon a very small movable part of the surface of a flat plate. These forces, which range from about 1 milligram to about 100 milligrams, are measured by means of a reluctance measuring device. The apparatus was first applied to measurements in the low-speed range, both for laminar and turbulent boundary layers. The measured skin friction coefficients show excellent agreement with Blasius' and Karman's results respectively. The device was then applied to high-speed subsonic flow and the turbulent skin friction coefficients were determined up to a Mach number of about 0.8. A few measurements in supersonic floor were also made.</p>
<p>The paper describes the design and construction of the device and the results of the measurements.</p>https://thesis.library.caltech.edu/id/eprint/3779Mean-Speed Measurements in Two-Dimensional, Incompressible, Fully-Developed Turbulent Channel Flow
https://resolver.caltech.edu/CaltechTHESIS:07092015-140302816
Authors: {'items': [{'id': 'Skinner-George-Tolmie', 'name': {'family': 'Skinner', 'given': 'George Tolmie'}, 'show_email': 'NO'}]}
Year: 1951
DOI: 10.7907/CGEH-Q720
<p>Mean velocity profiles were measured in the 5” x 60” wind channel of the turbulence laboratory at the GALCIT, by the use of a hot-wire anemometer. The repeatability of results was established, and the accuracy of the instrumentation estimated. Scatter of experimental results is a little, if any, beyond this limit, although some effects might be expected to arise from variations in atmospheric humidity, no account of this factor having been taken in the present work. Also, slight unsteadiness in flow conditions will be responsible for some scatter.</p>
<p>Irregularities of a hot-wire in close proximity to a solid boundary at low speeds were observed, as have already been found by others.</p>
<p>That Kármán’s logarithmic law holds reasonably well over the main part of a fully developed turbulent flow was checked, the equation u/u<sub>t</sub> = 6.0 + 6.25 log<sub>10</sub> y<sup>u</sup>t/v being obtained, and, as has been previously the case, the experimental points do not quite form one straight line in the region where viscosity effects are small. The values of the constants for this law for the best over-all agreement were determined and compared with those obtained by others.</p>
<p>The range of Reynolds numbers used (based on half-width of channel) was from 20,000 to 60,000.</p>
https://thesis.library.caltech.edu/id/eprint/9055A General Similarity Theory of Partial Differential Equations and its Use in the Solution of Problems in Aeronautics
https://resolver.caltech.edu/CaltechETD:etd-03192009-091419
Authors: {'items': [{'id': 'Morgan-Antony-John-Andrew', 'name': {'family': 'Morgan', 'given': 'Antony John Andrew'}, 'show_email': 'NO'}]}
Year: 1951
DOI: 10.7907/9142-KZ49
A general similarity theory of systems of partial differential equations of any order in any number of independent variables is developed with the aid of the theory of continuous one-parameter groups of transformations. The theory is illustrated by means of several known examples of similarity equations, previously given without motivation, in Hydrodynamics. With the aid of the theory two new examples of similarity equations, one in Elasticity and one in Fluid Mechanics, have been found; these are discussed in the text.
https://thesis.library.caltech.edu/id/eprint/1024An Experimental Investigation of Transonic Flow Past Two-Dimensional Wedge and Circular Arc Sections Using a Mach-Zehnder Interferometer
https://resolver.caltech.edu/CaltechETD:etd-11062003-114932
Authors: {'items': [{'email': 'Brysonae@stanford.edu', 'id': 'Bryson-Arthur-Earl', 'name': {'family': 'Bryson', 'given': 'Arthur Earl'}, 'show_email': 'YES'}]}
Year: 1951
DOI: 10.7907/S45R-FG17
<p>Interferometer measurements are given of the flow fields near two-dimensional wedge and circular arc sections at zero angle of attack at high subsonic and low subsonic velocities. Both subsonic flow with local supersonic zone and supersonic flow with detached shock wave have been investigated. Pressure distributions and drag coefficients as functions of Mach number have been obtained. The wedge data are compared with the theoretical work on flow past wedge sections of Guderley and Yoshihara, Vincenti and Wagoner, and Cole.</p>
<p>It is shown that the local Mach number at any point on the surface of a finite three-dimensional body or an unswept two-dimensional body, moving through an infinite fluid, is a stationary value at Mach number one and, in fact, remains nearly constant for a range of speeds below and above Mach number one. On the basis of this concept and the experimental data, pressure distributions and drag coefficients for the wedge and circular arc sections are presented throughout the entire transonic range of velocities.</p>https://thesis.library.caltech.edu/id/eprint/4418On the Development of Turbulent Wakes from Vortex Streets
https://resolver.caltech.edu/CaltechETD:etd-10302003-144124
Authors: {'items': [{'id': 'Roshko-Anatol', 'name': {'family': 'Roshko', 'given': 'Anatol'}, 'show_email': 'NO'}]}
Year: 1952
DOI: 10.7907/4WDN-9807
Wave development behind circular cylinders at Reynolds numbers from 40 to 10,000 was investigated in a low speed wind tunnel. Standard hot-wire techniques were used to study the velocity fluctuations.
The Reynolds number range of periodic vortex "shedding" is divided into two distinct sub-ranges. At R = 40 to 150, called the stable range, regular vortex streets are formed and no turbulent motion is developed. R = 150 to 300 is a transition range to a regime called the irregular range, in which turbulent velocity fluctuations accompany the periodic formation of vortices. The turbulence is initiated by laminar-turbulent transition in the free layers which spring from the separation points on the cylinder. This transition first occurs in the range R = 150 to 300.
Spectrum and statistical measurements were made to study the velocity fluctuations. In the stable range the vortices decay by viscous diffusion. In the irregular range the diffusion is turbulent and the wake becomes fully turbulent in 40 to 50 diameters downstream.
It was found that in the stable range the vortex street has a periodic spanwise structure.
The dependence of shedding frequency on velocity was successfully used to measure flow velocity.
Measurements in the wake of a ring showed that an "annular" vortex street is developed.https://thesis.library.caltech.edu/id/eprint/4319A Ten Channel Statistical Analyzer for Use in Turbulence Research
https://resolver.caltech.edu/CaltechETD:etd-03302009-082004
Authors: {'items': [{'id': 'Robinson-Martin-Samuel', 'name': {'family': 'Robinson', 'given': 'Martin Samuel'}, 'show_email': 'NO'}]}
Year: 1952
DOI: 10.7907/3BGC-7N43
An experimental investigation of a stationary random process will involve the measurement of the mean values and probability distribution of a random function of time. This thesis describes an automatic ten channel "statistical analyzer" for measuring the probability distribution function of a continuous or discontinuous function of time that can be represented by a suitable electric voltage. The "statistical analyzer" is based upon a system of pulse amplitude modulation, followed by pulse height selection and pulse counting. An equation is developed by means of which the mean values can be computed from the distribution function. Finally, sample applications from the field of turbulence research are given.https://thesis.library.caltech.edu/id/eprint/1210Measurements in the Boundary Layer on a Smooth Flat Plate in Supersonic Flow
https://resolver.caltech.edu/CaltechETD:etd-05092003-180051
Authors: {'items': [{'id': 'Coles-Donald-Earl', 'name': {'family': 'Coles', 'given': 'Donald Earl'}, 'show_email': 'NO'}]}
Year: 1953
DOI: 10.7907/0DDW-9S38
<p>In Section I available measurements in low-speed turbulent boundary layer flow are compared with a simple analysis based on functional similarity, and the boundary layer is found to be unique within the accuracy of the experimental data. Some consequences of the mean equations of motion are obtained, including the distribution of shearing stress through the boundary layer, and an attempt is made to generalize the relationship known as the law of the wall to flows with variable density.</p>
<p>In Section II some problems encountered in the development and use of the floating surface element and other instrumentation are discussed in detail.</p>
<p>In Section III are presented measurements of mean and local surface friction carried out on a flat plate model in the 20-inch supersonic wind tunnel at the Jet Propulsion Laboratory. The boundary layer flow is studied for free stream Mach numbers of 2.0, 2.6, 3.7, and 4.5. The experiments, which involve nominal Reynolds numbers from 2 x 10<sup>5</sup> to 9 x 10<sup>6</sup>, include a few measurements in laminar flow, but emphasize transition and the turbulent regime. The effectiveness of various tripping devices is mentioned, and the problem of defining an effective Reynolds number for the fully turbulent flow is discussed at length. Finally, turbulent boundary layer profile measurements are examined for consistency with low-speed data, with a generalized mixing length theory, and with the analysis of Section I of the present report.</p>https://thesis.library.caltech.edu/id/eprint/1703The Development and Utilization of Some Equipment for Low Reynolds Number Supersonic Flow Research
https://resolver.caltech.edu/CaltechETD:etd-04292003-103202
Authors: {'items': [{'id': 'Chuan-Raymond-Lu-Po', 'name': {'family': 'Chuan', 'given': 'Raymond Lu-Po'}, 'show_email': 'NO'}]}
Year: 1953
DOI: 10.7907/B6T3-QB91
NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.
A low Reynolds number supersonic wind tunnel is a useful tool for the investigation of viscous effects in a high-speed flow. In order to avoid some of the difficulties inherent in a conventional wind tunnel system when operating at low Reynolds numbers, a two-phase cycle is proposed. By examining the thermodynamics of the wind tunnel the relative merits of two methods of operation -- the one-phase cycle and the two-phase cycle -- are compared, indicating certain advantages the two-phase cycle possesses over the conventional one-phase cycle when the tunnel is operated at high-speed and low Reynolds number. The design, construction and operation of a small (about 5 cm.[superscript 2] test section area) supersonic (M[.....]2) wind tunnel using a two-phase cycle with water (in liquid and vapor phases) as the working medium are described.
Difficulties in pressure measurement and flow visualization, due to the nature of the working medium and the low density of the flow, are encountered. Means of meeting these difficulties are proposed, including a critical analysis of the schlieren technique, from which is evolved a workable arrangement for visualizing the low Reynolds number flow.
As an example of the possible utilizations of the tunnel, the curvature, due to viscosity, of the attached shock wave on a wedge in uniform supersonic flow is investigated, using schlieren photography. The effective shape of the wedge is deduced from the shape of the shock wave, and is compared to theory with satisfactory qualitative agreement.https://thesis.library.caltech.edu/id/eprint/1538Transonic Flow Past Cone-Cylinders
https://resolver.caltech.edu/CaltechETD:etd-05122003-103200
Authors: {'items': [{'id': 'Solomon-George-Edward', 'name': {'family': 'Solomon', 'given': 'George Edward'}, 'show_email': 'NO'}]}
Year: 1953
DOI: 10.7907/DE4W-ZJ43
Experimental results are presented for transonic flow past cone-cylinder, axially symmetric bodies. The drag coefficient, surface Mach number, etc. are studied as the free stream Mach number is varied and, wherever possible, the experimental results are compared with theoretical predictions. Interferometric results for several typical flow configurations are shown and an example of shock-free supersonic to subsonic compression is experimentally demonstrated.
The theoretical problem of transonic flow past finite cones is discussed briefly and an approximate solution of the axially symmetric transonic equations, valid for a semi-infinite cone, is presented.https://thesis.library.caltech.edu/id/eprint/1732The Development of Direct and Alternating Current Glow Discharge Anemometers for the Study of Turbulence Phenomena in Supersonic Flow
https://resolver.caltech.edu/CaltechETD:etd-01222004-111758
Authors: {'items': [{'id': 'Vrebalovich-Thomas', 'name': {'family': 'Vrebalovich', 'given': 'Thomas'}, 'show_email': 'NO'}]}
Year: 1954
DOI: 10.7907/95XT-RN93
A direct current glow discharge anemometer (D.C. glow) was designed and constructed. This instrument was calibrated in low speed flow. Shock tube experiments with the D.C. glow indicated that its frequency response was greater than 50 kc. However, the shortcomings of the D.C. glow such as sputtering and asymmetric burning properties of the discharge became apparent. Therefore, a 700 kc. alternating current (A.C.) glow was designed and constructed. The time stability properties of this instrument were found to be much better than those of the D.C. glow. Since no frequency compensation circuits were used with the A.C. glow, the signal to noise ratio was much higher than that of a hot wire. This A.C. glow was used to survey the profile of the fluctuations in a turbulent boundary layer in supersonic flow at Mach numbers between 1.3 and 4. Power spectrum measurements of the fluctuations in this boundary layer were also made with the A.C. glow. These measurements indicated that there was energy in the spectrum above 100 kc. Finally, measurements of frequencies in excess of 100 kc. were made by the A.C. glow in a sound field produced by a source of single frequency ultrasonic sound waves in supersonic flow.https://thesis.library.caltech.edu/id/eprint/268The Lift of Thin Airfoils at High-Subsonic Speeds
https://resolver.caltech.edu/CaltechETD:etd-01222004-114509
Authors: {'items': [{'id': 'Willmarth-William-Walter', 'name': {'family': 'Willmarth', 'given': 'William Walter'}, 'show_email': 'NO'}]}
Year: 1954
DOI: 10.7907/DFFC-8041
Experimental results are presented for the lift characteristics of thin, two-dimensional airfoils at high-subsonic speeds and small angles of attack. Symmetrical airfoils with different locations of maximum thickness were investigated using a surface pressure probe technique which should find use in other applications.
