WorldWideScience

Sample records for cavitation

  1. Rotating Cavitation Supression Project

    Data.gov (United States)

    National Aeronautics and Space Administration — FTT proposes development of a rotating cavitation (RC) suppressor for liquid rocket engine turbopump inducers. Cavitation instabilities, such as rotating...

  2. Quantum Cavitation

    CERN Document Server

    Zizzi, Paola; Cardone, Fabio

    2010-01-01

    We consider the theoretical setting of a superfluid like 3He in a rotating container, which is set between the two layers of a type-II superconductor. We describe the superfluid vortices as a 2-dimensional Ising-like model on a triangular lattice in presence of local magnetic fields. The interaction term of the superfluid vortices with the Abrikosov vortices of the superconductor appears then as a symmetry breaking term in the free energy. Such a term gives a higher probability of quantum tunnelling across the potential barrier for bubbles nucleation, thus favouring quantum cavitation.

  3. Cavitation in Hydraulic Machinery

    Energy Technology Data Exchange (ETDEWEB)

    Kjeldsen, M.

    1996-11-01

    The main purpose of this doctoral thesis on cavitation in hydraulic machinery is to change focus towards the coupling of non-stationary flow phenomena and cavitation. It is argued that, in addition to turbulence, superimposed sound pressure fluctuations can have a major impact on cavitation and lead to particularly severe erosion. For the design of hydraulic devices this finding may indicate how to further limit the cavitation problems. Chapter 1 reviews cavitation in general in the context of hydraulic machinery, emphasizing the initial cavitation event and the role of the water quality. Chapter 2 discusses the existence of pressure fluctuations for situations common in such machinery. Chapter 3 on cavitation dynamics presents an algorithm for calculating the nucleation of a cavity cluster. Chapter 4 describes the equipment used in this work. 53 refs., 55 figs.,10 tabs.

  4. Cavitation simulation on marine propellers

    DEFF Research Database (Denmark)

    Shin, Keun Woo

    Cavitation on marine propellers causes thrust breakdown, noise, vibration and erosion. The increasing demand for high-efficiency propellers makes it difficult to avoid the occurrence of cavitation. Currently, practical analysis of propeller cavitation depends on cavitation tunnel test, empirical...... are investigated, and one of the cavitation models is verified for the cavitation simulation on marine propellers. Three cavitation models with a vapor transport equation and a cavitation model with a barotropic state law are implemented in the in-house RANS solver, EllipSys. The numerical results for...

  5. Dynamics of Vortex Cavitation

    NARCIS (Netherlands)

    Pennings, P.C.

    2016-01-01

    This thesis describes the mechanisms with which tip vortex cavitation is responsible for broadband pressure fluctuations on ship propellers. Hypotheses for these are described in detail by Bosschers (2009). Validation is provided by three main cavitation-tunnel experiments, one on a model propeller

  6. Fundamentals of Cavitation

    CERN Document Server

    Franc, Jean-Pierre

    2005-01-01

    The present book is aimed at providing a comprehensive presentation of cavitation phenomena in liquid flows. It is further backed up by the experience, both experimental and theoretical, of the authors whose expertise has been internationally recognized. A special effort is made to place the various methods of investigation in strong relation with the fundamental physics of cavitation, enabling the reader to treat specific problems independently. Furthermore, it is hoped that a better knowledge of the cavitation phenomenon will allow engineers to create systems using it positively. Examples in the literature show the feasibility of this approach.

  7. Cavitation During Superplastic Forming

    Directory of Open Access Journals (Sweden)

    John Campbell

    2011-07-01

    Full Text Available Cavitation is the opening of pores during superplastic forming, typically at grain boundary triple points or on second phase grain boundary particles during slip of grain boundaries. Theories for the initiation of cavitation are reviewed. It seems that cavitation is unlikely to occur by processes intrinsic to metals such as dislocation mechanisms or point defect condensation. It is proposed that cavitation can only occur at non-bonded interfaces such as those introduced extrinsically (i.e., from the outside during the original casting of the metal. These defects, known as oxide bifilms, are naturally introduced during pouring of the liquid metal, and are frozen into the solid, often pushed by dendritic growth into grain boundaries where they are difficult to detect because of their extreme thinness, often measured in nanometres. Their unbonded central interface acts as a crack and can initiate cavitation. Second phase precipitates probably do not nucleate and grow on grain boundaries but grow on bifilms in the boundaries, explaining the apparent association between boundaries, second phase particles and failure initiation. Improved melting and casting techniques can provide metal with reduced or zero bifilm population for which cavitation would not be possible, promising significant improvements in superplastic behaviour.

  8. Cavitation guide for control valves

    Energy Technology Data Exchange (ETDEWEB)

    Tullis, J.P. [Tullis Engineering Consultants, Logan, UT (United States)

    1993-04-01

    This guide teaches the basic fundamentals of cavitation to provide the reader with an understanding of what causes cavitation, when it occurs, and the potential problems cavitation can cause to a valve and piping system. The document provides guidelines for understanding how to reduce the cavitation and/or select control valves for a cavitating system. The guide provides a method for predicting the cavitation intensity of control valves, and how the effect of cavitation on a system will vary with valve type, valve function, valve size, operating pressure, duration of operation and details of the piping installation. The guide defines six cavitation limits identifying cavitation intensities ranging from inception to the maximum intensity possible. The intensity of the cavitation at each limit Is described, including a brief discussion of how each level of cavitation influences the valve and system. Examples are included to demonstrate how to apply the method, including making both size and pressure scale effects corrections. Methods of controlling cavitation are discussed providing information on various techniques which can be used to design a new system or modify an existing one so it can operate at a desired level of cavitation.

  9. Cavitation guide for control valves

    International Nuclear Information System (INIS)

    This guide teaches the basic fundamentals of cavitation to provide the reader with an understanding of what causes cavitation, when it occurs, and the potential problems cavitation can cause to a valve and piping system. The document provides guidelines for understanding how to reduce the cavitation and/or select control valves for a cavitating system. The guide provides a method for predicting the cavitation intensity of control valves, and how the effect of cavitation on a system will vary with valve type, valve function, valve size, operating pressure, duration of operation and details of the piping installation. The guide defines six cavitation limits identifying cavitation intensities ranging from inception to the maximum intensity possible. The intensity of the cavitation at each limit Is described, including a brief discussion of how each level of cavitation influences the valve and system. Examples are included to demonstrate how to apply the method, including making both size and pressure scale effects corrections. Methods of controlling cavitation are discussed providing information on various techniques which can be used to design a new system or modify an existing one so it can operate at a desired level of cavitation

  10. Cavitation in medicine.

    Science.gov (United States)

    Brennen, Christopher Earls

    2015-10-01

    We generally think of bubbles as benign and harmless and yet they can manifest the most remarkable range of physical effects. Some of those effects are the stuff of our everyday experience as in the tinkling of a brook or the sounds of breaking waves at the beach. But even these mundane effects are examples of the ability of bubbles to gather, focus and radiate energy (acoustic energy in the above examples). In other contexts that focusing of energy can lead to serious technological problems as when cavitation bubbles eat great holes through ships' propeller blades or cause a threat to the integrity of the spillways at the Hoover Dam. In liquid-propelled rocket engines, bubbles pose a danger to the stability of the propulsion system, and in artificial heart valves they can cause serious damage to the red blood cells. In perhaps the most extraordinary example of energy focusing, collapsing cavitation bubbles can emit not only sound, but also light with black body radiation temperatures equal to that of the sun (Brennen 1995 Cavitation and bubble dynamics). But, harnessed carefully, this almost unique ability to focus energy can also be put to remarkably constructive use. Cavitation bubbles are now used in a remarkable range of surgical and medical procedures, for example to emulsify tissue (most commonly in cataract surgery or in lithotripsy procedures for the reduction of kidney and gall stones) or to manipulate the DNA in individual cells. By creating cavitation bubbles non-invasively thereby depositing and focusing energy non-intrusively, one can generate minute incisions or target cancer cells. This paper will begin by briefly reviewing the history of cavitation phenomena and will end with a vision of the new horizons for the amazing cavitation bubble. PMID:26442145

  11. Cavitation problems in sodium valves

    International Nuclear Information System (INIS)

    Cavitation poses few problems for sodium valves, in spite of the fact that the loops are not pressurized. This is no doubt due to the low flow velocities in the pipes. For auxiliary loop valves we are attempting to standardize performances with respect to cavitation. For economic reasons cavitation thresholds are approached with large diameter valves. (author)

  12. Cavitation in liquid helium

    Energy Technology Data Exchange (ETDEWEB)

    Finch, R. D.; Kagiwada, R.; Barmatz, M.; Rudnick, I.

    1963-11-15

    Ultrasonic cavitation was induced in liquid helium over the temperature range 1.2 to 2.3 deg K, using a pair of identical transducers. The transducers were calibrated using a reciprocity technique and the cavitation threshold was determined at 90 kc/s. It was found that this threshold has a sharp peak at the lambda point, but is, at all temperatures quite low, with an approximate range of 0.001 to 0.01 atm. The significance of the results is discussed. (auth)

  13. Taming Acoustic Cavitation

    CERN Document Server

    Rivas, David Fernandez; Enriquez, Oscar R; Versluis, Michel; Prosperetti, Andrea; Gardeniers, Han; Lohse, Detlef

    2012-01-01

    In this fluid dynamics video we show acoustic cavitation occurring from pits etched on a silicon surface. By immersing the surface in a liquid, gas pockets are entrapped in the pits which upon ultrasonic insonation, are observed to shed cavitation bubbles. Modulating the driving pressure it is possible to induce different behaviours based on the force balance that determines the interaction among bubbles and the silicon surface. This system can be used for several applications like sonochemical water treatment, cleaning of surfaces with deposited materials such as biofilms.

  14. Characteristics of Vibration Induced by Cavitation

    Institute of Scientific and Technical Information of China (English)

    WANG Guo-yu; TAO Lei; LIU Shu-yan; QIAN Jian-jun

    2005-01-01

    Cavitation-induced vibration characteristics and the relations between the vibration and cavitation are studied. Cavitation vibrations are measured around a model hollow-jet valve by an accelerometer under cavitating and non-cavitating conditions. The measurement data is analyzed by FFT method. The corresponding cavitating flow patterns are photographed by a high-speed camera with an xenon flash lamp. The frequency band of the vibration induced by cavitation is determined. To compare the vibration intensities under different cavitation conditions, a definition of vibration acceleration level is introduced based on power spectral density of the vibration. By the analysis of vibration, the definitions of characteristic cavitation number are suggested. According to these cavitation numbers, the cavitation process is divided into three stages, that is, incipient cavitation, subcavitation and supercavitation.

  15. Acoustic cavitation and sonochemistry

    OpenAIRE

    Stricker, L.

    2013-01-01

    Sonochemistry is the use of cavitation for achieving a chemical conversion. When microbubbles are driven in the nonlinear regime, localized extreme temperatures (up to 10000 K) and pressures (up to 1000 bar) can be reached upon collapse, the surrounding liquid remaining ambient,thus giving origin to intriguing phenomena, such as light emission (sonoluminescence) and high temperature chemical reactions (sonochemistry). These reaction products then diffuse outside the bubble and dissolve inside...

