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A Caltech Library Repository Feedhttp://www.rssboard.org/rss-specificationpython-feedgenenSat, 13 Apr 2024 00:48:17 +0000Design of a tension load cell
https://resolver.caltech.edu/CaltechETD:etd-09102002-145241
Authors: {'items': [{'id': 'Calle-J', 'name': {'family': 'Calle', 'given': 'Jean-Michel'}, 'show_email': 'NO'}]}
Year: 1965
DOI: 10.7907/HBSD-J913
A tension load cell is designed along the two following main ideas:
- Decrease the pressure by which the applied load is measured.
- Design a thinner and therefore more flexible diaphragm.
After calculation of the stresses produced in the diaphragm, a thinner but still strong diaphragm is designed as well as the equipment necessary to build it.
The shape and dimensions of the diaphragm being determined, the tension load cell is then designed.
Working drawings of the parts of the mold and the tension load cell are given at the end of the work, in the appendix.https://thesis.library.caltech.edu/id/eprint/3425Entrainment and Flame Geometry of Fire Plumes
https://resolver.caltech.edu/CaltechETD:etd-09192006-141619
Authors: {'items': [{'email': 'cetegen@engr.uconn.edu', 'id': 'Cetegen-Baki-Mehmet', 'name': {'family': 'Cetegen', 'given': 'Baki Mehmet'}, 'show_email': 'YES'}]}
Year: 1982
DOI: 10.7907/CJ4E-W053
<p>This study concerns the flame structure and fire plume entrainment of natural gas diffusion flames on 0.10, 0.19 and 0.50 m. diameter burners. The heat release rates ranged from 10 kW to 200 kW. Flame heights based on high speed photography and eye averages show a transition in the dependence of flame height on a dimensionless heat addition parameter around unity. For flames taller than three burner diameters, the initial diameter of the fire does not affect the length of these flames whereas for short flames initial geometry becomes important. Another prominent feature of these flames is the presence of large scale ring vortex-like structures which are formed close to the burner surface more or less regularly. It is found that these structures are responsible for the fluctuations of the flame top.</p>
<p>Entrainment measurements spanned heights starting very close to the burner surface to distances about six times the average flame heights. Experiments indicate the presence of three regions; a region close to the burner surface where plume entrainment rates are independent of the fuel flow (or heat release) rates; a far field region above the flame top, where a simple point source model correlates the data reasonably well; and a not so well-defined intermediate region where entrainment seems to be similar to that of a turbulent flame with plume-like characteristics. It is also found that the disturbances in the ambient atmosphere will greatly enhance the fire plume entrainment. Finally, a theoretical study of a steady, buoyant, diffusion flame indicated the importance of the puffing in the entrainment process.</p>https://thesis.library.caltech.edu/id/eprint/3640Scale 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/3659The Rheology of a Bituminous Coal
https://resolver.caltech.edu/CaltechETD:etd-09122006-151359
Authors: {'items': [{'email': 'jcs@alumni.caltech.edu', 'id': 'Stevenson-John-Cary', 'name': {'family': 'Stevenson', 'given': 'John Cary'}, 'show_email': 'YES'}]}
Year: 1982
DOI: 10.7907/06Q1-DZ20
<p>The fluidity of a rapidly heated, bituminous coal was studied with a capillary rheometer. Quantitative measurements of overall fluidity, of transition from no flow to flow, and of the effects of presence of the gaseous phase were the principal objectives.</p>
<p>Separate measurements of the density of the coal indicated that the major changes in density with time were due to the production of gas by decomposition. The volume fraction of gas was calculated from the density measurements.</p>
<p>The relationships between volumetric flow rate and pressure drop were expressed in terms of an overall, or "effective," viscosity. The overall viscosity displayed values as low as thirty poise, and its rheological classification was Newtonian within the accuracy of the experimental equipment. The transition from no flow to flow was quite sudden, and it was independent of the volume of gas present in the reservoir.</p>
<p>The multi-component, multi-phase flow of coal was considered to be a two-component, two-phase, liquid-gas system. Various correlations found in the literature were applied to the overall viscosity data, and estimates of the viscosity of the liquid phase were made. A constitutive relationship for the density as a function of temperature, time, and pressure was developed. Closed-form solutions of the simplified momentum equation were generated based on definitions of a mean viscosity as a function of the viscosities of the liquid and the gas, and the volume fractions of the liquid and the gas. Because of the magnitude of the volume fraction of gas, the viscosity of the liquid phase was greater than the overall viscosity of the mixture.</p>
https://thesis.library.caltech.edu/id/eprint/3501Cavitation 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/331Unsteady Two-Phase Flow Instrumentation and Measurement
https://resolver.caltech.edu/CaltechETD:etd-05122004-092752
Authors: {'items': [{'id': 'Bernier-Robert-J-N', 'name': {'family': 'Bernier', 'given': 'Robert J. N.'}, 'show_email': 'NO'}]}
Year: 1982
DOI: 10.7907/8KSZ-8796
<p>The performance of a transverse field electromagnetic flowmeter in a steady two-phase flow was investigated analytically for a disperse and an annular flow regime. In both cases the flowmeter output voltage was found to be proportional to the mean velocity of the liquid phase. Experiments in a steady air-water mixture showed good agreement with the analysis.</p>
<p>An impedance void fraction meter was designed and built to conduct measurements of unsteady void fractions. Short electrodes excited by voltages of opposite polarity were used in combination with a highly sensitive signal processor. The steady state calibration indicated that the meter was somewhat sensitive to the void fraction distribution for the bubbly flow regime. However, the transition to a churn turbulent regime greatly affected the meter steady state response. The dynamic capability of the void fraction meter was estimated by comparison of the statistical properties of the voltage fluctuations in a nominally steady bubbly flow with those of a shot-noise process. The filter function associated with the finite volume of the electric field within the fluid cell could be determined from the measured autocorrelation function and was shown to be mainly a function of the velocity of the disperse phase. Also some properties of the disperse phase could be inferred from the statistical analysis.</p>
<p>Two void fraction meters were used to measure the propagation speed of kinematic shocks in an air-water bubbly mixture for various void fractions and water flow rates. The relative velocity of the disperse phase calculated from these measurements decreased with an increase in the disperse phase concentration. However, this effect disappeared at higher water flow rates and the relative velocity became independent of void fraction. Measurements of the propagation speed of shocks of decreasing strength provided a good verification of the kinematic wave theory. The shock thicknesses could also be determined leading to the conclusion that an important diffusion mechanism was responsible for arresting the steepening of the wave.</p>