The flow fields over each airfoil are discussed and the quantitative results for the lift and location of the center of lift are compared with theory whenever possible. The effects of flow separation caused by boundary-layer shock-wave interaction are noted and discussed. In particular, the possibility of the forced oscillation of control surfaces due to boundary layer separation is mentioned.https://thesis.library.caltech.edu/id/eprint/272Supersonic Diffuser Instability
https://resolver.caltech.edu/CaltechETD:etd-12102003-101604
Authors: {'items': [{'id': 'Dailey-Charles-Lee', 'name': {'family': 'Dailey', 'given': 'Charles Lee'}, 'show_email': 'NO'}]}
Year: 1954
DOI: 10.7907/V9XM-W683
Steady operation of supersonic diffusers near critical mass flow is interrupted by a transient process known as buzz. This phenomenon consists of a random sequence of individual relaxation cycles. Mass flow entering the diffuser during steady operation is suddenly cut off by a strong interaction between the subcritical shock and boundary layer on the surface of the external compression generator, which blocks the inlet. Air in the plenum chamber, stored at high pressure, then ?blows down? until the inlet can restart. The subsequent supercritical flow entering the diffuser exceeds the flow rate at the exit and the plenum chamber is re-charged to the original condition.
A distinction is drawn between this phenomenon and a high frequency wave-type resonance noticed at low mass flows and during an individual buzz cycle after the diffuser shock system has been expelled. For the large diffuser tested here, this high frequency oscillation compares well to the 8th closed-end organ pipe mode of the diffuser at low mass flows and to the 9th mode during the shock-expelled phase of the buzz cycle.
It is shown that burning almost always ceases in the presence of buzz. When burning was maintained during buzz, it was found to have no qualitative effect on the buzz cycle.https://thesis.library.caltech.edu/id/eprint/4918Measurements of Skin Friction in Turbulent Boundary Layers at Transonic Speeds
https://resolver.caltech.edu/CaltechETD:etd-12152003-084052
Authors: {'items': [{'id': 'Hakkinen-Raimo Jaakko', 'name': {'family': 'Hakkinen', 'given': 'Raimo Jaakko'}, 'show_email': 'NO'}]}
Year: 1954
DOI: 10.7907/WAX3-QV41
The first part of this report describes the design and construction of a floating element skin friction balance. This instrument, which is essentially an improved version of Dhawan's balance, was applied to measurements of local skin friction in the turbulent boundary layer of a smooth flat plate at high subsonic Mach numbers and supersonic Mach numbers up to M = 1.75. The measured skin friction coefficients are consistent with the results of other investigations at subsonic and also at high supersonic speeds. The principal difficulties which exist in comparing skin friction coefficients at various Mach numbers are discussed.
The second part of this report describes the application of the Stanton tube technique to skin friction measurements near the base of a shock wave impinging upon a turbulent boundary layer. The floating element technique is inherently difficult to apply for skin friction measurements in non-uniform flow. Hence, a Stanton tube is calibrated by means of a floating element balance in a uniform flow field and then used to measure skin friction near the base of an impinging shock. Oblique shock waves were produced by two wedges of 2.5[degree] and 4.6[degree] semi-angles and a normal shock was generated by a choked channel. Skin friction and velocity profiles were obtained for these three cases at a free stream Mach number of 1.48.https://thesis.library.caltech.edu/id/eprint/4999An Experimental Investigation of Heat Transfer from Fine Wires to Still Air at Low Density
https://resolver.caltech.edu/CaltechETD:etd-02032004-142252
Authors: {'items': [{'id': 'Williamson-William-Jeffris', 'name': {'family': 'Williamson', 'given': 'William Jeffris'}, 'show_email': 'NO'}]}
Year: 1955
DOI: 10.7907/J54H-9F64
Heat transfer from electrically heated wires of 0.00025 cm nominal diameter to still air at room temperature has been investigated at pressures ranging from 1 to 0.0076 atmospheres. Three wires, having ratios of length to diameter in the approximate proportion 1:5:10, were tested in the vertical position. Due to time limitations, only the shortest of these was tested in a horizontal position. A check was made to determine whether the results were influenced by the geometry of the enclosing vessel.
For pressures at which the molecular mean free path is smaller than the wire diameter, the results appear to satisfy a relation of a form derived for free-molecule heat conduction. Small departures from this behavior at the higher pressures are attributed to the effects of natural convection. The Nusselt number was found not to be uniquely related to the product of the Grashof and Prandtl numbers, as has been proposed, for values of this product below 10[^-5].
It was found that, at the lowest pressures reached, solid boundaries located at distances of the order of 3 x 10[^4] diameters from the wire cannot be considered infinitely remote.https://thesis.library.caltech.edu/id/eprint/478A Time Correlator for Problems in Aerodynamics
https://resolver.caltech.edu/CaltechETD:etd-12122003-092906
Authors: {'items': [{'id': 'Skinner-George-Tolmie', 'name': {'family': 'Skinner', 'given': 'George Tolmie'}, 'show_email': 'NO'}]}
Year: 1955
DOI: 10.7907/6B8H-3139
An instrument, of fairly simple design, for measuring time correlation functions of two stationary random electrical signals is discussed. It is intended primarily for use in problems connected with aerodynamically produced acoustic fields, but has suitable properties for application to a rather wide range of aerodynamic problems involving turbulent fields. It has been designed and constructed with a view to economy, and simplicity of operation, and makes extensive use of the general statistical properties of the problems for which it is intended.
A few experimentally determined auto-correlation functions are given in order to indicate the degree of accuracy achieved, and the Fourier transform of the auto-correlation function of a random input is compared with the power-spectrum of the same function.
Some practical points of general interest are discussed.https://thesis.library.caltech.edu/id/eprint/4953An Experimental Investigation of the Transfer of Heat from Small Wires to a Viscous Compressible Fluid
https://resolver.caltech.edu/CaltechETD:etd-12042003-100200
Authors: {'items': [{'id': 'Magnus-Richard-Jeffrey', 'name': {'family': 'Magnus', 'given': 'Richard Jeffrey'}, 'show_email': 'NO'}]}
Year: 1955
DOI: 10.7907/4ZYH-PF56
A steam tunnel, suitable for making experimental measurements of the heat transfer from fine wires to a viscous compressible fluid, was developed and constructed.
Measurements of Nusselt numbers and recovery temperatures were carried out using small-diameter (0.00038 to 0.00254 cm.) tungsten wires in steam flow with Reynolds numbers ranging from about 1 to 12 and with nominal Mach numbers of 0.5 to 1.7.
Considerable difference was found between the Nusselt numbers for wires in subsonic and supersonic flow at corresponding Reynolds numbers. The results could be fairly well represented by an available theory based on the assumption that a temperature discontinuity of the fluid existed at the wire surface; however, they did not agree very well with other available data in the same range of Mach and Reynolds numbers.
In supersonic flow, the wire recovery temperatures were found to be consistently higher than the tunnel stagnation temperature.
An experimental procedure for making end-loss corrections to the heat transfer and temperature recovery tests was used and found to give satisfactory correlation of data taken with wires ranging in aspect ratio from 220 to 3040. Some experiments were performed to check the validity of the simple linear theory which is usually used to calculate end loss corrections; the theory was found to be adequate in the experimental range covered.https://thesis.library.caltech.edu/id/eprint/4762Boundary Layer Measurements at Supersonic Nozzle Throats
https://resolver.caltech.edu/CaltechETD:etd-08182006-150720
Authors: {'items': [{'email': 'Merwin_Sibulkin@brown.edu', 'id': 'Sibulkin-Merwin', 'name': {'family': 'Sibulkin', 'given': 'Merwin'}, 'show_email': 'NO'}]}
Year: 1956
DOI: 10.7907/1JZK-HZ46
<p>Wall static pressure measurements and boundary layer pitot pressure surveys were made near the throat of a flexible wall supersonic wind-tunnel nozzle at three settings having throat radii of curvature from 33 to 59 inches. It is found that the longitudinal static pressure gradient at the nozzle throat calculated from one-dimensional flow theory agreed with the measured wall static pressure gradient.</p>
<p>The boundary-layer velocity profiles at the nozzle throat are presented and discussed. The boundary layers were turbulent and 0.046 to 0.107 inch thick. It is found that the boundary-layer momentum thickness at the nozzle throat calculated using the momentum-integral-equation and several approximations agrees with the values determined from the measured boundary layer profiles. Finally, it is noted that in spite of the different static pressure gradients, the boundary-layer velocity profiles for the different nozzle settings are similar, and it is shown analytically that this similarity is to be expected.</p>https://thesis.library.caltech.edu/id/eprint/3165Turbulence in the Wake of a Thin Airfoil at Low Speeds
https://resolver.caltech.edu/CaltechETD:etd-03192004-142218
Authors: {'items': [{'id': 'Campbell-George-Stuart', 'name': {'family': 'Campbell', 'given': 'George Stuart'}, 'show_email': 'NO'}]}
Year: 1956
DOI: 10.7907/T35K-QF86
Experiments have been made to determine the nature of turbulence in the wake of a two-dimensional airfoil at low speeds. The experiments were motivated by the need for data which can be used for analysis of the tail-buffeting problem in aircraft design. Turbulent intensity and power spectra of the velocity fluctuations were measured at a Reynolds number 1.6 x 10[superscript 5] for several angles of attack. Total-head measurements were also obtained in an attempt to relate steady and fluctuating wake properties.
Mean-square downwash was found to have nearly the same dependence on vertical position in the wake as that shown by total-head loss. For this particular wing, turbulent intensity, integrated across the wake, increased roughly as the 3 /2 power of the drag coefficient.
Power-spectrum measurements indicated a decrease in frequency as wing angle of attack was increased. The average frequency in the wake was proportional to the ratio of mean wake velocity to wake width.https://thesis.library.caltech.edu/id/eprint/1005Sound Radiation from Surface Cutouts in High Speed Flow
https://resolver.caltech.edu/CaltechETD:etd-03262004-114458
Authors: {'items': [{'id': 'Karamcheti-Krishnamurty', 'name': {'family': 'Karamcheti', 'given': 'Krishnamurty'}, 'show_email': 'NO'}]}
Year: 1956
DOI: 10.7907/1CRR-9Y28
In an experimental investigation of subsonic and supersonic flows of air past rectangular cavities cut into a flat surface it was discovered that the cavities emit a strong acoustic radiation.
The frequency of the sound-producing oscillations measured by a hot wire in the cavity was found to be inversely proportional to the breadth for fixed depth. For fixed breadth the frequency was found to increase, though not systematically, with a decrease in depth.
A non-dimensional frequency S is defined in terms of the frequency of emission, the gap breadth, and the free stream velocity. The dependence of S on the various parameters in the problem, such as Mach number, Reynolds number and ratio of the boundary layer thickness to a dimension of the cavity, is discussed in light of appropriate experiments.
An estimate of the intensity of the radiation was obtained by means of an optical interferometer of the Mach-Zehnder type. For points located at 3 to 4 cavity breadths from the cavity, intensities of the order of 100 - 150 decibels were found for sound fields from cavities 0.1" deep and 0.1 to 0.2 inch broad at Mach numbers 0.7 to 0.85.
