Dissertations / Theses: 'Cavitating Flows'

1

Wang, Yi-Chun Brennen Christopher E. "Shock waves in bubbly cavitating flows /." Diss., Pasadena, Calif. : California Institute of Technology, 1996. http://resolver.caltech.edu/CaltechETD:etd-02282006-144334.

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Ahmed, Zayed. "Quantitative flow measurement and visualization of cavitation initiation and cavitating flows in a converging-diverging nozzle." Thesis, Kansas State University, 2017. http://hdl.handle.net/2097/35522.

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Master of Science
Department of Mechanical and Nuclear Engineering
B. Terry Beck
Mohammad H. Hosni
Cavitation is the formation of vapor phase from the liquid phase by reduction in its absolute pressure below the saturation pressure. Unlike boiling, where the temperature of the liquid is increased to cause vaporization, the reduction in the pressure alone can cause the liquid to turn into vapor. Cavitation is undesirable in many engineering applications as it is associated with reduction in efficiency and is known to cause damage to pump and propeller components. However, the endothermic nature of cavitation could be utilized to create a region of low temperature that could be utilized to develop a new refrigeration cycle. The work presented in this thesis is part of ongoing research into the potential cooling capacity of cavitation phenomena, where the cavitation in a converging-diverging nozzle is being investigated. Due to the constricting nature of the throat of the converging-diverging nozzle, the liquid velocity at the throat is increased, obeying the continuity law. With an increase in velocity, a reduction in absolute pressure is accompanied at the throat of the nozzle according to the Bernoulli’s principle. The local absolute pressure at the throat can go lower than the saturation vapor pressure, thereby causing the fluid to cavitate. The effect of water temperature on the flowrates, the onset of cavitation within the nozzle, and the resulting length of the cavitation region within the nozzle are the subject of this thesis. Experimental results and analysis are presented which also show that near the onset of cavitation, the flowrate can go beyond the choked flowrate, causing the local pressure in the throat to go well below zero for an extended amount of time in the metastable state, before nucleating (cavitating) into a stable state. Flow visualization using a high speed digital camera under different operating conditions was aimed at investigating the region of cavitation onset, which appears to be associated with boundary layer separation just downstream of the nozzle throat. In order to delay the boundary layer separation point in the downstream section of the nozzle, the diffuser region of the nozzle was modified to enable two flow paths, where one path would suck the flow near the inner walls of the nozzle and the other would allow the bulk of the flow to pass through. This was achieved with the use of inserts. Various inserts were tested in an attempt to capture the effect of inserts on the cavitation phenomena. Their effect on the flowrates, length of two phase region, and cavitation onset are presented in this thesis.

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Preston, Alastair Thomas Colonius Timothy E. "Modeling heat and mass transfer in bubbly cavitating flows and shock waves in cavitating nozzles /." Diss., Pasadena, Calif. : California Institute of Technology, 2004. http://resolver.caltech.edu/CaltechETD:etd-12182003-150738.

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4

Sezal, İsmail Hakkı. "Compressible dynamics of cavitating 3-D multi-phase flows." München Verl. Dr. Hut, 2009. http://mediatum2.ub.tum.de/node?id=684068.

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Şenocak, Inanç. "Computational methodology for the simulation of turbulent cavitating flows." [Gainesville, Fla.] : University of Florida, 2002. http://purl.fcla.edu/fcla/etd/UFE1001181.

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Jeshani, Mahesh. "Optical characterisation of cavitating flows in diesel fuel injection equipment." Thesis, City University London, 2013. http://openaccess.city.ac.uk/3414/.

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The recent advances in Fuel Injection Equipment (FIE) have led to the identification of deposits found in the fuel filters and injector equipment. The work carried out here identifies the effects of cavitating flows on the physical and chemical properties of diesel fuel in order to try to evaluate the mechanism for deposit formation in FIE equipment using optical techniques to characterise the cavitating flows. Two sets of experiments have been carried out in order to understand the impact of cavitating flow on diesel fuels. The first experiment investigated the effects of sustained cavitating flow using a fuel recirculation rig. Samples of commercial diesel were subjected to forty hours of intense cavitating flow across a diesel injector in a specially designed high-pressure recirculation flow rig. Changes to the optical absorption and scattering properties of the diesel over time were identified by the continuous measurement of spectral attenuation coefficients at 405 nm by means of a simple optical arrangement. Identical diesel samples ~ere maintained at 70°C for forty hours in a heated water bath, in order to distinguish the effects of hydrodynamic cavitation and the regulated temperature on the cavitated diesel samples. The commercial diesel samples subjected to high pressure cavitating flow and heat tests revealed a response to the flow and temperature history that was identified by an increase in the optical attenuation coefficients of the cavitated and heated samples. The contribution of cavitating flow and temperature to the variation in spectral attenuation coefficient was identified. It was hypothesised that the increases observed in the spectral attenuation coefficients of the cavitated commercial diesels were caused by the cavitation affecting the aromatics in the commercial diesel . samples. The fuels were sent for a GC x GC and particle count analysis and results show significant increase in particle number count in the fuels as a result of cavitating flow. An increase in particle count to such high magnitudes was not observed for the heat test samples. Qualitative chemical modelling results of the pyrolysis of fuel vapour cavities during collapse at high pressures and temperatures have shown possible pathways leading to the formation of particulates. The presence of aromatics in diesel fuel was considered to be key species to the formulation of soot particles, however at extreme pressures and temperature paraffins may also have the propensity to breakdown into aromatics and further on to the formation of soot particles as observed by the pathway analysis in the modelling in the appendix. The second study undertaken involved the analysis of the near nozzle external spray dropsizing and atomisation characteristics of fuels with different distillation profiles using LIF-MIE image ratios. The LIF -Mie image ratios were simultaneously captured synchronously with the internal nozzle hole cavitating flow. Internal nozzle flow and sac observations after needle return have led to the conclusions that flow angular momentum is sustained in the sac flow after needle return. This flow was observed to have a high angular momentum which reduced over time. During the end of needle return, bubbles were observed in the sac hole forming as a result of needle cavitation. These bubbles retained the angular momentum of the flow post injection (after needle seal). The vortical motion in the sac lead to regions of high and low pressures in the sac volume and thus resulted in suction and discharge of bubble in the nozzle holes. The bubbles may have a high propensity of containing a mixture of fuel and air vapour whereas the suction and discharge offers a pathway to external gases entering the nozzle holes and sac volume. For operating engine conditions this would be post-combustion exhaust gases re-entering the nozzle holes. The combination of the bubble formation, its vOI1Ical motion due to the angular momentum of the liquid flow, its composition and high temperature, may form ideal conditions for pyrolysis like reactions which may lead to the formation of soot particles and deposits in the nozzle hole, sac and needle. Fuels with different distillation profiles were investigated to observe their external drop sizing distributions at 350 bar injection pressure. Results showed that fuels with lighter fractional compositions which also had lower viscosity produced lower Sauter Mean Diameter (SMD) distributions than fuels with higher distillation fractions and higher viscosity. Whether this is as a consequence of the distillation profile alone and is not influenced by the viscosity differences has not been investigated yet and would form the basis of further investigations and publications.