<p>Cross-correlations of the fluctuating voltage of two void fraction meters in a steady bubbly flow were determined. The speed measured by this technique was identified as the infinitesimal wave speed of the void fraction and not the velocity of the dispersed phase as postulated by some authors. The normalized cross-correlation maxima showed that the small amplitude void fraction disturbances were short-lived structures, which were created and diffused on a continuous basis. The cross spectral density revealed that the waves present in these disturbances were nondispersive.</p>https://thesis.library.caltech.edu/id/eprint/1745A General Solution Strategy for Large Scale Static and Dynamic Nonlinear Finite Element Problems Employing the Element-by-Element Factorization Concept
https://resolver.caltech.edu/CaltechETD:etd-09012006-080048
Authors: {'items': [{'id': 'Levit-Itzhak', 'name': {'family': 'Levit', 'given': 'Itzhak'}, 'show_email': 'NO'}]}
Year: 1983
DOI: 10.7907/jqbq-rc43
<p>It is proposed to solve large-scale finite-element equation systems arising in structural and solid mechanics by way of an element-by-element approximate factorization technique which obviates the need for a global coefficient matrix. The procedure has considerable operation count and I/O advantages over direct elimination schemes and it is easily implemented. Numerical results demonstrate the effectiveness of the method and suggest its potential for the analysis of large-scale systems.</p>https://thesis.library.caltech.edu/id/eprint/3308Forces 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/3551Edgetones and Acoustic Resonances in a Duct
https://resolver.caltech.edu/CaltechETD:etd-01222007-092606
Authors: {'items': [{'id': 'Aaron-Kim-Maynard', 'name': {'family': 'Aaron', 'given': 'Kim Maynard'}, 'show_email': 'NO'}]}
Year: 1985
DOI: 10.7907/bfy8-1995
<p>Undesirable sound generation in the combustion chamber of segmented solid propellant rocket motors has been attributed to vortex shedding from obstructions that are uncovered as the propellant burns back. This phenomenon has been investigated experimentally and the mechanism explained.</p>
<p>A pair of aluminum baffles within a lucite duct through which air is drawn models the important aspects which enable the sound generation mechanism to operate. The baffles form an edgetone system which interacts with the longitudinal acoustic modes of the chamber. Acoustic tones occur spontaneously, at frequencies determined by the acoustic resonances, when the spacing between the baffles satisfies certain criteria.</p>
<p>Flow visualization using smoke and a strobe light triggered by the pressure oscillations indicate that vortex shedding occurs at the first baffle in phase with the acoustic velocity oscillations there. The interaction of these vortices with the downstream baffle drives the acoustic resonance which, in turn, triggers the formation of new vortices at the upstream separation point.</p>
<p>The phase relations for this feedback to operate require that there be close to an integral number of wavelengths, or vortices, from the separation point to the impingement point.</p>
<p>A model has been developed which predicts the experimentally observed behaviour well. Pressure amplitudes are predicted within an order of magnitude. Mean flow rates and baffle spacings yielding maximum response are determined correctly by the model.</p>https://thesis.library.caltech.edu/id/eprint/274Laser Doppler Velocity and Vorticity Measurements in Turbulent Shear Layers
https://resolver.caltech.edu/CaltechETD:etd-08312005-112325
Authors: {'items': [{'email': 'dbl@tyrvos.caltech.edu', 'id': 'Lang-Daniel-Bernard', 'name': {'family': 'Lang', 'given': 'Daniel Bernard'}, 'show_email': 'NO'}]}
Year: 1985
DOI: 10.7907/YFR4-VE59
<p>A Laser Doppler Velocimeter (LDV) system was developed to measure the instantaneous spanwise vorticity, -w<sub>z</sub>, in a turbulent shear layer. It was necessary to design and fabricate the LDV optics and processing electronics, as no commercially available LDV systems met the specifications of measuring the velocity at four closely spaced points to the requisite accuracy. Measurements were also made of the instantaneous u, v, u', v', and -u'v'. The instantaneous vorticity was processed to obtain an estimate of its probability density function, from which the mean and rms values were estimated. It was also possible to separate the irrotational fraction of the flow (-w<sub>z</sub> ≈ 0) from the rotational (intermittent) fraction of the flow (-w<sub>z</sub> ≠ 0). The development of the intermittency profiles, based on vorticity, as a function of the downstream distance from the splitter plate was studied. A notable feature is that the vorticity is found to have values opposite the mean sense of rotation, i.e., -w<sub>z</sub>(t) < 0, a significant fraction of the time. Additionally, a detailed study was performed to evaluate the approximation of -∂v/∂x, in terms of various local temporal derivatives ∂v/u(y)∂t. The optimum choice for u(y) can be found and is influenced by the relative local convection velocities of the small and large scale structures.</p>
https://thesis.library.caltech.edu/id/eprint/3291An Experimental Study of Convective Heat Transfer, Friction, and Rheology for Non-Newtonian Fluids: Polymer Solutions, Suspensions of Fibers, and Suspensions of Particulates
https://resolver.caltech.edu/CaltechETD:etd-03272007-105407
Authors: {'items': [{'id': 'Matthys-Eric-Francois', 'name': {'family': 'Matthys', 'given': 'Eric Francois'}, 'show_email': 'NO'}]}
Year: 1985
DOI: 10.7907/pr91-d523
<p>An experimental investigation was conducted on the convective heat transfer, friction, and rheological properties of various types of non-newtonian fluids in circular tube flows.</p>
<p>If an apparent Reynolds number is used and if the temperature and degradation effects are properly taken into account, the reduced turbulent friction and heat transfer results, respectively, are then shown to be well correlated by the same expressions for different fluids, regardless of the nature of the fluids and whether they are shear-thinning or shear-thickening. This representation can also separate the reductions in turbulent heat transfer and friction that are induced by viscoelasticity from those induced by pseudoplasticity.</p>
<p>Polyacrylamide solutions inducing asymptotic and intermediate drag reduction regimes were investigated over a broad range of Reynolds numbers. The minimum heat transfer asymptote was determined for fully-developed conditions and for the very long (up to x/D = 600) entrance region observed. Solutions subjected to various degrees of intentional pre-degradation were studied to separate this effect from that of the degradation induced in the test tube itself.</p>
<p>A kerosene-based antimisting polymer solution was also studied. It was found to exhibit a complex viscous behavior involving time-dependency, shear-thickening beyond a critical shear rate, high susceptibility to degradation, and large sensitivity to temperature variations. The unusual friction and heat transfer results obtained with this fluid were, however, reduced to simple correlations for asymptotic drag reduction if an appropriate computational model is used.</p>
<p>Suspensions of bentonite of various concentrations were investigated in laminar and turbulent regimes, and the results for fully-developed and entrance flows were well correlated by newtonian relationships when an adequate wall viscosity concept was used. A combination of bentonite and polymer was found to be unusually susceptible to mechanical degradation, which affected significantly the viscosity and the level of drag and heat transfer reductions obtained.</p>
<p>A suspension of organic pulp based on tomato puree was shown to exhibit up to 40% of viscoelastic-type reduction in heat transfer and friction coefficients with respect to newtonian fluids in the turbulent regime. For laminar flow, however, these coefficients were larger than expected. Combinations of pulp and polymer were investigated as well.</p>