Possible mechanisms for the sound production by the cavities are discussed.https://thesis.library.caltech.edu/id/eprint/1129Measurements of Lift Fluctuations Due to Turbulence
https://resolver.caltech.edu/CaltechETD:etd-03262004-115115
Authors: {'items': [{'id': 'Lamson-Philip', 'name': {'family': 'Lamson', 'given': 'Philip'}, 'show_email': 'NO'}]}
Year: 1956
DOI: 10.7907/2ZDV-9T79
The fluctuating lift of a rigid wing in turbulent flow is studied. The power spectra of the lift and of the turbulent fluctuations are measured. From these measurements the aerodynamic admittance of the wing is obtained.
The ratio of span/scale of turbulence is varied by means of movable end plates. For a distance between the end plates of the order of the scale of turbulence the aerodynamic admittance is expected to approach the computed values of Sears.
This is shown to be the case if the reduced frequencies are larger than k = 0.8. For smaller k the experimental admittance falls below Sears' values. For large ratios of span/scale of turbulence the aerodynamic admittance is decreased for all frequencies and becomes nearly independent of frequency in the investigated range 0.2 <= k <= 2.
In general the measurements support the simplifying assumptions made in the statistical approach to gust loads and buffeting initiated by Clementson and by Liepmann.https://thesis.library.caltech.edu/id/eprint/1130The Effect of Uniformly Distributed Roughness on Turbulent Skin Friction Drag at Supersonic Speeds
https://resolver.caltech.edu/CaltechETD:etd-07132004-115342
Authors: {'items': [{'id': 'Goddard-Frank-Eber', 'name': {'family': 'Goddard', 'given': 'Frank Eber'}, 'show_email': 'NO'}]}
Year: 1957
DOI: 10.7907/BA5G-7H43
NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.
An experimental program was carried out in the 18 x 20-inch supersonic wind tunnel of the Jet Propulsion Laboratory at the California Institute of Technology to determine the effect of uniformly distributed sand-grain roughness on the skin friction drag of a body of revolution for the case of a turbulent boundary layer. The Mach-number range covered was 1.98 to 4.54 and the Reynolds number varied from about [...] to [...]. Some data were also obtained at a Mach-number of 0.70.
At speeds up to a Mach number of 5 and for roughness sizes such that the quadratic resistance law holds, the compressibility effect is indirect and the skin friction drag is a function only of the roughness Reynolds number, [...], just as in the incompressible case.
The critical roughness below which the surface is hydraulically smooth is [...] and this is equal to the thickness of the laminar sublayer for a smooth surface for both compressible and incompressible flows.
Over the range of roughness sizes considered here there appears to be no wave drag associated with the drag due to roughness.
The shift in the turbulent velocity profile [...] for a rough surface at supersonic speeds is a function only of the roughness Reynolds number, [...], and quantitatively follows identically the same law as in the incompressible case.https://thesis.library.caltech.edu/id/eprint/2868The Vibration and Acoustic Radiation of Thin-Walled Cylinders Caused by Internal Turbulent Flow
https://resolver.caltech.edu/CaltechETD:etd-02062006-134627
Authors: {'items': [{'id': 'Weyers-Paul-Frederick-Robert', 'name': {'family': 'Weyers', 'given': 'Paul Frederik Robert'}, 'show_email': 'NO'}]}
Year: 1959
DOI: 10.7907/QTM4-9Z19
<p>The investigation concerned noise produced by turbulent flow adjacent to a flexible wall. Measurements of the spectrum and intensity of the pressure field outside thin-walled Mylar cylinders containing turbulent pipe flow have been made. The resulting spectra could be interpreted in relation to the elastic properties of the cylinders and the character of the turbulent fluctuations inside the flow. The eigen frequencies of the cylinders could be identified and similarity parameters for the spectra were established. The effect of cylinder wall thickness on the spectrum and intensity of the pressure fluctuations was investigated. It was found that the intensity of the external pressure field scaled with the fifth power of the velocity at the center of the pipe.</p>
<p>For one particular case the spectrum and intensity of the pressure fluctuations exerted by the turbulent flow on the wall were measured. The intensity of the pressure fluctuations at the wall scaled with the fourth power of the velocity as expected. The ratio of the root-mean-square wall pressure to the dynamic pressure was found to be independent of Mach number and equal to a constant (0.0078). Similarity laws for the spectra of the wall pressure fluctuations were also confirmed.</p>https://thesis.library.caltech.edu/id/eprint/518Problems in Effusion
https://resolver.caltech.edu/CaltechETD:etd-02072006-131514
Authors: {'items': [{'id': 'Stockmair-Wilfried', 'name': {'family': 'Stockmair', 'given': 'Wilfried'}, 'show_email': 'NO'}]}
Year: 1959
DOI: 10.7907/KH55-XN11
The flow of rarefied gases from a vessel through an orifice into vacuum is studied here. Special conditions of this study are that the mean free path of the molecules is of the same order of magnitude as the hole diameter; furthermore the thickness of the wall is neglected. Knudsen [1,2] investigated this effusion problem for constant conditions throughout the gas, assuming Maxwellian velocity distribution and very large mean free paths. In the present study the influence of a one-dimensional temperature gradient extending from the wall upstream into the gas is investigated. Formulae for the massflux and the spatial intensity distribution of the outflowing molecules are calculated for steady flow conditions. Finally the behavior corresponding to a nonstationary temperature gradient (according to suddenly heated or cooled wall) is studied.https://thesis.library.caltech.edu/id/eprint/535An Investigation of Temperature Fluctuations on Bluff Bodies
https://resolver.caltech.edu/CaltechETD:etd-02242006-083641
Authors: {'items': [{'id': 'Gorecki-Jacek-Piotr', 'name': {'family': 'Gorecki', 'given': 'Jacek Piotr'}, 'show_email': 'NO'}]}
Year: 1960
DOI: 10.7907/KV3S-CJ64
Temperature fluctuations and recovery temperatures on the surface of a circular cylinder (with axis normal to a subsonic compressible flow) and the field of flow about the cylinder, particularly the wake area, are investigated experimentally in range between M = 0.35, Re = 117,000 and M = 0.70, Re = 201,000.
Spectral analysis of fluctuations on body surface and other evidence indicate that formation of discrete vortex cores from the separated shear layers is initially an impulsive random process (of the generalized "shot effect" type), although the wake farther downstream from the model has a definitely periodic structure.
Impulsive formation of vortex cores can be enhanced by wind tunnel resonance or by a high turbulence level in the free stream and is accompanied by abnormal cooling of the model surface in the separated area - the mechanism of these effects is also investigated.https://thesis.library.caltech.edu/id/eprint/736The Effusion of Charged Particles from a Shock Heated Gas
https://resolver.caltech.edu/CaltechETD:etd-12302004-145356
Authors: {'items': [{'id': 'Sturtevant-Bradford', 'name': {'family': 'Sturtevant', 'given': 'Bradford'}, 'show_email': 'NO'}]}
Year: 1960
DOI: 10.7907/PCNN-DW03
NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.
An experimental and theoretical investigation is made of the application of a molecular beam type sampling device for studying low density shock tube flows to the case of slowly ionizing argon behind a reflected shock wave. The flux of charged particles from a gas heated to about 10,OOO[degrees]K and 20 mm. Hg. through a small orifice in the shock tube end wall is measured. The processes determining this flux are the initial stages of ionization in argon and the diffusion of charged particles to a cold metallic wall. Providing the diffusion process is understood, the measurements constitute a direct observation of incipient ionization ([...]).
The transient charge diffusion mechanism is studied in detail theoretically, avoiding the assumption of ambipolar diffusion. It is concluded that the major problem lies in the understanding of the wall-gas interaction as represented by boundary conditions at the wall. An approximate relation for charge effusion is derived.
It is concluded from the experimental results that the initial ionization can not be due to a single step, electron-atom collision process but must result from a series of several atom-atom collisions resulting in the ionization of argon atoms.https://thesis.library.caltech.edu/id/eprint/5170Some Flow Problems in Rarefied Gas Dynamics
https://resolver.caltech.edu/CaltechETD:etd-11042003-095050
Authors: {'items': [{'id': 'Narasimha-Roddam', 'name': {'family': 'Narasimha', 'given': 'Roddam'}, 'show_email': 'NO'}]}
Year: 1961
DOI: 10.7907/1S8T-QA38
This thesis discusses three rather loosely connected problems in free molecule and nearly free molecule flow. First the expansion of a gas cloud into perfect vacuum is considered on the basis of the collision-less Boltzmann equation, and it is shown that if the initial distribution is an isothermal Maxwellian, the density obeys a diffusion equation with a diffusion coefficient proportional to the time. This leads to the description of the free expansion of symmetric clouds in terms of a thick 'diffusion front' traveling at the initial isothermal speed of sound. The expansion of asymmetric clouds and the flow due to sources and jets are also studied.
Second, a method of iteration proposed by Willis for calculating nearly free molecular flow is extended to general unsteady flows; it is then applied to the flow through an orifice to show that the correction to the mass flow is of the first order in the inverse Knudsen number. The coefficient, estimated by making some reasonable assumptions about the three-dimensional nature of the flow, is found to agree quite well with Liepmann's measurements.
Finally a physical basis is suggested for Krook's collision model used in the above calculations. Several consequences of the model are then derived, including the important one that, in the Navier-Stokes limit, the model implies a Stokesian gas with a Prandtl number of unity. The value to be given to the parameter in the model is also discussed at some length.https://thesis.library.caltech.edu/id/eprint/4400Measurements of Aerodynamic Noise on a Flat Plate in Supersonic Flow
https://resolver.caltech.edu/CaltechETD:etd-07052006-084242
Authors: {'items': [{'id': 'Chen-William-S', 'name': {'family': 'Chen', 'given': 'William S.'}, 'show_email': 'NO'}]}
Year: 1961
DOI: 10.7907/SEEW-5974
NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.
Measurements of aerodynamic noise, in the form of pressure fluctuations in a turbulent boundary layer, were made on a smooth flat plate in the 12- and 20-in. supersonic wind tunnels at the Jet Propulsion Laboratory. The noise was measured with small piezoelectric pressure transducers (0.015-0.03 in. diameter) constructed of barium titanate crystals which were flush-mounted in the flat plate.
Spectral-energy distributions of the pressure fluctuations are obtained up to a frequency of 0.5 mc at freestream Mach numbers from 2.0 to 5.0, and Reynolds numbers based an bound layer-displacement thickness from 5 x 10(3) to 5 x 10(4). By grouping the test variables into the proper nondimensional forms and correcting for the finite transducer size, the energy spectra are found to be similar and uniquely related to both Mach number and Reynolds number. The total, or integrated, level of noise at the plate surface, in terms of root-mean-square values of the pressure fluctuations, is a constant equal to about 10 times the shear stress [...] the wall. The intensity, [...], is directly proportional to the fourth power of the freestream Mach number.
Correlation measurements in time and in the streamwise direction in space show that the noise at the plate surface to convected downstream with a characteristic velocity equal to 75% of the freestream velocity. The correlation dies off rapidly with spacing between pickup points, and the convection velocity shows no dependence on either Mach number or Reynolds number.https://thesis.library.caltech.edu/id/eprint/2811Measurements of Drag Coefficients for Falling and Rising Spheres in Free Motion
https://resolver.caltech.edu/CaltechETD:etd-12192005-145326
Authors: {'items': [{'id': 'Preukschat-A-Werner', 'name': {'family': 'Preukschat', 'given': 'A. Werner'}, 'show_email': 'NO'}]}
Year: 1962
DOI: 10.7907/94MG-ZS76
The purpose of this thesis is to investigate the drag coefficient of spheres in free motion, falling and rising, in water.
Following the introduction the test set-up, sphere release mechanism, spheres and timing device and recorder are described.
Section 3 gives the results of the drag coefficient measurements for free falling spheres which show good agreement with the known measurements, quoted, for instance, in the Handbuch der Experimentalphysik.
Section 4 deals with the measurement of drag coefficients of free-rising spheres. It was found that the freely rising spheres move in an oscillatory path of which wavelength and amplitude depend on the ratio of sphere density and water density.