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Podbevsek, Darjan. "Optical probing of thermodynamic parameters and radical production in cavitating micro-flows." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSE1210/document.

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Une zone de constriction dans un micro-canal fluidique peut générer, si le débit est suffisant, un écoulement bi-phasique. Ceci est l’origine de la cavitation hydrodynamique. Les échanges de chaleur latente générés par l’apparition et l’implosion des bulles impliquent une variabilité importante de la température dans les zones au-delà de la constriction. En ajoutant des sondes de température nanométriques dans le fluide et en utilisant un microscope confocal on peut déterminer la température en un point. Ainsi on a pu établir des cartographies thermiques en 2 et 3 dimensions à l’intérieur d’un écoulement stationnaire bi-phasique. La technique permet en outre d’avoir accès à la quantité de gaz ce qui permet de corréler les gradients de température avec les zones de transitions de phases. Des zones de très forts refroidissements sont observées après la constriction, là où les bulles apparaissent. Par contre on n’observe pas les zones d’échauffement attendu à cause de la condensation. Une méthode complémentaire, moins sensible, utilisant la spectroscopie Raman a aussi été utilisée pour confirmer ce résultat. Par ailleurs une nouvelle classe de matériaux luminescents sensible à la température et la pression a été étudiée. Enfin une étude de la production de radicaux lors de l’implosion des bulles a été menée en utilisant la chimiluminescence du luminol. La technique utilisée par comptage de photons a permis de quantifier cette production et une cartographie de l’émission du luminol a permis d’associer celle-ci avec la zone d’implosion des bulles
A constriction in the microchannel can be used to establish a two-phase flow, when a sufficient liquid flux is introduced. This is known as hydrodynamic cavitation. The latent heat resulting from the growing and collapsing vapor bubbles makes it interesting to observe the temperature conditions in the flow downstream of the constriction. Using fluorescence microscopy, with the addition of temperature sensitive nano probes into the working fluid, we can determine the temperature at a single point, averaged over the integration time. Coupled with a confocal microscope, we were able to produce two and three dimensional temperature maps of the steady state flow in the microchannel by the use of ratiometric intensity measurements. This technic allows us to observe temperature gradients in two-phase flow as well yielding the void fraction information. Areas of substantial cooling are observed downstream the constriction in the two-phase flow, linked to the bubble growth, while heating regions due to condensations are missing. A complementary, yet less sensitive probe-less technique using the inherent Raman scattering signal of the liquid, was used to confirm the findings. A separate study evaluating a new group of luminescent materials for optical temperature and pressure probes is performed and discussed herein. Finally, the luminol chemiluminescent reaction with radicals produced by the cavitating flow, is used to obtain a corresponding photon yield. By counting the photons produced, an estimate on the radical yield can be obtained. Additionally, rudimentary mapping of the chemiluminescence signal allows the localization of the bubble collapse regions

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Gaschler, Maria [Verfasser], and Moustafa [Akademischer Betreuer] Abdel-Maksoud. "Numerical modelling and simulation of cavitating marine propeller flows / Maria Gaschler ; Betreuer: Moustafa Abdel-Maksoud." Hamburg : Universitätsbibliothek der Technischen Universität Hamburg-Harburg, 2017. http://d-nb.info/1136955143/34.

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Egerer, Christian [Verfasser], Nikolaus A. [Akademischer Betreuer] [Gutachter] Adams, and Stefan [Gutachter] Hickel. "Large-Eddy Simulation of Turbulent Cavitating Flows / Christian Egerer ; Gutachter: Stefan Hickel, Nikolaus A. Adams ; Betreuer: Nikolaus A. Adams." München : Universitätsbibliothek der TU München, 2016. http://d-nb.info/1124154744/34.

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Beban, Bruno [Verfasser], Nikolaus A. [Akademischer Betreuer] Adams, Romuald [Gutachter] Skoda, and Nikolaus A. [Gutachter] Adams. "Numerical Simulation of Submerged Cavitating Throttle Flows / Bruno Beban ; Gutachter: Romuald Skoda, Nikolaus A. Adams ; Betreuer: Nikolaus A. Adams." München : Universitätsbibliothek der TU München, 2019. http://d-nb.info/1187443921/34.

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Örley, Felix [Verfasser], Nikolaus A. [Akademischer Betreuer] [Gutachter] Adams, and Stefan [Gutachter] Hickel. "Numerical Simulation of Cavitating Flows in Diesel Injection Systems / Felix Örley ; Gutachter: Stefan Hickel, Nikolaus A. Adams ; Betreuer: Nikolaus A. Adams." München : Universitätsbibliothek der TU München, 2016. http://d-nb.info/1120584299/34.

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Mihatsch, Michael Simon [Verfasser], Nikolaus A. [Akademischer Betreuer] Adams, Manolis [Gutachter] Gavaises, and Nikolaus A. [Gutachter] Adams. "Numerical Prediction of Erosion and Degassing Effects in Cavitating Flows / Michael Simon Mihatsch ; Gutachter: Manolis Gavaises, Nikolaus A. Adams ; Betreuer: Nikolaus A. Adams." München : Universitätsbibliothek der TU München, 2017. http://d-nb.info/1151322172/34.