<p>A method was developed to predict the "diameter effect" for viscoelastic fluids.</p>https://thesis.library.caltech.edu/id/eprint/1172Formation and Control of Atmospheric Aerosol Nitrate and Nitric Acid
https://resolver.caltech.edu/CaltechETD:etd-03252008-090855
Authors: {'items': [{'id': 'Russell-Armistead-Goode', 'name': {'family': 'Russell', 'given': 'Armistead Goode'}, 'show_email': 'NO'}]}
Year: 1985
DOI: 10.7907/rdz0-9a12
<p>This work focuses on the formation, transport and control of atmospheric nitric acid and nitrate aerosol using both theoretical modeling and experimental techniques. A mathematical model was developed that describes the formation and transport of photochemically produced atmospheric gases and nitrate aerosol, using fundamental thermodynamic data to determine the quantity and state of the aerosol nitrate produced. Model predictions compared favorably with the field data available. A sensitivity study of the model indicated that the predicted aerosol nitrate concentrations are highly dependent on temperature. The trajectory model was used to study the fate of nitrogen oxides emissions and the chemical reactions responsible for the formation of atmospheric nitric acid. A majority of the NO<sub>x</sub> emissions deposit out within 24 hours, primarily as HNO<sub>3</sub>. Previously it was believed that almost all of the atmospheric nitric acid was produced during daylight hours, however model results indicate that nighttime reactions can produce comparable quantities, especially in the upper portions of the boundary layer more than a hundred meters above ground.</p>
<p>An experimental program was designed and executed to collect a set of data for use in studying nitrate formation, and for use in evaluating the accuracy of air quality models. A large quantity of aerosol nitrate was observed to accumulate overnight near the coast, presumably due to the reaction between HNO<sub>3</sub> and sea salt aerosol or soil dust—like material. This aerosol is then transported inland the following afternoon, and can contribute to the high particulate nitrate levels found inland. Data from the experiment were used to test the hypothesis that atmospheric HNO<sub>3</sub> and NH<sub>3</sub> are in equilibrium with the aerosol phase. Most of the data are consistent with the assumption that an external mixture containing some pure NH<sub>4</sub>NO<sub>3</sub> is present. Additional improvement is obtained if an internally mixed NH<sup>+</sup><sub>4</sub>-NO<sup>-</sup><sub>3</sub>-SO<sup>=</sup><sub>4</sub> aerosol is assumed to be present.</p>
<p>Further evaluation of the air quality model against the data described above showed that the model accurately predicts the measured concentrations of O<sub>3</sub>, NO<sub>2</sub>, total nitrate, HNO<sub>3</sub>, and NH<sub>3</sub>. Representative emission control programs were tested using the model, and results indicated that NO<sub>x</sub> emission control will reduce HNO<sub>3</sub>(g), aerosol nitrate and PAN concentrations. For the particular trajectories studied, NO<sub>x</sub> control would also have reduced the peak O<sub>3</sub> concentrations. Reducing NH<sub>3</sub> emissions will reduce aerosol nitrate formation at the expense of increasing HNO<sub>3</sub> concentrations. Controlling organic gas emissions will reduce O<sub>3</sub> and PAN. Further research areas suggested by this work also are presented.</p>https://thesis.library.caltech.edu/id/eprint/1118Analyses 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/1141Two-Phase Soil Study: A. Finite Strain Consolidation. B. Centrifuge Scaling Considerations
https://resolver.caltech.edu/CaltechETD:etd-03082008-084249
Authors: {'items': [{'id': 'Tan-Thiam-Soon', 'name': {'family': 'Tan', 'given': 'Thiam-Soon'}, 'show_email': 'NO'}]}
Year: 1986
DOI: 10.7907/agt3-mf84
<p>Two different aspects of the behavior of soil as a two-phase medium are studied, namely, the consolidation of soil and scaling relations for soils in centrifuge testing.</p>
<p>PART A</p>
<p>First a consistent approach is presented that unifies all current theories of consolidation of soil. For one-dimensional finite strain consolidation, a Lagrangian finite element scheme is then given and tested against three different experiments and found to give consistent results. For a quick solution to a particular problem, the regular perturbation method applied to the formulation in which the dependent variable is the natural strain is shown to give the most consistent results. For the Eulerian formulation, the material derivative contains a convective term. This convective effect is then analytically studied and found not to be negligible for a final natural strain greater than 10%. A method is then introduced that can account for both the moving boundary and the convective effect. This method is tested in a finite difference scheme and found to give identical results with the Lagrangian finite element scheme for the one-dimensional case. Finally the method is used for the axisymmetric problem of consolidation by vertical drain. The solution to this case suggests that arching and subsequent load redistribution should be considered.</p>
<p>PART B</p>
<p>Conceptually, when a centrifuge is used to test models, the centrifuge is assumed to produce an equivalent ng gravitational field (as on another planet) and the behavior of the model in the ng field is then assumed to be similar to that of the prototype. For most static problems, the centrifuge does model the prototype well but for some dynamic problems, these assumptions can break down. To investigate this, the similarity requirements are examined for the case of a single particle moving in a fluid. It is found that for the post-liquefaction process and for seepage flow, unless the Reynolds number is much less than one in both model and prototype, the centrifuge is not a good simulation of the prototype situation. But, perhaps contrary to expectations, the breakdown is due to the fact that the behavior in the ng planet is not similar to the prototype ig planet, whereas the centrifuge does simulate the ng planet well. Further, it is shown that the concept of "modeling of models" can lead to misleading results. Lastly, for cratering experiments, it is concluded that the centrifuge will only model the crater shape just after an explosion and not the final crater shape.</p>https://thesis.library.caltech.edu/id/eprint/902Cavitation 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/1246Experimental 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/1144Experimental 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/1150Laboratory Analysis of Settling Velocities of Wastewater Particles in Seawater using Holography
https://resolver.caltech.edu/CaltechETD:etd-02022007-152444
Authors: {'items': [{'id': 'Wang-Rueen-Fang-Theresa', 'name': {'family': 'Wang', 'given': 'Rueen-Fang Theresa'}, 'show_email': 'NO'}]}
Year: 1988
DOI: 10.7907/0zds-gj34
<p>Ocean discharge of treated sewage and digested sludge has been a common practice for the disposal of municipal and industrial wastewaters for years. Since the particles in the discharge cause much of the adverse effect on the marine environment, the transport processes and the final destinations of particles and the associated pollutants have to be studied to evaluate the environmental impact and the feasibility of disposal processes. The settling velocity of particles and the possible coagulation inside the discharge plume are among the most important factors that control the transport of particles.</p>
<p>A holographic camera system was developed to study the settling characteristics of sewage and sludge particles in seawater after simulated plume mixing with possible coagulation. Particles were first mixed and diluted in a laboratory reactor, which was designed to simulate the mixing conditions inside a rising plume by varying the particle concentration and turbulent shear rate according to predetermined scenarios. Samples were then withdrawn from the reactor at different times for size and settling velocity measurements. Artificial seawater without suspended particles was used for dilution.</p>