  16. Cavitation noise from butterfly valves

    International Nuclear Information System (INIS)

    Cavitation in valves can produce levels of intense noise. It is possible to mathematically express a limit for a design level of cavitation noise in terms of the cavitation parameter sigma. Using the cavitation parameter or limit, it is then possible to calculate the flow conditions at which a design level of cavitation noise will occur. However, the intensity of cavitation increases with the upstream pressure and valve size at a constant sigma. Therefore, it is necessary to derive equations to correct or scale the cavitation limit for the effects of different upstream pressures and valve sizes. The following paper discusses and presents experimental data for the caviation noise limit as well as the cavitation limits of incipient, critical, incipient damage, and choking cavitation for butterfly valves. The main emphasis is on the design limit of caviation noise, and a noise level of 85 decibels was selected as the noise limit. Tables of data and scaling exponents are included for applying the design limits for the effects of upstream pressure and valve size. (orig.)

  17. Cavitation instabilities in hydraulic machines

    International Nuclear Information System (INIS)

    Cavitation instabilities in hydraulic machines, hydro turbines and turbopump inducers, are reviewed focusing on the cause of instabilities. One-dimensional model of hydro turbine system shows that the overload surge is caused by the diffuser effect of the draft tube. Experiments show that this effect also causes the surge mode oscillations at part load. One dimensional model of a cavitating turbopump inducer shows that the mass flow gain factor, representing the cavity volume increase caused by the incidence angle increase is the cause of cavitation surge and rotating cavitation. Two dimensional model of a cavitating turbopump inducer shows that various modes of cavitation instabilities start to occur when the cavity length becomes about 65% of the blade spacing. This is caused by the interaction of the local flow near the cavity trailing edge with the leading edge of the next blade. It was shown by a 3D CFD that this is true also for real cases with tip cavitation. In all cases, it was shown that cavitation instabilities are caused by the fundamental characteristics of cavities that the cavity volume increases with the decrease of ambient pressure or the increase of the incidence angle

  18. Underwater explosions and cavitation phenomena

    Energy Technology Data Exchange (ETDEWEB)

    Kamegai, M.

    1979-08-28

    Some aspects of underwater explosions and cavitation phenomena have been studied by using a thermodynamic equation of state for water and a one-dimensional Lagrangian hydrocode. The study showed that surface cavitation is caused by the main blast wave and a bubble pulse from rebound of a release wave moving toward the center of the exploding bubble. Gravity has little effect on the surface cavitation. In nuclear explosions the bubble is bounded by a two-phase region rather than a gas-water interface. The two-phase region cavitates as the bubble expands, changing the optical absorption coefficient by many orders of magnitude and significantly affecting the optical signature. In assessing cavitation damage, it is concluded that a water jet of unstable bubble collapse erodes solid walls. The study leads to suggestions for future research.

  19. Underwater explosions and cavitation phenomena

    International Nuclear Information System (INIS)

    Some aspects of underwater explosions and cavitation phenomena have been studied by using a thermodynamic equation of state for water and a one-dimensional Lagrangian hydrocode. The study showed that surface cavitation is caused by the main blast wave and a bubble pulse from rebound of a release wave moving toward the center of the exploding bubble. Gravity has little effect on the surface cavitation. In nuclear explosions the bubble is bounded by a two-phase region rather than a gas-water interface. The two-phase region cavitates as the bubble expands, changing the optical absorption coefficient by many orders of magnitude and significantly affecting the optical signature. In assessing cavitation damage, it is concluded that a water jet of unstable bubble collapse erodes solid walls. The study leads to suggestions for future research

  20. Application of cavitation in uranium leaching

    International Nuclear Information System (INIS)

    Cavitation mostly considered as an operational problem and not a desirable phenomena. The rapid creation and collapse of bubbles can destroy pump and erode other equipment. But recently cavitation has been explored to enhance mass transfer and enhance or alter chemical reactions. Cavitation by definition is the formation, growth and rapid collapse of bubbles. Cavitation can be generated by different techniques

  1. Alternate blade cavitation on inducer; Inducer no kogoyoku cavitation

    Energy Technology Data Exchange (ETDEWEB)

    Aoki, M. [Ebara Research Co. Ltd., Kanagawa (Japan); Huang, J.; Zhang, J.

    1996-08-25

    Concerning a flat-helical inducer with two blades, examinations on suction performance, cavitation development and internal flow conditions of the impeller were performed. As the suction pressure is reduced, the balanced cavity development on both blades is destroyed. Alternate blade cavitation, in which cavity development evolves on one blade while weakens on the other, can occur. When the alternate blade cavitation occurs, the theoretical and actual pump heads can decrease quickly. The following investigations were conducted to determine how this phenomenon develops. 6 refs., 8 figs.

  2. Fracture of elastomers by cavitation

    KAUST Repository

    Hamdi, Adel

    2014-01-01

    Cavitation phenomenon is studied in rubber-like materials by combining experimental, theoretical and numerical approaches. Specific tests are carried out on a Styrene Butadiene Rubber to point out main characteristics of cavitation phenomenon. Hydrostatic depression is numerically modelled using finite element method. Numerical results are compared to Ball\\'s and Hou & Abeyaratne\\'s models with regard to cavity nucleation in the material. Both models well fit experimental observations suggesting that the cavitation nucleation in elastomers depends on the confinement degree of the specimen. Finally, critical hydrostatic pressure and critical global deformation are proved to govern cavitation nucleation in the studied material. Critical loadings are identified by comparing experimental and numerical load-displacement curves. © 2013 Elsevier Ltd.

  3. Cavitation performance evaluation for a condensate pump

    International Nuclear Information System (INIS)

    Cavitation in a condensate pump with specific speed of 95 m·m3s−1·min−1 was treated in this study. Cavitation performance for the pump was tested experimentally, and the steady state cavitating flows in the pump impeller were simulated by RANS method as well as a homogeneous cavitation model. It is noted that cavitating flow simulation reasonably depicted cavitation development in the pump. Compared to the tested results, the numerical simulation basically predicted later performance drops due to cavitation. Unfortunately, the cavitation simulation at the operation condition of 50% best efficiency point could not predict the head drop up to 3%. By applying the concept of relative cavity length cavitation performance evaluation is achieved. For better application, future study is necessary to establish the relation between relative cavity length and performance drop

  4. Blood vessel rupture by cavitation

    OpenAIRE

    Chen, Hong; Brayman, Andrew A.; Bailey, Michael R.; Matula, Thomas J.

    2010-01-01

    Cavitation is thought to be one mechanism for vessel rupture during shock wave lithotripsy treatment. However, just how cavitation induces vessel rupture remains unknown. In this work, a high-speed photomicrography system was set up to directly observe the dynamics of bubbles inside blood vessels in ex vivo rat mesenteries. Vascular rupture correlating to observed bubble dynamics were examined by imaging bubble extravasation and dye leakage. The high-speed images show that bubble expansion ca...

  5. PRESSURE CHARACTERISTICS OF CAVITATION CONTROL BY AERATION

    Institute of Scientific and Technical Information of China (English)

    DONG Zhi-yong; LU Yang-quan; JU Wen-jie; CAI Xin-ming; DING Chun-sheng

    2005-01-01

    This experimental investigation was systematically conducted with the aid of a non-circulating water tunnel in the Hydraulics Laboratory at Zhejiang University of Technology in China.The test velocity is between 20m/s and 40m/s.The least air concentration to prevent cavitation erosion lies between 1.7% and 4.5%.Pressure waveforms with and without aeration in cavitation and cavitation erosion regions were measured.Time-averaged pressure profiles with and without aeration were compared.Pressure characteristics corresponding to least air concentration to prevent cavitation erosion in cavitation and cavitation erosion regions were analyzed.

  6. Visualization of cavitation bubbles; Visualisation de bulles de cavitation

    Energy Technology Data Exchange (ETDEWEB)

    Chouvellon, M.; Fournel, Th.; Ducottet, Ch. [Universite Jean Monnet, 31 Saint-Etienne (France). Laboratoire Traitement du Signal et Instrumentation-UMR CNRS 5516

    1999-07-01

    A high frequency ultrasonic reactor allows the degradation of some organic compounds which are not or poorly biodegradable by usual methods in industrial flows. The propagation of an ultrasonic wave in a liquid induces cavitation phenomena. The implosion of cavitation bubble locally causes a temperature of about several thousand Kelvins and a pressure of about several hundred bars. Such conditions allow the creation of the hydroxyl radicals and then the oxidation of organic compounds. The aim of this paper is to describe the method used to visualize cavitation bubbles in an ultrasonic reactor at a frequency of 500 kHz. The experimental set-up and the measurement of both the bubble radius and the fringe separation are presented. (authors)

  7. Sound signature of propeller tip vortex cavitation

    OpenAIRE

    Pennings, P.C.; Westerweel, J.; Van Terwisga, T.J.C.

    2015-01-01

    The design of an efficient propeller is limited by the harmful effects of cavitation. The insuffcient understanding of the role of vortex cavitation in noise and vibration reduces the maximum effciency by a necessary safety margin. The aim in the present study is to directly relate propeller cavitation sound to tip vortex cavity dynamics. This is achieved by a dedicated experiment in a cavitation tunnel on a specially designed two-bladed propeller using a high-speed video camera and a hydroph...

  8. Experimental research of a microjet cavitation

    Directory of Open Access Journals (Sweden)

    Olšiak Róbert

    2012-04-01

    Full Text Available The paper presents some results of a cavitation research behind a micro-orifice. Investigated were the conditions of the origin of cavitation represented by parameters such as upstream pressure, downstream pressure, liquid temperature and cavitation number. Presented are also images of a cavitating microjet made by the high speed high definition camera RedLake Y3. Dimensions of a microjet are: diameter 0,3 mm; length 0,5 mm.

  9. Size effects on cavitation instabilities

    DEFF Research Database (Denmark)

    Niordson, Christian Frithiof; Tvergaard, Viggo

    2006-01-01

    growth is here analyzed for such cases. A finite strain generalization of a higher order strain gradient plasticity theory is applied for a power-law hardening material, and the numerical analyses are carried out for an axisymmetric unit cell containing a spherical void. In the range of high stress......In metal-ceramic systems the constraint on plastic flow leads to so high stress triaxialities that cavitation instabilities may occur. If the void radius is on the order of magnitude of a characteristic length for the metal, the rate of void growth is reduced, and the possibility of unstable cavity...... triaxiality, where cavitation instabilities are predicted by conventional plasticity theory, such instabilities are also found for the nonlocal theory, but the effects of gradient hardening delay the onset of the instability. Furthermore, in some cases the cavitation stress reaches a maximum and then decays...