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Schmidt, Steffen Joachim [Verfasser], Nikolaus A. [Akademischer Betreuer] [Gutachter] Adams, and Terwisga Tom J. C. [Gutachter] van. "A low Mach number consistent compressible approach for simulation of cavitating flows / Steffen Joachim Schmidt ; Gutachter: Tom J. C. van Terwisga, Nikolaus A. Adams ; Betreuer: Nikolaus A. Adams." München : Universitätsbibliothek der TU München, 2015. http://d-nb.info/1121206689/34.

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Chebli, Rezki. "Simulation 2D et 3D des écoulements cavitants : développement d'un algorithme original dans Code_Saturne et étude de l'influence de la modélisation de la turbulence." Thesis, Paris, ENSAM, 2014. http://www.theses.fr/2014ENAM0040/document.

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La cavitation est l'un des phénomènes physiques les plus contraignants influençant les performances des machines hydrauliques. Il est donc primordial de savoir prédire son apparition et son développement, et de quantifier les pertes de performances qui lui sont associées. L'objectif de ce travail est de développer un algorithme 3D instationnaire pour la simulation numérique de la cavitation dans le code industriel « Code_Saturne ». Il est basé sur la méthode à pas fractionnaires et préserve le principe du minimum/maximum sur le taux de vide. Un solveur implicite, basé sur l'équation de transport du taux de vide couplée avec les équations Navier-Stokes est proposé. Un traitement numérique spécifique des termes sources de cavitation permet d'obtenir des valeurs physiques du taux de vide (entre 0 et 1) sans aucune limitation artificielle. L'influence des modèles de turbulence RANS sur la simulation de la cavitation est étudiée sur deux types de géométries 2D (Venturi et Hydrofoil). Cela confirme que la modification de Reboud et al. (1998) appliquée aux modèles à viscosité turbulente à deux équations, k-epsilon et k-omega-SST, permet de reproduire les principales caractéristiques du comportement instationnaire de la poche de cavitation. Le modèle du second ordre RSM-SSG, basé sur le transport des contraintes de Reynolds, se révèle capable de reproduire le comportement instationnaire de l'écoulement sans aucune modification arbitraire. Les effets tridimensionnels intervenant dans les mécanismes d'instabilité de la poche sont également analysés. Ce travail nous permet d'aboutir à un outil numérique, validé sur des configurations d'écoulements cavitants complexes, afin d'améliorer la compréhension des mécanismes physiques qui contrôlent les effets instationnaires tridimensionnels intervenants dans les mécanismes d'instabilité
Cavitation is one of the most demanding physical phenomena influencing the performance of hydraulic machines. It is therefore important to predict correctly its inception and development, in order to quantify the performance drop it induces, and also to characterize the resulting flow instabilities. The aim of this work is to develop an unsteady 3D algorithm for the numerical simulation of cavitation in an industrial CFD solver « Code_saturne ». It is based on a fractional step method and preserves the minimum/maximum principle of the void fraction. An implicit solver, based on a transport equation of the void fraction coupled with the Navier-Stokes equations is proposed. A specific numerical treatment of the cavitation source terms provides physical values of the void fraction (between 0 and 1) without including any artificial numerical limitation. The influence of RANS turbulence models on the simulation of cavitation on 2D geometries (Venturi and Hydrofoil) is then studied. It confirms the capability of the two-equation eddy viscosity models, k-epsilon and k-omega-SST, with the modification proposed by Reboud et al. (1998) to reproduce the main features of the unsteady sheet cavity behavior. The second order model RSM-SSG, based on the Reynolds stress transport, appears able to reproduce the highly unsteady flow behavior without including any arbitrary modification. The three-dimensional effects involved in the instability mechanisms are also analyzed. This work allows us to achieve a numerical tool, validated on complex configurations of cavitating flows, to improve the understanding of the physical mechanisms that control the three-dimensional unsteady effects involved in the mechanisms of instability

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Jayaprakash, Arvind Prakash. "Cavitating Flow over Stationary and Oscillating Hydrofoils." Cincinnati, Ohio : University of Cincinnati, 2008. http://www.ohiolink.edu/etd/view.cgi?acc%5Fnum=ucin1205164937.

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Thesis (M.S.)--University of Cincinnati, 2008.
Committee/Advisors: Urmila Ghia PhD (Committee Chair), Kirti Ghia PhD (Committee Co-Chair), Milind Jog PhD (Committee Member). Title from electronic thesis title page (viewed Sep.3, 2008). Includes abstract. Keywords: Cavitation; Stationary; Oscillating; Hydrofoils. Includes bibliographical references.

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JAYAPRAKASH, ARVIND PRAKASH. "Cavitating Flow over Stationary and Oscillating Hydrofoils." University of Cincinnati / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1205164937.

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Wilms, Jeffrey. "Flow visualization of cavitation." Thesis, Kansas State University, 2013. http://hdl.handle.net/2097/32158.

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Master of Science
Department of Mechanical and Nuclear Engineering
Mohammad Hosni
A typical refrigeration loop is composed of an evaporator, compressor, condenser, and an expansion valve. There are many possible refrigerants that can be used, but the physical properties of water make it ineffective in the traditional refrigeration loop. But if water could be used it would have many advantages as it is abundant, cheap, and is safe for the environment. This research focuses on a different kind of refrigeration loop using water. This new refrigeration loop utilizes water flowing through a nozzle, initiating cavitation. Cavitation is generally defined as creating vapor from liquid, not through adding heat, but by decreasing the pressure. In a converging/ diverging nozzle, as the cross sectional area is constricted, the velocity of the flow will increase, decreasing the pressure. Therefore, by flowing water through the nozzle it will cavitate. Transforming liquid into gas requires a certain amount of energy, defined as the latent heat. When a liquid is turned to vapor by an increase in the temperature, the latent heat is provided by the heat transfer to the system. As no energy is being added to the nozzle to cause the cavitation, the energy transfer to create the vapor comes from the remaining liquid, effectively causing a temperature drop. This research focused on the flow visualization of water cavitating as it travelled through a converging/ diverging nozzle. Under different flow conditions and different nozzle geometries, the cavitation manifested itself in different formations. When gasses were entrained in the water they formed bubbles, which acted as nucleation sites as they moved through the nozzle. This was called travelling bubble cavitation. In venturi nozzles the cavitation nucleated off of the wall, forming attached wall cavitation. When water flowed out of an orifice, a turbulent mixture of liquid and vapor, orifice jet, was formed which caused vapor to form around it. This was known as shear cavitation. When the water was rotated prior to the throat of an orifice, the orifice jet expanded radially and formed swirl cavitation. In addition to studying how the cavitation was formed, the void fraction and velocity were measured for attached wall cavitation.