The local drag coefficient of the spheres was measured to be the same as for falling spheres. It was found to be independent of the sphere motion.
No critical Reynolds number was found for the onset of the oscillatory motion of the sphere. The oscillatory motion appeared to be independent of initial disturbances of the sphere motion.
From photographs of the sphere paths Strouhal numbers were formed which are about one third the value given for circular cylinders in the same Reynolds number range.
A theoretical oscillatory force coefficient, based on a force balance on the sphere, was obtained. It was found to be of the same order of magnitude as the correspondent, actually measured oscillatory force coefficient on a circular cylinder.
The Strouhal number based on the main theoretical frequency was found to be four times as high as the one calculated from the frequency of the sphere path. It could be, dependent on the sphere density, as high as twice the Strouhal number found for circular cylinders in the same Reynolds number range.https://thesis.library.caltech.edu/id/eprint/5062Magnetohydrodynamic Surface Waves
https://resolver.caltech.edu/CaltechETD:etd-03262008-082838
Authors: {'items': [{'id': 'Hoult-David- Parks', 'name': {'family': 'Hoult', 'given': 'David Parks'}, 'show_email': 'NO'}]}
Year: 1962
DOI: 10.7907/RVM0-1T80
This is an experimental and theoretical study of deep water gravity-like waves which are induced in a liquid metal by a changing magnetic field. The dominant feature of such waves is the emission of Alfven waves from the free surface. A linearized theory is derived and compared with experiments.https://thesis.library.caltech.edu/id/eprint/1152I. Design and Application of Piezoceramic Transducers to Transient Pressure Measurements. II. Some Measurements of Curvature and Thickness of Reflecting Normal Shocks at Low Initial Pressures
https://resolver.caltech.edu/CaltechETD:etd-12222005-102730
Authors: {'items': [{'id': 'Johnson-Douglas-Stoddard', 'name': {'family': 'Johnson', 'given': 'Douglas Stoddard'}, 'show_email': 'NO'}]}
Year: 1962
DOI: 10.7907/BJ82-FM97
A small pressure transducer, using the piezoelectric properties of a manufactured ceramic, was designed, constructed and installed in the end plate of the GALCIT 17-inch shock tube to obtain high-speed measurements of the pressure field behind a reflecting shock.
The design problem for piezoceramic pressure transducers and some possible solutions are discussed in detail. Results of transducer calibration and recommendations for improvement of the instrument are presented.
An initial program to determine the curvature of a shock at low initial pressures was run concurrently with calibration of five of the above pressure transducers. The results of this program are described in as much detail as the data obtained to date will permit.
At an initial pressure of 30 microns in the GALCIT 17-inch tube, the shock obtained at a Mach number of about 7.5 in argon is observed to have a total curvature of approximately 10 millimeters, or approximately two per cent of the tube diameter. The shock thickness observed under these conditions is approximately 5 millimeters. These results indicate that it may be entirely possible to obtain good optical measurements inside the shock, but that it may be necessary to resort to special techniques to avoid optical distortion caused by curvature.https://thesis.library.caltech.edu/id/eprint/5118Experiments on the Upstream Wake in Magneto-Fluid Dynamics
https://resolver.caltech.edu/CaltechETD:etd-12082005-111323
Authors: {'items': [{'id': 'Ahlstrom-Harlow-Garth', 'name': {'family': 'Ahlstrom', 'given': 'Harlow Garth'}, 'show_email': 'NO'}]}
Year: 1963
DOI: 10.7907/NAR6-M485
<p>Measurements have been made of the perturbation magnetic field in front of a semi-infinite Rankine body moving parallel to a uniform impressed magnetic field in a conducting fluid. The purpose of these experiments was to investigate the so-called upstream wake effect which has been predicted by theory. It is believed that these are the first experiments in which the upstream wake was observed. Although the wake was found to exist as predicted when the Alfvén number is greater than one, its decay behavior was remarkably different from that which was predicted. The solutions for infinite medium predicted that in the wake the perturbations should decay inversely as the distance from the body. However the experiments showed that the perturbations decayed exponentially. It was finally shown that this change in the decay behavior was an effect of the walls and the conducting material surrounding the fluid.</p>
https://thesis.library.caltech.edu/id/eprint/4858Measurements of the Acceleration of Reflected Shock Waves by Means of a New Heat Transfer Gauge
https://resolver.caltech.edu/CaltechETD:etd-10182005-093601
Authors: {'items': [{'id': 'Slachmuylders-Erik-Jaak', 'name': {'family': 'Slachmuylders', 'given': 'Erik Jaak'}, 'show_email': 'NO'}]}
Year: 1963
DOI: 10.7907/5G88-B054
A small heat transfer probe, operating in the free molecule tow regime, was developed with the purpose of obtaining accurate x, t diagrams of a reflected shock wave close to the end wall of the GALCIT 17-inch shock tube.
The sensitive element of the probe consists of a .005" diameter filament of non-conducting material coated with a thin metallic film. The sensitivities of a filament probe and a conventional cold wire are compared analytically and it is found that the filament probe has favorable characteristics for measurement times of the order of a few microseconds. This is confirmed by the experiments.
The probe was mounted in the end wall of the 17-inch shock tube and x, t diagrams of reflected shock waves were measured at three levels of the initial pressure. The initial motion of the reflected shock is governed by heat loss to the reflecting wall; the wave velocity approaches its ideal value only asymptotically. The asymptotic approach agrees closely with the results of a boundary layer theory. The measurements indicate that the trajectory of the reflected shock close to the end wall is characterized by three different regions; the region in which boundary layer theory is valid, a region closer to the wall in which deviations from boundary layer theory are observed, and a non-continuum region adjacent to the wall in which the reflected shock is formed. The reflected shock wave is found to leave the formation region with a velocity which is approximately 20 per cent below the ideal velocity. It then accelerates toward this ideal velocity, approaching within 3 per cent at distances from the end wall of about 1000 mean free paths. The boundary layer approximation is found to be valid for distances greater than about 70 mean free paths. Accordingly, a non-uniform temperature profile is to be expected in a layer of approximately 100 mean free paths from the end wall.https://thesis.library.caltech.edu/id/eprint/4157Influence of Radiative Dissipation on the Shock Wave Structure
https://resolver.caltech.edu/CaltechETD:etd-10172005-111721
Authors: {'items': [{'id': 'Rupert-Viviane-Claude', 'name': {'family': 'Rupert', 'given': 'Viviane Claude'}, 'show_email': 'NO'}]}
Year: 1963
DOI: 10.7907/41E3-T691
The influence of radiation on a steady, one dimensional flow is considered. Only radiative heat transfer is taken into account; viscosity, heat conduction and mass diffusion are neglected. It is further assumed that the radiative heat transfer is adequately described by the quasi equilibrium theory relative to a grey gas.
Under these conditions, the velocity of the fluid satisfies an integral equation which has been investigated by various methods. It is shown that under certain conditions the influence of radiation alone is not sufficient to smooth out the shock profile and a discontinuity in velocity still appears; mass diffusion processes are dominant in these cases.https://thesis.library.caltech.edu/id/eprint/4126Experiments in a Cylindrical Magnetic Shock Tube
https://resolver.caltech.edu/CaltechTHESIS:10092012-110749746
Authors: {'items': [{'id': 'Vlases-George-Charpentier', 'name': {'family': 'Vlases', 'given': 'George Charpentier'}, 'show_email': 'NO'}]}
Year: 1963
DOI: 10.7907/1EHZ-AZ30
<p>An investigation has been conducted with the two-fold purpose
of producing very high Mach number shock waves and studying their
interaction with an external magnetic field parallel to the shock front.
By means of the technique of electromagnetic driving, stable reproducible, outward-going cylindrical shock waves in the Mach number
range from 20 to 100 have been produced and studied.</p>
<p>Theory predicts fundamental differences between the interaction
of a magnetic field with a shock moving into a highly conducting
fluid and the interaction of a field with a strong gas-ionizing shock.
In the former case a true mhd shock is produced. In the latter the
field interacts directly only with the piston and the shock remains
an ordinary one. The effect of a conducting wall surrounding the
chamber also differs substantially in the two cases.</p>
<p>Detailed experiments have been carried out on gas-ionizing
shocks. While the overall motion is very nearly that predicted by the
theory, anomalies have arisen in the details of the flow and are
explained in a qualitative manner.</p>
<p>Methods of producing sufficient initial conductivity to obtain a
thin magnetohydrodynamic shock are discussed, together with some
preliminary experiments along these lines.</p>https://thesis.library.caltech.edu/id/eprint/7231Experiments on the Wall-Pressure History in Shock Reflection Processes
https://resolver.caltech.edu/CaltechETD:etd-09122002-083236
Authors: {'items': [{'id': 'Baganoff-Donald', 'name': {'family': 'Baganoff', 'given': 'Donald'}, 'show_email': 'NO'}]}
Year: 1964
DOI: 10.7907/XK5D-HZ55
NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.
The normal reflection of a plane shock from a plane wall is investigated experimentally using a pressure gauge which has a risetime of 0.1 [....] and no overshoot. Pressure histories of 5 [.....] duration can be obtained with this gauge. The experiments were conducted on the end wall of the GALCIT 17-in.-diameter shock tube.
Experimental results for three aspects of the reflection process are discussed: (1) profile for the reflected shock front, (2) effect of a cold wall, and (3) effect of a real gas.
It is concluded that the effect of a cold wall must play a comparatively minor role in the reflection process since the thickness of the recorded profile is comparable to the thickness of the incident shock, and the pressure jump across the profile is about 85 per cent of the ideal value. Also, the pressure history immediately behind the reflected shock can be approximated by boundary layer theory. The effect of a real gas was studied in carbon dioxide and it is shown that the relaxation process behind the incident shock produces a large effect on the recorded pressure history which provides a method of measuring the vibrational relaxation time in carbon dioxide for high temperatures.https://thesis.library.caltech.edu/id/eprint/3478Investigation of Shock Front Topography in Shock Tubes
https://resolver.caltech.edu/CaltechETD:etd-12082005-105038
Authors: {'items': [{'id': 'Bowman-Robert-Marcus', 'name': {'family': 'Bowman', 'given': 'Robert Marcus'}, 'show_email': 'NO'}]}
Year: 1966
DOI: 10.7907/XPM1-ZZ53
<p>An experimental investigation of the shape of shock waves in a circular shock tube is conducted. It is found that there are three distinct regimes governed, in a given tube, by the initial pressure in the test section.</p>
<p>At very low pressures, where the shock thickness is greater than about half the tube radius, the axial extent (deviation from a plane) of the shock is roughly constant and dominated by the viscous interaction between the "shock", the boundary layer, and the driving piston of gas. This range of pressures is called the viscosity-dominated regime.</p>
<p>At intermediate pressures, the shape of the shock is very nearly that predicted by the theory of de Boer, the shock curvature being produced by the boundary layer and the axial extent being roughly inversely proportional to the square root of the initial pressure. This is the boundary layer regime. de Boer's work is extended and the shock shapes for both the two-dimensional and axisymmetric cases are computed and plotted.</p>
<p>At high pressures, the shape of the shock is complex and varies periodically down the tube. This shape is determined by transverse waves produced at the diaphragm (or other upstream disturbance) and reflecting back and forth across the tube, decaying with the square root of the distance down the tube. In this transverse wave regime, the axial extent of the shock is essentially independent of initial pressure and is much greater than had been expected.</p>
<p>The square root decay of the transverse wave disturbances is in contrast to the 3/2 power decay predicted by Freeman and apparently verified by Lapworth. The experimental data of Lapworth is re-plotted and it is shown that if this data is analyzed in a slightly different manner it appears to exhibit square root decay.</p>
<p>It is shown that the shock perturbations which exist in the transverse wave regime are absent at lower pressures. The transition region where these disturbances suddenly disappear seems to correspond approximately to the initial pressure at which the boundary layer (appropriately defined) at the disturbance fills the tube.</p>
<p>A rule of thumb is developed from which it should be possible to predict the transition initial pressure (which separates the transverse wave and boundary layer regimes) in any given shock tube. This pressure occurs when the quantity L/p<sub>1</sub>R<sup>2</sup> is of order one, the tube dimensions being in millimeters and the initial pressure in millimeters of mercury. This rule of thumb is used to analyze the results of several shock tube experiments published by other researchers.</p>
<p>Using this rule of thumb as an important constraint, a low pressure shock tube design chart is developed, from which, given the type of experiments contemplated and the nature of the instrumentation available, the proper shock tube dimensions and operating pressures may be determined.</p>
<p>Finally, avenues of future research are suggested, wherein it may be possible to design a new type of "hi-fi" shock tube, capable of producing more nearly plane shock fronts for use in shock structure and relaxation time studies, especially where methods such as integrated schlieren, optical reflectivity, or electron beam scattering are to be used.</p>
https://thesis.library.caltech.edu/id/eprint/4856On the Generation of Shock Waves in an Inverse Pinch
https://resolver.caltech.edu/CaltechETD:etd-03312009-155713
Authors: {'items': [{'id': 'Sorrell-Furman-Yates', 'name': {'family': 'Sorrell', 'given': 'Furman Yates, Jr.'}, 'show_email': 'NO'}]}
Year: 1966
DOI: 10.7907/ZCDM-SF32
A problem inherent in magnetic shock tubes is the difficulty of achieving separation of the driving current sheet and the shock wave. If such devices are to be applied to produce shock waves for experimentation, then separation will usually be a necessary requirement. In the present experiments in an inverse pinch shock tube, preliminary measurements showed that not only was separation not achieved, but under certain conditions the shock was actually found to be located far behind the front of the current sheet. This appeared to be a paradoxical case of the shock wave pushing the piston. Moreover, measurements of the current sheet velocity indicated that the interaction of the current sheet with the gas should be strong enough to sweep up all the gas encountered by the current sheet and thus to produce a shock wave moving ahead of it. In order to find explanations for the absence of separation and for some other puzzling aspects of these early experiments, further measurements were made to study in more detail the processes taking place in the device. These included measurements of the radial electric field with electrostatic probes and of the ionization levels by the technique of spectral line broadening. The results of these measurements show that the degree of ionization is surprisingly low and that the amount of gas leaking through the current sheet is significantly high in some cases. The conclusion is then reached that although the so-called "snowplow model" is successful in predicting the current sheet velocity, it does not lead to the correct picture of the physical processes taking place. Finally, conditions for which separation may be achievable are inferred from the experiments.https://thesis.library.caltech.edu/id/eprint/1236Aligned Fields Magneto-Fluid Dynamic Flow Past Bodies
https://resolver.caltech.edu/CaltechETD:etd-09122002-094628
Authors: {'items': [{'id': 'Yonas-Gerold', 'name': {'family': 'Yonas', 'given': 'Gerold'}, 'show_email': 'NO'}]}
Year: 1966
DOI: 10.7907/XGWS-3X78
NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.