  10. Cavitation inception from bubble nuclei

    DEFF Research Database (Denmark)

    Mørch, Knud Aage

    2015-01-01

    experimental investigations of bubbles and cavitation inception have been presented. These results suggest that cavitation nuclei in equilibrium are gaseous voids in the water, stabilized by a skin which allows diffusion balance between gas inside the void and gas in solution in the surrounding liquid. The...... cavitation nuclei may be free gas bubbles in the bulk of water, or interfacial gaseous voids located on the surface of particles in the water, or on bounding walls. The tensile strength of these nuclei depends not only on the water quality but also on the pressure-time history of the water. A recent model...... and associated experiments throw new light on the effects of transient pressures on the tensile strength of water, which may be notably reduced or increased by such pressure changes....

  11. Thermodynamic effects on limited cavitation

    International Nuclear Information System (INIS)

    Experimental and theoretical data are presented for limited cavitation on hemispherical-nosed bodies in water and Freon 113. The experiments were conducted with 0.25 inch and 0.50 inch diameter models over a temperature range and velocity range of 80-260 deg F and 40-130fps, respectively. In general the experimental data do not display the decrease in cavitation number with temperature as predicted by the theory. It is feld that at least part of the differences between experimental and theoretical data are due to the effects of non condensable gas, laminar separation and boundary layer transition

  12. Cavitation Effects in Centrifugal Pumps- A Review

    Directory of Open Access Journals (Sweden)

    Maxime Binama

    2016-05-01

    Full Text Available Cavitation is one of the most challenging fluid flow abnormalities leading to detrimental effects on both the centrifugal pump flow behaviors and physical characteristics. Centrifugal pumps’ most low pressure zones are the first cavitation victims, where cavitation manifests itself in form of pitting on the pump internal solid walls, accompanied by noise and vibration, all leading to the pump hydraulic performance degradation. In the present article, a general description of centrifugal pump performance and related parameters is presented. Based on the literature survey, some light were shed on fundamental cavitation features; where different aspects relating to cavitation in centrifugal pumps were briefly discussed

  13. Cavitation Behavior of A5083 Alloy by Vibratory Cavitation Tester

    International Nuclear Information System (INIS)

    The cavitation behavior of A5083 alloy is investigated utilizing a vibratory cavitation tester. The tester(20.3kHz frequency) was manufactured according to ASTM G-32. The cavitation behavior of the specimens was examined by weight loss measurement and surface morphology change with peak-to-peak amplitudes and solutions. In order to investigate the cause of the damaged specimen's surface morphology change, the fluid velocity profile adjacent to vibrating specimen was measured by laser doppler velocimeter(LDV). The amount of weight loss was increased linearly with time after an incubation period. Cavitation test data in 3.5wt% NaCl solution showed that the amount of weight loss at small peak-to-peak amplitude(10μm) was increased by synergy effect of mechanical vibration and electrochemical corrosion. Such synergy effect, however, became less significant in deionized water and 3.5wt% NaCl solution with bigger amplitude(>20μm) where the mechanical damage predominates the corrosion damage. As the peak-to-peak amplitude was altered the damaged specimen exhibited significant morphology change. The circular type of damaged surface was shifted to the outer rim of the specimen and the damage intensity was increased with increasing amplitude. This morphology change could be attributed to the turbulence intensity whose maximum is found at the rim of specimen. LDV results have shown that turbulence intensity, which causes cavitative damage, increases with increasing amplitude, resulting in more intense damage. It is also suggested that the mechanism of morphology change could be resolved through farther LDV experiments. However, the obtained data did not showed exact correlation with the damaged surface morphology because the data were not obtained at the exact spots but relatively apart spots. We found some relationships with the damaged surface morphology and the LDV data

  14. Quantum cavitation in liquid helium

    OpenAIRE

    Guilleumas, Montserrat; Barranco Gómez, Manuel; Jezek, Dora M.; Lombard, Roland J.; Pi Pericay, Martí

    1996-01-01

    Using a functional-integral approach, we have determined the temperature below which cavitation in liquid helium is driven by thermally assisted quantum tunneling. For both helium isotopes, we have obtained the crossover temperature in the whole range of allowed negative p essures. Our results are compatible with recent experimental results on 4He.

  15. Cavitation inception from bubble nuclei.

    Science.gov (United States)

    Mørch, K A

    2015-10-01

    The tensile strength of ordinary water such as tap water or seawater is typically well below 1 bar. It is governed by cavitation nuclei in the water, not by the tensile strength of the water itself, which is extremely high. Different models of the nuclei have been suggested over the years, and experimental investigations of bubbles and cavitation inception have been presented. These results suggest that cavitation nuclei in equilibrium are gaseous voids in the water, stabilized by a skin which allows diffusion balance between gas inside the void and gas in solution in the surrounding liquid. The cavitation nuclei may be free gas bubbles in the bulk of water, or interfacial gaseous voids located on the surface of particles in the water, or on bounding walls. The tensile strength of these nuclei depends not only on the water quality but also on the pressure-time history of the water. A recent model and associated experiments throw new light on the effects of transient pressures on the tensile strength of water, which may be notably reduced or increased by such pressure changes. PMID:26442138

  16. Study of eddy-initiated cavitation; cavitation in a venturi: analogy between water and sodium

    International Nuclear Information System (INIS)

    The test facilities and experimental research techniques are described: sodium loop, water loop, visualization of cavitation in water behind openings, cavitation detection. A theoretical study is then devoted to cavitation through separate bubbles, with special emphasis on flow in a venturi of gradually changing profile, and the relative motion of a cavitation bubble; a coherent model of equations describing the evolution of an isolated spherical bubble is given. A theoretical study of eddy-initiated cavitation is also presented. Finally the results of cavitation experiments carried out on the venturi line are given for sodium (at 5500, 4500, 2500) and water (at 160, 370, 570 and 700C)

  17. Cavitation in Single-Vane Sewage Pumps

    Directory of Open Access Journals (Sweden)

    P. Springer

    2008-12-01

    Full Text Available Chair fluidsystemdynamics at TU Berlin investigated the cavitation behavior of a full-size single-vane sewage pump. Single-vane pumps are used for raw sewage with high content of dirt and sediments in larger sewage pumping stations. Cavitation measurement was done by using standard NPSH3% and the more sensitive incipient cavitation NPSHIC. Also, vibration and noise where observed. Contrary to very low NPSH3% values, very high NPSHIC values were measured. In a second step, the impeller was modified with special cavitation bores to reduce the cavitation effects. The NPSH3% values increased with cavitation bores, which underlines that this value is not a sufficient criteria describing cavitation. Using the much more sensitive NPSHIC, a significant reduction was obtained. Moreover, the cavitation formation was changed from a relative concentrated cloud to a distributed bubble form, which is much less aggressive in view of noise and erosion. Operational behavior improved with cavitation bores, noise and vibration levels especially came down to acceptable level. Practical experience demonstrates also avoidance of cavitation erosion.

  18. Prediction of cryogenic cavitation around hydrofoil by an extensional Schnerr-Sauer cavitation model

    Science.gov (United States)

    Sun, T. Z.; Wei, Y. J.; Wang, C.

    2015-12-01

    Developing a robust computational strategy to address the rich physics characteristic involved in the thermodynamic effects on the cryogenic cavitation remains a challenging problem. The objective of this present study is to model the numerical methodology to simulate the cryogenic cavitation by implanting the thermodynamic effects to the Schnerr-Sauer cavitation model, and coupling the energy equation considered the latent heat. For this purpose, cavitating flows are investigated over a three dimensional hydrofoil in liquid hydrogen and nitrogen. Experimental measurements of pressure and temperature are utilized to validate the extensional Schnerr-Sauer cavitation model. Specifically, the further analysis of the cavitation solution with respect to the thermodynamic term is conducted. The results show that the extensional Schnerr-Sauer cavitation model predicts better accuracy to the quasi-steady cavitation over hydrofoil in the two cryogenic fluids.

  19. Pump cavitation and inducer design

    International Nuclear Information System (INIS)

    Details of past work on sodium pump development and cavitation studies executed mainly for SNR 300 were reported earlier. Among the requirements for large sodium pumps are long life (200000 hours up to 300000 hours) and small size of impeller and pump, fully meeting the process and design criteria. These criteria are the required 'Q, H, r characteristics' in combination with a low NPSH value and the avoidance of cavitation damage to the pump. The pump designer has to develop a sound hydraulic combination consisting of suction arrangement, impeller design and diffuser. On the other hand the designer is free to choose an optimal pump speed. The pump speed in its turn influences the rotor dynamic pump design and the pump drive. The introduction of the inducer as an integral part of the pump design is based on following advantages: no tip cavitation; (possible) cavitation bubbles move to the open centre due to centrifugal forces on the fluid; the head of the inducer improves the inlet conditions of the impeller. The aim of an inducer is the increase in the suction specific speed (SA value) of a pump whereby the inducer functions as a pressure source improving the impeller inlet conditions. With inducer-impeller combinations values up to SA=15000 are realistic. With the use of an inducer the overall pump sizes can be reduced with Ca. 30%. Pumps commonly available have SA values up to a maximum of ca. 10000. A development programme was executed for SNR 300 in order to reach an increase of the suction specific speed of the impeller from SA 8200 to SA 11000. Further studies to optimize pumps design for the follow up line introduced the 'inducer acting as a pre-impeller' development. This programme was executed in the period 1979-1981. At the FDO premises a scale 1 2.8 inducer impeller combination with a suction specific speed SA=15000 was developed, constructed and tested at the water test rig. This water test rig is equipped with a perspex pipe allowing also visualisation

  20. Noise caused by cavitating Butterfly and Monovar Valves. Effects of cavitation on acoustic sources; numerical simulation

    International Nuclear Information System (INIS)

    An experimental study of the effects of cavitation was carried out through an analysis of cavitating Butterfly and Monovar valves. For each variation case, the nature of the dominant source is determined in relation to frequency. Once the parameters of the cavitation zone are identified, a three-zone model is used in order to pinpoint the acoustic sources with cavitation. In order to determine acoustic sources, we present a numerical simulation using a bubbles population. (authors)

  1. Numerical and Experimental Studies of Cavitation Behavior in Water-Jet Cavitation Peening Processing

    OpenAIRE

    Zhang, H.; Han, B.; X.G. Yu; Ju, D.Y.

    2013-01-01

    Water-jet cavitation peening (WCP) is a new technology for the surface modification of metallic materials. The cavitation behavior in this process involves complex and changeable physics phenomena, such as high speed, high pressure, multiple phases, phase transition, turbulence, and unstable features. Thus, the cavitation behavior and impact-pressure distribution in WCP have always been key problems in this field. Numerous factors affect the occurrence of cavitation. These factors include flo...

  2. Cavitation study of a pump-turbine at turbine mode with critical cavitation coefficient condition

    Science.gov (United States)

    Wang, J.; Yang, D.; Xu, J. W.; Liu, J. T.; Jiao, L.