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Fine, Neal E. "Nonlinear analysis of cavitating propellers in nonuniform flow." Thesis, Massachusetts Institute of Technology, 1992. http://hdl.handle.net/1721.1/12564.

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Whitfield, Claire Margaret Frances. "Investigation of cavitating flow luminescence for analytical spectroscopy." Thesis, University of Plymouth, 2015. http://hdl.handle.net/10026.1/3464.

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Cavitating Flow Luminescence (CFL) is spontaneous photon emission associated with hydrodynamic cavitation which occurs when a flowing liquid passes through a Venturi.1 In this work, cavitation and micro-plasma generation in a flowing liquid, using a micro-Venturi, has been investigated. A bench-top system was designed and constructed to study CFL in a variety of liquids. The system comprised a high flow, liquid handling manifold and micro-Venturi with a variety of orifice sizes ranging from 160 – 220 μm i.d. The CFL was detected for the first time on a micro-scale using a PMT. The effect of various parameters such as temperature, flow rate (a proxy for the pressure differential) and orifice diameter were investigated to optimise the system. Studies were carried out using DDW and the effect of temperature, pressure and orifice size on CFL; it was found that low temperatures and high pressures resulted in more intense CFL. The effect of re-gassing with different noble gases was investigated and resulted in a large increase in CFL. Investigations in to the effect of solute concentration on CFL were performed using dimethylsulphoxide, polyethyleneglycol-200, isopropanol, diethyleneglycol and Triton X 100 & titanium sulphate nano-particles. Solutes with low vapour pressures resulted in an increase in CFL whereas solutes with a high vapour pressure supressed CFL, due to quenching effects. Low resolution spectra were produced using bandwidth filters to identify wavelength areas of strong emission from CFL.

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Haese, Peter Michael. "Interior source methods for planar and axisymmetric supercavitating flows." Title page, contents and abstract only, 2003. http://web4.library.adelaide.edu.au/theses/09PH/09phh136.pdf.

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"May 2003." Bibliography: leaves 125-130. This study considers use of an interior source method for modelling supercavitation in 2-dimensional (planar) and 3-dimensional axisymmetric flows. Aspects considered include the determination of where the fluid separates from the body, the shapes of the cavities formed, the pressure distribution on the body and the pressure on the cavity surface, and the resulting drag and lift forces on the body.

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Wu, Jiongyang. "Filter-based modeling of unsteady turbulent cavitating flow computations." [Gainesville, Fla.] : University of Florida, 2005. http://purl.fcla.edu/fcla/etd/UFE0011587.

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Szymczak, Michel. "Flow visualization of cavitating, high-speed, submerged water jets." Thesis, University of Ottawa (Canada), 1988. http://hdl.handle.net/10393/5159.

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Tanguay, Michel Colonius Timothy E. "Computation of bubbly cavitating flow in shock wave lithotripsy /." Diss., Pasadena, Calif. : California Institute of Technology, 2004. http://resolver.caltech.edu/CaltechETD:etd-05282004-130028.

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Yazici, Bora. "Numerical And Experimental Investigation Of Flow Through A Cavitating Venturi." Master's thesis, METU, 2006. http://etd.lib.metu.edu.tr/upload/3/12607924/index.pdf.

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Cavitating venturies are one of the simplest devices to use on a flow line to control the flow rate without using complex valve and measuring systems. It has no moving parts and complex electronic systems. This simplicity increases the reliability of the venturi and makes it a superior element for the military and critical industrial applications. Although cavitating venturis have many advantages and many areas of use, due to the complexity of the physics behind venturi flows, the characteristics of the venturies are mostly investigated experimentally. In addition, due to their military applications, resources on venturi flows are quite limited in the literature. In this thesis, venturi flows are investigated numerically and experimentally. Two dimensional, two-dimensional axisymmetric and three dimensional cavitating venturi flows are computed using a commercial flow solver FLUENT. An experimental study is then performed to assess the numerical solutions. The effect of the inlet angle, outlet angle, ratio of throat length to inlet diameter and ratio of throat diameter to inlet diameter on the discharge coefficient, and the oscillation behavior of the cavitating bubble are investigated in details.

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Harp, Susan R. "A computational method for evaluating cavitating flow between rough surfaces." Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/16838.

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Fine, Neal E. "Computational and experimental investigations of the flow around cavitating hydrofoils." Thesis, Massachusetts Institute of Technology, 1988. http://hdl.handle.net/1721.1/35344.

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Hart, Douglas P. Acosta Allan J. Brennen Christopher E. "Cavitation and wake structure of unsteady tip vortex flows /." Diss., Pasadena, Calif. : California Institute of Technology, 1993. http://resolver.caltech.edu/CaltechETD:etd-03272007-131947.

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Brewer, Wesley H. (Wesley Huntington). "A computational and experimental study of viscous flow around cavitating propulsors." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/38100.

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Bourg, David M. "Development of the Distributed Points Method with Application to Cavitating Flow." ScholarWorks@UNO, 2008. http://scholarworks.uno.edu/td/904.

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A mesh-less method for solving incompressible, multi-phase flow problems has been developed and is discussed along with the presentation of benchmark results showing good agreement with theoretical and experimental results. Results of a systematic, parametric study of the single phase flow around a 2D circular cylinder at Reynolds numbers up to 1000 are presented and discussed. Simulation results show good agreement with experimental results. Extension of the method to deal with multiphase flow including liquid-to-vapor phase transition along with applications to cavitating flow are discussed. Insight gleaned from numerical experiments of the cavity closure problem are discussed along with recommendations for additional research. Several conclusions regarding the use of the method are made.

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MAHALATKAR, KARTIKEYA. "CAVITATING FLOW OVER OSCILLATING HYDROFOILS AND HYDROFOIL-BASED SHIP STABILIZATION SYSTEM." University of Cincinnati / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1154301156.