The drag of spheres and disks has been measured in a flow of liquid sodium with an aligned magnetic field. The experiments were carried out for 10[superscript 4] < Re < 25 x 10 [superscript 4] and N , the interaction parameter, satisfying 0.1 < N < 80 . The sphere C[subscript D] was not a function of N for N < or = 0.3, began to increase appreciably for N ~ 1.0 , and reached an asymptotic dependence proportional to [square root]N for N > 10 . The disk gave a C[subscript D] which was relatively unchanged for N< 10 , began to increase for N~10 , and had approximately the same value as for spheres for N > 20 . We conclude, that for high N , flows are characterized by C[subscript D] insensitive to body shape and emphasize this range in our discussion. A physical model is presented which involves stagnant regions which grow in length as N increases, and are separated from the outer flow by thin dissipation layers. A singular perturbation technique is suggested for the theoretical treatment of such layers.https://thesis.library.caltech.edu/id/eprint/3484Magnetofluid-Dynamic Drag Measurements on Semi-Infinite Bodies in Aligned Fields
https://resolver.caltech.edu/CaltechETD:etd-11152005-154514
Authors: {'items': [{'id': 'Suzuki-Bob-Hiro', 'name': {'family': 'Suzuki', 'given': 'Bob Hiro'}, 'show_email': 'NO'}]}
Year: 1967
DOI: 10.7907/JWK4-BM31
NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.
Experiments are described in which measurements were made of the drag of semi-infinite bodies moving parallel to a uniform magnetic field in a conducting fluid. Two of these bodies were moderately streamlined halfbodies and a third was a blunt halfbody. The drag coefficients of all three bodies were found to increase monotonically as a function of the interaction parameter, N. This parameter was varied in the experiments from 0 to about 24. The drag coefficients of the streamlined halfbodies were found to increase linearly with N for N <= 0(1) in agreement with a simple theory based on a calculation of the Joule dissipation. On the other hand, for the same range of N, the drag coefficient of the blunt halfbody was found to increase negligibly from its zero-field value of 0.66. For N>>1, the drag coefficients of all three bodies were of 0(1) and appeared to be asymptotically converging to some common limiting value. Although the drag could not be calculated for large, finite values of N, an inviscid theoretical model of the flow is described from which it is concluded that the drag coefficient of any halfbody must approach unity as [...].
In addition to the experiments with the semi-infinite bodies, experiments are also described in which measurements were made of the non-magnetic drag of impulsively-started flat disks. Some unexpected and interesting transient variations in this drag were observed and are attributed to the vortex formation process in the wake.https://thesis.library.caltech.edu/id/eprint/4578Mass Spectrometric Studies of Ionization in Shock Heated Gas Mixtures
https://resolver.caltech.edu/CaltechETD:etd-11142005-104254
Authors: {'items': [{'id': 'Wang-Charles-Chang-Ping', 'name': {'family': 'Wang', 'given': 'Charles Chang-Ping'}, 'show_email': 'NO'}]}
Year: 1967
DOI: 10.7907/GN3Q-Y356
The initial stage of thermal ionization in gas mixtures behind strong normal shock waves has been studied using a mass spectrometer. The sampling process, the unique role of mass spectrometric analysis, the ionization mechanism and the effect of impurities on the ionization relaxation time of the inert gases are discussed. A detailed analysis of ion diffusion through the end wall thermal boundary layer to investigate the effect of the sampling process on the reaction and reaction products are described. The experiments were conducted in argon and xenon at temperatures of from 10,000 ºK to 30,000 ºK and pressures from 15 mmHg to 80 mmHg. A large number of different ions were detected in "pure" (the estimated level of naturally occurring impurities was 50 ppm) argon. H+ and O+ were found in much greater amounts than any of the other products. The roles of H and O were studied further by mixing a small amount of H2 or O2 in argon. The activation energy and the effective cross section for ionization were obtained from the measured ionization rate. For argon, the activation energy agrees within experimental accuracy with the result of Kelly (1966). For hydrogen the activation energy is about 10 ev, and this value coincides with its first excited state. The effective cross section is a thousand times larger than the corresponding effective cross section for the ionization of argon. This explains why small amounts of hydrogen affect the argon ionization relaxation time.https://thesis.library.caltech.edu/id/eprint/4548I. The Use of a Large Conventional Shock Tube as a Pre-Ionizer for an Inverse Pinch Shock Tube. II. The Application of Thin-Film Heat Transfer Gauges and Flush Electrostatic Probes to Partially Ionized Flows in Shock Tubes
https://resolver.caltech.edu/CaltechETD:etd-12292005-133945
Authors: {'items': [{'id': 'Klein-Alan-Frank', 'name': {'family': 'Klein', 'given': 'Alan Frank'}, 'show_email': 'NO'}]}
Year: 1967
DOI: 10.7907/G7GV-GX76
<p>Part 1.</p>
<p>A large diameter (17"), conventional shock tube has been used as the pre-ionizer for an inverse pinch shock tube in an attempt to achieve separation of the shock front and the current sheath in the inverse pinch. The inverse pinch was mounted in the endwall of the shock tube and was operated without an anode, either behind the incident or reflected shock wave generated by the pre-ionizer shock tube. The test gases used were Xenon, Argon, and Helium. Separation was not achieved, but in Argon the pressure front did move closer to the front of the current sheath. In Xenon, no improvement in the performance of the inverse pinch was observed as a result of the pre-ionization, and in one case it was noticeably degraded, with the piston appearing to leak excessively. Because of test time limitations it was only possible to operate the inverse pinch behind the incident shock wave in Xenon. By measuring the ionization relaxation time in Xenon it was found that for all the conditions of the present experiments, ionization equilibrium was not attained in the times available. Therefore, the inverse pinch was being operated in a slightly ionized, relaxing gas. The electrical conductivity of such a gas was calculated for Xenon and Argon and the results in Argon were found to be in good agreement with previous shock tube measurements of the conductivity. The relaxation time measurements, conducted primarily in the GALCIT 6" shock tube, show that P₁τ, the product of the initial pressure and the relaxation time behind the incident shock, depends strongly upon the magnitude of P₁, especially for P₁ < .5 mm Hg of Xenon. The dependence decreases as the Mach number is increased in the range 10 < M<sub>s</sub> < 20.6.</p>
<p>Part 2.</p>
<p>Previous shock tube observations of "spurious" signals in the output of thin-film heat gauges at Mach number for which the shocked gas becomes partially ionized are summarized. It is shown that these effects, and those observed the the present experiments in Xenon, cannot be explained in terms of a shorting gauge model. It is demonstrated that the effects are due to the gauge acting more as an electrostatic probe than as a heat gauge. Under these conditions it is shown that the heat gauge provides an accurate measurement of the ionization relaxation time as well as still being useful for determining the shock velocity. The thin-film is also operated as a flush electrostatic probe to measure the ion density in the shock tube wall boundary layer, and the experimental results are in good agreement with the theoretical predictions of two solutions of the boundary layer problem: one based on an approximate solution of the transformed boundary layer equations, and the other based on the solution of the equivalent Couette flow problems. The applicability of these solutions is found to be limited to conditions for which the ionization relaxation time is either very long or very short. Because of the computational simplifications involved it is seen that the Couette flow solution is preferred under most conditions.</p>https://thesis.library.caltech.edu/id/eprint/5165Magnetohydrodynamic Shock Production and Current Sheet Diffusion
https://resolver.caltech.edu/CaltechETD:etd-12292005-135853
Authors: {'items': [{'id': 'Hoffman-Alan-Lowell', 'name': {'family': 'Hoffman', 'given': 'Alan Lowell'}, 'show_email': 'NO'}]}
Year: 1967
DOI: 10.7907/4WVH-W290
NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.
Current sheets in inverse pinch MHD shock tubes exhibit the strange property of forming shocks in the very rear of the sheet when accelerating heavy gases. When accelerating light gases, shocks are formed further to the front in the sheet, but in no case do the shocks separate from the driving current sheet. This "piston dragging shock" effect is explained on the basis of a single-fluid model with variable conductivity. Shocks are shown to always form within current sheets which move at supersonic speeds with respect to the driven gas. The relevant parameters for determining the shock position are the Mach number and the magnetic Reynolds number. Large magnetic Reynolds numbers and small Mach numbers enhance forward shock formation. These conditions are obtained in light gases with high speeds of sound. Similarity methods are developed to estimate gas conductivities, electron temperatures, and degrees of ionization for the experiments which are conducted. In hydrogen typical electron temperatures of 4 ev are produced by the ohmic heating, but twice this value is shown necessary to achieve separation at the current sheet speeds of 2-3 [...] used. Higher current sheet speeds produce shocks in the rear of the current sheet where separation can never occur. The correct method of procedure and the relevant design parameters to achieve separation are given. The success of single-fluid methods in explaining plasma phenomena is especially notable, and these methods can be extended to other similar problems. Based on these methods, multiple-fluid and microscopic effects are easily detectable and can be accounted for.https://thesis.library.caltech.edu/id/eprint/5166Mass spectrometric studies of ionization precursors ahead of strong shock waves
https://resolver.caltech.edu/CaltechETD:etd-11222005-155153
Authors: {'items': [{'id': 'Robinson-W-M', 'name': {'family': 'Robinson', 'given': 'William McKinley'}, 'show_email': 'NO'}]}
Year: 1969
DOI: 10.7907/0QN4-MY03
NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.