<p>An in-line laser holographic technique was employed to measure the size distributions and the settling velocities of the particles. Doubly exposed holograms were used to record the images of particles for the fall velocity measurement. Images of individual particles were reconstructed and displayed on a video monitor. The images were then digitized by computer for calculating the equivalent diameter, the position of the centroid, the deviations along the principal axes, and the orientation of particles. A special analysis procedure was developed to eliminate sampling biases in the computation of cumulative frequency distributions. The principal advantages of this new technique over the conventional settling column (used in the early part of this research) are that: (1) the coagulation and settling processes can be uncoupled by use of extremely small concentrations (less than 2 mg/l) in the holographic sample cell, and (2) the individual particle sizes and shapes can be observed for correlation with measured fall velocities.</p>
<p>Four sets of experiments were conducted with blended primary/secondary effluent from the County Sanitation Districts of Los Angeles County and the digested primary sludge from the County Sanitation Districts of Orange County (proposed deep ocean outfall) using different mixing processes. Experimental results show that the sludge and effluent particles have very similar settling characteristics, and that particle coagulation is small under the simulated plume mixing conditions used in these experiments. The median and 90-percentile fall velocities and the fractions of particles with fall velocities larger than 0.01 cm/sec of the digested primary sludge and the effluent are summarized in the following table. The experimental results from the conventional settling column are also included for comparison. In general, the holographic technique indicates slower settling velocities than all the previous investigations by other procedures.</p>
<p>[Table; see abstract in scanned thesis for details.]</p>https://thesis.library.caltech.edu/id/eprint/469Studies of Inertial Deposition of Particles onto Heat Exchanger Elements
https://resolver.caltech.edu/CaltechETD:etd-11012007-135053
Authors: {'items': [{'id': 'Fuhs-Susan-Elizabeth', 'name': {'family': 'Fuhs', 'given': 'Susan Elizabeth'}, 'show_email': 'NO'}]}
Year: 1988
DOI: 10.7907/jh2a-bh94
<p>Although the magnitude of the fouling problem in heat transfer equipment is well recognized, few investigations have been conducted into the mechanisms that lead to such fouling. The work reported in this thesis has been designed to examine gas-side fouling mechanisms that involve the inertial impaction of small particles onto tubular heat exchanger surfaces.</p>
<p>An aerosol processes wind tunnel has been constructed which facilitates quantitative studies of particle interactions with heat exchanger surfaces. Three sets of experiments were performed. First, single heat exchanger tubes were exposed to a cross-flow of particle laden air. Stainless steel tubes coated with a thin layer of grease to ensure that particle collisions resulted in capture were used to verify a numerical model for the inertial transport of ammonium fluorescein particles to the tube surface. Particle bounce has been quantified for the case of clean tubes and solid particles. Experimental results compared favorably with the results of a numerical simulation based on the concept of a critical incident particle velocity normal to the surface needed to induce the particle to bounce with enough energy to escape collection by the tube.</p>
<p>Second, the transient deposition of particles onto single heat exchanger tubes in cross-flow was studied. It was found that a steady-state condition could be reached for cases in which particle bounce occurred. Finally, the deposition patterns for the aerosol particles as they passed through a tube bank were studied. The quantities of aerosol deposited on various tubes depended on tube surface condition, tube position within the tube bank, and the overall geometry of the bank.</p>
<p>Conditions have been identified in which the aerosol deposits that lead to gas-side heat exchanger fouling can be kept to very low levels by deliberately selecting high fluid velocities that induce solid particles to bounce upon impact with the heat exchanger surfaces. Transient fouling experiments have identified conditions under which high fluid velocities can be used to achieve very low, steady-state particle accumulations on tubes in a cross-flow of solid particles. Using these findings, heat exchangers can be designed that will resist gas-side fouling.</p>
https://thesis.library.caltech.edu/id/eprint/4365Tip 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 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/467Observations of the Dynamics and Acoustics of Travelling Bubble Cavitation
https://resolver.caltech.edu/CaltechETD:etd-12092004-154832
Authors: {'items': [{'email': 'ceccio@umich.edu', 'id': 'Ceccio-Steven-Louis', 'name': {'family': 'Ceccio', 'given': 'Steven Louis'}, 'show_email': 'NO'}]}
Year: 1990
DOI: 10.7907/427S-BC75
<p>Individual travelling cavitation bubbles generated on two axisymmetric headforms were detected using a surface electrode probe. The growth and collapse of the bubbles, almost all of which were quasi-spherical caps moving close to the headform surface, were studied photographically. Although the growth patterns for the two headforms were similar, the collapse mechanisms were quite different. These differences were related to the pressure fields and viscous flow patterns associated with each headform. Measurements of the acoustic impulse generated by the bubble collapse were analyzed and found to correlate with the maximum volume of the bubble for each headform. Numerical solutions of the Rayleigh-Plesset equation were generated for the same flows and compared with the experimental data. The experiments revealed that for smaller bubbles the impulse-volume relationship is determinate, but for larger bubbles the impulse becomes more uncertain. The theoretical impulse was at least a factor of two greater than the measured impulse, and the impulse-volume relationship was related to the details of the collapse mechanism. Acoustic emission of individual cavitation events was spectrally analyzed and the results were compared with relevant theoretical and emperical predictions. Finally, the cavitation nuclei flux was measured and compared to the cavitation event rate and the bubble maximum size distribution through the use of a simple model. The nuclei number distribution was found to vary substantially with tunnel operating conditions, and changes in the nuclei number distribution significantly influenced the cavitation event rate and bubble maximum size distribution. The model estimated the cavitation event rate but failed to predict the bubble maximum size distribution. With the above theoretical and experimental results, the cavitation rate and resulting noise production may be estimated from a knowledge of the non-cavitating flow and the free stream nuclei number distribution.</p>https://thesis.library.caltech.edu/id/eprint/4897Ultrasonic irradiation of chemical compounds in aqueous solutions
https://resolver.caltech.edu/CaltechETD:etd-08062007-152346
Authors: {'items': [{'email': 'natasha@meteo.noa.gr', 'id': 'Kotronarou-A', 'name': {'family': 'Kotronarou', 'given': 'Anastassia'}, 'show_email': 'NO'}]}
Year: 1992
DOI: 10.7907/RR28-5R10
NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.