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Asher, William. "Fluid dynamics of cavitating sonic two-phase flow in a converging-diverging nozzle." Thesis, Kansas State University, 2014. http://hdl.handle.net/2097/17621.

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Master of Science
Department of Mechanical and Nuclear Engineering
Steven Eckels
Both cavitating and flashing flows are important phenomena in fluid flow. Cavitating flow, a common consideration in valves, orifices, and metering devices, is also a concern in loss of coolant accidents for liquid water in power plants when saturation pressures are below atmospheric pressure. Flashing flow is a common consideration for devices such as relief and expansion valves and fluid injectors as well as for loss of coolant accidents in which the coolant’s saturation pressure is above atmospheric. Of the two phenomena, flashing flow has received greater interest due to its applicability to safety concerns, though cavitating flow is perhaps of greater interest in terms of energy efficiency. It is possible for cavitating and flashing flow to actually become sonic. That is, the local velocity of a fluid can exceed the local speed of sound due to the unique properties of two-phase mixtures. When a flow becomes sonic, it is possible for the flow to accelerate and impose additional energy losses that would not otherwise occur. Models of this aspect of two-phase flow are not well developed, typically only being presented for the case of constant area ducts. In this paper two models for cavitating sonic flow are developed and described by applying the integral forms of the mass, momentum, and energy equations to a control volume of variable cross-sectional area. These models, based on the homogeneous equilibrium model (HEM) and separated flow model, are then applied to experimental data taken by the author with R-134a as the fluid of interest. Experimental data were taken with four instrumented converging-diverging nozzles of various geometries using a custom testing rig that allowed for precise control and measurement of flow parameters such as mass flow, temperature, and pressure. The resultant data from the models are then examined, focusing on the resultant velocities, Mach numbers, quality, and shear stresses.

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Mishima, Shigenori. "Design of cavitating propeller blades in non-uniform flow by numerical optimization." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/41006.

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Miah, Wadud. "Numerical modelling of material interfaces and cavitation in high speed flows." Thesis, Imperial College London, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.427920.

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Alrifaai, Hatim. "Experimental Investigation of Cavitation Using Refrigerant in a Two-Phase Flow System." Thesis, Kansas State University, 2017. http://hdl.handle.net/2097/38553.

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Master of Science
Department of Mechanical and Nuclear Engineering
Mohammad H. Hosni
Cavitation is a phase change process and its conversion of fluid from liquid to vapor requires pressure reduction. In this thesis, cavitation of R134a refrigerant is evaluated experimentally. This work is part of an ongoing project that seeks to develop a novel cooling cycle based on the cooling potential of the fluid during cavitation. A blowdown system was designed, built, and used for conducting the experiments. This system included a special test section containing a unique converging-diverging nozzle system designed for this investigation. In the end, cavitation was achieved by flowing the test fluid through a converging-diverging nozzle. As the fluid flows through the nozzle throat, the velocity increases while the pressure decreases and cavitation occurs when its static pressure drops below its vapor pressure. The onset of cavitation was evaluated by measuring pressure, temperature, and refrigerant flow rate, and by visualizing the flow using a high-speed video camera.

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Ndamuso, N. "Parametric studies of cavitation dependence on hydrocarbon and biodiesel fuel injection flows." Thesis, City, University of London, 2017. http://openaccess.city.ac.uk/19228/.

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The parametric studies investigated the cavitation phenomena occurring in Diesel Fuel Injection Equipment using immersed jets. The studies looked at cavitation from the incipient stage, to the fully developed stage, to leaving the fuel to cavitate for a sustained period of time. The studies were conducted with the aim of understanding the cavitation phenomena occurring inside the Fuel Injection Equipment making use of purposed built continuous flow rigs. The first part investigated the onset of cavitation taking place inside a mechanical 80 bar continuous recirculated flow rig that mimicked the flow inside the injectors spill valves as well as the flow inside the high-pressure pumps spill valves during the first stages of cavitation. High velocity jets of variable concentration were considered, from the incipient stage to the fully developed stage, focusing on the impact that changing the fuel composition has on the jets as well as on the impact it has on the geometrical parameters of the nozzle valves. The rig made use of custom made Acrylic, Brass and Aluminum-steel nozzles of Cylindrical, Hemispherical and Conical geometries respectively. The n-Octane, n-Decane, n-Dodecane, n-Tetradecane and n-Hexadecane mixtures were directed into an optically accessible receiver using single hole injector nozzles of 0.14mm and 0.25 mm hole diameters respectively. Parameters such as the fuel composition, the geometry and the material of the nozzles, as well as the operating conditions of the fuels were looked into where 25 repetitive sets of measurements were completed taking into consideration each parameter respectively. Incipient cavitation was associated with the flow outside of the nozzle and was visually observed at the top of the nozzle hole. Cavitation additionally occurred between the layers of the turbulent high immersed jet flow and the stagnant fluid inside the receiver. The onset of cavitation was obtained using the fuel Upstream Pressure to Downstream Pressure ratio. At the point of onset, the results showed that the Upstream Pressure to Downstream Pressure ratio decreased with the increase of n-Octane percentage in the mixture when considering the Cylindrical and the Hemispherical nozzles. When considering the Conical nozzle on the other hand, the critical Upstream Pressure to Downstream Pressure ratio increased with the increase of n-Octane concentration. The results also showed that the jet length and width increased when varying the diameter of the nozzle hole from 0.14 mm to 0.25 mm. Furthermore, the total Saturated Vapour Pressure increased with the increase in n-Octane concentration, where the increase in the propensity of the flowing fuel through the Cylindrical and Hemispherical nozzles, to cavitate was noted. On the other hand, the propensity of the Conical nozzles to cavitate decreased with the increase in Saturated Vapour Pressure. The second part of the study investigated the sustained hydrodynamic cavitation taking place inside a mechanical 1650 bar continuous recirculated flow rig, mimicking the flow inside the injectors spill valves and high-pressure pumps spill valves at a later stage of cavitation as the fuel was left to cavitate for a longer period of time, leading to the degradation of the fuel due to changes in the fuel’s chemical composition taking place during cavitation. A needleless 0.213 mm single hole diameter Cylindrical nozzle was considered, as the Commercial Diesel fuel, the biofuel Rape Methyl Ester and the Gas to Liquids paraffin blend were left consecutively to cavitate for a period of 30 hours. The volume flow rate was obtained as 1.129 Liter per minutes considering a Discharge Coefficient of 0.8. The results showed that by passing a 405nm laser over the 30 hours period through the cavitated fuel mixtures, a decrease with time of the transmission signal of the laser beam penetrating all tested fuels respectively was noticed. The laser beams experienced a decrease in strength due to the changes in the chemical composition of the fuel as high pressures and high temperatures took place inside the receiver. The effect of heating the fuels overnight inside a modified Water Bath tea urn at 60 degrees Celsius was looked into in order to separate the impact of temperature to the impact of cavitation alone. The effect of subjecting to fuel to cavitation and heating was greater than the effect of subjecting the fuel to heating alone. The Gas to Liquids fuel was visually transparent compared to the commercial Diesel fuel and had the highest laser transmission signal. Of all three fuels, the Commercial Aged Diesel fuel had the lowest laser transmission signal as the impurities inside the fuel changed the chemical composition of the fuel due to sustained hydrodynamic cavitation.