    2016-05-01

    To study the cavitation phenomenon of a pump-turbine at turbine mode when it ran at the critical cavitation coefficient condition, a high-head model pump-turbine was disperse using hexahedron grid. Three dimensional, steady cavitating flow was numerically studied using SST k-ω model. It is confirmed that ZGB cavitation model and SST k-ω model are useful ways to study the two-phase cavitation flow in pump-turbine. Mass flow inlet and pressure outlet were specified at the casing inlet and draft tube outlet, respectively. The static pressure was set according to the cavitation coefficient. The steady cavitating flows at critical cavitation coefficient condition were analysed. The cavitation area in the runner was investigated. It was found that the pressure of the suction on the blade surface was decreasing gradually with the decrease of the cavitation coefficient. In addition, the vortex flow in the draft tube was observed at the critical cavitation coefficient. It was found that the vortex flow appeared at the center of the draft tube inlet with the decreasing of the cavitation coefficient. Compared with the experimental data, the simulation results show reasonable agreement with the experimental data.

  3. Cavitation for improved sludge conversion into biogas

    OpenAIRE

    Stoop, A.H.; Bakker, T.W.; Kramer, H.J.M.

    2015-01-01

    In several studies the beneficial influence of pre-treatment of waste activated sludge with cavitation on the biogas production was demonstrated. It is however, still not fully certain whether this effect should be mainly contributed to an increase in conversion rate of organics into biogas by anaerobic bacteria, and how much cavitation increases the total biogas yield. An increase in yield is only the case if cavitation can further disrupt otherwise inaccessible cell membrane structures and ...

  4. Cavitation-Induced Fusion: Proof of Concept

    OpenAIRE

    Fomitchev-Zamilov, Max I.

    2012-01-01

    Cavitation-induced fusion (also known as bubble fusion or sonofusion) has been a topic of much debate and controversy and is generally (albeit incorrectly) perceived as unworkable. In this paper we present the theoretical foundations of cavitation-induced fusion and summarize the experimental results of the research conducted in the past 20 years. Based on the systematic study of all available data we conclude that the cavitation-induced fusion is feasible, doable, and can be used for commerc...

  5. A Visual Observation of Cavitating Inducer Instability

    OpenAIRE

    Kamijo, Kenjiro; Shimura, Takashi; 渡辺, 光男; WATANABE, Mitsuo; 上条, 謙二郎; 志村, 隆

    1980-01-01

    This paper presents the results of experiments on the instability of a cavitating inducer, which is considered to be closely related with the POGO phenomena in liquid propellant rockets. The present experiment employed a high speed camera for visual observations. The dynamic pressure of both the inducer upstream and downstream was also measured. The difference between rotating cavitation and cavitation induced low cycle oscillations was examined. The cavities moved around the periphery of the...

  6. Classification of lubricants according to cavitation criteria

    OpenAIRE

    Meged, Y.; Venner, C.H.; Napel, ten, H.M.Th.D.

    1995-01-01

    Cavitation in lubrication liquids has long been known to be detrimental to components in hydraulic systems. Damage has been detected in journal bearings, especially under severe dynamic loading, gears, squeeze film dampers and valves. These findings have led to intensive studies of metal resistance to cavitation erosion, in order to minimize the damage. Results of these studies have been: 1. (a) classification of known materials according to their resistance to cavitation erosion; 2. (b) deve...

  7. Memory-Effect on Acoustic Cavitation

    OpenAIRE

    Yavaṣ, Oğuz; Leiderer, Paul; Park, Hee K.; Grigoropoulos, Costas P.; Poon, Chie C.; Tam, Andrew C.

    1994-01-01

    The formation of bubbles at a liquid-solid interface due to acoustic cavitation depends particularly on the preconditions of the interface. Here, it wiIl be shown that following laser-induced bubble formation at the interface the acoustic cavitation efficiency is strongly enhanced. Optical reflectance measurements reveal that this observed enhancement of acoustic cavitation due to preceding laser-induced bubble formation, which could be termed as memory effect, decays in a few hundred microse...

  8. Surge Instability on a Cavitating Propeller

    OpenAIRE

    Duttweiler, Mark E.; Brennen, Christopher E.

    2001-01-01

    This study details experiments investigating a previously unrecognized surge instability on a cavitating propeller in a water tunnel. The surge instability is furst explored through visual observation of the cavitation on the propeller blades and in the tip vortices. Similarities between the instability and previously documented cavitation phenomena are noted. Measurements of the radiated pressure are then obtained, and the acoustic signature of the instability is identified. The magnitud...

  9. Cavitation Nuclei: Experiments and Theory

    DEFF Research Database (Denmark)

    Mørch, Knud Aage

    2009-01-01

    The Swedish astrophysicist and Nobel Prize winner Hannes Alfven said: Theories come and go - the experiment is here forever. Often a theory, which we set up to describe an observed physical phenomenon, suffers from the lack of knowledge of decisive parameters, and therefore at best the theory...... becomes insufficient. Contrary, the experiment always reveals nature itself, though at prevailing experimental conditions. With essential parameters being out of control and even maybe unidentified, apparently similar experiments may deviate way beyond our expectations. However, these discrepancies offer...... us a chance to reflect on the character of the unknown parameters. In this way non-concordant experimental results may hold the key to the development of better theories - and to new experiments for the testing of their validity. Cavitation and cavitation nuclei are phenomena of that character....

  10. Mesenteric lymph node cavitation syndrome

    Institute of Scientific and Technical Information of China (English)

    Hugh; James; Freeman

    2010-01-01

    The mesenteric lymph node cavitation syndrome consists of central necrosis of mesenteric lymph nodes and may occur with either celiac disease or a sprue-like intestinal disease that fails to respond to a gluten-free diet. Splenic hypofunction may also be present. The cause is not known but its development during the clinical course of celiac disease is usually indicative of a poor prognosis for the intestinal disorder, a potential for signif icant compli-cations including sepsis and malignancy, particularly...

  11. Method of similarity for cavitation

    International Nuclear Information System (INIS)

    The knowledge of possible cavitation in subassembly nozzles of the fast reactor core implies the realization of a fluid dynamic model test. We propose a method of similarity based on the non-dimensionalization of the equation of motion for viscous capillarity fluid issued from the Cahn and Hilliard model. Taking into account the dissolved gas effect, a condition of compatibility is determined. This condition must be respected by the fluid in experiment, along with the scaling between the two similar flows. (author)

  12. Reflections on cavitation nuclei in water

    DEFF Research Database (Denmark)

    Mørch, Knud Aage

    2007-01-01

    The origin of cavitation bubbles, cavitation nuclei, has been a subject of debate since the early years of cavitation research. This paper presents an analysis of a representative selection of experimental investigations of cavitation inception and the tensile strength of water. At atmospheric...... on the surface of particles and bounding walls. Such nuclei can be related to the full range of tensile strengths measured, when differences of experimental conditions are taken into consideration. The absence or presence of contamination on surfaces, as well as the structure of the surfaces, are...

  13. Numerical Prediction of Unsteady Behavior of Cavitating Flow on Hydrofoils using Bubble Dynamics Cavitation Model

    Directory of Open Access Journals (Sweden)

    Nur-E- Mostafa

    2016-01-01

    Full Text Available This paper presents a numerical study with pressure-based finite volume method for prediction of non-cavitating and time dependent cavitating flow on hydrofoil. The phenomenon of cavitation is modeled through a mixture model. For the numerical simulation of cavitating flow, a bubble dynamics cavitation model is used to investigate the unsteady behavior of cavitating flow and describe the generation and evaporation of vapor phase. The non-cavitating study focuses on choosing mesh size and the influence of the turbulence model. Three turbulence models such as Spalart-Allmaras, Shear Stress Turbulence (SST k-ω model and Re-Normalization Group (RNG k-ε model with enhanced wall treatment are used to capture the turbulent boundary layer on the hydrofoil surface. The cavitating study presents an unsteady behavior of the partial cavity attached to the foil at different time steps for σ=0.8. Moreover, this study focuses on cavitation inception, the shape and general behavior of sheet cavitation, lift and drag forces for different cavitation numbers. Finally, the flow pattern and hydrodynamic characteristics are also studied at different angles of attack.

  14. Evaluation of Corrosion and the Anti-Cavitation Characteristics of Cu Alloy by Water Cavitation Peening

    International Nuclear Information System (INIS)

    Cu alloy is widely used for marine applications due to its excellent ductility and high resistance for corrosion as wells as cavitation. However, long term exposure of the material to marine environments may result in damages caused by cavitation and corrosion. Water cavitation peening has been introduced in order to improve resistance of Cu alloy to corrosion and cavitation. The technology induces compressive residual stress onto the surface, and thus enhances the fatigue strength and life. In this study, the characteristics of the material were investigated by using water cavitaiton peening technique, and results showed that 2 minutes of water cavitation peening indicated the considerable improvement in hardness. On the other hand, over 10 minutes of water cavitation peening accelerated damages to the surface. In the case of ALBC3, water cavitation peening in the range of 2 to 10 minutes has shown the excellent durability and corrosion resistance while minimizing surface damages

  15. Acoustic source strength of propeller cavitation

    NARCIS (Netherlands)

    Bruijn, A. de

    1979-01-01

    The acoustic source strength i.e. the volume velocity of propeller cavitation for six single-screw ships are presented. Plotting the data in the form of dimensionleee volume velocity and as a function of the cavitation number based on the rotation speed and the immersion depth, a certain differentia

  16. Detection of cavitation in hydraulic turbines

    Science.gov (United States)

    Escaler, Xavier; Egusquiza, Eduard; Farhat, Mohamed; Avellan, François; Coussirat, Miguel

    2006-05-01

    An experimental investigation has been carried out in order to evaluate the detection of cavitation in actual hydraulic turbines. The methodology is based on the analysis of structural vibrations, acoustic emissions and hydrodynamic pressures measured in the machine. The proposed techniques have been checked in real prototypes suffering from different types of cavitation. In particular, one Kaplan, two Francis and one Pump-Turbine have been investigated in the field. Additionally, one Francis located in a laboratory has also been tested. First, a brief description of the general features of cavitation phenomenon is given as well as of the main types of cavitation occurring in hydraulic turbines. The work presented here is focused on the most important ones which are the leading edge cavitation due to its erosive power, the bubble cavitation because it affects the machine performance and the draft tube swirl that limits the operation stability. Cavitation detection is based on the previous understanding of the cavity dynamics and its location inside the machine. This knowledge has been gained from flow visualisations and measurements in laboratory devices such as a high-speed cavitation tunnel and a reduced scale turbine test rig. The main techniques are the study of the high frequency spectral content of the signals and of their amplitude demodulation for a given frequency band. Moreover, low frequency spectral content can also be used in certain cases. The results obtained for the various types of cavitation found in the selected machines are presented and discussed in detail in the paper. Conclusions are drawn about the best sensor, measuring location, signal processing and analysis for each type of cavitation, which serve to validate and to improve the detection techniques.

  17. Energy analysis in acoustic cavitation

    Energy Technology Data Exchange (ETDEWEB)

    Vichare, N.P.; Senthilkumar, P.; Moholkar, V.S.; Gogate, P.R.; Pandit, A.B.