The ultrasonic irradiation of para-nitrophenol, S(-II), and parathion is studied in aqueous solutions at 20 kHz and [...] 75 [...]. Para-nitrophenol was degraded primarily by denitration and secondarily by [...] radical attack to yield [...], [...], benzoquinone, hydroquinone, 4-nitrocatechol, formate and oxalate. These reaction products and the kinetic observations are consistent with a model involving high-temperature reactions of p-nitrophenol in the interfacial region of cavitation bubbles. The average effective temperature of the interfacial region surrounding the cavitation bubbles was estimated to be T [...] 800 K.
Ultrasonic irradiation of S(-II) is studied in aqueous solutions over the pH range 7 - 12. The reaction of HS- with [...] is the principal pathway for the oxidation of S(-II) at pH [...] 10; the oxidation products are [...], [...], and [...]. Upon prolonged sonication, [...] is the only observed product. At pH [...] 8.5, thermal decomposition of H2S within or near collapsing cavitation bubbles becomes the important pathway and elemental sulfur is found as an additional product of the sonolysis of S(-II). The sonolytic oxidation of H2S at pH [...] 10 was successfully modeled with an aqueous-phase free-radical chemistry mechanism and assuming continuous and uniform [...] input into solution from the imploding cavitation bubbles.
Parathion degradation occurred primarily by enhanced hydrolysis and secondarily by direct [...] radical attack.
The effect of various physical and chemical parameters on sonolytic yields is examined. The observed effects are in qualitative agreement with the sonolysis mechanisms proposed for the chemicals of interest and the existing hydrodynamic theories of acoustic cavitation.
The formation of iodine upon ultrasonic irradiation of potassium iodide solutions and the sonolysis of S(-II) are used as probes to compare the sonochemical efficiency of different experimental set-ups.
This work elucidates the mechanisms of the ultrasonic decomposition of typical organic and inorganic pollutants. It is shown that ultrasound has the potential to become a viable alternative for the destruction of chemical contaminants in water and wastewater. The current limitation of sonolysis is its low energy utilization efficiency, but there is room for improvement by optimizing reactor design and physical/chemical operation conditions. This work offers some recommendations and insight in that respect.https://thesis.library.caltech.edu/id/eprint/3030Rotordynamic forces generated by discharge-to-suction leakage flows in centrifugal pumps
https://resolver.caltech.edu/CaltechETD:etd-03272007-091813
Authors: {'items': [{'id': 'Guinzburg-A', 'name': {'family': 'Guinzburg', 'given': 'Adiel'}, 'show_email': 'NO'}]}
Year: 1992
DOI: 10.7907/dv7v-hy83
In recent years, increasing attention has been given to fluid-structure interaction problems in turbomachines. The present research focuses on just one such fluid-structure interaction problem, namely the role played by fluid forces in determining the rotordynamic stability and characteristics of a centrifugal pump. While the geometry of the impeller shroud/pump casing annulus varies considerably, previous studies indicate that the contributions from the leakage flow can be of the same order as the contributions from the nonuniform pressure acting on the impeller discharge. Thus, the emphasis of this study is to investigate the contributions to the rotordynamic forces from the discharge-to-suction leakage flows between the front shroud of the rotating impeller and the stationary pump casing. An experiment was designed to measure the rotordynamic shroud forces due to simulated leakage flows for different parameters such as flow rate, shroud clearance, face-seal clearance and eccentricity. The data demonstrates substantial rotordynamic effects and a destabilizing tangential force for small positive whirl ratios; this force decreased with increasing flow rate. The rotordynamic forces appear to be inversely proportional to the clearance and change significantly with the flow rate. Two sets of data taken at different eccentricities yielded quite similar nondimensional rotordynamic forces indicating that the experiments lie within the linear regime of eccentricity.
Like earlier measurements of the total fluid induced rotordynamic forces on impellers [Chamieh et al. (1985), Jery et al. (1985), Adkins et al. (1988)], the forces measured in these experiments scaled with the square of the rotor speed. The functional dependence on the ratio of whirl frequency to rotating frequency (termed the whirl ratio) is very similar to that measured in experiments and similar to that predicted by the theoretical work of Childs. Childs' bulk flow model yielded some unusual results including peaks in the rotordynamic forces at particular positive whirl ratios, a phenomenon which Childs tentatively described as a "resonance" of the leakage flow. This unexpected phenomenon developed at small positive whirl ratios when the inlet swirl velocity ratio exceeded about 0.5. Childs points out that a typical swirl velocity ratio at inlet (pump discharge) would be about 0.5 and may not therefore be large enough for the resonance to be manifest. To explore whether this effect occurs, an inlet guide vane was constructed which introduced a known amount of swirl into the flow upstream of the leakage flow inlet. A detailed comparison of model predictions with the present experimental program is presented. The experimental results showed no evidence of the "resonances", even at much larger swirl inlet velocities than explored by Childs.
https://thesis.library.caltech.edu/id/eprint/1170Shear-induced transport properties of granular material flows
https://resolver.caltech.edu/CaltechETD:etd-08292007-090134
Authors: {'items': [{'id': 'Hsiau-S', 'name': {'family': 'Hsiau', 'given': 'Shu-San'}, 'show_email': 'NO'}]}
Year: 1993
DOI: 10.7907/yj3a-tm14
A granular flow is a two-component flow with an assembly of discrete solid particles dispersed in a fluid. Because of the similarity between the random motion of particles in a granular flow and the motion of molecules in a gas, the dense-gas kinetic theory has been broadly employed to analyze granular flows. However, most research only discusses aspects of momentum transport; three issues have received less attention: the diffusion process, the heat transfer problem, and the behavior of binary mixtures. The current research emphasizes these aspects.