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36

Tomov, Petar. "Étude expérimentale et numérique de la cavitation et la cavitation aérée. Vers une application à l’alimentation en carburant d’un moteur d’avion." Thesis, Paris, ENSAM, 2016. http://www.theses.fr/2016ENAM0011/document.

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En fonction de la configuration avion, de son altitude du vol, du type de carburant, différents phénomènes physiques modifient les caractéristiques de l'alimentation du moteur en carburant. En effet, il se produit principalement un phénomène de dégazage qui pourrai être couplé à de la cavitation. Les écoulements diphasiques ainsi obtenus contiennent des microbulles, des bulles ou des poches de gaz qui risquent d'induire des dysfonctionnements du moteur. Ces dysfonctionnements se traduisent par des fluctuations de poussée pouvant conduire à une perte de contrôle de l’appareil. De cette problématique industrielle découlent de nombreux verrous scientifiques encore mal connus. Dans le cadre de cette thèse des travaux sur la modélisation numérique et la caractérisation expérimentale du couplage entre la cavitation et le dégazage. Pour cela deux bancs d’essai et un code propre capable d'étudier la problématique scientifique retenue ont été développés et exploités. Trois régimes de cavitation pure et trois autres de cavitation aérée sur une géométrie de venturi 8° symétrique ont été étudiés."
Depending on the configuration of the plane, its flight altitude, the type of fuel, different physical phenomena significantly change the characteristics of the fuel supply to the engine. Indeed, it primarily occurs a fuel degassing phenomenon that could be coupled to the cavitation phenomenon. As a result, the thus obtained multiphase flows contain micro bubbles, larger bubbles or vapor pockets which might induce engines malfunctions. The latter result in thrust fluctuations which can lead to a loss of power. The scientific context of the industrial problem lies in the development of a numerical and experimental representation of the cavitation and degassing phenomena on a smaller scale. As a result, it is of primary importance for one to understand the mechanisms of occurrence of gas and cavitation in the given industrial configuration. In order to deal with those issues, two test benches have been developed, as well as an in-house numerical code capable of simulating aerated cavitation phenomenon. Therefore, three different pure cavitation regimes and three other aerated cavitation are shown, as a result of the experimental work. The multiphase flow observations are based on a statistical post-processing of images taken by a high-speed camera. Moreover, two 2D aerated cavitation numerical simulations, as well as the first 3D pure cavitation simulation have been shown

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37

Lauer, Eric [Verfasser]. "Numerical simulation and investigation of high-speed bubble-dynamics in cavitating flow. / Eric Lauer." München : Verlag Dr. Hut, 2013. http://d-nb.info/1045989126/34.

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38

Kozák, Jiří. "Cavitation Induced by Rotation of Liquid." Doctoral thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2020. http://www.nusl.cz/ntk/nusl-409529.

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Tato disertační práce se zabývá experimentálním a numerickým výzkumem kavitace vyvolané rotací. Pro potřeby tohoto výzkumu byla využita transparentní osově symetrická Venturiho dýza, díky čemuž bylo možné zkoumat dynamiku kavitujícího proudění pomocí analýzy vysokorychlostních nahrávek.

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39

Yuhua, Yan. "Cavitation phenomena and the admittance of air in the flow through an orifice." Thesis, University of Cambridge, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.257548.

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40

Kinnas, Spyridon Athanasios. "Non-linear corrections to the linear theory for the prediction of the cavitating flow around hydrofoils." Thesis, Massachusetts Institute of Technology, 1985. http://hdl.handle.net/1721.1/15257.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 1985.
MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING.
Bibliography: leaves 116-120.
by Spyridon Athanasios Kinnas.
Ph.D.

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41

Schümichen, Michel, Frank Rüdiger, Jochen Fröhlich, and Jürgen Weber. "Simulation of the cavitating flow in a model oil hydraulic spool valve using different model approaches." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-199607.

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The contribution compares results of Large Eddy Simulations of the cavitating flow in a model oil hydraulic spool valve using an Euler-Euler and a one-way coupled Euler- Lagrange model. The impact of the choice of the empirical constants in the Kunz cavitation model is demonstrated. Provided these are chosen appropriately the approach can yield reasonable agreement with the corresponding experiment. The one-way Euler-Lagrange model yields less agreement. It is demonstrated that this is due to the lack of realistic volumetric coupling, rarely accounted for in this type of method. First results of such an algorithm are presented featuring substantially more realism.

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42

Pettersson, Kristoffer. "Design of aerators for prevention of cavitation – The Höljes Dam." Thesis, KTH, Vattendragsteknik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-99352.

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Major cavitation damages can seriously endanger the stability of hydraulic structures, in worst case lead to dam failure. To remedy the effect of cavitation on spillway chutes the most common method today is aeration of the flow. Aerators introduce air to the bottom layers of the flow, enough to prevent damages to occur in the concrete lining. The design of an aerator system is of a complex manner due to the many involving parameters such as the channel slope, ramp angle, Froude number, flow velocity. In this report the susceptibility of the Höljes Dam to cavitate has been outlined with the result that this would occur at an extreme and most unlikely situation and remedial measures have been proposed. The design of an aerator system has been proposed as the result from theoretical research. A physical hydraulic model to assess the efficiency of a proposed aerator design is highly recommended. Alternative causes to the damages observed in the spillway chute are discussed.