    2000-05-01

    In sonochemical processes, the physical and chemical effects are attributed to the phenomenon of cavitation, which is the formation, growth, and collapse of the cavities termed as activity of cavities. Energy analysis of a single cavity has been considered in order to explain, qualitatively, the effects of acoustic parameters such as intensity and frequency of ultrasonic equipment on sonochemical reactions. The experimental observations of the sonochemical reactions available in the literature are found to be consistent with the simulation results. Energy analysis of the cavity gives the possible reasons for the various sonochemical effects observed, and also the optimum equipment operating parameters can be predicted.

  18. Visualization of cavitating micro jets

    Directory of Open Access Journals (Sweden)

    Knížat Branislav

    2012-04-01

    Full Text Available The paper deals with one experimental set up integrated for research of the cavitating micro flows, which is incipient behind the micro channel or micro discharge nozzle outlet port. Experimental system is integrated from three major systems: hydraulic circuit with installed discharge nozzle (or micro channel, subsystem for data acquisition and data processing (DAQ system and vision system compound of high speed video camera and pulse light source with highfrequency repetition. First few results of experiments (parameters such as inlet pressure, downstream pressure were changed is also discussed.;

  19. Enterobacter Asburiae Pneumonia with Cavitation

    Energy Technology Data Exchange (ETDEWEB)

    Cha, Seung Woo; Heo, Jeong Nam; Park, Choong Ki [Dept. of Radiology, Hanyang University College of Medicine, Guri Hospital, Guri (Korea, Republic of); Choi, Yo Won; Jeon, Seok Chol [Dept. of Radiology, Hanyang University College of Medicine, Seoul Hospital, Seoul (Korea, Republic of)

    2013-03-15

    Enterobacter species have increasingly been identified as pathogens over the past several decades. These bacterial species have become more important because most are resistant to cephalothin and cefoxitin, and can produce extended-spectrum {beta}-lactamase. Enterobacter asburiae (E. asburiae) is a gram-negative rod of the family Enterobacteriaceae, named in 1986. Since then, there has been only one clinical report of E. asburiae pneumonia. We report a case of E. asburiae pneumonia with cavitation and compare it with the previous case.

  20. Numerical simulation of multiphase cavitating flows around an underwater projectile

    Institute of Scientific and Technical Information of China (English)

    2011-01-01

    The present simulation investigates the multiphase cavitating flow around an underwater projectile.Based on the Homogeneous Equilibrium Flow assumption,a mixture model is applied to simulate the multiphase cavitating flow including ventilated cavitation caused by air injection as well as natural cavitation that forms in a region where the pressure of liquid falls below its vapor pressure. The transport equation cavitating model is applied.The calculations are executed based on a suite of CFD code.The hyd...

  1. Periodic cavitation shedding in a cylindrical orifice

    Energy Technology Data Exchange (ETDEWEB)

    Stanley, C.; Barber, T.; Milton, B.; Rosengarten, G. [University of New South Wales, School of Mechanical and Manufacturing Engineering, Sydney (Australia)

    2011-11-15

    Cavitation structures in a large-scale (D = 8.25 mm), plain orifice style nozzle within a unique experimental rig are investigated using high-speed visualisation and digital image processing techniques. Refractive index matching with an acrylic nozzle is achieved using aqueous sodium iodide for the test fluid. Cavitation collapse length, unsteady shedding frequency and spray angles are measured for cavitation conditions from incipient to supercavitation for a range of Reynolds numbers, for a fixed L/D ratio of 4.85. Periodic cavitation shedding was shown to occur with frequencies between 500 and 2,000 Hz for conditions in which cavitation occupied less than 30% of the nozzle length. A discontinuity in collapse length was shown to occur once the cavitation exceeded this length, coinciding with a loss of periodic shedding. A mechanism for this behaviour is discussed. Peak spray angles of approximately {theta} {approx} 14 were recorded for supercavitation conditions indicating the positive influence of cavitation bubble collapse on the jet atomisation process. (orig.)

  2. Released air during vapor and air cavitation

    Science.gov (United States)

    Jablonská, Jana; Kozubková, Milada

    2016-06-01

    Cavitation today is a very important problem that is solved by means of experimental and mathematical methods. The article deals with the generation of cavitation in convergent divergent nozzle of rectangular cross section. Measurement of pressure, flow rate, temperature, amount of dissolved air in the liquid and visualization of cavitation area using high-speed camera was performed for different flow rates. The measurement results were generalized by dimensionless analysis, which allows easy detection of cavitation in the nozzle. For numerical simulation the multiphase mathematical model of cavitation consisting of water and vapor was created. During verification the disagreement with the measurements for higher flow rates was proved, therefore the model was extended to multiphase mathematical model (water, vapor and air), due to release of dissolved air. For the mathematical modeling the multiphase turbulence RNG k-ɛ model for low Reynolds number flow with vapor and air cavitation was used. Subsequently the sizes of the cavitation area were verified. In article the inlet pressure and loss coefficient depending on the amount of air added to the mathematical model are evaluated. On the basis of the approach it may be create a methodology to estimate the amount of released air added at the inlet to the modeled area.

  3. A cavitation aggressiveness index within the Reynolds averaged Navier Stokes methodology for cavitating flows

    Institute of Scientific and Technical Information of China (English)

    KOUKOUVINIS P.; BERGELES G.; GAVAISES M

    2015-01-01

    The paper proposes a methodology within the Reynolds averaged Navier Stokes (RANS) solvers for cavitating flows capable of predicting the flow regions of bubble collapse and the potential aggressiveness to material damage. An aggressiveness index is introduced, called cavitation aggressiveness index (CAI) based on the total derivative of pressure which identifies surface areas exposed to bubble collapses, the index is tested in two known cases documented in the open literature and seems to identify regions of potential cavitation damage.

  4. Cavitation-Induced Fusion: Proof of Concept

    CERN Document Server

    Fomitchev-Zamilov, Max I

    2012-01-01

    Cavitation-induced fusion (also known as bubble fusion or sonofusion) has been a topic of much debate and controversy and is generally (albeit incorrectly) perceived as unworkable. In this paper we present the theoretical foundations of cavitation-induced fusion and summarize the experimental results of the research conducted in the past 20 years. Based on the systematic study of all available data we conclude that the cavitation-induced fusion is feasible, doable, and can be used for commercial power generation. We present the results of our own research and disclose a commercial reactor prototype.

  5. Analyses of cavitation instabilities in ductile metals

    DEFF Research Database (Denmark)

    Tvergaard, Viggo

    Cavitation instabilities have been predicted for a single void in a ductile metal stressed under high triaxiality conditions. In experiments for a ceramic reinforced by metal particles a single dominant void has been observed on the fracture surface of some of the metal particles bridging a crack...... for the influence of such size-effects on cavitation instabilities are presented. When a metal contains a distribution of micro voids, and the void spacing compared to void size is not extremely large, the surrounding voids may affect the occurrence of a cavitation instability at one of the voids...

  6. Cavitation studies on axi-symmetric underwater body with pumpjet propulsor in cavitation tunnel

    Science.gov (United States)

    Suryanarayana, Ch.; Satyanarayana, B.; Ramji, K.; Rao, M. Nageswara

    2010-12-01

    A pumpjet propulsor (PJP) was designed for an underwater body (UWB) with axi-symmetric configuration. Its performance was predicted through CFD study and models were manufactured. The propulsor design was evaluated for its propulsion characteristics through model tests conducted in a Wind Tunnel (WT). In the concluding part of the study, evaluation of the cavitation performance of the pumpjet was undertaken in a cavitation tunnel (CT). In order to assess the cavitation free operation speeds and depths of the body, cavitation tests of the PJP were carried out in behind condition to determine the inception cavitation numbers for rotor, stator and cowl. The model test results obtained were corrected for full scale Reynolds number and subsequently analyzed for cavitation inception speeds at different operating depths. From model tests it was also found that the cavitation inception of the rotor takes place on the tip face side at higher advance ratios and cavitation shifts towards the suction side as the RPS increases whereas the stator and cowl are free from cavitation.

  7. Research on the noise induced by cavitation under the asymmetric cavitation condition in a centrifugal pump

    Science.gov (United States)

    Lu, J. X.; Yuan, S. Q.; Yuan, J. P.; Ren, X. D.; Pei, J.; Si, Q. R.

    2015-12-01

    An experimental investigation has been carried out to research the noise induced by cavitation under the asymmetric cavitation (AC) condition in a centrifugal pump. The acoustic pressure signals at the pump inlet and outlet were measured respectively during the development of cavitation in a closed hydraulic test rig. It could be found that both the pump inlet and outlet acoustic pressures changed obviously with the development of cavitation. The time domain and the power spectrum density of the pump inlet and outlet acoustic pressure pulsations were analyzed. The broadband pulses of the acoustic pressure pulsations were found and the reasons for the phenomenon were given.

  8. Cavitation mode analysis of pump inducer

    International Nuclear Information System (INIS)

    The onset of cavitation causes head and efficiency a main pump to be reduced significantly and generates vibration and noise. In order to avoid these phenomena, the inlet of the pump is fitted with a special rotor called an inducer, which can operate satisfactorily with extensive cavitation. The motivation of this study is to find out cavitation modes from the inducer inlet pressure signals and event characteristics from outlet ones at various operating conditions. The cavitation modes are analyzed by using a cross-spectral density of fluctuating pressures at the inducer inlet. The time-frequency characteristics of wall pressures downstream of the inducer are presented in terms of event frequency, its duration time, and number of events by using the Choi-Williams distribution

  9. Cavitation in pumps, pipes and valves

    International Nuclear Information System (INIS)

    The phenomenon of cavitation, often perceived as merely a nuisance, may have far more serious implications. These are discussed here. They include noise, loss of performance and damage to the constituent parts. (author)

  10. Cavitation for improved sludge conversion into biogas

    Science.gov (United States)

    Stoop, A. H.; Bakker, T. W.; Kramer, H. J. M.

    2015-12-01

    In several studies the beneficial influence of pre-treatment of waste activated sludge with cavitation on the biogas production was demonstrated. It is however, still not fully certain whether this effect should be mainly contributed to an increase in conversion rate of organics into biogas by anaerobic bacteria, and how much cavitation increases the total biogas yield. An increase in yield is only the case if cavitation can further disrupt otherwise inaccessible cell membrane structures and long chain organic molecules. In this study the influence of hydrodynamic cavitation on sludge that was already digested for 30 days was investigated. The total biogas yield could indeed be increased. The effect of the backpressure behind the venturi tube on the yield could not yet be established.