An experimental study was conducted to identify the nature and origin of precursor ions produced by photoionization ahead of strong shock waves in xenon. A magnetic mass spectrometer is mounted at the end of a hydrogen-driven shock tube. Ions produced upstream of a shock wave are sampled by the spectrometer and the collected current provides a continuous time history of a particular ionic species. A mass spectrum is obtained in the precursor region for all impurities found in the shock tube. The incident shock Mach number is varied from 11.9 to 21.3, the initial pressure is varied from 0.050 to 0.500 torr, and the impurity level is altered. In all the conditions studied, the dominant ion present in the precursor is Xe+, although in certain instances, the impurity ion currents are found to be of the same order of magnitude as the xenon ion current. For small impurity levels, photoionization processes in xenon and impurities are apparently independent. Independent double probe measurements determine the total ion density to be about [...] at the shock front, the observable precursor extending about 150 cm from the shock wave.
A theoretical model accounting for one-step and multi-step photoionization of xenon and impurities is used to find the ionization level ahead of a shock wave. The calculated ion density profiles agree well with experimental observations at the low pressures, where it appears that one-step photoionization predominates. Lack of agreement at high pressures, where, apparently, multi-step ionization is more efficient than the single-step process, suggests inadequacies in the treatment of photoexcitation and multi-step photoionization. Additional areas for experimental study are suggested.
The mass spectrometric data yield a better understanding of the role of radiation in shock structure, of the kinetics of photoionization processes in rare gases, and of the influence of impurities in the experimental facility on the radiation mechanisms.
https://thesis.library.caltech.edu/id/eprint/4638Velocity measurements ahead of a semi-infinite body in magnetohydrodynamic flow with aligned fields
https://resolver.caltech.edu/CaltechETD:etd-12282005-142805
Authors: {'items': [{'id': 'Lake-B-M', 'name': {'family': 'Lake', 'given': 'Bruce Meno'}, 'show_email': 'NO'}]}
Year: 1969
DOI: 10.7907/PN2X-JB97
NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.
Experiments are described in which velocities were measured ahead of a semi-infinite Rankine body moving parallel to a uniform magnetic field in a conducting fluid. The flow disturbance in front of the body is found to increase in length as [...], where N is the interaction parameter. In most of the experiments this parameter was varied from 4 to about 50. Measurements made along the axis of symmetry in the flow show that there is a relatively short region of stagnant fluid directly ahead of the body. The major part of the disturbance is found to consist of a much longer region in which the flow undergoes transition from conditions in the freestream to conditions near the body. Velocity profiles across the flow in this region show that for increased N, at a fixed distance ahead of the body, the velocity defect increases and the disturbance becomes more confined radially. Although the radial gradients in the flow increase with N, they are found to be much smaller than would be expected in a flow containing thin current layers. A physical model of the flow which has currents and pressures consistent with these results is discussed.https://thesis.library.caltech.edu/id/eprint/5157Laser velocimeter measurement of Reynolds stress and turbulence in dilute polymer solutions
https://resolver.caltech.edu/CaltechTHESIS:08202010-110214903
Authors: {'items': [{'id': 'Logan-Samuel-Ernest', 'name': {'family': 'Logan', 'given': 'Samuel Ernest'}, 'show_email': 'NO'}]}
Year: 1972
DOI: 10.7907/BD39-BV19
Measurements of Reynolds stress and axial and transverse
turbulence intensities have been made in drag-reducing
turbulent pipe flow of a dilute solution of high molecular
weight polymer and compared to measurements made with pure
water. A newly developed laser velocimeter capable of
measuring these turbulence parameters has been utilized and
is described in detail.
Axial turbulence intensities measured in polymer solution
are consistent with previous polymer results and
viscous sublayer thickening is observed. New results include
demonstration that the turbulent shearing stress is
reduced in the turbulent core by an amount proportional to
the observed decrease in pressure gradient at the wall, and
extrapolates to a wall value in agreement with calculated
local wall shear. Near the wall polymer solution Reynolds
stress is reduced below that measured for water consistent
with observed velocity profiles. Polymer radial turbulence
intensities are comparable with those for water in the
turbulent core, but exhibit similar dramatic suppression
near the wall. These and other recent results strongly
suggest that dilute polymer solution drag reduction is
primarily a wall phenomenon. Polymers appear to have little
or no effect on turbulent flow away from a solid boundary
where turbulent velocities scale with u_τ, the shear
velocity based on the observed wall shear.
https://thesis.library.caltech.edu/id/eprint/6002I. Nonlinear gas oscillations in pipes. II. Wavetrains with small dissipation.
https://resolver.caltech.edu/CaltechTHESIS:08172011-101324443
Authors: {'items': [{'id': 'Jimenez-J', 'name': {'family': 'Jimenez', 'given': 'Javier'}, 'show_email': 'NO'}]}
Year: 1973
DOI: 10.7907/HRSK-FC56
In part I of this thesis we study theoretically the problem of forced acoustic oscillations in a pipe. The oscillations are produced by a moving piston in one end of the pipe, while a variety of boundary conditions ranging from a completely closed end to a completely open mouth are considered at the other end. All these boundary conditions are modelled by two parameters: a length correction and a reflection coefficient equivalent to the acoustic impedance.
The linear theory predicts large amplitudes near resonance and non-linear effects become crucially important. By expanding the equations of motion in a series of the Mach number, both the amplitude and waveform of the oscillations are predicted there.
In both the open and closed-end cases the need for shock waves in some range of parameters is found. The amplitude of the oscillation is different for the two cases, however, being proportional to the square root of the piston amplitude in the closed end case, and to the cube root in the open end.
This part of the thesis was first published in the Journal of Fluid Mechanics.
In part II we modify the averaged Lagrangian method used by Whitham to analyze slowly varying non-linear wavetrains to include cases with a small dissipation. To do this, we use a pseudo-variational principle introduced by Prigogine in which the Lagrangian depends on the variable and the solution of the problem, and which can be used to describe irreversible processes.
We prove the corresponding averaged equations to all orders and describe practical ways to use them to lowest order.https://thesis.library.caltech.edu/id/eprint/6586Investigation of Supercritical Heat Flow in Helium II
https://resolver.caltech.edu/CaltechETD:etd-11032003-094055
Authors: {'items': [{'id': 'Dimotakis-P-E', 'name': {'family': 'Dimotakis', 'given': 'Paul Emmanuel'}, 'show_email': 'NO'}]}
Year: 1973
DOI: 10.7907/WMV3-FJ63
<p>To investigate the validity of appending the Gorter-Mellink friction term to the equations of motion of liquid helium the temperature was measured along the axis of a channel carrying a supercritical heat current. A single thermometer on a traversing assembly was used permitting local measurements both in the interior of the channel and in the jet formed in the free fluid.</p>
<p>The temperature gradient in the interior of the channel is found to be in agreement with the Gorter-Mellink law up to the lamda point, but goes to zero within a channel diameter, in the free jet. Since the relative velocity between the two fluids is probably continuous along the axis of the jet in the vicinity of the exit, the disappearance of the temperature gradient appears to be inconsistent with the predictions of the Gorter-Mellink term.</p>
<p>The Gorter-Mellink A(T) was also measured up to the lamda point. A much stronger divergence is found as T<sub>λ</sub> is approached than was indicated by previous measurements.</p>https://thesis.library.caltech.edu/id/eprint/4378Experimental study of shock wave strengthening by a positive density gradient in a cryogenic shock tube
https://resolver.caltech.edu/CaltechTHESIS:08272010-083731520
Authors: {'items': [{'id': 'Rupert-V-C', 'name': {'family': 'Rupert', 'given': 'Viviane Claude'}, 'show_email': 'NO'}]}
Year: 1973
DOI: 10.7907/ZXBM-7809
An experimental investigation of the strengthening of a shock wave propagating through an isobaric region of increasing density is presented. A new experimental configuration consisting of a pressure-driven shock tube mounted vertically with the test section partially immersed in a cryogenic bath is used. The resulting test gas density distribution consists of a uniform region of low density near the shock tube diaphragm, then a strong local gradient followed by another uniform region of high density. The
Mach number of the shock initiated at the diaphragm is determined as the shock emerges from the gradient from velocity and temperature measurements for various initial conditions.
The experimental data are compared with predictions from approximate theoretical models and a numerical integration of the exact flow equations for the shock-gradient interaction. The measured Mach numbers are considerably higher than these predictions indicating that the models are not adequate to represent the experimental configuration. Calculations show that the additional strengthening of the shock results from multiple interactions between waves generated within the gradient and flow nonuniformities due to the shock formation mechanism.
https://thesis.library.caltech.edu/id/eprint/6012I. Development of a Cryogenic Shock Tube. II. Experimental Investigation of the Interaction of a Shock Wave with Liquid Helium and I and II
https://resolver.caltech.edu/CaltechTHESIS:10072010-095321580
Authors: {'items': [{'email': 'jccummi@comcast.net', 'id': 'Cummings-John-Chester', 'name': {'family': 'Cummings', 'given': 'John Chester'}, 'show_email': 'YES'}]}
Year: 1973
DOI: 10.7907/AM0F-DB64
<p>I. Development of a cryogenic shock tube</p>
<p>A cryogenic shock tube has been developed as a tool for research in fluid mechanics and low temperature physics. The shock tube is designed to operate with the test section immersed in a cryogenic liquid. A unique diaphragm changing mechanism makes this shock tube an economical and practical device.</p>
<p>There are several advantages in operating a shock tube at cryogenic temperatures. Shock waves of very large Mach number can be produced. The flow field can be accurately calculated using ideal shock tube - perfect gas theory. Boundary layer effects are decreased so that long test times are possible.</p>
<p>The cases which have been studied are test gas temperatures of 300, 77, 4.2, and 2.3°K. Helium is used as both test and driver gas. The largest Mach numbers which have been observed range from 2.4 at 300°K to 32 at 2.3°K (several runs at 1.46°K have produced Mach 40 shocks). As the test gas temperature is decreased the observed Mach numbers approach those calculated using the ideal shock tube equation. The observed test times can be interpreted using laminar or turbulent boundary layer theory if the effects of shock formation distance and wall temperature rise are taken into account.</p>
<p>As a laboratory tool the cryogenic shock tube may be applied in many areas and modified for use in even more. Large Mach number shocks and large Reynolds number flows can be produced with this device. The rapid increase in temperature and pressure across a shock wave is useful for studies of sublimation, evaporation, or chemical reactions. Quantum mechanical effects in cryogenic materials, superconductors, or superfluid helium can also be investigated.</p>
<p>II. Experimental investigation of the interaction of a shock wave with liquid helium I and II</p>
<p>The flow field produced by a shock wave reflecting from a helium gas -liquid interface has been investigated using a new cryogenic shock tube. Incident and reflected shock waves have been observed in the gas; transmitted first and second sound shocks have been observed in the liquid. Wave diagrams have been constructed to compare the data to theoretical wave trajectories. Qualitative agreement between data and theory has been shown. Quantitative differences between data and theory indicate a need for further analysis of both the gas-liquid interface and the propagation of nonlinear waves in liquid helium.</p>
<p>This work is essentially a first step in the experimental investigation of a very complex nonequilibrium state. The well controlled jump in temperature and pressure across the incident shock wave provides unique initial conditions for the study of dynamic phenomena in superfluid helium.</p>
<p>The results clearly demonstrate the usefulness of the cryogenic shock tube as a research tool.</p>https://thesis.library.caltech.edu/id/eprint/6115Second sound attenuation in a liquid helium counterflow jet
https://resolver.caltech.edu/CaltechTHESIS:09282010-140423372
Authors: {'items': [{'id': 'Laguna-G-A', 'name': {'family': 'Laguna', 'given': 'Glenn A.'}, 'show_email': 'NO'}]}
Year: 1975
DOI: 10.7907/7C0G-HK08
The attenuation of a beam of high frequency second sound traversing a counterflow jet in liquid helium has been measured in the temperature range 1.6 to 2.06°K. Combined use of thin film superconducting thermometers with specially developed low noise amplifiers allowed a temperature resolution of better than one part in 10^8 °K. The additional attenuation due to the jet was found to be less than 10 percent of the predicted value using the theory of mutual friction in a supercritical counterflow, and consistent with the result of earlier temperature gradient and ion beam attenuation measurements.https://thesis.library.caltech.edu/id/eprint/6069A chemical reaction in a turbulent jet
https://resolver.caltech.edu/CaltechETD:etd-11282006-152216
Authors: {'items': [{'email': 'jshea@ida.org', 'id': 'Shea-J-R', 'name': {'family': 'Shea', 'given': 'John R.'}, 'show_email': 'YES'}]}
Year: 1976
DOI: 10.7907/BJQT-9A50
<p>The turbulent mixing and subsequent chemical reaction of gases is an essential part of many technological processes ranging from gas furnaces to chemical lasers. Surprisingly, there is very little information, either theoretical or experimental, about the actual rate of the chemical reaction in such processes. Generally the chemical kinetics are well understood, but the process of turbulent mixing is not. Many measurements of mixing in turbulent jets have been made in the past, but they have generally failed to distinguish essentially unmixed gas in the turbulent mixing zone from gas which is mixed on a molecular scale. Knowledge of where turbulent fluid is mixed on a molecular scale is critical for predicting chemical reaction rates in the flow.</p>
<p>In this experiment the rate of a chemical reaction in an axisymmetric turbulent jet is studied, and the results are used to determine the rate of molecular mixing in the jet. A turbulent jet containing dilute ozone in an inert mixture of nitrogen and oxygen flows into a stagnant tank of nitric oxide and nitrogen. When the gases mix on a molecular scale, the ozone and nitric oxide rapidly react to produce oxygen and nitrogen dioxide. The rate at which the mixing and chemical reaction proceeds is determined by using an ultraviolet light absorption technique to measure the time averaged ozone concentration at points throughout the jets mixing zone.</p>
<p>The experiment establishes a criterion for determining when a reaction of known chemical kinetics is sufficiently rapid that chemical nonequilibrium has a negligible effect on the mean reactant profile. When a reacting jet satisfies this criterion for equilibrium chemistry, the reactant profiles are found to be independent of jet Reynolds numbers from 4,000 to 32,000 based on the nozzle diameter.</p>
<p>In addition, a mixing fraction, η, is defined to measure the extent of local molecular scale mixing independently of a chemical reaction occurring in the jet. The fraction assumes values of unity in the unmixed primary jet, zero in unmixed ambient fluid, and intermediate fractions for mixtures of all proportions. Points on nonreacting jet profiles are related to time averages of η. A limiting highly reacting ozone profile, found when a large excess of nitric oxide is present in the ambient fluid, is related to the time average of an intermittency function, J(η), defined equal to unity when η is within a specified neighborhood of one and zero elsewhere. Thus the experimental measurements of ozone profiles are directly related to the statistics of molecular scale mixing in the jet.</p>https://thesis.library.caltech.edu/id/eprint/4675A study of the trailing vortices behind a ring wing
https://resolver.caltech.edu/CaltechETD:etd-11092006-132109
Authors: {'items': [{'id': 'Bofah-Kwasi-Kete', 'name': {'family': 'Bofah', 'given': 'Kwasi Kete'}, 'show_email': 'NO'}]}
Year: 1976
DOI: 10.7907/050Z-4228
NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.