A granular flow diffusion experiment was conducted in a vertical channel to investigate the effects that result in mixing of the material. The mean velocities, the longitudinal fluctuating velocities, and the mixing-layer thickness were measured. A simple analysis based on the diffusion equation shows that the thickness of the mixing layer increases with the square-root of downstream distance and depends on the magnitude of the velocity fluctuations relative to the mean velocity. The experimental velocity profiles were also compared with profiles calculated from theoretical analysis based on kinetic theory.
The analytical relations were developed for the flow-induced particle diffusivity and the thermal conductivity based on dense-gas kinetic theory. The two coefficients were found to increase with the square-root of the granular temperature, a term that quantifies the specific kinetic energy of the flow. The theoretical particle diffusivity was used to compare with the current experimental measurements involving the granular flow mixing layer. The analytical expression for the effective thermal conductivity was also compared with experimental measurements. The differences between the predictions and the measurements suggest limitations in some of the underlying kinetic-theory assumptions.
The constitutive relations were presented for a binary-mixture of granular materials as derived from the revised Enskog theory. The current research focuses on the process of granular thermal diffusion - a diffusion process resulting from the granular temperature gradient. A granular flow of binary-mixtures in an oscillatory no-flow system, in a sheared system, and in a vertical channel were examined, and indicated a complete segregation when granular thermal diffusion effect was sufficiently large.https://thesis.library.caltech.edu/id/eprint/3267Robotic hand-eye motor learning
https://resolver.caltech.edu/CaltechETD:etd-12052007-130729
Authors: {'items': [{'id': 'Ruoff-Carl-F', 'name': {'family': 'Ruoff', 'given': 'Carl F.'}, 'show_email': 'NO'}]}
Year: 1993
DOI: 10.7907/47t1-2f31
This thesis investigates the use of neural networks and nonlinear estimation in robotic motor learning. It presents a detailed experimental investigation of the performance and parametric sensitivity of resource-allocating neural networks along with a new learning algorithm that offers rapid adaptation and excellent accuracy. It also includes an appendix that relates feed-forward neural networks to familiar mathematical ideas.
In addition, it presents two learning hand-eye calibration systems, one based on neural networks and the other on nonlinear estimation. The network-based system learns to correct robot positioning errors arising from the use of nominal system kinematics, while the estimation-based system identifies the robot's kinematic parameters. Both systems employ the same two-link robot with stereo vision, and include noise and various other error sources. The network-based system is robust to all error sources considered, though noise naturally limits performance. The estimation-based system has significantly better performance when the robot and vision systems are well modeled, but is extremely sensitive to unmodeled error sources and noise.
Finally, it presents a robot control system based on neural networks that learns to catch balls perfectly without requiring explicit programming or conventional controllers. It uses only feed-forward pursuit motions learned through practice, and is initially incapable of even moving its arm in response to external stimuli. It learns to identify and control its pursuit movements, to identify and predict ball behavior, and, with the aid of advice from a critic, to modify its movement commands to improve catching success. The system, which incorporates information from visual, arm state, and drive force sensors, characterizes control situations using input/response pairs. This allows it to learn and respond to plant variations without requiring parametric models or parameter identification. It achieves robust execution by comparing predicted and observed behavior, using inconsistencies to trigger learning and behavioral change. The architectural approach, which involves both declarative and analog knowledge as well as short- and long-term memory, can be extended to learning other sensor-motor skills like mechanical assembly and synchronizing motor actions with external processes.https://thesis.library.caltech.edu/id/eprint/4800Cavitation 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/1175The study of Taylor-Couette flows with superimposed isothermal and heated axial flows at high Taylor numbers
https://resolver.caltech.edu/CaltechETD:etd-12112007-104052
Authors: {'items': [{'id': 'Shih-A-C', 'name': {'family': 'Shih', 'given': 'Angela Chao-Hsuan'}, 'show_email': 'NO'}]}
Year: 1994
DOI: 10.7907/3r06-hm27
This experimental study investigates the effect of an isothermal or heated superimposed axial flow on a Taylor-Couette flow in an open, vertical annulus with the inner cylinder rotating. The tangential component of the velocity is measured using a hot-wire anemometer, and the velocity power spectra are calculated. The flows studied are for Taylor numbers ranging from 1.2 x 10[superscript 7] to 2.4 x 10 [superscript 7], and the axial Reynolds number from 0 to 2500. At a low axial Reynolds number, the power spectrum of the velocity measurements shows a single dominant frequency. The frequency is indicative of the uniformly-spaced vortices passing through the anemometer, and roughly corresponds with the axial velocity divided by the vortex spacing. As the rotational speed is increased at a fixed axial flow rate, the dominant frequency decreases, indicating a change in the size of the vortices. As the axial Reynolds number is increased at a fixed rotational speed, the power spectra first indicate a decrease in the dominant frequency, and then a subsequent increase in the other frequencies. For very large axial flow rates, the power spectra indicate a broad distribution in frequencies.
The experiment also include the measurements of the transient and the local fluid temperatures, and the corresponding temperature spectra are calculated. Heating of the axial flow also changes the characteristic of the velocity spectra, where peaks at higher frequencies emerge in the spectra. In heated flows, the peaks of the greatest spectral strength in the velocity and temperature spectra are different, possibly indicating that the largest temperature and velocity fluctuations occur in different directions. The average temperature measurements indicate that as the axial flow rate is increased, the mean temperature distribution curves shift upward. The temperature ratio, (T[subscript max] - T[subscript min])/(T[subscript in] - T[subscript out]), also increases with an increasing in the axial Reynolds numbers.