  11. Solvent cavitation under solvophobic confinement.

    Science.gov (United States)

    Ashbaugh, Henry S

    2013-08-14

    The stability of liquids under solvophobic confinement can tip in favor of the vapor phase, nucleating a liquid-to-vapor phase transition that induces attractive forces between confining surfaces. In the case of water adjacent to hydrophobic surfaces, experimental and theoretical evidence support confinement-mediated evaporation stabilization of biomolecular and colloidal assemblies. The macroscopic thermodynamic theory of cavitation under confinement establishes the connection between the size of the confining surfaces, interfacial free energies, and bulk solvent pressure with the critical evaporation separation and interfacial forces. While molecular simulations have confirmed the broad theoretical trends, a quantitative comparison based on independent measurements of the interfacial free energies and liquid-vapor coexistence properties has, to the best of our knowledge, not yet been performed. To overcome the challenges of simulating a large number of systems to validate scaling predictions for a three-dimensional fluid, we simulate both the forces and liquid-vapor coexistence properties of a two-dimensional Lennard-Jones fluid confined between solvophobic plates over a range of plate sizes and reservoir pressures. Our simulations quantitatively agree with theoretical predictions for solvent-mediated forces and critical evaporation separations once the length dependence of the solvation free energy of an individual confining plate is taken into account. The effective solid-liquid line tension length dependence results from molecular scale correlations for solvating microscopic plates and asymptotically decays to the macroscopic value for plates longer than 150 solvent diameters. The success of the macroscopic thermodynamic theory at describing two-dimensional liquids suggests application to surfactant monolayers to experimentally confirm confinement-mediated cavitation. PMID:23947875

  12. Numerical analysis of cavitation within slanted axial-flow pump

    Institute of Scientific and Technical Information of China (English)

    张睿; 陈红勋

    2013-01-01

    In this paper, the cavitating flow within a slanted axial-flow pump is numerically researched. The hydraulic and cavitation performance of the slanted axial-flow pump under different operation conditions are estimated. Compared with the experimental hydraulic performance curves, the numerical results show that the filter-based model is better than the standard k-e model to predict the parameters of hydraulic performance. In cavitation simulation, compared with the experimental results, the proposed numerical method has good predicting ability. Under different cavitation conditions, the internal cavitating flow fields within slanted axial-flow pump are investigated. Compared with flow visualization results, the major internal flow features can be effectively grasped. In order to explore the origin of the cavitation performance breakdown, the Boundary Vorticity Flux (BVF) is introduced to diagnose the cavitating flow fields. The analysis results indicate that the cavitation performance drop is relevant to the instability of cavitating flow on the blade suction surface.

  13. Detection of cavitation in hydraulic turbines

    OpenAIRE

    Escaler, X.; Egusquiza, E.; Farhat, M.; Avellan, F.

    2006-01-01

    An experimental investigation has been carried out in order to evaluate the detection of cavitation in actual hydraulic turbines. The methodology is based on the analysis of structural vibrations, acoustic emissions and hydrodynamic pressures measured in the machine. The proposed techniques have been checked in real prototypes suffering from different types of cavitation. In particular, one Kaplan, two Francis and one Pump-Turbine have been investigated in the field. Additionally, one Francis...

  14. Modelling vaporous cavitation on fluid transients

    OpenAIRE

    Shu, Jian-Jun

    2014-01-01

    A comprehensive study of the problem of modelling vaporous cavitation in transmission lines is presented. The two-phase homogeneous equilibrium vaporous cavitation model which has been developed is compared with the conventional column separation model. The latter predicts unrealistically high pressure spikes because of a conflict arising from the prediction of negative cavity sizes if the pressure is not permitted to fall below the vapour pressure, or the prediction of negative absolute pres...

  15. Control of Propeller Cavitation in Operational Conditions

    OpenAIRE

    Vrijdag, A.

    2009-01-01

    Off design conditions can have a severe impact on ship propulsion system behaviour. Resistance increase for instance leads to a higher engine loading, and can also easily lead to a decrease of cavitation inception speed with respect to calm water conditions. Wakefield variations due to ship motions, waves and manoeuvres also have effect on engine loading and on propeller cavitation. This dissertation discusses the model based development of a propulsion control system aiming at increased cavi...

  16. Intense cavitation at extreme static pressure.

    Science.gov (United States)

    Pishchalnikov, Yuri A; Gutierrez, Joel; Dunbar, Wylene W; Philpott, Richard W

    2016-02-01

    Cavitation is usually performed at hydrostatic pressures at or near 0.1 MPa. Higher static pressure produces more intense cavitation, but requires an apparatus that can build high amplitude acoustic waves with rarefactions exceeding the cavitation threshold. The absence of such an apparatus has prevented the achievement of intense acoustic cavitation, hindering research and the development of new applications. Here we describe a new high-pressure spherical resonator system, as well as experimental and modeling results in water and liquid metal (gallium), for cavitation at hydrostatic pressures between 10 and 150 MPa. Our computational data, using HYADES plasma hydrodynamics code, show the formation of dense plasma that, under these conditions, reaches peak pressures of about three to four orders of magnitude greater than the hydrostatic pressure in the bulk liquid and temperatures in the range of 100,000 K. Passive cavitation detection (PCD) data validate both a linear increase in shock wave amplitude and the production of highly intense concentrations of mechanical energy in the collapsing bubbles. High-speed camera observations show the formation of bubble clusters from single bubbles. The increased shock wave amplitude produced by bubble clusters, measured using PCD and fiber optic probe hydrophone, was consistent with current understanding that bubble clusters enable amplification of energy produced. PMID:26341849

  17. AN ATTRIBUTION OF CAVITATION RESONANCE: VOLUMETRIC OSCILLATIONS OF CLOUD

    Institute of Scientific and Technical Information of China (English)

    ZUO Zhi-gang; LI Sheng-cai; LIU Shu-hong; LI Shuang; CHEN Hui

    2009-01-01

    In order to further verify the proposed theory of cavitation resonance, as well as to proceed the investigations into microscopic level, a series of studies are being carried out on the Warwick venturi. The analysis of the oscillation characteristics of the cavitation resonance has conclusively verified the macro-mechanism proposed through previous studies on other cavitating flows by the authors. The initial observations using high-speed photographic approach have revealed a new attribution of cavitation resonance. That is, the volumetric oscillation of cavitation cloud is associated with the cavitation resonance, which is a collective behaviour of the bubbles in the cloud.

  18. Numerical and Experimental Studies of Cavitation Behavior in Water-Jet Cavitation Peening Processing

    Directory of Open Access Journals (Sweden)

    H. Zhang

    2013-01-01

    Full Text Available Water-jet cavitation peening (WCP is a new technology for the surface modification of metallic materials. The cavitation behavior in this process involves complex and changeable physics phenomena, such as high speed, high pressure, multiple phases, phase transition, turbulence, and unstable features. Thus, the cavitation behavior and impact-pressure distribution in WCP have always been key problems in this field. Numerous factors affect the occurrence of cavitation. These factors include flow-boundary conditions, absolute pressure, flow velocity, flow viscosity, surface tension, and so on. Among these factors, pressure and vapor fraction are the most significant. Numerical simulations are performed to determine the flow-field characteristics of both inside and outside the cavitating nozzle of a submerged water jet. The factors that influence the cavitation intensity of pressure are simulated. Fujifilm pressure-sensitive paper is used to measure the distribution of impact pressure along the jet direction during the WCP process. The results show that submerged cavitation jets can induce cavitation both inside and outside a conical nozzle and a convergent-divergent nozzle when the inlet pressure is 32 MPa. Moreover, the shock wave pressure induced by the collapse of the bubble group reaches up to 300 MPa.

  19. Effect of hydrodynamic cavitation on zooplankton: A tool for disinfection

    Digital Repository Service at National Institute of Oceanography (India)

    Sawant, S.S.; Anil, A.C.; Venkat, K.; Gaonkar, C.; Kolwalkar, J.; Khandeparker, L.; Desai, D.V.; Mahulkar, A.V.; Ranade, V.V.; Pandit, A.B.

    and that created by flowing through a cavitating element (orifice plates) on the microbes (zooplankton in sea water) is described. The experimental results are compared with modelling of cavitating conditions that includes cavity dynamics, turbulence generated...

  20. Advanced experimental and numerical techniques for cavitation erosion prediction

    CERN Document Server

    Chahine, Georges; Franc, Jean-Pierre; Karimi, Ayat

    2014-01-01

    This book provides a comprehensive treatment of the cavitation erosion phenomenon and state-of-the-art research in the field. It is divided into two parts. Part 1 consists of seven chapters, offering a wide range of computational and experimental approaches to cavitation erosion. It includes a general introduction to cavitation and cavitation erosion, a detailed description of facilities and measurement techniques commonly used in cavitation erosion studies, an extensive presentation of various stages of cavitation damage (including incubation and mass loss), and insights into the contribution of computational methods to the analysis of both fluid and material behavior. The proposed approach is based on a detailed description of impact loads generated by collapsing cavitation bubbles and a physical analysis of the material response to these loads. Part 2 is devoted to a selection of nine papers presented at the International Workshop on Advanced Experimental and Numerical Techniques for Cavitation Erosion (Gr...

  1. DETECTION OF CAVITATION IN CENTRIFUGAL PUMP BY VIBRATION METHODS

    Institute of Scientific and Technical Information of China (English)

    NI Yongyan; YUAN Shouqi; PAN Zhongyong; YUAN Jianping

    2008-01-01

    For the purpose of detecting the cavitation of centrifugal pump onsite and real time, the vibration signals on varied operation conditions of both cavitation and non-cavitation obtained through acceleration sensors were analyzed. When cavitation occurs, the cavities near the leading edge of the blade will appear periodic oscillating, which will induce quasi-synchronous vibration. The frequency of the quasi-synchronous vibration symmetrically appears on the two sides of the blade passing frequency, by which the cavitation incipiency can be detected. During the developing process of the cavitation, as the severe complexity of the unsteady flow, it is very difficult to detect the development of cavitation by classical analysis methods. Fractal method of Higuchi is successfully used for detecting the incipiency, fully development of cavitation and the development between them.

  2. High Speed Imaging of Cavitation around Dental Ultrasonic Scaler Tips

    OpenAIRE

    Vyas, Nina; Pecheva, Emilia; Dehghani, Hamid; Sammons, Rachel L; Wang, Qianxi X.; Leppinen, David M.; Walmsley, A Damien

    2016-01-01

    Cavitation occurs around dental ultrasonic scalers, which are used clinically for removing dental biofilm and calculus. However it is not known if this contributes to the cleaning process. Characterisation of the cavitation around ultrasonic scalers will assist in assessing its contribution and in developing new clinical devices for removing biofilm with cavitation. The aim is to use high speed camera imaging to quantify cavitation patterns around an ultrasonic scaler. A Satelec ultrasonic sc...

  3. Cavitation and Bubble Formation in Water Distribution Systems

    OpenAIRE

    Novak, Julia Ann

    2005-01-01

    Gaseous cavitation is examined from a practical and theoretical standpoint. Classical cavitation experiments which disregard dissolved gas are not directly relevant to natural water systems and require a redefined cavitation inception number which considers dissolved gases. In a pressurized water distribution system, classical cavitation is only expected to occur at extreme negative pressure caused by water hammer or at certain valves. Classical theory does not describe some practical phen...

  4. Suitability research on the cavitation model and numerical simulation of the unsteady pulsed cavitation jet flow

    Science.gov (United States)

    Chen, S. Y.; Yu, X. F.; Luan, D. Y.; Qu, Y. P.; Zhou, C.

