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A Caltech Library Repository Feedhttp://www.rssboard.org/rss-specificationpython-feedgenenSat, 13 Apr 2024 00:48:15 +0000Cavitation Studies in Axial Inducers
https://resolver.caltech.edu/CaltechETD:etd-06162004-153833
Authors: {'items': [{'id': 'Nawoj-Henry-John', 'name': {'family': 'Nawoj', 'given': 'Henry John'}, 'show_email': 'NO'}]}
Year: 1956
DOI: 10.7907/FJCF-EC97
Cavitation development was investigated in axial inducers from inception to impeller breakdown using the conventional hydraulic parameters and direct visual observation. Five distinct regimes of cavitation development were observed, and the noise and vibration associated with cavitating pumps was found to occur principally in only one regime of cavitation development. Cavitation in a highly cavitating inducer was found to be adequately modeled using the cavitation similarity number introduced by Prandtl. A simple model is presented for impeller breakdown and experimental data indicate that the general requirements for impeller breakdown given by the model are exhibited in the experimental impellers. A modification to the cavitation number is suggested to accommodate the effusion of dissolved gases from the working fluid into the cavities.https://thesis.library.caltech.edu/id/eprint/2621Performance of Cavitating Axial Inducers with Varying Tip Clearance and Solidity
https://resolver.caltech.edu/CaltechETD:etd-01122004-115641
Authors: {'items': [{'id': 'Carpenter-Stanley-Hammack', 'name': {'family': 'Carpenter', 'given': 'Stanley Hammack'}, 'show_email': 'NO'}]}
Year: 1957
DOI: 10.7907/35Z3-YN17
The performance of a helical axial inducer pump was investigated in non-cavitating and heavily cavitating regimes over a wide range of tip clearance and solidity. It was found that cavity length is related to the occurrence of two cavitation phenomena: a non-steady or oscillating form of cavitation occurs when the cavity length is nearly equal to the spacing between the impeller blades, and complete pump failure is imminent if the cavity is nearly as long as the blade chord. The extent of the oscillating cavitation regime was little affected by the variation of tip clearance or solidity in the range investigated. However, an increase in tip clearance or a decrease in solidity definitely impairs cavitation performance at low inlet pressures. On the basis of these experiments a cavitation number limit is proposed for safe inducer operation.https://thesis.library.caltech.edu/id/eprint/134Experimental Investigation of Oilfilm Behaviour in Short Journal Bearings
https://resolver.caltech.edu/CaltechETD:etd-01272006-130027
Authors: {'items': [{'id': 'Auksmann-Boris', 'name': {'family': 'Auksmann', 'given': 'Boris'}, 'show_email': 'NO'}]}
Year: 1959
DOI: 10.7907/Y6X7-4C85
This report contains the description of the test apparatus that was designed and built for experimental investigation of oilfilm behaviour in short full-journal bearings of circumferential feed groove type. An account of the engineering problems solved in connection with the design and development of the apparatus is also given.
Complete pressure distributions were obtained for a two inch diameter, one inch long bearing operating at 3500 rpm under 30 and 60 lb. applied loads and with various axial pressure gradients and supply pressures. The results are presented in graphical form and a comparison is made with the short bearing theory developed by F. W. Ocvirk. Agreement with theory was found to be very good when operating with low axial pressure gradient and high supply pressure (cavitation completely suppressed), while with high axial pressure gradient substantial differences in pressure distribution were found.
Visual observations of oilfilm behaviour were made with a transparent plastic bearing of the same proportions, operating with a 60 lb. load at 3500 rpm. Cavitation behaviour under various axial pressure gradients and supply pressures is discussed, and photographic records of typical cavitation behaviour are presented in the report.
Eccentricity and attitude angle measurements were made in all tests and experimental results are presented with pressure distribution data and cavitation behaviour records.https://thesis.library.caltech.edu/id/eprint/376An Experimental Investigation of a Fully Cavitating Two-Dimensional Flat Plate Hydrofoil Near a Free Surface
https://resolver.caltech.edu/CaltechETD:etd-01272006-130656
Authors: {'items': [{'id': 'Dawson-Thomas-Emmett', 'name': {'family': 'Dawson', 'given': 'Thomas Emmett'}, 'show_email': 'NO'}]}
Year: 1959
DOI: 10.7907/Y3SP-XX86
A fully cavitating two-dimensional flat plate hydrofoil at and below a free surface was investigated. The effects of proximity to the free surface, angle of attack, cavitation number and Froude number or gravity on the normal force, the moment about the leading edge, the center of pressure location, the cavity length and the air flow rate into the cavity are discussed. Comparisons to other experiments and theories also are made.https://thesis.library.caltech.edu/id/eprint/377The Effect of Tip Clearance Flows on Performance of Axial Flow Compressors
https://resolver.caltech.edu/CaltechETD:etd-12092005-163445
Authors: {'items': [{'id': 'Williams-Allen-Dean', 'name': {'family': 'Williams', 'given': 'Allen Dean'}, 'show_email': 'NO'}]}
Year: 1960
DOI: 10.7907/7T14-SP07
The change in rotor performance with tip clearance of an axial flow compressor over a wide range of flow rates above stall was investigated to gain more understanding of the effect of the tip flow mechanism on rotor performance.
The experimental results were compared with a flow model proposed previously and found to be in reasonable agreement.https://thesis.library.caltech.edu/id/eprint/4908Application of Cascade Theories to Axial Flow Pumps
https://resolver.caltech.edu/CaltechETD:etd-06162006-080927
Authors: {'items': [{'id': 'Linhardt-Hans-Dieter', 'name': {'family': 'Linhardt', 'given': 'Hans-Dieter'}, 'show_email': 'NO'}]}
Year: 1960
DOI: 10.7907/RHMN-2J84
It is demonstrated with experiments and theory that the performance of an axial flow pump can be described very accurately by application of two-dimensional cascade theories including the thickness effect of the blades on the flows. The blade thickness is found to be an important parameter which is mainly responsible for discrepancies between the experimental results and predictions of "thin airfoil" cascade theories. Three-dimensional effects and the effect of the boundary-displacement thickness on the cascade flow are shown to be negligible for the case of the axial flow pump of high stagger angle and low aspect ratio, which was the case for the present work.https://thesis.library.caltech.edu/id/eprint/2624Cavitation Similarity Studies with Water and Freon-113
https://resolver.caltech.edu/CaltechETD:etd-12052005-155203
Authors: {'items': [{'id': 'Sarosdy-Louis-Robert', 'name': {'family': 'Sarosdy', 'given': 'Louis Robert'}, 'show_email': 'NO'}]}
Year: 1960
DOI: 10.7907/CZWP-PB71
The development of cavitation behind a disc in water and Freon-113 was investigated in a cavitation tunnel designed for this purpose. Measurements of pressure within the cavities formed in water indicated that the vapor pressure within the cavity was less than the vapor pressure of the fluid at the bulk temperature. Observations of the cavities formed in the two liquids showed qualitative differences, and some possible reasons for this behavior are discussed.https://thesis.library.caltech.edu/id/eprint/4794Investigations on cavitating hydrofoils
https://resolver.caltech.edu/CaltechETD:etd-01222004-112658
Authors: {'items': [{'id': 'Wade-R-B', 'name': {'family': 'Wade', 'given': 'Richard B'}, 'show_email': 'NO'}]}
Year: 1965
DOI: 10.7907/8YEC-DS05
Experimental and theoretical results are presented for the non-cavitating and cavitating performances of a plano-convex hydrofoil in both the isolated and cascade configurations.
In the isolated hydrofoil tests special emphasis is placed on the unsteady region of cavitation separating the partially cavitating region from the fully cavitating region. The detailed behavior of the oscillating cavity together with the magnitude of the force vibrations that occur in this region are investigated from both a qualitative and a quantitative viewpoint. The dependence of the reduced frequency of these oscillations on the angle of attack, cavitation number and flow velocity is also discussed.