https://thesis.library.caltech.edu/id/eprint/4947Internal 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/818A 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/1145Rotordynamic Forces Due to Annular Leakage Flows in Shrouded Centrifugal Pumps
https://resolver.caltech.edu/CaltechETD:etd-03262007-103727
Authors: {'items': [{'id': 'Sivo-Joseph-Michael', 'name': {'family': 'Sivo', 'given': 'Joseph Michael'}, 'show_email': 'NO'}]}
Year: 1997
DOI: 10.7907/bpfm-0a24
<p>Previous experimental and analytical results have shown that discharge-to-suction leakage flows in the annulus of a shrouded centrifugal pump contribute substantially to the fluid induced rotordynamic forces (Adkins, 1988). Experiments conducted in the Rotor Force Test Facility (RFTF) at Caltech on an impeller undergoing a prescribed circular whirl have indicated that the leakage flow contribution to the normal and tangential forces can be as much as 70% and 30% of the total, respectively (Jery, 1986). Recent experiments at Caltech have examined the rotordynamic consequences of leakage flows and have shown that the rotordynamic forces are functions not only of the whirl ratio but also of the leakage flow rate and the impeller shroud to pump housing clearance. The forces were found to be inversely proportional to the clearance and a region of forward subsynchronous whirl was found for which the average tangential force was destabilizing. This region decreased with flow coefficient (Guinzburg, 1992).</p>
<p>The present research is a continuation of the previous experimental work and has been motivated by the rotordynamic stability problems with the recently developed Alternate Turbopump Design (ATD) of the Space Shuttle High Pressure Oxygen Turbopump. The present study investigates the influence of swirl brakes, installed in the annular leakage path, as a means of reducing the undesirable rotordynamic forces over a range of flow rates. Also, the present study evaluates the effect on the rotordynamic forces of tip leakage restrictions at discharge used by the ATD for establishing axial thrust balance. As a first step to understanding the flow field in the leakage annulus, the region is probed with a laser velocimeter to provide basic information on these unsteady turbulent three-dimensional leakage flows and to serve as a standard of comparison for approximate theoretical models as well as applications of computational fluid dynamics.</p>https://thesis.library.caltech.edu/id/eprint/1138An Investigation of Velocity and Temperature Fields in Taylor-Couette Flows
https://resolver.caltech.edu/CaltechETD:etd-01102008-131126
Authors: {'items': [{'id': 'Kedia-Rajesh', 'name': {'family': 'Kedia', 'given': 'Rajesh'}, 'show_email': 'NO'}]}
Year: 1997
DOI: 10.7907/0AAS-AW20
NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.
In many experiments, especially those investigating aspects of fluid flow, it is common to observe time series data exhibiting chaos. Chaos lies in the realm of nonlinear dynamics, and specialized methods are available for the analysis of nonlinear time series. One particular method, called time delay analysis, is particularly useful for extracting information from time series representing measurements at a single point in space. In this thesis, hot-wire anemometry is used to obtain velocity time series from experiments on isothermal Taylor-Couette flow. For R/R[subscript c]=1.6, a simple limit cycle is observed, yielding an attractor of dimension of 1. For R/R[subscript c]=11.1, the attractor dimension increases, and the reconstructed attractor exhibits features characteristic of a transition to turbulence. In addition, various other states and transitions of the Taylor-Couette system are studied as well.
Direct numerical simulations (DNS) have also been performed to study the effects of the gravitational and the centrifugal potentials on the stability of heated, incompressible Taylor-Couette flow. The flow is confined between two differentially heated, concentric cylinders and the inner cylinder is allowed to rotate. The Navier-Stokes equations and the coupled energy equation are solved using a spectral method. To validate the code, comparisons are made with existing linear stability analysis and with experiments. The code is used to calculate the local and average heat transfer coefficients for a fixed Reynolds number (R=100) and a range of Grashof numbers. The variation of the local coefficients of heat transfer on the cylinder surface is investigated, and maps showing different stable states of the flow are presented. Calculations of the time and space averaged equivalent conductivity show that the heat transfer decreases with Grashof number in axisymmetric Taylor vortex flow regime and increases with Grashof number after the flow becomes non-axisymmetric.
The numerical simulations also demonstrate the existence of a hysteresis loop in heated Taylor-Couette flow, obtained by slowly varying the Grashof number. Two different stable states with same heat transfer are found to exist at the same Grashof number. The validity of Colburn's correlation is investigated as well; the Prandtl number dependence is found to be slightly different from Pr[...] for the range of Reynolds number investigated. Finally, a time delay analysis of the radial velocity and the local heat transfer coefficient time series obtained from the numerical simulation of the radially heated Taylor-Couette flow is performed. The two-dimensional projection of the reconstructed attractor shows a limit cycle for Gr[...]-1700. The limit cycle behavior disappears at Gr[...]-2100, and the reconstructed attractor becomes irregular. The attractor dimension increases to about 3.2 from a value of 1 for the limit cycle case.
https://thesis.library.caltech.edu/id/eprint/112Studies of Rotordynamic Forces Generated by Annular Flows
https://resolver.caltech.edu/CaltechETD:etd-03272007-111205
Authors: {'items': [{'id': 'Uy-Robert-Vincent', 'name': {'family': 'Uy', 'given': 'Robert Vincent'}, 'show_email': 'NO'}]}
Year: 1998
DOI: 10.7907/9nq0-qp03
Fluid-induced rotordynamic forces in pumping machinery are well documented but poorly understood. The present research focuses on the rotordynamics due to fluid flow in annuli, in particular, the discharge-to-suction leakage flow in centrifugal pumps. There are indications that the contribution of the front shroud leakage flow can be of the same order of magnitude as contributions from the nonuniform pressure acting on the impeller discharge. Previous investigations have established some of the basic traits of these flows. This work further elaborates both the experimental and computational approach to quantify and predict the shroud contribution to the rotordynamic stability of pumping machinery.
Experimental results presented show the contributions of the curvature of the leakage path to the rotordynamics both with and without inlet swirl. The effect of different inlet swirl rates at constant flow rate is examined. Anti-swirl devices are evaluated for their effectiveness in reducing instability. Geometrical changes to the high-pressure and low-pressure seals for the leakage path are quantified. All results are in good agreement with other reported measurements.