    2016-05-01

    In order to explore the cavitation jet mechanism, it can first study its critical state of single-phase flow before cavity occurrence to explore the trend of pulsed cavitation jet. Then select the cavitation model to simulate the complex multiphase flow state. Such a step-by-step approach is beneficial to advance research reliably and steady, relying on the foundation for further solving the problem. Three turbulence models such as Euler Hybrid Model, Euler Two Phase Model and Euler Lagrange Model are discussed on their suitability. In this paper, it states only RNG k- ε turbulent model can simulate small scale vortex of jet in the transient simulation. Grid independent verification and the effect of time step is presented. The simulation results show that a large scale vortex ring surrounding jet flow in the nozzle, the pressure of vortex core is slightly lower than the upstream nozzle pressure. Considering the capture ability of small scale eddies, an equivalent pressure is established. The single-phase flow turbulence model is modified to simulate the turbulence flow in the self-excited pulsed cavitation after the cavitation occurs. Through different results comparison of not modified cavitation model and the modified cavitation model to the experimental results, it proves that the latter simulation results are relatively accurate.

  5. Static and Transient Cavitation Threshold Measurements for Mercury

    Energy Technology Data Exchange (ETDEWEB)

    Moraga, F.; Taleyarkhan, R.P.

    1999-11-14

    Transient and static cavitation thresholds for mercury as a function of the cover gas (helium or air), and pressure are reported. Both static and transient cavitation onset pressure thresholds increase linearly with cover gas pressure. Additionally, the cavitation thresholds as a function of dissolved gases were also measured and are reported.

  6. Cavitation erosion in a 400 deg. C sodium flow

    International Nuclear Information System (INIS)

    This paper presents the results of cavitation erosion tests conducted in the Cavitation Tunnel at the Cadarache Nuclear Research Center. The CANASTA system was used for acoustic monitoring of cavitation noise during the experiments. Comparative results are also presented for sodium and water tests. (author)

  7. Real-time two-dimensional imaging of microbubble cavitation

    Science.gov (United States)

    Vignon, Francois; Shi, W. T.; Powers, J. E.; Liu, J.; Drvol, L.; Lof, J.; Everbach, C.; Gao, S.; Xie, F.; Porter, T.

    2012-10-01

    Ultrasound cavitation of microbubble contrast agents has a potential for therapeutic applications, including sonothrombolysis in acute ischemic stroke. For safety, efficacy, and reproducibility of treatment, it is critical to evaluate the cavitation state (e.g. stable versus inertial forms of cavitation) and intensity in and around a treatment area. Acoustic Passive Cavitation Detectors (PCDs) have been used but do not provide spatial information. This paper presents a prototype of a 2D cavitation imager capable of producing images of the dominant cavitation state and intensity in a region of interest at a frame rate of 0.6Hz. The system is based on a modified ultrasound scanner (iE33, Philips) with a sector imaging probe (S5-1). Cavitation imaging is based on the spectral analysis of the acoustic signal radiated by the cavitating microbubbles: ultraharmonics of the excitation frequency indicate stable cavitation, while noise bands indicate inertial cavitation. The system demonstrates the capability to robustly identify stable and inertial cavitation thresholds of Definity microbubbles (Lantheus) in a vessel phantom through 3 ex-vivo human temporal bones, as well as to spatially map cavitation activities.

  8. Modeling of hydrodynamic cavitation reactors: a unified approach

    NARCIS (Netherlands)

    Moholkar, V.S.; Pandit, A.B.

    2001-01-01

    An attempt has been made to present a unified theoretical model for the cavitating flow in a hydrodynamic cavitation reactor using the nonlinear continuum mixture model for two-phase flow as the basis. This model has been used to describe the radial motion of bubble in the cavitating flow in two geo

  9. Prediction of cavitation erosion for marine applications

    Science.gov (United States)

    Maquil, T.; Yakubov, S.; Rung, T.

    2015-12-01

    The paper presents the development of a cavitation erosion prediction method. The approach is tailored to marine applications and embedded into a VoF-based procedure for the simulation of turbulent flows. Supplementary to the frequently employed Euler-Euler models, Euler-Lagrange approaches are employed to simulate cavitation. The study aims to convey the merits of an Euler-Lagrange approach for erosion simulations. Accordingly, the erosion model is able to separate different damage mechanisms, e.g. micro-jets, single and collective bubble collapse, and also quantifies their contribution to the total damage. Emphasis is devoted to the prediction of the cavitation extend, the influence of compressible effects and the performance of the material damage model in practical applications. Examples included refer to 2D validation test cases and reveal a fair predictive accuracy.

  10. Size-effects on cavitation instabilities

    DEFF Research Database (Denmark)

    Niordson, Christian Frithiof; Tvergaard, Viggo

    2005-01-01

    growth is here analyzed for such cases. A finite strain generalization of a higher order strain gradient plasticity theory is applied for a power-law hardening material, and the numerical analyses are carried out for an axisymmetric unit cell containing a spherical void. In the range of high stress......In metal-ceramic systems the constraint on plastic flow leads to so high stress triaxialities that cavitation instabilities may occur. If the void radius is on the order of magnitude of a characteristic length for the metal, the rate of void growth is reduced, and the possibility of unstable cavity...... triaxiality, where cavitation instabilities are predicted by conventional plasticity theory, such instabilities are also found for the nonlocal theory, but the effects of gradient hardening delay the onset of the instability. Furthermore, in some cases the cavitation stress reaches a maximum and then decays...

  11. Analogy between fluid cavitation and fracture mechanics

    Science.gov (United States)

    Hendricks, R. C.; Mullen, R. L.; Braun, M. J.

    1983-01-01

    When the stresses imposed on a fluid are sufficiently large, rupture or cavitation can occur. Such conditions can exist in many two-phase flow applications, such as the choked flows, which can occur in seals and bearings. Nonspherical bubbles with large aspect ratios have been observed in fluids under rapid acceleration and high shear fields. These bubbles are geometrically similar to fracture surface patterns (Griffith crack model) existing in solids. Analogies between crack growth in solid and fluid cavitation are proposed and supported by analysis and observation (photographs). Healing phenomena (void condensation), well accepted in fluid mechanics, have been observed in some polymers and hypothesized in solid mechanics. By drawing on the strengths of the theories of solid mechanics and cavitation, a more complete unified theory can be developed.

  12. Modelling vaporous cavitation on fluid transients

    CERN Document Server

    Shu, Jian-Jun

    2014-01-01

    A comprehensive study of the problem of modelling vaporous cavitation in transmission lines is presented. The two-phase homogeneous equilibrium vaporous cavitation model which has been developed is compared with the conventional column separation model. The latter predicts unrealistically high pressure spikes because of a conflict arising from the prediction of negative cavity sizes if the pressure is not permitted to fall below the vapour pressure, or the prediction of negative absolute pressures if the cavity size remains positive. This is verified by a comparison of predictions with previously published experimental results on upstream, midstream and downstream cavitation. The new model has been extended to include frequency-dependent friction. The characteristics predicted by the frequency-dependent friction model show close correspondence with experimental data.

  13. Paint Test for Centifugal Pump Cavitation

    International Nuclear Information System (INIS)

    The cavitation phenomenon in centrifugal pumps is occurred when the static pressure within the pumps decreases below the boiling pressure of the fluid. This can cause severe damages or failures of the pumps such as the impeller wear or the pump degradation. Many researches to resolve the problem have been performed. Gluich carried out wear prediction based on the Cooper's empirical relation on a cavity length. Grist suggested paint test as a useful tool to measure the cavity length. In the present study, a fluid test system is made, which can create cavitation artificially. A series of visualization tests for cavitation erosion using various paints are made. By comparing the paint test results and the Cooper's correlation, the effectiveness of the paint test for the cavity length estimation is noted

  14. Towards numerical prediction of cavitation erosion.

    Science.gov (United States)

    Fivel, Marc; Franc, Jean-Pierre; Chandra Roy, Samir

    2015-10-01

    This paper is intended to provide a potential basis for a numerical prediction of cavitation erosion damage. The proposed method can be divided into two steps. The first step consists in determining the loading conditions due to cavitation bubble collapses. It is shown that individual pits observed on highly polished metallic samples exposed to cavitation for a relatively small time can be considered as the signature of bubble collapse. By combining pitting tests with an inverse finite-element modelling (FEM) of the material response to a representative impact load, loading conditions can be derived for each individual bubble collapse in terms of stress amplitude (in gigapascals) and radial extent (in micrometres). This step requires characterizing as accurately as possible the properties of the material exposed to cavitation. This characterization should include the effect of strain rate, which is known to be high in cavitation erosion (typically of the order of several thousands s(-1)). Nanoindentation techniques as well as compressive tests at high strain rate using, for example, a split Hopkinson pressure bar test system may be used. The second step consists in developing an FEM approach to simulate the material response to the repetitive impact loads determined in step 1. This includes a detailed analysis of the hardening process (isotropic versus kinematic) in order to properly account for fatigue as well as the development of a suitable model of material damage and failure to account for mass loss. Although the whole method is not yet fully operational, promising results are presented that show that such a numerical method might be, in the long term, an alternative to correlative techniques used so far for cavitation erosion prediction. PMID:26442139

  15. Cavitation Inception in Immersed Jet Shear Flows

    Science.gov (United States)

    Lockett, R. D.; Ndamuso, N.; Price, R.

    2015-12-01

    Cavitation inception occurring in immersed jets was investigated in a purpose-built mechanical flow rig. The rig utilized custom-built cylindrical and conical nozzles to direct high-velocity jets of variable concentration n-octane-hexadecane mixtures into a fused silica optically accessible receiver. The fluid pressure upstream and down-stream of the nozzles were manually controlled. The study employed a variety of acrylic and metal nozzles. The results show that the critical upstream pressure to downstream pressure ratio for incipient cavitation decreases with increasing n-octane concentration for the cylindrical nozzles, and increases with increasing n-octane concentration for the conical nozzle.

  16. CAVITATION BIFURCATION FOR COMPRESSIBLE ANISOTROPIC HYPERELASTIC MATERIALS

    Institute of Scientific and Technical Information of China (English)

    ChengChangjun; RenJiusheng

    2004-01-01

    The effect of material anisotropy on the bifurcation for void tormation in anisotropic compressible hyperelastic materials is examined. Numerical solutions are obtained in an anisotropic sphere, whose material is transversely isotropic in the radial direction. It is shown that the bifurcation may occur either to the right or to the left, depending on the degree of material anisotropy. The deformation and stress contribution in the sphere before cavitation are different from those after cavitation. The stability of solutions is discussed through a comparison of energy.

  17. Effect of cavitation on comminution of mica powder

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    The cavitation abrasive water jet was used in the comminution of mica. By applying a cavitation nozzle in the abrasive water jet system to enhance the effect of cavitation and friction, better comminution results were obtained. The JME-200CX transmission electron microscope was used for observing the size distribution of particles. As using cavitation abrasive water jet, the relative comminution effect is raised by more than 25% compared with using abrasive water jet only. Itcan be concluded that the effect of cavitation is much more significant than that of impacting in the comminution of mica.