The performance of the hydrofoil under steady conditions in both the cavitating and non-cavitating regions is also presented. Details of the test equipment and procedures used and various data corrections made are given.
A linearized partially cavitating theory for this plano-convex hydrofoil is also developed which includes camber and thickness effects. The results from this theory are compared with the experimental data obtained.
In the cascade experiments a feasibility study is undertaken to determine the possibility of using the high speed water tunnel at the California Institute of Technology as a cascade tunnel for investigating the cavitating performance of compressor and turbine cascades. A comprehensive design study is given of the modifications made to the existing tunnel to achieve this aim. The experimental procedures used in conducting the experiments are then discussed. Tests are performed on two compressor cascades of plano-convex hydrofoils having solidities of 1.25 and 0.625 and cascade angle of 45 degrees, for all conditions of cavitation from the fully wetted to the fully choked conditions. A study is also made of a turbine cascade of solidity 1.25 for the same cascade angle in the non-cavitating region only. Comparisons of the experimental data with several theories indicate that the cascade tests are indeed fulfilling their purpose in proving the methods used in simulating cascade conditions in the tunnel.
Proposals for modifying the system used to avoid several experimental difficulties are presented. Finally, a linearized theory for a cascade of partially cavitating flat plate hydrofoils is developed which is compared with the data obtained.https://thesis.library.caltech.edu/id/eprint/269Unsteady Forces on Oscillating Hydrofoils
https://resolver.caltech.edu/CaltechETD:etd-09252002-112500
Authors: {'items': [{'id': 'Klose-Gerhard-Joachim', 'name': {'family': 'Klose', 'given': 'Gerhard Joachim'}, 'show_email': 'NO'}]}
Year: 1966
DOI: 10.7907/96CP-GE12
An experimental apparatus is described which has proved to be well suited to the determination of the unsteady lift forces on a hydrofoil oscillating in heave under a free surface.
Results are presented for tests covering a wide range of reduced frequency with several foil models in fully wetted, base-ventilated, and supercavitating flow. Tests were performed with aspect ratio one foils and also in two-dimensional flow. The effects of submergence depth below the free surface, angle of attack, and oscillation amplitude were investigated. The experimental findings for the fully wetted foils generally agree fairly well with the available theoretical results.
In supercavitating flow, the cavities were established by forced ventilation. The characteristics of the ventilated cavities under oscillation are discussed. The variation in the unsteady lift coefficients with cavity length, and the attendant unsteady cavity pressure, are also presented. The average values of the unsteady lift coefficients are found to differ appreciable from theoretical calculations, and some factors which may contribute to this difference are considered.
The present work represents the first extensive set of unsteady force measurements on oscillating hydrofoils, and several new phenomena are revealed by the results. The implications of these findings for practical problems are discussed, and some suggestions are offered for further investigations.https://thesis.library.caltech.edu/id/eprint/3752On the Added Mass of a Sphere in a Circular Cylinder Considering Real Fluid Effects
https://resolver.caltech.edu/CaltechTHESIS:10052015-161503645
Authors: {'items': [{'id': 'Mellsen-Stanley-Brun', 'name': {'family': 'Mellsen', 'given': 'Stanley Brun'}, 'show_email': 'NO'}]}
Year: 1966
DOI: 10.7907/63N8-1N50
<p>An experimental method combined with boundary layer theory is given for evaluating the added mass of a sphere moving along the axis of a circular cylinder filled with water or oil. The real fluid effects are separated from ideal fluid effects.</p>
<p>The experimental method consists essentially of a magnetic steel sphere propelled from rest by an electromagnetic coil in which the current is accurately controlled so that it only supplies force for a short time interval which is within the laminar flow regime of the fluid. The motion of the sphere as a function of time is recorded on single frame photographs using a short-arc multiple flash lamp with accurately controlled time intervals between flashes.</p>
<p>A concept of the effect of boundary layer displacement on the fluid flow around a sphere is introduced to evaluate the real fluid effects on the added mass. Surprisingly accurate agreement between experiment and theory is achieved. </p>
https://thesis.library.caltech.edu/id/eprint/9202Laminar Flow of Dilute Polymer Solutions Around Circular Cylinders
https://resolver.caltech.edu/CaltechETD:etd-09132002-124902
Authors: {'items': [{'id': 'James-David-Fielding', 'name': {'family': 'James', 'given': 'David Fielding'}, 'show_email': 'NO'}]}
Year: 1967
DOI: 10.7907/G1Z1-PH10
Experimental results are presented for heat transfer by free and forced convection at low velocities from small heated cylinders in dilute solutions of polyethylene oxide in water. The experiments were conducted for a range of velocities (less than 1. 0 ft/sec) and polymer concentrations, with several cylinder diameters, and for several polymer molecular weights. Experimental results are also presented for the drag of a small cylinder in similar liquids and for a comparable range of velocities.
The heat transfer and drag results at low velocities were identical to those for a Newtonian liquid; at high velocities, the measured values departed considerably from Newtonian results. These departures result from the viscoelastic nature of the polymer solutions. Visualization studies of the flow around a cylinder and of a minute laminar jet were conducted to determine the gross magnitude of the viscoelastic effects. Due to the liquid's elasticity, a significant enlargement of the flow field was observed for both configurations above a critical Reynolds number. An attempt is made to explain the heat transfer and drag results in light of these observations.