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Sarkar, Snigdha. "Numerical Investigation of Vapor and Gaseous Cavitation in Squeeze-Film Damper Bearings." University of Cincinnati / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1523636346718425.

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44

Bachmann, Mathieu [Verfasser]. "Dynamics of cavitation bubbles in compressible two-phase fluid flow / Mathieu Bachmann." Aachen : Hochschulbibliothek der Rheinisch-Westfälischen Technischen Hochschule Aachen, 2013. http://d-nb.info/1036241467/34.

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45

Shahmohamadi, Hamed. "Multi-phase thermal cavitation flow in rough conforming and partially conforming conjunctions." Thesis, Loughborough University, 2015. https://dspace.lboro.ac.uk/2134/18460.

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The main aim of this research was to investigate the mechanism of cavitation in conforming and partially conforming tribological conjunctions. The effect of cavitation on load carrying capacity and frictional performance of is also investigated. This is important with regards to fuel efficiency in internal combustion (IC) engines. Friction accounts for 15–20% of IC engine losses. The piston–cylinder system contributes to 40–50% of these, with the compression ring(s) being responsible for most of this. This is because the primary function of the ring is to seal the combustion chamber, thus small emerging gaps lead to increased friction. In fact, compression ring(s) expend 3–5% of engine input fuel energy. The share of frictional losses of engine bearings is approximately 20–25%. Traditionally, prediction of performance of tribological conjunctions has been studied using Reynolds equation. When the effect of cavitation is considered, various cavitation algorithms with associated boundary conditions for lubricant rupture and reformation are proposed. These include Elrod, and Elrod and Coyne algorithms, as well as boundary conditions such as Swift-Stieber, JFO and Prandtl-Hopkins. There are a number of assumptions embodied in these approaches, as well as the use of Reynolds equation itself. These approaches do not uphold the continuity of mass and momentum in multi-phase flow, in cavitation beyond the lubricant film rupture. A detailed methodology for multi-phase flow, comprising simultaneous solution of Navier-Stokes, energy and lubricant rheological state equations is developed.

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46

Teng, Penghua. "CFD MODELLING OF TWO-PHASE FLOWS AT SPILLWAY AERATORS." Licentiate thesis, KTH, Vattendragsteknik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-202392.

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Due to the high-speed flow in a chute spillway, cavitation damages often occur. This undesired phenomenon threatens the safety of the structure. For the purpose of eliminating the damages, an aerator is often installed in the spillway. To understand its characteristics, physical model tests are a popular method. To complement the model tests, computation fluid dynamics (CFD) simulations are used to study aerator flows. To represent the two-phase flows, multiphase models should be employed. This thesis examines two of them, namely, the Volume-Of-Fluid model (VOF) and Two-Fluid model. Based on the background of the Bergeforsen dam, the aerator flow is modelled by means of the VOF model. The simulated spillway discharge capacity is in accordance with the experimental data. Compared with the results, empirical formulas fail to evaluate the air supply capacity of aerator as it is wider than the conventional width. A hypothetical vent modification is proposed. For the original and proposed layouts, the study illustrates the difference in the air-flow conditions. The results show that a larger vent area is, for a large-width aerator, preferable in the middle of the chute. To study the flip bucket-shaped aerators in the Gallejaur dam, physical model tests and prototype observations are conducted. The results lead to contradicting conclusions in terms of jet breakup and air entrainment. A CFD model is, as an option, employed to explain the reason of the discrepancy. The numerical results coincide with the prototype observations. The jet breakup and air entrainment are evaluated from air cavity profiles; the air-pressure drops are small in the cavity. The discrepancy is due to overestimation of the surface-tension effect in the physical model tests. Based on the experimental data of an aerator rig at the Laboratory of Hydraulics, Hydrology and Glaciology (VAW), ETH Zurich, the Two-Fluid model is used to predict air concentration distributions in the aerated flow. The model includes relevant forces governing the motion of bubbles and considers the effects of air bubble size. The numerical results are conformable to the experiments in the air cavity zone. Downstream of the cavity, the air concentration near the chute bottom is higher, which is presumably caused by the fact that the interfacial forces in the Two-Fluid model are underestimated.

QC 20170224

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47

Pinho, Jorge. "Experimental investigation of cavitation in a safety relief valve using water: extension to cryogenic fluids." Doctoral thesis, Universite Libre de Bruxelles, 2015. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209095.

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This thesis addresses the experimental investigation of the cavitation phenomenon and its main consequences on the normal operation of a safety relief valve (SRV). More particularly, limitation of the mass flux discharged and alteration of the hydraulic fluid forces behavior is of main interest for the proper design and sizing of such devices. In nuclear or thermal engineering systems, the use of SRVs is mandatory since it represents the ultimate protection device before an accident occurs, caused by a sudden pressurization of the system. A careful design and sizing of the SRV is therefore essential. The complete understanding of the physics taking place in the flow through the valve is required to guaranty and optimize the security of the protected process.

In order to investigate the above effects of cavitation in a SRV, two different orifice sized valves (API 2J3 type and a transparent model based on an API 1 1/2G3 type) are tested in two different experimental facilities expressly built for this purpose. Instead of using a spring, the design of both valves allows the adjustment of the disc at any desired lift. Hence the static behavior of the valves is investigated. Both facilities, operating at different magnitude scales, allow the study of single phase and cavitating flow conditions required to properly determine the most important hydraulic characteristics, and access on any potential scaling effect between both sized SRVs. Experimental techniques used for the determination of the hydraulic characteristics include temperature, flow rate, fluid forces and pressure measurements both upstream and downstream the test sections.

Results show a similar influence of cavitation on the flow characteristics of both valves, minimizing any potential scaling effect. The liquid pressure recovery factor FL, which is normally used to identify a choked flow condition in a control valve, is experimentally determined for the first time in a SRV. The existence of a local minimum located at small openings of the lift indicates a change on the flow characteristics of both valves, which is related to the location of the minimum cross section of the flow that does not remain constant for every lift position. An extended experimental campaign is performed to analyse the effect of the blowdown ring adjustment located around the nozzle of the API 2J3 valve. Results confirm that the position of the ring has an important contribution for the hydraulic forces acting on the valve disc.