Childs' bulk flow model for leakage paths is carefully examined, and convective relations for vorticity and total pressure are deduced. This analysis suggests a new solution procedure of the bulk flow equations which does not resort to linearization or assumed harmonic forms of the flow variables.https://thesis.library.caltech.edu/id/eprint/1173Surge Instability on a Cavitating Propeller
https://resolver.caltech.edu/CaltechETD:etd-03262007-112838
Authors: {'items': [{'email': 'duttweiler.m.e@gmail.com', 'id': 'Duttweiler-Mark-Edward', 'name': {'family': 'Duttweiler', 'given': 'Mark Edward'}, 'show_email': 'NO'}]}
Year: 2001
DOI: 10.7907/07RB-NX02
<p>The present study details results from experiments investigating a surge instability on a cavitating propeller. Initially, the stable behavior of the propeller is explored, and the nature and extent of the cavitation is documented at various experimental conditions, including propeller yaw. The cavitation surge instability is first explored through visual observation of the cavitation on the propeller blades and in the tip vortices. Particular note is made of similarities between the behavior of the re-entrant jets and that noted by other investigators. It is also observed that the nature of the instability is closely related to the partial cavity instability observed on single, two-dimensional hydrofoils.</p>
<p>The flow conditions that lead to instability are determined and it is shown that onset corresponds to a specific configuration of attached cavity lengths on an individual propeller blade. Pressure measurements are obtained from transducers within the experimental facility, and the acoustic signature of the instability is identified. The magnitude of the fluctuating pressures is very large, presumably capable of producing severe hull vibration. A simple model is developed based on cavity volume estimates obtained from high speed video footage, and the predictions of the model are compared with the experimentally obtained pressures.</p>
<p>To assess the significance of the surrounding facility in initiating and sustaining the instability, a model is developed for the experimental facility dynamics. The predictions of this model are then compared with an experimentally determined facility response to a volumetric excitation imposed by an oscillating piston. To quantify the response of the cavitation to fluctuations in test section conditions, quasistatic estimates are obtained for the cavitation compliance and mass flow gain factor of the propeller. These parameters have previously been employed in developing system transfer functions for cavitating pumps.</p>
<p>Finally, a model is developed for the complete system, incorporating both the cavitation and facility dynamics. The model predicts active system dynamics and therefore potentially unstable behavior for two distinct frequency ranges, and one such range is hypothesized to correspond to the observed instability. The ability of the model to predict the observed characteristics of the instability is then evaluated.</p>https://thesis.library.caltech.edu/id/eprint/1143Rotordynamic Forces Generated by Annular Leakage Flows in Centrifugal Pumps
https://resolver.caltech.edu/CaltechTHESIS:12022010-081219787
Authors: {'items': [{'id': 'Hsu-Yun', 'name': {'family': 'Hsu', 'given': 'Yun'}, 'show_email': 'NO'}]}
Year: 2001
DOI: 10.7907/fr51-ft92
Fluid-induced rotordynamic forces in pumping machinery are well documented but poorly understood. The present research focuses on the rotordynamics due to fluid flow in annuli, in particular, the discharge-to-suction leakage flow in centrifugal pumps. There are indications that the contribution of the front shroud leakage flow can be of the same order of magnitude as contributions from the nonuniform pressure acting on the impeller discharge. Previous investigations have established some of
the basic traits of these flows. This work furthers the experimental and computational approach to quantify and predict the shroud contribution to the rotordynamic
stability of pumping machinery.
Childs' bulk flow model for leakage paths is carefully examined, and convective relations for vorticity and total pressure are deduced. This analysis leads to a new
solution procedure for the bulk flow equations which does not resort to linearization or assumed harmonic forms of the flow variables.
Experimental results presented show the contributions of the inlet swirl velocities
to the rotordynamic forces. Antiswirl devices are evaluated for their effectiveness in reducing instability. Additional tests measuring the pressure distributions and the inlet swirl velocities of the leakage flow confirm some of the predictions by numerical analysis.https://thesis.library.caltech.edu/id/eprint/6192Modeling Heat and Mass Transfer in Bubbly Cavitating Flows and Shock Waves in Cavitating Nozzles
https://resolver.caltech.edu/CaltechETD:etd-12182003-150738
Authors: {'items': [{'id': 'Preston-Alastair-Thomas', 'name': {'family': 'Preston', 'given': 'Alastair Thomas'}, 'show_email': 'NO'}]}
Year: 2004
DOI: 10.7907/ZHSN-D849
<p>Two problems are considered in this thesis: the modeling of heat and mass diffusion effects on the dynamics of spherical bubbles, and the computation of unsteady, bubbly cavitating flows in nozzles. The goal of Part I is to develop a reduced-order model that is able to accurately and efficiently capture the effect of heat and mass transfer on the dynamics of bubbles. Detailed computations of forced and oscillating bubbles including heat and mass diffusion show that the assumptions of polytropic behavior, constant vapor pressure, and an effective liquid viscosity do not accurately account for diffusive damping and thus do not accurately capture bubble dynamics. While the full bubble computations are readily performed for single bubbles, they are too expensive to implement into continuum models of complex bubbly flows where the radial diffusion equations would have to be solved at each grid point. Therefore reduced-order models that accurately capture diffusive effects are needed.</p>
<p>We first develop a full bubble computation, where the full set of radial conservation equations are solved in the bubble interior and surrounding liquid. This provides insight as to which equations, or terms in equations, may be able to be neglected while still accurately capturing the bubble dynamics. Motivated by results of the full computations, we use constant heat and mass transfer coefficients to model the transfer at the bubble wall. In the resulting reduced-order model the heat and mass diffusion equations are each replaced by a single ordinary differential equation. The model is therefore efficient enough to implement into continuum computations. Comparisons of the reduced-order model to the full computations over a wide range of parameters indicate agreement that is superior to existing models.</p>
<p>In Part II we investigate the effects of unsteady bubble dynamics on cavitating flow through a converging-diverging nozzle. A continuum model that couples the Rayleigh-Plesset equation with the continuity and momentum equations is used to formulate unsteady, quasi-one-dimensional partial differential equations. Flow regimes studied include those where steady state solutions exist, and those where steady state solutions diverge at the so-called flashing instability. These latter flows consist of unsteady bubbly shock waves traveling downstream in the diverging section of the nozzle. An approximate analytical expression is developed to predict the critical back pressure for choked flow. The results agree with previous barotropic models for those flows where bubble dynamics are not important, but show that in many instances the neglect of bubble dynamics cannot be justified. Finally the computations show reasonable agreement with an experiment that measures the spatial variation of pressure, velocity and void fraction for steady shock free flows, and good agreement with an experiment that measures the throat pressure and shock position for flows with bubbly shocks. In the model, damping of the bubble radial motion is restricted to a simple "effective" viscosity to account for diffusive effects. However, many features of the nozzle flow are shown to be independent of the specific damping mechanism. This is confirmed by the implementation of the more sophisticated diffusive modeling developed in Part I.</p>https://thesis.library.caltech.edu/id/eprint/5040