Photographic materials on pp. 111 - 149 are essential and will not reproduce clearly on Xerox copies. Photographic copies should be orderedhttps://thesis.library.caltech.edu/id/eprint/3513Quasi Two-Dimensional Flows Through Cascades
https://resolver.caltech.edu/CaltechETD:etd-10012002-093723
Authors: {'items': [{'id': 'Mani-Ramani', 'name': {'family': 'Mani', 'given': 'Ramani'}, 'show_email': 'NO'}]}
Year: 1967
DOI: 10.7907/01sg-we85
<p>The present thesis is an attempt to develop a thin airfoil theory for an airfoil which spans the gap between a pair of stream surfaces which are slowly diverging or converging, the motivation being to predict, theoretically, the effect of varying axial velocity on cascade performance of axial flow compressor rows.</p>
<p>The procedure involves, firstly, derivation of approximate equations satisfied by suitably defined average potentials and stream functions in such quasi two-dimensional flows. The flow is assumed to be inviscid, irrotational, and incompressible, but as will be argued later, the quasi two-dimensional type equations also result from less restrictive assumptions. Next, fundamental solutions to these equations, corresponding to bound, line sources and vortices, are found. A distribution of such solutions is used to formulate the airfoil problem, using the condition that the flow be tangential to the airfoil contour. The vorticity distribution appears as the solution to a singular integral equation, which is solved by an approximate method. Simple yet physically realistic assumptions are made concerning the gap width as a function of the streamwise length, to obtain numerical results for the effect of contraction of the stream surfaces. Varying degrees of approximation, later discussed, are used in the calculation procedures. A wide variety of the location and the extent of the contraction, with respect to the airfoil, is investigated.</p>
<p>In all cascade calculations the contraction of the stream surfaces was assumed to be in the same direction as the cascade axis. The main conclusions of the thesis can be summarized as below:</p>
<p>1. The theory predicts a lesser circulation round an airfoil in a contracting flow as compared to the circulation round the same airfoil in a plane flow. There is a similar reduction of circulation for a cascade of airfoils. The percentage reduction of circulation is greater for the cascade case as compared to the isolated case, assuming the contractions to be geometrically similar in both cases. The effect on the circulation of contractions, considered physically reasonable in extent and magnitude, either fully upstream or fully downstream of the airfoil, is quite small.</p>
<p>2. As a very rough rule of thumb, it may be stated that the reduction of circulation as compared to the two-dimensional theory, in the range of parameters applicable to compressors, has about the same magnitude as the reduction of gap between the stream surfaces taking place across the airfoil chords.</p>
<p>3. In a comparison with fixed mean angle of attack, the change in flow turning and deviation angles of the flow are much smaller than changes of circulation and may be stated to be of the order of one degree or less for contraction extents and magnitudes considered realistic for compressor cascades.</p>
https://thesis.library.caltech.edu/id/eprint/3843The Unsteady Forces on Slender Delta Wing Hydrofoils Oscillating in Heave
https://resolver.caltech.edu/CaltechTHESIS:12072015-164403874
Authors: {'items': [{'id': 'Delong-Raymond-Kay', 'name': {'family': 'DeLong', 'given': 'Raymond Kay'}, 'show_email': 'NO'}]}
Year: 1968
DOI: 10.7907/H7R1-KF18
<p>The investigations described herein are both experimental and theoretical. An experimental technique is described by which the models tested could be oscillated sinusoidally in heave. The apparatus used to gather the unsteady lift, drag and pitching moment data is also described.</p>
<p>The models tested were two flat delta wings with apex angles of 15° and 30° and they had sharp leading edges to insure flow separation. The models were fabricated from 0.25 inch aluminum plate and were approximately one foot in length.</p>
<p>Three distinct types of flow were investigated: 1) fully wetted, 2) ventilated and 3) planing. The experimental data are compared with existing theories for steady motions in the case of fully wetted delta wings. Ventilation measurements, made only for the 30° model at 20° angle of attack, of lift and drag are presented.</p>
<p>A correction of the theory proposed by M.P. Tulin for high speed planing of slender bodies is presented and it is extended to unsteady motions. This is compared to the experimental measurements made at 6° and 12° angle of attack for the two models previously described. </p>
<p>This is the first extensive measurement of unsteady drag for any shape wing, the first measurement of unsteady planing forces, the first quantitative documentation of unstable oscillations near a free surface, and the first measurements of the unsteady forces on ventilated delta wings. The results of these investigations, both theoretical and experimental, are discussed and further investigations suggested. </p>
https://thesis.library.caltech.edu/id/eprint/9314The Unsteady Cavity in Internal Flows
https://resolver.caltech.edu/CaltechTHESIS:06112018-095816439
Authors: {'items': [{'id': 'Kim-Jong-Hyun', 'name': {'family': 'Kim', 'given': 'Jong Hyun'}, 'show_email': 'NO'}]}
Year: 1971
DOI: 10.7907/Q343-FG73
<p>The problems of the two-dimensional unsteady cavity in internal flow are treated and linear theories are developed. In Part I, the two- dimensional supercavitating flow past a flat plate heaving and pitching with small amplitudes in a choked tunnel is investigated and a linearized solution is obtained using the acceleration potential. The flat plate is inclined at a small angle of attack to the oncoming flow and the cavity pressure is assumed to be constant. Force and moment coefficients are calculated for the case of the foil placed in the middle of the walls as functions of reduced frequency and the ratio of tunnel height to chord length. The pressure disturbances caused by the unsteady motion of the foil do not die out far upstream; these also depend on the chord-tunnel height ratio and reduced frequency.</p>
<p>Another type of cavity problem in an internal flow is studied in Part II. Here, the finite cavity flow over a wedge held stationary in the middle of a tunnel is investigated. A salient feature of the problem is that the mass oscillation is allowed. Also the pressure on the cavity is allowed to vary in a prescribed manner. The problem is linearized using the complex perturbation velocity and the formal solution is obtained. The choked case in the presence of the overall mass fluctuation is obtained as a limiting case. Throughout the analysis, it is assumed that the change of the cavity length with time is small.</p>
https://thesis.library.caltech.edu/id/eprint/11061A singular perturbation method of calculating the behavior of supercavitating hydrofoils with rounded noses
https://resolver.caltech.edu/CaltechTHESIS:04082016-141758840
Authors: {'items': [{'id': 'Furuya-Okitsugu', 'name': {'family': 'Furuya', 'given': 'Okitsugu'}}]}
Year: 1972
DOI: 10.7907/A946-HN67
<p>A simple, direct and accurate method to predict the pressure distribution on supercavitating hydrofoils with rounded noses is presented. The thickness of body and cavity is assumed to be small. The method adopted in the present work is that of singular perturbation theory. Far from the leading edge linearized free streamline theory is applied. Near the leading edge, however, where singularities of the linearized theory occur, a non-linear local solution is employed. The two unknown parameters which characterize this local solution are determined by a matching procedure. A uniformly valid solution is then constructed with the aid of the singular perturbation approach.</p>
<p>The present work is divided into two parts. In Part I isolated supercavitating hydrofoils of arbitrary profile shape with parabolic noses are investigated by the present method and its results are compared with the new computational results made with Wu and Wang's exact "functional iterative" method. The agreement is very good. In Part II this method is applied to a linear cascade of such hydrofoils
with elliptic noses. A number of cases are worked out over a range of cascade parameters from which a good idea of the behavior of this type of important flow configuration is obtained.</p>
<p>Some of the computational aspects of Wu and Wang's functional iterative method heretofore not successfully applied to this type of problem are described in an appendix.</p>
https://thesis.library.caltech.edu/id/eprint/9663Viscous effects in inception and development of cavitation on axi-symmetric bodies. Cavitation inception. A semi-empirical method to predict caviation separation on smooth bodies
https://resolver.caltech.edu/CaltechETD:etd-03272007-081335
Authors: {'items': [{'id': 'Arakeri-V-H', 'name': {'family': 'Arakeri', 'given': 'Vijay Hanumappa'}, 'show_email': 'NO'}]}
Year: 1973
DOI: 10.7907/JJ3M-ZA06
The schlieren method was developed as a flow visualization technique for use in water tunnels. The process of cavitation development on two axi-symmetric bodies was studied using this approach and found to be greatly influenced by the presence of a previously unreported viscous laminar separation. On these bodies, cavitation inception was observed to take place within this separated region which occurs far downstream of the minimum pressure point. On one of these bodies, the incipient cavitation index was found to be closely correlated with the negative value of the pressure coefficient at the point of laminar separation. Approximate computations of the position of transition on a body without laminar separation indicate that the incipient cavitation index is closely correlated with the negative value of the pressure coefficient at the predicted point of transition.