In the second part of the research, precise optical diagnostic techniques are successfully applied in the transparent valve to locally characterize the flow topology in a SRV experiencing cavitation. These results are innovative and enrich the experimental database available in the literature for the characterization and understanding of the flow physics in such devices. In a first configuration, high speed visualization is applied to observe qualitatively the flow pattern and the inception of liquid vaporization. Particle tracking results suggest that vapor bubbles are formed in the core of vortices detached from the shear layers attached to the valve. These rotational structures promote lower pressure regions allowing the liquid to vaporize. In the second configuration, particle image velocimetry is applied to extract the velocity field in both single phase and cavitating flow conditions. Results of PIV confirm the existence of a submerged jet just downstream the minimum section. This jet is characterized by two non-symmetric shear layers at its sides. Under cavitation conditions, PIV results confirm that vapor bubbles are formed preferentially inside the jet shear layers. The phenomenon of mass flux limitation caused by cavitation is reproduced at small openings of the valve and interaction with the flow topology is highlighted. It is observed that limitation of the flow occurs when the vena contracta is shifted towards the minimum geometrical section of the flow. Finally, instabilities of the flow downstream the critical section are investigated in the frequency domain by means of time resolved data. Results suggest that vortex shedding mechanism is dominated by a constant Strouhal number which is slightly affected by the valve opening.

In the last part of the research, the methodology used in water is extended and applied to cryogenic liquids. Two different geometries are investigated experimentally and numerically using water and liquid nitrogen as working fluids. Results suggest that both the flow coefficient (determined at single flow conditions), and the liquid recovery factor (used to identify choked flows), are independent on the fluid properties and therefore, an hydraulic similarity relation can be proposed.

This research project was carried out at the von Karman Institute for Fluid Dynamics (VKI), in Belgium, in close collaboration and with the funding of Centre Technique des Industries Mécaniques (CETIM) in France.
Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished

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48

Schmidt, Aaron James. "Quantitative measurement and flow visualization of water cavitation in a converging-diverging nozzle." Thesis, Kansas State University, 2016. http://hdl.handle.net/2097/32587.

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Master of Science
Department of Mechanical and Nuclear Engineering
B. Terry Beck
Mohammad H. Hosni
Cavitation is the change of a liquid to a two-phase mixture of liquid and vapor, similar to boiling. However, boiling generates a vapor by increasing the liquid temperature while cavitation generates vapor through a decrease in pressure. Both processes are endothermic, removing heat from the surroundings. Both the phase change and heat absorption associated with cavitation provide many engineering applications, including contributing to a new type of refrigeration cycle under development. Cavitation can occur at or below the vapor pressure; conditions that delay cavitation and allow for a metastable liquid are not well understood. A converging-diverging nozzle was designed and fabricated to create a low pressure region at the nozzle throat. The converging section of the nozzle increased the water velocity and decreased the pressure, according to Bernoulli’s principle. A cavitation front was formed slightly past the nozzle throat. The cavitation location suggested that the water was metastable near the nozzle throat. Flow through the system was controlled by changing the nozzle inlet and outlet pressures. The flowrate of water was measured while the outlet pressure was lowered. The flowrate increased as the outlet pressure dropped until cavitation occurred. Once cavitation initiated, the flow became choked and remained constant and independent of the nozzle outlet pressure. High-speed imagery was used to visualize the flow throughout the nozzle and the formation and collapse of cavitation in the nozzle’s diverging section. High-speed video taken from 1,000 to 35,000 frames per second captured the formation of the cavitation front and revealed regions of recirculating flow near the nozzle wall in the diverging section. Particle Image Velocimetry (PIV) was used to measure the velocity vector field throughout the nozzle to characterize flow patterns within the nozzle. PIV showed that the velocity profile in the converging section and throat region were nearly uniform at each axial position in the nozzle. In the diverging section, PIV showed a transient, high-velocity central jet surrounded by large areas of recirculation and eddy formation. The single-phase experimental results, prior to cavitation onset, were supplemented by Computational Fluid Dynamics (CFD) simulations of the velocity distribution using Fluent software.

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49

Brewer, Wesley Huntington. "On simulating tip-leakage vortex flow to study the nature of cavitation inception." Diss., Mississippi State : Mississippi State University, 2002. http://library.msstate.edu/etd/show.asp?etd=etd-04102002-134949.

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50

Ruh, Christian. "Performance of boiling and hot sparged agitated reactors." Thesis, University of Surrey, 1997. http://epubs.surrey.ac.uk/844300/.

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In this dissertation the power draw, the mass transfer and the liquid mixing behaviour of boiling and hot sparged stirred tank reactors (STRs) were investigated. The power draw characteristics of six different impellers were studied under varying operating conditions and expressed in terms of the relative power draw, RPD. Generally the impellers showed considerably higher power draw in hot gassed than in comparable cold conditions. The main phenomenon in hot systems, the evaporation of liquid into a gas bubble suddenly exposed to it, was investigated experimentally. The growth of nitrogen and air bubbles in hot water was found to be very fast and be completed typically within milliseconds after their exposure to the liquid. This was confirmed by studies applying acoustic bubble sizing techniques which were carried out together with Richard Manasseh from CSIRO, Melbourne, Australia. Experimental studies of the gas-liquid mass transfer in hot sparged STRs were carried out using a tank of 450 mm in diameter agitated by a 180 mm Rushton turbine. Experiments involving the temperature kinetics in an air-water system and absorption and desorption of ammonia were used to determine gas and also some liquid side mass transfer coefficients. The gas side coefficients kga were found to be typically in the order of 0.01 s-1. An enhancement of the liquid side mass transfer was also observed. Both Fick and Stefan-Maxwell models were employed to express gas side mass transfer coefficients. The models predict there will be a decrease of the coefficients at high concentrations. In the hot sparged tank the temperature is essentially uniform throughout the STR. Liquid mixing times have been measured for various boil-off and sparging rates. No significant deviations from the single phase or the cold gassed mixing times in this equipment were recorded.

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