The flow field of a laminar vortex wake behind a ring wing was investigated. Experiments were conducted in the GALCIT Low Speed Water Channel, using laser Doppler velocimetry techniques to measure vertical and axial velocity components in the trailing vortex wake. A thin cylindrical ring wing model was tested at various axial angles of attack and free stream velocities. Velocity profiles were measured at several downstream stations from the trailing edge to 45 wing diameters downstream.
The inviscid roll-up of the trailing vortex sheet shed by a ring wing was numerically examined. A line vortex representation was used to calculate the evolution of the initially cylindrical vortex sheet. The vortex sheet was found to distort in shape and then smoothly roll up into a pair of doubly connected spirals whose centers originate from approximately the center of gravity of vorticity in the upper quadrants of the ring wing's circular trailing edge. (This origin is at an angle of 38° measured from the horizontal wing diameter.)
The experimental and flow visualization results are consistent with the numerical data and show that a pair of counter-rotating vortices do develop from the rolling up of the vortex sheet shed by a ring wing in a nonaxial flow. The vortices trail, downstream of the wing, with their vorticity centroids spaced by [...]/4 wing diameters.
Saffman and Moore's theory of axial flow in laminar trailing vortices was adapted and found to be in reasonable agreement with the experimental results. The flow field near the trailing edge was found to be in fair agreement with Weissinger's inviscid calculations.https://thesis.library.caltech.edu/id/eprint/4475An experimental investigation of propagation of weak shock waves in a random medium
https://resolver.caltech.edu/CaltechETD:etd-01042006-154703
Authors: {'items': [{'id': 'Hesselink-L', 'name': {'family': 'Hesselink', 'given': 'Lambertus'}, 'show_email': 'NO'}]}
Year: 1977
DOI: 10.7907/XKHF-VD55
NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.
An apparatus has been constructed for generating a 25 cm cube of randomly inhomogeneous gas in the GALCIT 17-inch diameter shock tube. It consists of a two-dimensional 7 x 8 array of fine jets alternately of helium and freon-12 behind coarse grids located on opposite sides of a box. The two other side walls of the box are fitted with optical windows for diagnostics. The up-stream and downstream faces of the box are movable and can be opened rapidly just before shock arrival. This process is automated, and the arrival time of the shock wave relative to the decay of the turbulent density field can be varied. The gas mixture is made neutrally buoyant so that the mean interface between the scattering region and the uniform air in the shock tube is parallel to the plane of the incoming wave. Furthermore, the mean acoustic impedance of the mixture is matched to that of the quiescent air in the shock tube to minimize the effect of the air-gas mixture interface on the shock wave.
In this experiment shock waves of strengths varying from [...] = 1.007 to 1.1 scatter from random variations of acoustical impedance and index of refraction (defined as the ratio of the sound speed in air to the local, variable, sound speed in the scattering medium) which occur during the turbulent mixing of the two different gases. The scale and amplitude of the fluctuations before interaction with the shock wave are obtained from optical and point density measurements; the method of Uberoi and Kovasznay (Ref. 10) has been used to obtain length scales of the flow from shadowgraph and schlieren pictures, and the Brown-Rebollo (Ref. 11) density probe is used to measure local mean and rms density fluctuations, and space- and cross-correlation functions.
To study the interaction of the shock with the turbulence, spark shadowgraph and schlieren pictures have been taken and pressure measurements have been made. Arrays of pressure transducers located in a false endwall downstream of the scattering volume record the shock front topology and the spatial variation of shock amplitude.
The pressure measurements indicate a substantial modification of the unperturbed shock profile. Data are presented which indicate the effect of the Mach number on the scattering process.
Optical measurements show that length scales in the fluid, which is processed by all but the weakest shocks, have changed due to the interaction process.https://thesis.library.caltech.edu/id/eprint/24Experimental investigation of second sound shock waves in liquid helium II
https://resolver.caltech.edu/CaltechETD:etd-11012006-135258
Authors: {'items': [{'id': 'Rogers-P-L', 'name': {'family': 'Rogers', 'given': 'Philip Louis'}, 'show_email': 'NO'}]}
Year: 1979
DOI: 10.7907/y2bj-vw94
Second sound shock waves in liquid helium II were studied experimentally using superconducting thin film detectors. The temperature waves were generated electrically using an evaporated thin film heater and the effects of variations in pulse power (input power to the heater as large as 150 Watts/cm(2)) and pulse duration (from less than 100 µsec to 10 msec) were examined. A number of different materials were tested for use as detectors with the best results obtained from evaporated gold on tin.
Qualitative agreement with Khalatnikov's theory was obtained; however, breakdown of the theoretical model was observed for heater input powers greater than 20 - 30 Watts/cm(2), in agreement with other known results. Quantitative data for shock strength, i.e., temperature amplitude, wave speed, and pulse power, were obtained. The critical counterflow velocities calculated from these data, w = 2.51 to 3.77 m/sec, indicate that heat fluxes at least an order of magnitude greater than those reported for steady channel flow can be transported using the pulsed techniques.
https://thesis.library.caltech.edu/id/eprint/4360A chemically reacting, turbulent shear layer
https://resolver.caltech.edu/CaltechETD:etd-10272006-111937
Authors: {'items': [{'id': 'Breidenthal-R-E', 'name': {'family': 'Breidenthal', 'given': 'Robert Edward'}, 'show_email': 'NO'}]}
Year: 1979
DOI: 10.7907/hj67-9h91
A chemically reacting turbulent shear layer was investigated in a new, blow-down water tunnel. In a diffusion-limited reaction, a pH indicator, phenolphthalein, in one stream mixed and reacted with a base, sodium hydroxide, in the other stream to form a visible reaction product. Using optical densitometry techniques, the amount of product was measured as a function of Reynolds number, at a relatively high Schmidt number of approximately 600. The results were compared with both the previous mixing measurements of Konrad in a gaseous shear layer (Sc = 0.7) and the simple mixing model of Broadwell.
The product was found to be distributed, as expected, in concentrated lumps associated with the large, spanwise-coherent structures of the turbulence. The time averaged amount of product in the layer exhibited a rapid transition at a large-structure Reynolds number of about 5 x 10(3) for a velocity ratio of 0.38. Above the transition, the amount of product within the layer was independent of Reynolds number.
This transition is related to the introduction of small scale, three-dimensional motions into the layer. In the initial region, where the flow was already unsteady and contained large structures but was strictly two-dimensional, very little mixing was observed. Downstream the flow became unstable to three-dimensional perturbations and small scale, three-dimensional motions were introduced into the layer. Across this transition, the aqueous mixing increased by an order of magnitude, indicating the sensitivity of mixing to small scales of the turbulence in a high Schmidt number fluid. At high Reynolds numbers, changing the Schmidt number by three orders of magnitude only altered the molecular mixing by about a factor of two or less. The mixing model of Broadwell, which addresses the effect of Schmidt number, is in satisfactory qualitative agreement with the observations.
The unique flow visualization of the visible reaction product in water permitted a study of the three-dimensional instability and evolution of small scale motions in the layer. Streamwise streaks which had been previously observed in the Brown-Roshko gas apparatus were found to originate from a spanwise-sinuous wiggle which appeared at a large-structure Reynolds number which varied with velocity ratio, indicating an influence of initial conditions on the instability.
https://thesis.library.caltech.edu/id/eprint/4277Experimental investigation of first- and second-sound shock waves in liquid helium II
https://resolver.caltech.edu/CaltechETD:etd-11032006-095703
Authors: {'items': [{'id': 'Wise-J-L', 'name': {'family': 'Wise', 'given': 'Jack LeRoy'}, 'show_email': 'NO'}]}
Year: 1979
DOI: 10.7907/c49w-bh82
The cryogenic shock tube is used to generate a gasdynamic shock which propagates through saturated helium vapor and subsequently reflects from the upper surface of a column of LHeII. Superconducting thin-film detectors, produced by evaporation of aluminum in an oxygen atmosphere, yield highly repeatable arrival time data for the incident gasdynamic shock and the resultant first- and second-sound shocks in the liquid. Accurate x-t diagrams of the shock trajectories have been constructed for initial liquid temperatures of T(0) = 1.522, 1.665, 1.751, 1.832, 1.989, 2.031, and 2.095°K. Consistent discrepancies are observed between experimental and theoretical wave trajectories.
The detector signals qualitatively verify theoretical predictions that the temperature decreases through the pressure shock and increases through the temperature shock. Amplitude measurements based on static detector calibrations indicate that the magnitude of the temperature jump across the pressure shock agrees approximately with the theoretical calculation. Temperature jump measurements for the coupled second-sound shock imply shock-induced relative velocities, w =v(n)-v(s), on the order of 2.5 m/sec.
For initial conditions close to the [lambda]-transition (e.g., T(0) = 2.095°K), the pressure jump across the first-sound shock is sufficient to cause a change in phase from LHeII to LHeI. This change is experimentally evidenced by detector outputs indicating the absence of the temperature shock in the wake of a sufficiently strong pressure shock.https://thesis.library.caltech.edu/id/eprint/4395Second sound shock waves and critical velocities in liquid helium II
https://resolver.caltech.edu/CaltechETD:etd-10132006-075044
Authors: {'items': [{'id': 'Turner-T-N', 'name': {'family': 'Turner', 'given': 'Timothy Neal'}, 'show_email': 'NO'}]}
Year: 1980
DOI: 10.7907/cg05-6436
NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.