Cavitation separation under fully developed conditions is found to be preceded by a viscous laminar boundary layer separation on bodies which possess the latter separation under fully wetted conditions. An empirical method is proposed to compute the position of cavitation separation on such bodies and the method applied to a sphere and a cylinder showed good agreement with experimentshttps://thesis.library.caltech.edu/id/eprint/1167Dynamic response of cavitation turbomachines
https://resolver.caltech.edu/CaltechETD:etd-02272003-122146
Authors: {'items': [{'id': 'Ng-S', 'name': {'family': 'Ng', 'given': 'Sheung-Lip'}, 'show_email': 'YES'}]}
Year: 1976
DOI: 10.7907/KC09-P112
Stimulated by the pogo instability encountered in many liquid propellant rockets, the dynamic behavior of cavitating inducers is the subject of the present thesis. An experimental facility where the upstream and downstream flows of a cavitating inducer could be perturbed was constructed and tested. The upstream and downstream pressure and mass flow fluctuations were measured. Matrices representing the transfer functions across the inducer pump were calculated from these measurements and from the hydraulic system characteristics for two impellers in various states of cavitation. The transfer matrices when plotted against the perturbing frequency showed significant departure from steady state or quasi-steady predictions especially at higher frequencies.https://thesis.library.caltech.edu/id/eprint/777The influence of freestream turbulence, freestream nuclei populations and a drag-reducing polymer on cavitation inception on two axisymmetric bodies
https://resolver.caltech.edu/CaltechTHESIS:08122014-083534353
Authors: {'items': [{'id': 'Gates-E-M', 'name': {'family': 'Gates', 'given': 'Edward M.'}, 'show_email': 'NO'}]}
Year: 1977
DOI: 10.7907/GH1H-3780
<p>The influence upon the basic viscous flow about two axisymmetric
bodies of (i) freestream turbulence level and (ii) the injection
of small amounts of a drag-reducing polymer (Polyox WSR 301) into
the test model boundary layer was investigated by the schlieren flow
visualization technique. The changes in the type and occurrence of
cavitation inception caused by the subsequent modifications in the
viscous flow were studied. A nuclei counter using the holographic
technique was built to monitor freestream nuclei populations and a
few preliminary tests investigating the consequences of different populations
on cavitation inception were carried out.</p>
<p>Both test models were observed to have a laminar separation
over their respective test Reynolds number ranges. The separation on
one test model was found to be insensitive to freestream turbulence
levels of up to 3.75 percent. The second model was found to be very
susceptible having its critical velocity reduced from 30 feet per second
at a 0.04 percent turbulence level to 10 feet per second at a 3.75 percent
turbulence level. Cavitation tests on both models at the lowest
turbulence level showed the value of the incipient cavitation number
and the type of cavitation were controlled by the presence of the laminar
separation. Cavitation tests on the second model at 0.65 percent turbulence
level showed no change in the inception index, but the appearance
of the developed cavitation was altered.</p>
<p>The presence of Polyox in the boundary layer resulted in a
cavitation suppression comparable to that found by other investigators.
The elimination of the normally occurring laminar separation on these
bodies by a polymer-induced instability in the laminar boundary layer
was found to be responsible for the suppression of inception.</p>
<p>Freestream nuclei populations at test conditions were measured
and it was found that if there were many freestream gas bubbles the
normally present laminar separation was elminated and travelling bubble
type cavitation occurred - the value of the inception index then depended
upon the nuclei population. In cases where the laminar separation
was present it was found that the value of the inception index was
insensitive to the free stream nuclei populations.</p>https://thesis.library.caltech.edu/id/eprint/8632Scale Effects on Cavitation Inception in Submerged Jets
https://resolver.caltech.edu/CaltechETD:etd-09202006-102904
Authors: {'items': [{'id': 'Ooi-Kean-Khoon', 'name': {'family': 'Ooi', 'given': 'Kean Khoon'}, 'show_email': 'NO'}]}
Year: 1982
DOI: 10.7907/qvn5-1075
<p>The present work is an investigation into the scale effects on cavitation inception in submerged water jets. Four scale effects were studied: (i) jet size, (ii) jet velocity, (iii) dissolved air content, and (iv) the nuclei population in the flow. The nuclei population was artificially altered by "electrolysis seeding."</p>
<p>Holography and schlieren photography were used to observe the flow. Direct measurements of the nuclei population were also accomplished by holography. In addition, the instantaneous pressure field in the jet was successfully mapped out using specially tailored bubbles as pressure sensors.</p>
<p>It was found that inception did not generally occur in the cores of the turbulent eddies and that the region in which the cavities were first seen were dependent on the size of the jet.</p>
<p>Pressure measurements showed that negative peak pressure fluctuation intensities of as high as 120 percent of the dynamic head existed in the jet. The results also revealed that the instantaneous pressure fluctuations have a slightly skewed bell shape probability distribution.</p>
<p>For the present tests, the inception index was independent of the exit velocity for a constant size jet. However, when the flow was seeded, the inception number showed a linear dependence on velocity and this dependence increased with increased number of seeded nuclei. The effects of the nuclei number density and pressure fluctuations are incorporated in a "probable cavitation occurrence" parameter which shows promise in reducing scatter in this type of experiment.</p>https://thesis.library.caltech.edu/id/eprint/3659Cavitation Inception in Separated Flows
https://resolver.caltech.edu/CaltechETD:etd-01252005-084230
Authors: {'items': [{'email': 'katz@jhu.edu', 'id': 'Katz-Joseph', 'name': {'family': 'Katz', 'given': 'Joseph'}, 'show_email': 'NO'}]}
Year: 1982
DOI: 10.7907/VP9N-K847
<p>The phenomenon of cavitation was studied on four axisymmetric bodies whose boundary layers underwent a laminar separation and subsequent turbulent reattachment. The non-cavitating flow was studied by holography and the Schlieren flow visualization technique. Surface distributions of the mean and the fluctuating pressures were also measured. The conditions for cavitation inception and desinence were determined and several holograms were recorded just prior to and at the onset of cavitation. The population of microbubbles and the nature of the subsequent development of visible cavitation was determined from the reconstructed image.</p>
<p>High rms and peak values of the fluctuating pressure were measured (up to 90 percent of the dynamic head), the negative peaks being larger than the positive ones except for the reattachment zone where large positive peaks existed. The power spectra contained peaks thought to originate within the large eddies of the mixing layer and in one case there were also peaks due to the laminar boundary layer instability waves.</p>
<p>Cavitation inception occurred in the turbulent shear layer downstream of the transition region. When the separation zone was large the inception region was located within the most developed section of the mixing layer but upstream of the reattachment zone. When the separation region was small inception occurred close to the reattachment zone but still detached from the body surface. A comparison between the surface minimum pressure and the cavitation inception indices also indicated that inception could not occur near the surface of the bodies having a large separation region.</p>
<p>The appearance of visible cavities was preceded by the appearance of a cluster of microbubbles only in the cavitation inception region. The nuclei population in the other sections of the flow field remained fairly uniform. This observation supports the assumption that cavitation is initiated from microscopic free stream nuclei. The rate of cavitation events was estimated from the nuclei population and from the dimensions of the separation region. It was shown for one of the bodies that at least one bubble larger than 10 micrometers radius was exposed every second to a pressure peak which was sufficiently large to cause a cavitation event.</p>
https://thesis.library.caltech.edu/id/eprint/331Forces on a Whirling Centrifugal Pump-Impeller
https://resolver.caltech.edu/CaltechETD:etd-09152006-083609
Authors: {'items': [{'id': 'Chamieh-Dimitri-Suhayl', 'name': {'family': 'Chamieh', 'given': 'Dimitri Suhayl'}, 'show_email': 'NO'}]}
Year: 1983
DOI: 10.7907/vnqy-ne26
<p>The present work is an experimental and theoretical investigation of the possible forces of fluid dynamic origin that can act on a turbomachine rotor particularly when it is situated off its normal center position. An experimental facility, the Rotor Force Test Facility, has been designed and constructed in order to measure these kinds of forces acting on a centrifugal pump impeller when the latter is made to whirl in a slightly eccentric circular orbit. The rotor speed, eccentric orbital radii and whirl speed could be varied independently. The scope of the present experimental work consists of measuring quasi-steady forces on the impeller as it whirls slowly about the axis of the pump rotation. These forces are due to interaction between the impeller and volute; they are decomposed into force components relative to the geometric center of the volute and to those proportional to displacement from this center. These latter are interpreted as stiffness matrices. These matrices were measured on two widely differing volute types and both were found to have the property of being skew-symmetric. It can be shown that a stiffness matrix of this type can lead to dynamic instability of the impeller shaft system in certain circumstances. This new experimental finding may explain some operational problems of "high speed" hydraulic machinery.</p>
<p>In the theoretical part of this thesis, a somewhat more physical model of a rotor pump is proposed other than has been used heretofore in most works namely an actuator disk having infinitely many blades. As a simplification it is assumed that the flow field is irrotational. Forces and stiffness matrices are calculated on this basis but the stiffness matrix so found does not reveal the skew-symmetric property of the experiments.</p>https://thesis.library.caltech.edu/id/eprint/3551Analyses of Hydrodynamic Forces on Centrifugal Pump Impellers
https://resolver.caltech.edu/CaltechETD:etd-03262007-111453
Authors: {'items': [{'id': 'Adkins-Douglas-Ray', 'name': {'family': 'Adkins', 'given': 'Douglas Ray'}, 'show_email': 'NO'}]}
Year: 1986
DOI: 10.7907/X6KZ-W852
<p>It has been experimentally determined by previous investigators that hydrodynamic forces can cause a centrifugal pump impeller to whirl in a volute. The present work was undertaken to develop a theoretical model of the interactions that occur between an impeller and a volute, and to identify the source of the hydrodynamic forces. Experiments were then conducted to test the predictions of the model. The theoretical analysis presents a quasi-one dimensional treatment of the flow in the volute and accounts for the disturbance at the impeller discharge that is caused by the volute. The model also considers the lack of perfect guidance through the blade passages. Extending this model allowed for the calculation of hydrodynamic force perturbations that result when the impeller whirls eccentrically in the volute. These force perturbations were shown to encourage, rather than dissipate the whirling motion. The predictions of the model gave reasonable comparisons with the experimental data obtained in this study. Further, it was experimentally observed that pressure forces acting on the front shroud of the impeller could have a major influence on the hydrodynamic force perturbations acting on an eccentrically positioned impeller.</p>https://thesis.library.caltech.edu/id/eprint/1141Experimental and Theoretical Study on Cavitation Inception and Bubbly Flow Dynamics: I. Design, Development and Operation of a Cavitation Susceptibility Meter. II. Linearized Dynamics of Bubbly and Cavitating Flows with Bubble Dynamics Effects
https://resolver.caltech.edu/CaltechETD:etd-03262007-150544
Authors: {'items': [{'email': 'luca.dagostino@ing.unipi.it', 'id': "d'Agostino-Luca", 'name': {'family': "d'Agostino", 'given': 'Luca'}, 'show_email': 'YES'}]}
Year: 1987
DOI: 10.7907/HK8Q-VQ14
<p>The first and main part of this work presents the design, development and operation of a Cavitation Susceptibility Meter based on the use of a venturi tube for the measurement of the content of active cavitation nuclei in water samples. The pressure at the venturi throat is determined from the upstream pressure and the local flow velocity without corrections for viscous effects because the flow possesses a laminar potential core in all operational conditions. The detection of cavitation and the measurement of the flow velocity are carried out optically. The apparatus comprises a Laser Doppler Velocimeter for the measurement of the flow velocity and the detection of cavitation, a custom-made electronic Signal Processor for real time generation and temporary storage of the data and a computerized system for the final acquisition and reduction of the collected data. The various steps and considerations leading to the present design concept are discussed in detail and the implementation of the whole system is described in order to provide the all the information necessary for its calibration and operation. Finally, the results of application of the Cavitation Susceptibility Meter to the measurement of the water quality of tap water samples are presented and critically discussed with reference to other similar or alternative methods of cavitation nuclei detection and to the current state of knowledge on cavitation inception.</p>
<p>The second part of the present work presents the results of an investigation on the linearized dynamics of two-phase bubbly flows with the inclusion of bubble dynamics effects. Two flow configurations have been studied: the time dependent one-dimensional flow of a spherical bubble cloud subject to harmonic excitation of the far field external pressure and the steady state two-dimensional flow of a bubbly mixture on a slender profile of arbitrary shape. The inclusion of bubble dynamic damping and of the relative motion between the two phases and the extension of the results to the case of arbitrary excitation are discussed when examining the second flow configuration. The simple linearized dynamical analysis developed so far clearly demonstrates the importance of the complex phenomena connected to the interaction of the dynamics of the bubbles with the flow and provides an introduction to the study of the same flows with non-linear bubble dynamics.</p>https://thesis.library.caltech.edu/id/eprint/1150Experimental Study of Unsteady Hydrodynamic Force Matrices on Whirling Centrifugal Pump Impellers
https://resolver.caltech.edu/CaltechETD:etd-03262007-130547
Authors: {'items': [{'id': 'Jery-Belgacem', 'name': {'family': 'Jery', 'given': 'Belgacem'}, 'show_email': 'NO'}]}
Year: 1987
DOI: 10.7907/cmn0-qk37
<p>An experimental facility was constructed and instrumented. A study was conducted on a set of centrifugal flow pumps whose impellers were made to follow a controlled circular whirl motion. The aim was to characterize the steady and unsteady fluid forces measured on the impeller under various pump operating conditions. The postulation was that the unsteady lateral forces result from interactions between the impeller and the surrounding diffuser and or volute (via the working fluid), and that under certain flow regimes these forces can drive unstable lateral motions of the pump rotor.</p>
<p>The lateral hydrodynamic forces were decomposed into their steady and unsteady parts, the latter being further expressed in terms of a generalized fluid stiffness matrix. A study of this matrix as a function of the whirl to pump speed ratio supported the following chief conclusions:</p>
<p>i) the common assumption of matrix skew-symmetry is justified;</p>
<p>ii) the magnitudes and signs of the matrix elements are such that rotor whirl can indeed be caused by the hydrodynamic forces, in pumps operated well above their first critical speed,</p>
<p>iii) as expected, the matrix is very sensitive to the value of the flow coefficient, especially at flow rates below the design;</p>
<p>iv) the commonly postulated quadratic variation of the matrix elements with the reduced whirl frequency, resulting in the so-called rotordynamic coefficients (stiffness, damping and inertia) is not justified for flow coefficients significantly below design; and</p>
<p>v) surprisingly, it was discovered that the presence, number and orientation of diffuser guide vanes have little effect on the forces.</p>
<p>Conclusions regarding the effect of impeller geometry could not be reached given the similarity of the tested designs. However, other results on phenomena such as skin friction and leakage flow are presented. Some of the findings are compared to experimental and theoretical data from other sources. Finally, the rotordynamic consequences of the results are discussed as the present data were applied by another author to the case of the Space Shuttle Main Engine's (SSME) High Pressure Oxidizer Turbopump (HPOTP).</p>https://thesis.library.caltech.edu/id/eprint/1144Cavitation Inception Scale Effects: I. Nuclei Distributions in Natural Waters. II. Cavitation Inception in a Turbulent Shear Flow
https://resolver.caltech.edu/CaltechETD:etd-04022004-094117
Authors: {'items': [{'id': "O'Hern-Timothy-John", 'name': {'family': "O'Hern", 'given': 'Timothy John'}, 'show_email': 'NO'}]}
Year: 1987
DOI: 10.7907/G8TY-K105
<p>Cavitation scale effects can be grouped into two major categories: susceptibility of the water to cavitation, i.e., the amount, size, and type of microbubbles or microparticulates in the water acting as inception nuclei, and flow field effects due to such factors as velocity and pressure distributions, body size and shape, viscous effects, and turbulent phenomena. Experimental investigations into these two aspects of scale effects were performed in the present study.</p>
<p>Field investigations of marine nuclei populations were made using underwater holography to observe microbubbles and particulates, including microplankton in oceanic waters of Los Angeles Harbor, San Pedro Channel and near Santa Catalina Island. Holographic detection was shown to be a reliable method of measuring the nuclei number concentration density distributions. Overall, very high concentrations of the various types of potential cavitation nuclei were observed at all of the test sites and depths examined, although the statistical significance of these results is strong only in the smaller size ranges (less than 50 µm), where a significant number of counts were made. Relatively high bubble concentrations during calm sea conditions, and their population inversion below the thermocline where organism activity was high, indicate a possible biological source of bubble production rather than the usual surface mechanisms of breaking waves and whitecaps. The measured population of particulates is somewhat higher than comparable data in the ocean or in cavitation test facilities, and the number density distribution of particulates decreases approximately as the fourth power of the particle size, as often reported in the literature. An increase in particle concentration near the bottom of the thermocline in clear coastal waters is observed. The total concentration of particles and bubbles in a liquid provides an upper bound on the number of potentially active cavitation nuclei. The measured bubble sizes can be used to indicate that the average tensile strength of the ocean waters examined in this study should be on the order of a few thousand Pascals, with a minimum expected value of about one hundred Pascals. The present results support the recommendation of Billet (1985), that a concentration of at least 3 bubbles per cm<sup>3</sup> in the 5 to 20 µm radius range is needed in test facility water in order to model marine conditions.</p>