Large amplitude second-sound shock waves have been generated and the experimental results compared to the theory of nonlinear second-sound. The structure and thickness of second-sound shock fronts is calculated and compared to experimental data. Theoretically it is shown that at T = 1.88°K, where the nonlinear wave steepening vanishes, the thickness of a very weak shock must diverge. In a region near this temperature, a finite-amplitude shock pulse will evolve into an unusual double-shock configuration consisting of a front steepened, temperature raising shock followed by a temperature lowering shock. Double-shocks are experimentally verified. The theoretical dependence of the shock induce temperature jump on the Mach number is successfully verified for large amplitudes ([...]) after the response of a thin-film superconducting temperature sensor is analyzed.
The ability of second-sound shock waves to simultaneously produce and measure very large relative velocities in regions away from the disruptive influence of walls makes them an invaluable tool in the study of critical velocities intrinsic to the fluid. It was experimentally discovered that very large second-sound shock waves initiate a breakdown in the superfluidity of helium II, which is dramatically displayed as a limit to the maximum attainable shock strength. Although the observed breakdown could not be definitely attributed to a critical velocity, the value of the maximum shock-induced relative velocity represents a significant lower bound to the intrinsic critical velocity of helium II. The observed limits within which superfluidity was still maintained (w=3.67 m/sec at T = 1.45°K, and w = 3.20 m/sec at T = 1.85°K) are the largest counterflow velocities ever obtained outside of restricted geometries.https://thesis.library.caltech.edu/id/eprint/4071Passive and Active Control of Boundary Layer Transition
https://resolver.caltech.edu/CaltechETD:etd-09182006-135720
Authors: {'items': [{'email': 'dan@princeton.edu', 'id': 'Nosenchuck-Daniel-Mark', 'name': {'family': 'Nosenchuck', 'given': 'Daniel Mark'}, 'show_email': 'YES'}]}
Year: 1982
DOI: 10.7907/CKFA-E875
<p>It is well known that laminar-turbulent boundary layer transition is initiated by the formation of Tollmien-Schlichting laminar instability waves. The amplification rates of these waves are strongly dependent on the shape of the boundary layer velocity profile. Consequently, the transition process can be controlled by modifying the velocity profile. This can be accomplished by controlling the pressure gradient (dp/dx), using boundary layer suction, installing surface roughness elements, or by surface heating or cooling. Methods used to modify the transition process through changes in the mean velocity profile are called "passive" in this paper. There exists a large set of experiments and theory on the application of passive methods for boundary layer control. In the present work only surface heating will be addressed.</p>
<p>Transition measurements were made on a heated flat plate in water. Results are presented for several plate wall temperature distributions. An increase by a factor of 2.5 in transition Reynolds number was observed for a 5°C isothermal wall overheat. Buoyancy effects on transition were minimal due to the small Richardson and Grashof numbers encountered in the experiments.</p>
<p>The amplification of laminar instability waves is comparatively to process, taking place over many boundary layer thicknesses. After the slow amplification of the laminar instability waves, transition occurs by a strong three dimensional dynamic instability. It appears possible to attenuate (or reinforce) the instability waves by introducing amplitude-and phase-controlled perturbations into the laminar boundary layer using feedback control system. This method is called "active" control and forms the larger part of the research reported in this thesis.</p>
<p>A combination of sensors, activators and feedback control electronics is required for active control. The sensors used in the experiments are flush-mounted hot film wall shear robes. A new type of activator was developed using thin, flush-mounted surface heating elements to excite instability waves in the laminar boundary layer by periodic (active) heating.</p>
<p>Experimental evidence is presented illustrating the effects of periodically heated flush mounted strips in perturbing a flat plate boundary layer in water. The results of superposition of forced laminar instability waves are also given. Finally, an active feedback-control system using a single hot film probe and strip heater was developed to control natural laminar instability waves in real time. It is shown that when the natural waves were attenuated, the transition length was increased by 25%, requiring only 10 watts of strip heater power. To accomplish the same transition delay using passive heating, the internal heating pads had to supply 1900 watts of power.</p>https://thesis.library.caltech.edu/id/eprint/3620Acoustic Transmission Imaging for Flow Diagnostics
https://resolver.caltech.edu/CaltechETD:etd-10302003-145444
Authors: {'items': [{'id': 'Trebitz-Bernd-Otto', 'name': {'family': 'Trebitz', 'given': 'Bernd Otto'}, 'show_email': 'NO'}]}
Year: 1982
DOI: 10.7907/pnsp-rk30
<p>Wave propagation through a given flow field can be utilized to obtain information about the flow. Acoustic waves in particular offer the possibility of measuring velocity fields, because sound waves are convected with the flow, and temperature fields, because the acoustic index of refraction is a strong function of temperature. This work concentrates on situations where the first effect is dominating compared to the latter one.</p>
<p>A sound system capable of "illuminating" a flow field with ultrasonic waves and measuring the amplitude and phase distribution of the transmitted wave as a function of time was constructed. A large area transmitter and a linear receiving array were used as transducers. Parallel signal processing and interleaved data conversion and acquisition result in a maximum frame rate of 10 kHz.</p>
<p>The feasibility of measuring velocity disturbances with ultrasound was demonstrated by transmitting sound through a vortex, which was generated in a duct by an airfoil swirl generator. Assuming an exponential fit for the tangential velocity component, inner core radius and circulation can be determined directly from the phase change of the transmitted wave due to the vortex. A more accurate representation of the radial velocity profile can be found by digital reconstruction via the Abel inversion formula, which allows reconstruction of rotationally symmetric objects from line projections. Even though the flow field under investigation was steady, this is neither a restriction of the technique, nor of the apparatus. However, the repetition rate for consecutive data frames depends on the operating procedure.</p>https://thesis.library.caltech.edu/id/eprint/4320Second Sound Scattering in Superfluid Helium
https://resolver.caltech.edu/CaltechETD:etd-10292003-161340
Authors: {'items': [{'id': 'Rösgen-Thomas', 'name': {'family': 'Rösgen', 'given': 'Thomas'}, 'show_email': 'NO'}]}
Year: 1985
DOI: 10.7907/r8ge-j070
<p>Focusing cavities are used to study the scattering of second sound in liquid helium II. The special geometries reduce wall interference effects and allow measurements in very small test volumes.</p>
<p>In a first experiment, a double elliptical cavity is used to focus a second sound wave onto a small wire target. A thin film bolometer measures the side scattered wave component. The agreement with a theoretical estimate is reasonable, although some problems arise from the small measurement volume and associated alignment requirements.</p>
<p>A second cavity is based on confocal parabolas, thus enabling the use of large planar sensors. A cylindrical heater produces again a focused second sound wave. Three sensors monitor the transmitted wave component as well as the side scatter in two different directions. The side looking sensors have very high sensitivities due to their large size and resistance. Specially developed cryogenic amplifiers are used to match them to the signal cables.</p>
<p>In one case, a second auxiliary heater is used to set up a strong counterflow in the focal region. The second sound wave then scatters from the induced fluid disturbances.</p>
<p>Attempts to observe scattering from quantized vortex lines in the rotating parabolic cavity ultimately did not succeed, although a theoretical estimate seems to indicate a basic feasibility.</p>https://thesis.library.caltech.edu/id/eprint/4302The Nature of Oblique Instability Waves in Boundary Layer Transition
https://resolver.caltech.edu/CaltechETD:etd-05242007-150746
Authors: {'items': [{'id': 'Robey-Harry-Francis-III', 'name': {'family': 'Robey', 'given': 'Harry Francis, III'}, 'show_email': 'NO'}]}
Year: 1986
DOI: 10.7907/7VG8-Y513
<p>An experimental study of both the weakly non-linear as well as the three-dimensional nature of boundary layer transition is conducted using the active surface heating technique of Liepmann et al. In the present study, this technique is extended to provide a means for controllably and repeatably introducing three-dimensional disturbances into a laminar boundary layer. A review of the surface heating technique is presented along with a discussion of some peculiarities encountered in extending this technique to three-dimensional geometries. A thorough description of the design and operation of a programmable 32-element heater array and the supporting instrumentation are given as well.</p>
<p>The heater array is first used to study the effect of weak nonlinearity on boundary layer transition. By keeping the forced disturbances as two-dimensional as possible, it is shown that the effects of weak non-linearity are relatively benign. The growth rates are seen to follow the linear theory up to perturbation amplitudes (τ'<sub>w</sub>τ̅<sub>w</sub>) of nearly twelve percent. The only deviation from the linear theory arises in the form of non-linearly generated harmonics phase-locked to the fundamental. It is concluded that although these non-linearly generated harmonics do alter the wave behavior to some extent, they are by themselves not sufficient to explain the transition from small linear oscillations to the large amplitude, broad-band, three-dimensional oscillations characteristic of a fully turbulent boundary layer.</p>
<p>The effect of three-dimensionality on boundary layer transition is then investigated through an analytical and experimental study of single oblique instability waves. This subject has remained largely unexplored, as such disturbances were generally thought to be more stable and therefore less dangerous than their two-dimensional counterparts. Through a series of experiments, however, it is shown that certain conditions exist for which oblique waves are observed to be more unstable than any two-dimensional wave. It is shown that oblique waves exhibit a non-stationary period-doubling behavior that is not seen in two-dimensional disturbances. A vortex pairing mechanism is proposed to explain this behavior, and is shown to occur in a manner consistent with the Biot-Savart law for the induced velocity field.</p>https://thesis.library.caltech.edu/id/eprint/2023The Effects of Large-Eddy Manipulator Devices on the Turbulent Spot and the Turbulent Boundary Layer
https://resolver.caltech.edu/CaltechETD:etd-03102008-083411
Authors: {'items': [{'id': 'Taylor-Stephen', 'name': {'family': 'Taylor', 'given': 'Stephen'}, 'show_email': 'NO'}]}
Year: 1986
DOI: 10.7907/7520-qj30
<p>Recent experimental studies indicate that net drag reductions can be achieved in a turbulent boundary layer by placing a tandem configuration of large-eddy manipulator blades in the outer region of the boundary layer. However, the mechanisms responsible for the observed wall-shear reductions are not well understood. Furthermore, discrepancies exist among independent experimental studies regarding the magnitude of the attainable net drag reduction.</p>
<p>A fundamental argument is made regarding the source of the observed wall-shear reductions. It is shown that the tandem manipulator is not a low-drag device. The implication is that the momentum deficit in the wake of the manipulator is a prominent contributor to the observed wall-shear reductions, not necessarily that the ability of the large eddies to transport momentum is hampered. The behavior of the wall shear downstream of the device, obtained using hot-film wall-shear sensors, is consistent with the entrainment, mixing, and consequent deceleration of low-momentum fluid from the wake of the manipulator.</p>
<p>With the aid of direct measurements of wall shear, an upper bound is placed on the attainable net drag reduction by establishing a lower bound for the device drag. It is concluded that small net reductions (~ 5 percent) may be attained at large downstream distances (≳ 100 boundary-layer thicknesses). This conclusion is consistent with most net drag assessments made independently by others in which the momentum-balance technique was employed. However, the result is not consistent with reports of large net reductions (~ 20 percent) over shorter distances (~ 50 boundary-layer thicknesses).</p>
<p>Efforts are also made to explain the observed effects in terms of turbulent structure. The turbulent spot is employed as a prototype structure for the large-scale, organized motions in the turbulent boundary layer. Dramatic wall-shear reductions occur in the region of the spot occupied by the large vortex structure. Such reductions are also evident when the spot is propagating in transitional and fully turbulent ambient boundary layers. Although the transport properties of the vortex structure may be affected by the manipulator, it is proposed that an important source of the wall-shear reductions is the transport by the large vortex of low-momentum fluid in the wake of the manipulator.</p>
<p>Some effects of a three-dimensional manipulator are also explored. The design of the device is based on a crude model of the three-dimensional structure of the turbulent spot. Although it appears that the device inhibits the spanwise growth of the spot, its overall effect on the wall shear of the spot and the turbulent boundary layer does not represent an improvement over the effectiveness of a comparable tandem configuration.</p>https://thesis.library.caltech.edu/id/eprint/915