<p>Experimental studies were also made on the inception processes in a large turbulent free shear layer generated by a sharp edged plate in a water tunnel at Reynolds numbers up to 2 x 10<sup>6</sup>. Two distinct types of vortex motion were evident in the shear layer, the primary spanwise and the secondary longitudinal vortices. Cavitation inception occurs consistently in the secondary shear layer vortices and more fully developed cavitation is visible in both structures, with the streamwise cavities primarily confined to the braid regions between adjacent spanwise vortices. A Rankine vortex model indicates that the secondary vortex strength is always less than 10% of that of the primary structure. Measurements of fluctuating pressures in the turbulent shear layer are made by holographically monitoring the size of air bubbles injected into the non-cavitating flow, showing that pressure fluctuations were much stronger than previously reported, with positive and negative pressure peaks as high as 3 times the freestream dynamic pressure, sufficient to explain the occurrence of cavitation inception at high values of the inception index. Cavitation inception indices display a strong dependence on the dissolved air content and thus on the availability of freestream bubble cavitation nuclei. The present inception data do not display a clear dependence on freestream velocity (or Reynolds number) but do fall into the overall range of data of previous bluff body investigations. The occurrence of inception in the secondary vortices of the shear layer, and previous reports of velocity dependence of these cores (Bernal 1981) may provide the key to explaining the commonly observed Reynolds number scaling of the inception index in shear flows.</p>https://thesis.library.caltech.edu/id/eprint/1246Tip Vortices - Single Phase and Cavitating Flow Phenomena
https://resolver.caltech.edu/CaltechETD:etd-03262007-104625
Authors: {'items': [{'email': 'green@mech.ubc.ca', 'id': 'Green-Sheldon-Isaiah', 'name': {'family': 'Green', 'given': 'Sheldon Isaiah'}, 'show_email': 'NO'}]}
Year: 1988
DOI: 10.7907/23TX-JF33
<p>Tip vortices occur wherever a lifting surface terminates in a fluid. An understanding of tip vortices is salient to the solution of many engineering problems, including lift induced drag tip inefficiency, the overturning of small planes flown into the tip wake of larger aircraft, and marine propellor tip cavitation.</p>
<p>The tip vortex shed by several rectangular planform wings, fitted with three different tips, was studied in a water tunnel. Four techniques were employed to examine the tip vortex:</p>
<p>(i) Surface flow visualization to reveal the early stages of vortex rollup.</p>
<p>(ii) Double pulsed holography of buoyant, Lagrangian particle tracers for detailed tangential and axial velocity data around the vortex core. Holograms were also a source of instantaneous core structure information.</p>
<p>(iii) Single pulse holography of air bubbles, of uniform, measured, original size. The size of the bubbles is related to the instantaneous local static pressure. The bubbles are driven by the centripetal pressure gradient forces into the vortex core, providing a means of measuring the average and transient vortex core pressure non-intrusively.</p>
<p>(iv) Direct observation of vortex cavitation. These measurements are useful in their own right because of the considerable technological significance of tip vortex cavitation. In addition, many single phase tip flow characteristics have cavitating flow counterparts.</p>
<p>The present study has shown that one chord downstream of the wing trailing edge virtually all the foil bound vorticity has rolled up into the trailing vortex. Armed with this knowledge one may <i>a priori</i> evaluate, in the near field, the tangential velocity distribution, the core axial velocity excess, and the core mean pressure. These predictions are in agreement with the experimental measurements. Three aspects of the core flow, first observed in the present study, remain analytically inexplicable:</p>
<p>(i) The trend towards a Reynolds number dependent, axial velocity deficit with downstream distance.</p>
<p>(ii) The unsteady core velocity, particularly immediately downstream of the foil.</p>
<p>(iii) The vortex kinking which is coincident with highly unsteady axial core flow.</p>
<p>As a first approximation, cavitation inception occurs when the core pressure is reduced to the vapour pressure. The large measured fluctuating core pressure explains the occurrence of inception at core pressures somewhat above p<sub>v</sub> and the dependence of σ<sub>i</sub> on the dissolved air content.</p>
<p>Modifying the tip geometry profoundly affects the trailing vortex. Installation of a ring wing tip can reduce the inception index relative to that of a normal rounded tip foil by a factor of three. The reduction was caused primarily by the redistribution, in the Trefftz plane, of the shed vorticity about a line and circle. Fortuitously, this redistribution caused most of the wing bound vorticity to be shed from the ring, decreasing the tip effect lift loss over the foil body.</p>https://thesis.library.caltech.edu/id/eprint/1139Experimental Investigation of Rotor-Stator Interaction in Diffuser Pumps
https://resolver.caltech.edu/CaltechETD:etd-03262007-110354
Authors: {'items': [{'id': 'Arndt-Norbert-Karl-Erhard', 'name': {'family': 'Arndt', 'given': 'Norbert Karl Erhard'}, 'show_email': 'NO'}]}
Year: 1988
DOI: 10.7907/MR43-SR51
<p>The interaction between impeller blades and diffuser vanes in diffuser pumps was investigated. Steady and unsteady pressure measurements were made on the diffuser vanes and on the front shroud wall of a vaned and a vaneless diffuser. Two different impellers were used, one half of the impeller of the double suction pump of the HPOTP (High Pressure Oxygen Turbopump) of the SSME (Space Shuttle Main Engine), and a two-dimensional impeller. The measurements were made for different flow coefficients, shaft speeds, and radial gaps between the impeller blades and the diffuser vanes (1.5% and 4.5% of the impeller discharge radius for the impeller of the HPOTP, and 5% and 8% for the two-dimensional impeller). The vane pressure fluctuations were larger on the vane suction than on the vane pressure side attaining their maximum value, of the same order of magnitude as the total pressure rise across the pump, near the leading edge. The resulting lift on the vane, both steady and unsteady, was computed from the pressure measurements at mid vane height. The magnitude of the fluctuating lift was found to be larger than the steady lift. For the impeller of the HPOTP, pressure measurements on the front shroud of a vaned and a vaneless diffuser showed that the front shroud pressure fluctuations increased with the presence of the diffuser vanes.</p>
<p>For the two-dimensional impeller, also unsteady impeller blade pressure measurements were made. The largest blade pressure fluctuations, of the same magnitude as the large pressure fluctuations on the vane suction side, occurred at the blade trailing edge. However, the dependence of those pressure fluctuations on the flow coefficient was found to be different; on the vane suction side, the fluctuations were largest for maximum flow and decreased with decreasing flow coefficient, whereas at the blade trailing edge, the fluctuations were smallest for maximum flow and increased with decreasing flow coefficient. Increasing the vane number resulted in a significant decrease of the blade pressure fluctuations.</p>
<p>Lift, vane and blade pressure, and front shroud pressure fluctuations decreased strongly with increasing radial gap.</p>
https://thesis.library.caltech.edu/id/eprint/1140Experimental investigation of the hydrodynamic forces on the shroud of a centrifugal pump impeller
https://resolver.caltech.edu/CaltechTHESIS:09292010-111031034
Authors: {'items': [{'id': 'Zhuang-Fei', 'name': {'family': 'Zhuang', 'given': 'Fei'}, 'show_email': 'NO'}]}
Year: 1989
DOI: 10.7907/xywm-v650
Fluid-induced forces acting on a rotating impeller are known to cause rotor-dynamic problems in turbomachines. The forces generated by leakage flow along the front shroud surface of a centrifugal turbomachine impeller play an important role among these fluid-induced forces. The present research was aimed to gain a better understanding of these shroud forces. An experimental apparatus
was designed and constructed to simulate the impeller shroud leakage flow. Hydrodynamic forces, steady and unsteady pressure distributions on the rotating
shroud were measured as functions of eccentricity, width of shroud clearance, face seal clearance and shaft rotating speed. The forces measured from the dynamometer and manometers agreed well. The hydrodynamic force matrices
were found skew-symmetric and statically unstable. This is qualitatively similar to the result of previous hydrodynamic volute force measurements. Nondimensionalized
normal and tangential forces decrease slightly as Reynolds number increases. As the width of the shroud clearance decreases and/or the eccentricity increases, the hydrodynamic forces increase nonlinearly. There was some evidence found that increased front seal clearance could reduce the radial shroud forces and the relative magnitude of the destabilizing tangential force. Subharmonic
pressure fluctuations were also observed which may affect adversely the behavior of the rotor system.
https://thesis.library.caltech.edu/id/eprint/6075Experimental Investigation of the Effect of Cavitation on the Rotordynamic Forces on a Whirling Centrifugal Pump Impeller
https://resolver.caltech.edu/CaltechETD:etd-02022007-133417
Authors: {'items': [{'email': 'rfranz@energent.net', 'id': 'Franz-Ronald-John', 'name': {'family': 'Franz', 'given': 'Ronald John'}, 'show_email': 'NO'}]}
Year: 1989
DOI: 10.7907/5JXT-CZ84
The interaction of a rotating impeller and the working fluid introduce forces on the rotor. These fluid-induced forces can cause self-excited whirl, where the rotor moves away from and whirls along a trajectory eccentric to its undeflected position. When designing a turbomachine, particularly one which is to operate at high speed, it is important to be able to predict the fluid-induced forces, both steady and unsteady, acting on the various components of the machine. The fluid-induced rotordynamic forces acting upon the impeller and therefore on the bearings was investigated for a centrifugal impeller in a spiral volute in the presence of cavitation.
An experiment in forced vibration was made to study the fluid-induced rotordynamic force on an impeller whirling around its machine axis of rotation in water. The whirl trajectory of the rotor is prescribed to be a circular orbit of a fixed radius. A dynamometer mounted behind the rotor and rotating with it measures the force on the impeller. The force measured is a combination of a steady radial force due to volute asymmetries and an unsteady force due to the eccentric motion of the rotor. These measurements have been carried out over a full range of whirl/impeller speed ratios at different flow coefficients for various turbomachines. A destabilizing force was observed over a region of positive whirl ratio. Cavitation corresponding to a three percent head loss did not have a significant effect upon this destabilizing force. However, a lesser degree of cavitation at the design point for the impeller-volute combination tested increased this destabilizing force for a particular set of whirl ratioshttps://thesis.library.caltech.edu/id/eprint/467Cavitation and wake structure of unsteady tip vortex flows
https://resolver.caltech.edu/CaltechETD:etd-03272007-131947
Authors: {'items': [{'id': 'Hart-D-P', 'name': {'family': 'Hart', 'given': 'Douglas P.'}, 'show_email': 'NO'}]}
Year: 1993
DOI: 10.7907/ANNN-VC25
NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.
Unsteady flows are prevalent in virtually every fluid application yet, because of their intrinsic complexity, few attempts have been made to measure them or explain their behavior. This thesis presents an experimental study of one of the simplest unsteady flow induced effects, the periodic change in angle of attack of a lifting surface. Of particular interest is the influence this effect has on the tip vortex structure of a finite aspect ratio hydrofoil and the part it plays in the inception of cavitation.
An aspect ratio 2.3 hydrofoil was reflection-plane mounted to the test section floor of the Caltech Low Turbulence Water Tunnel and harmonically oscillated in pitch near its center of pressure. Observations of the growth and collapse of surface and tip vortex cavitation were made along with detailed observations of the interaction of the tip vortex formation with the spanwise wake structure. Measurements of the cavitation inception number for surface cavitation and tip vortex cavitation were made relative to the phase of the hydrofoil and the reduced frequency, k=[low-case omega]c/2U[...], of oscillation. Studies of the oscillation-induced spanwise trailing vortex structures and the Karman vortex street generated by the boundary layer were made of a two-dimensional hydrofoil. Laser Doppler Velocimetry (LDV) measurements were taken of the tip vortex velocity profile and the flow at the trailing edge of both the two-and the three-dimensional hydrofoils at reduced frequencies ranging from 0.5 to 2.0. Dynamic changes in bound circulaion and shed vorticity in the streamwise and spanwise directions relative to the freestream were calculated from these measurements at three locations along the span of the foil. The results of these measurements are compared to theoretical flow calculations and related to measurements of the cavitation inception number in the tip vortex region of the three-dimensional foilhttps://thesis.library.caltech.edu/id/eprint/1175Size segregation of binary granular materials in vertical channel flows
https://resolver.caltech.edu/CaltechTHESIS:04112011-111322619
Authors: {'items': [{'id': 'Beatty-S-M', 'name': {'family': 'Beatty', 'given': 'Susan M.'}, 'show_email': 'NO'}]}
Year: 1993
DOI: 10.7907/cnvy-9k28
This experimental research investigates transverse particle segregation in a binary mixture of spherical particles in air. in a gravity driven. vertical channel flow. Glass beads with similar properties, except for size and color, are randomly mixed in an upper hopper at the entrance of a vertical channel. When roughened channel walls are employed. particles show segregation by size, with a preferred position of larger particles at the centerline and approximately 80% of the distance between the centerline and the side walls. The concentration of the particles is found based on grey-scale color distribution as recorded by an image processing system. The effects of variations in flow rate. wall surface conditions, mixture ratios and channel width on segregation are studied as a function of downstream distance.
https://thesis.library.caltech.edu/id/eprint/6288Internal flows and force matrices in axial flow inducers
https://resolver.caltech.edu/CaltechETD:etd-03012005-141633
Authors: {'items': [{'email': 'abi.b2004@gmail.com', 'id': 'Bhattacharyya-A', 'name': {'family': 'Bhattacharyya', 'given': 'Abhijit'}, 'show_email': 'NO'}]}
Year: 1994
DOI: 10.7907/Q4ST-4X32
Axial flow pump runners known as inducers are subject to complex internal flows and fluid-induced lateral and rotordynamic forces. The internal flows in inducers are three dimensional and are characterized by complicated secondary flows. The current research investigates the boundary layer flows on the blades, hub and housing of unshrouded and shrouded axial flow inducers using flow visualization techniques. Rotordynamic and lateral force data on unshrouded inducers were also obtained under varying conditions of flow and whirl.
Studies on the internal flows showed that the blade boundary layer flow had strong radial components at off-design conditions. The flow remains attached to the blade surface of unshrouded inducers at all flow coefficients tested. The origin of the upstream swirling backflow was found to be at the discharge plane of the inducer. In addition, flow reversal was observed at the suction side blade tip near the leading edge in a shrouded inducer. Re-entry of the hub boundary layer flow (a downstream backflow) into the blade passage area was observed at flow coefficients below design. For unshrouded inducers the radially outward flow near the blade tip mixed with the tip clearance leakage flow to form the upstream backflow. These observations provide a better understanding of the internal flows and the occurrence of upstream backflows in inducers.
The rotordynamic forces acting on an inducer due to an imposed whirl motion was also investigated. It was found that the rotordynamic force data at various whirl frequency ratios does not allow a normal quadratic fit; consequently the conventional inertial, stiffness and damping coefficients cannot be obtained and a definite whirl ratio describing the instability region does not result. Rotordynamic forces were found to be significantly dependent on the flow coefficient. At flow coefficients below design, these forces are characterized by multiple zero crossings at various whirl frequencies and large destabilizing peeks. Theoretical estimates of the tangential rotordynamic force on a non-whirling inducer using actuator disk theory were significantly different, both in magnitude and direction, from the experimentally measured forces.
The effect of upstream and downstream flow distortions on the rotordynamic and lateral forces on an inducer were studied. It was found that at flow coefficients below design, large lateral forces occurred in the presence of a downstream asymmetry. The reverse flows occurring downstream which consist of high energy fluid are the possible cause of these large forces. The imposition of a uniform downstream condition reduced these forces to near zero values. Results of inlet distortion experiments show that a strong inlet shear causes a significant increase in the lateral force. However, weak inlet shear flows and the flow asymmetry due to a 180° upstream bend did not cause a significant lateral force. It was found that flow distortions upstream or downstream did not cause any significant effect on the rotordynamic forces. Cavitation was found to have important consequences for fluid-induced rotordynamic forces. These forces become destabilizing for both forward and reverse whirl. The magnitudes of the destabilizing forces were found to increase with decreasing cavitation numbers.
https://thesis.library.caltech.edu/id/eprint/818Hydrodynamics, acoustics and scaling of traveling bubble cavitation
https://resolver.caltech.edu/CaltechETD:etd-10202005-152545
Authors: {'items': [{'email': 'yankdc@slb.com', 'id': 'KuhndeChizelle-Y-P', 'name': {'family': 'Kuhn de Chizelle', 'given': 'Yan P.'}, 'show_email': 'NO'}]}
Year: 1994
DOI: 10.7907/E92Q-C197
Recent observations of the geometries of growing and collapsing bubbles over axisymmetric headforms have revealed the complexity of the "microfluidmechanics" associated with these flows (Hamilton et al., 1982, Briancon Marjollet and Franc, 1990, Ceccio and Brennen, 1991). Among the complex features observed were bubble to bubble interaction, cavitation noise generation and bubble interaction with the boundary layer which leads to the shearing of the underside of the bubble and alters the collapsing process. All of these previous tests were performed on small headform sizes. The focus of this research is to determine the dynamics governing the growth and collapse of traveling bubbles and to analyze the scaling effects due to variations in geometry size, Reynolds number and cavitation number. For this effect, cavitating flows over Schiebe headforms of different sizes (5.08cm, 25.4cm and 50.8cm in diameter) were studied in the David Taylor Large Cavitation Channel (LCC). This thesis presents the scaling effects captured on high-speed film and electrode sensors as well the noise signals generated during the collapse of the cavities. The influence of each of these parameters on the dynamics involved in the growth and collapse phases of the traveling bubble are presented, along with the acoustical impulse produced during the collapse of the bubble.
In order to model and analyze the dynamics of the three-dimensional bubble deformation in the presence of the pressure field around the Schiebe headform, an unsteady numerical code using traveling sources has been developed. This thesis presents calculations of the interaction between the irrotational flow outside the boundary layer of the headform and individual traveling bubbles. An error estimation of the method and comparisons with the LCC experiments are presented. This method is shown to predict some of the features of three-dimensional bubble growth and collapse dynamics remarkably well. Furthermore, analysis of these computations allow a better understanding bubble interaction and event rate prediction.
https://thesis.library.caltech.edu/id/eprint/4193Nuclei population dynamics and cavitation
https://resolver.caltech.edu/CaltechETD:etd-10222007-152116
Authors: {'items': [{'id': 'Liu-Zhenhuan', 'name': {'family': 'Liu', 'given': 'Zhenhuan'}, 'show_email': 'NO'}]}
Year: 1995
DOI: 10.7907/eq2r-9z75
The effect of the nuclei population in water on cavitation has not been investigated thoroughly due to the difficulties of measuring the microbubbles in water. In this thesis, a Phase Doppler Anemometer (PDA) was calibrated by a holographic method and used to measure the micro-bubble distribution in water. Substantial agreement was achieved between the PDA and the holographic method. After the calibration, the PDA was used to study the nuclei population dynamics in two water tunnels. It was also employed in a study of cavitation on an axisymmetric Schiebe body in which the cavitation on the headform and the upstream nuclei population were simultaneously observed.
Substantial changes in the nuclei number density distributions were found in these two water tunnels. The nuclei population in each water tunnel can also vary significantly, sometimes by as much as an order of magnitude. The nuclei population dynamics are complicated and are affected by the tunnel design, the tunnel operating condition and the air content. The cavitation event rate on the Schiebe headform is mainly determined by the cavitation number. It increases dramatically as the cavitation number is decreased. It also varies with the magnitude and the shape of the nuclei number distribution. As the upstream nuclei population increases, the cavitation event rate increases. During the experiments, cavitation acoustic emissions were also measured and analyzed.
An analytical model based on the spherical bubble assumption and the Rayleigh-Plesset theory is developed to relate the free stream nuclei population to the cavitation event rate and the acoustic noise on an axisymmetric body. Complications, such as the effect of the boundary layer flow rate, of the bubble screening, of the bubble/bubble interactions and of the observable bubble size are examined and included in the model. The predicted cavitation event rate and acoustic impulse are compared with the experimental observations. It is shown that the predicted event rates agree with the observations when the population is small, but that increasing discrepancies occur at lower cavitation numbers when the bubble density becomes larger. The predicted noise qualitatively agrees with the observations, but is generally larger than the observations, mainly due to the fact that the spherical bubble assumption usually departs from the observed bubble shape.https://thesis.library.caltech.edu/id/eprint/4217A Study of Tip Vortices and Cavitation on a Propeller in a Non-Uniform Flow Field
https://resolver.caltech.edu/CaltechETD:etd-03262007-131335
Authors: {'items': [{'email': 'mckenn1@earthlink.net', 'id': 'McKenney-Elizabeth-Anne', 'name': {'family': 'McKenney', 'given': 'Elizabeth Anne'}, 'show_email': 'NO'}]}
Year: 1995
DOI: 10.7907/7THC-NG74
Unsteady lifting surface flows are important subjects for study, both for the purposes of improving propulsive or lifting efficiency and also for mitigating the destructive effects and noise caused by cavitation. Some progress may be made by selecting a simple type of unsteadiness for closer study. In the present work, this tactic was implemented in two ways: the operation of a propeller at an angle of yaw to the freestream and the pitching oscillation of a finite-span hydrofoil.
A new facility was designed and constructed to set a propeller at an angle of yaw to the freestream, creating a fairly simple non-uniformity in the propeller inflow. Tip vortex cavitation inception measurements were made for a range of yaw angles and freestream velocities, and photographs of the cavitation were taken to illustrate the effects of the yaw angle.
The unsteady tip vortex flow field was measured on an oscillating finite aspect ratio hydrofoil using Particle Image Velocimetry (PIV), revealing how the circulation varied during a typical oscillation cycle. The results were compared with unsteady infinite-span theory, and also with recent measurements using LDV techniques on the same foil.
The hydrofoil was also the focus of a study of surface cavitation. High-speed motion pictures of the cavitation cycle helped to separate the process into its component stages, and variations with cavitation number and reduced frequency of oscillation were observed. The acoustic signals generated by the cavity collapse were correlated with the motion pictures, providing insights into the correspondence between the flow structures involved in the cavity collapse process and the sound generated by them.
The results from these studies provide valuable insights into the effects of unsteadiness in lifting surface flows.
https://thesis.library.caltech.edu/id/eprint/1145