  18. Effect of cavitation on comminution of mica powder

    Institute of Scientific and Technical Information of China (English)

    ChuwenGuo; LinshengLiu; 等

    2002-01-01

    The cavitation abrasive water jet was used in the comminution of mica.By applying a cavitation nozzle in the abrasive water jet system to enhance the effect of cavitation and friction,better comminution results were obtained.The JME-200CX transmission electron microscope was used for observing the size distribution of particles.As using cavitation abrasive water jet,the relative comminution effect is raised by more than 25% compared with using abrasive water jet oly.It can be concluded that the effect of cavitation is much more significant than that of impacting in the comminution of mica.

  19. Influence of the empirical coefficients of cavitation model on predicting cavitating flow in the centrifugal pump

    Science.gov (United States)

    Liu, Hou-lin; Wang, Jian; Wang, Yong; Zhang, Hua; Huang, Haoqin

    2014-03-01

    The phenomenon of cavitation is an unsteady flow, which is nearly inevitable in pump. It would degrade the pump performance, produce vibration and noise and even damage the pump. Hence, to improve accuracy of the nu¬merical prediction of the pump cavitation performance is much desirable. In the present work, a homogenous model, the Zwart-Gerber-Belamri cavitation model, is considered to investigate the influence of the empirical coefficients on predicting the pump cavitation performance, concerning a centrifugal pump. Three coefficients are analyzed, namely the nucleation site radius, evaporation and condensation coefficients. Also, the experiments are carried out to validate the numerical simulations. The results indicate that, to get a precise prediction, the approaches of declining the initial bubble radius, the condensation coefficient or increasing the evaporation coefficient are all feasible, especially for de¬clining the condensation coefficient, which is the most effective way.

  20. New insights into the Mechanisms of Cavitation Erosion

    Science.gov (United States)

    Dular, M.; Petkovšek, M.

    2015-12-01

    Recently simultaneous observation of both cavitation structures and cavitation damage, has pointed to the fact that the small scale structures and the topology of the cavitation clouds play a significant role in cavitation erosive potential. Although this opened some new insights to the physics of cavitation damage, many new questions appeared. In the present study we attached a thin aluminium foil to the surface of a transparent Venturi section using two sided transparent adhesive tape. The surface was very soft - prone to be severely damaged by cavitation in a very short period of time. Using high speed cameras, which captured the images at 30000 frames per second, we simultaneously recorded cavitation structures (from several perspectives) and the surface of the foil. Analysis of the images revealed that five distinctive damage mechanisms exist - spherical cavitation cloud collapse, horseshoe cavitation cloud collapse, the “twister” cavitation cloud collapse and in addition it was found that pits also appear at the moment of cavitation cloud separation and near the stagnation point at the closure of the attached cavity.

  1. Prevention of Pressure Oscillations in Modeling a Cavitating Acoustic Fluid

    Directory of Open Access Journals (Sweden)

    B. Klenow

    2010-01-01

    Full Text Available Cavitation effects play an important role in the UNDEX loading of a structure. For far-field UNDEX, the structural loading is affected by the formation of local and bulk cavitation regions, and the pressure pulses resulting from the closure of the cavitation regions. A common approach to numerically modeling cavitation in far-field underwater explosions is Cavitating Acoustic Finite Elements (CAFE and more recently Cavitating Acoustic Spectral Elements (CASE. Treatment of cavitation in this manner causes spurious pressure oscillations which must be treated by a numerical damping scheme. The focus of this paper is to investigate the severity of these oscillations on the structural response and a possible improvement to CAFE, based on the original Boris and Book Flux-Corrected Transport algorithm on structured meshes [6], to limit oscillations without the energy loss associated with the current damping schemes.

  2. Validation of full cavitation model in cryogenic fluids

    Institute of Scientific and Technical Information of China (English)

    CAO XiaoLi; ZHANG XiaoBin; QIU LiMin; GAN ZhiHua

    2009-01-01

    Numerical simulation of cavitation in cryogenic fluids is important in improving the stable operation of he propulsion system in liquid-fuel rocket. It also represents a broader class of problems where the fluid is operating close to its critical point and the thermal effects of cavitation are pronounced. The present article focuses on simulating cryogenic cavitation by implementing the "full cavitation model", coupled with energy equation, in conjunction with iteraUve update of the real fluid properties at local temperatures. Steady state computations are then conducted on hydrofoil and ogive in liquid nitrogen and hydrogen respectively, based on which we explore the mechanism of cavitation with thermal ef-fects. Comprehensive comparisons between the simulation results and experimental data as well as previous computations by other researchers validate the full cavitation model in cryogenic fluids. The sensitivity of cavity length to cavitation number is also examined.

  3. Numerical study of cavitation flows inside a tubular pumping station

    International Nuclear Information System (INIS)

    Based on RNG k−ε turbulence model and the full cavitation model, the cavitation flows inside a low-head tubular-pump model were predicted by using the FLUENT software. For a operating case of given flow rate, cavitation happens near the inlet on the suction surfaces of the impeller blades at the initial cavitating stage, and the cavitating area spreads to the impeller passage and hub as NPSH (net positive suction head) decreases, which will affect energy transformation. For various operating cases of cavitation flows at the given flow rates, the predicted velocity and pressure distributions as well as the vapor volumetric fraction are systematically analyzed. Finally, the cavitation performance curve of the tubular-pump model is obtained by means of the further post-processing. All the comparisons and analysis can be further employed to optimize the hydraulic and structural design of the tubular pump and to guide its safe operation.

  4. FOREWORD: International Symposium of Cavitation and Multiphase Flow (ISCM 2014)

    Science.gov (United States)

    Wu, Yulin

    2015-01-01

    The International Symposium on Cavitation and Multiphase Flow (ISCM 2014) was held in Beijing, China during 18th-21st October, 2014, which was jointly organized by Tsinghua University, Beijing, China and Jiangsu University, Zhenjiang, China. The co-organizer was the State Key Laboratory of Hydroscience and Engineering, Beijing, China. Cavitation and multiphase flow is one of paramount topics of fluid mechanics with many engineering applications covering a broad range of topics, e.g. hydraulic machinery, biomedical engineering, chemical and process industry. In order to improve the performances of engineering facilities (e.g. hydraulic turbines) and to accelerate the development of techniques for medical treatment of serious diseases (e.g. tumors), it is essential to improve our understanding of cavitation and Multiphase Flow. For example, the present development towards the advanced hydrodynamic systems (e.g. space engine, propeller, hydraulic machinery system) often requires that the systems run under cavitating conditions and the risk of cavitation erosion needs to be controlled. The purpose of the ISCM 2014 was to discuss the state-of-the-art cavitation and multiphase flow research and their up-to-date applications, and to foster discussion and exchange of knowledge, and to provide an opportunity for the researchers, engineers and graduate students to report their latest outputs in these fields. Furthermore, the participants were also encouraged to present their work in progress with short lead time and discuss the encountered problems. ISCM 2014 covers all aspects of cavitation and Multiphase Flow, e.g. both fundamental and applied research with a focus on physical insights, numerical modelling and applications in engineering. Some specific topics are: Cavitating and Multiphase Flow in hydroturbines, pumps, propellers etc. Numerical simulation techniques Cavitation and multiphase flow erosion and anti-erosion techniques Measurement techniques for cavitation and

  5. Mechanisms of thrombolysis acceleration by cavitation

    Science.gov (United States)

    Weiss, Hope; Selvaraj, Prashanth; Ahadi, Golnaz; Voie, Arne; Hoelscher, Thilo; Okita, Kohei; Matsumoto, Yoichiro; Szeri, Andrew

    2012-11-01

    Recent studies, in vitro and in vivo, have shown that High Intensity Focused Ultrasound (HIFU) accelerates thrombolysis, the dissolution of blood clots, for ischemic stroke. Although the mechanisms are not fully understood, cavitation is thought to play an important role in sonothrombolysis. The damage to a blood clot's fibrin fiber network from cavitation in a HIFU field is studied using two independent approaches for an embedded bubble. One method is extended to the more important scenario of a bubble outside a blood clot that collapses asymmetrically creating a jet towards the clot. There is significantly more damage potential from a bubble undergoing cavitation collapse outside the clot compared to a rapidly expanding bubble embedded within the clot structure. Also, the effects of the physical properties of skull bone when a HIFU wave propagates through it are examined by use of computer simulation. The dynamics of a test bubble placed at the focus is used in understanding of the pressure field. All other things being equal, the analysis suggests that skull thickness can alter the wave at the focus, which in turn can change the nature of cavitation bubble dynamics and the amount of energy available for clot damage. Now at MSOE.

  6. Cavitation of a Physically Associating Gel

    Science.gov (United States)

    Mishra, Satish; Kundu, Santanu

    Self-assembly of block copolymers in selective solvents form ordered structures such as micelles, vesicles, and physically crosslinked gels due to difference in their interaction with solvents. These gels have wide range of applications in tissue engineering, food science and biomedical field due to their tunable properties and responsiveness with changing environmental conditions. Pressurization of a defect inside a physically associating gel can lead to elastic instability (cavitation) leading to failure of the gel. The failure behavior involves dissociation of physical networks. A thermoreversible, physically associating gel with different volume fractions of a triblock copolymer, poly (methyl methacrylate)-poly (n-butyl acrylate)-poly (methyl methacrylate) [PMMA-PnBA-PMMA] in 2-ethyl 1-hexanol, a midblock selective solvent, is considered here. Mechanical properties were investigated using shear rheology and cavitation experiments. The experimental data is fitted with a constitutive model that captures the stiffening behavior followed by softening behavior of a physical gel. Finite element analysis has been performed on cavitation rheology geometry to capture the failure behavior and to calculate energy release rate during cavitation experiments.

  7. Classification of lubricants according to cavitation criteria

    NARCIS (Netherlands)

    Meged, Y.; Venner, C.H.; Napel, ten W.E

    1995-01-01

    Cavitation in lubrication liquids has long been known to be detrimental to components in hydraulic systems. Damage has been detected in journal bearings, especially under severe dynamic loading, gears, squeeze film dampers and valves. These findings have led to intensive studies of metal resistance

  8. Cavitation and multiphase flow forum - 1987

    International Nuclear Information System (INIS)

    These proceedings collect papers on cavitation phenomena. Topics include: multiphase flow, the two-phase water hammer in a nuclear power plant, phase separation of dispersed annular flow, liquid films, shock waves propagating through two-phase magnetic fluid, venturimeters, gas-particle flows, particle-wall interactions, and the evaluation of wear in centrifugal slurry pumps

  9. Scale effect on unsteady cloud cavitation

    Science.gov (United States)

    Dular, M.; Khlifa, I.; Fuzier, S.; Adama Maiga, M.; Coutier-Delgosha, O.

    2012-11-01

    No experiment was conducted, yet, to investigate the scale effects on the dynamics of developed cavitating flow with periodical cloud shedding. The present study was motivated by the unclear results obtained from the experiments in a Venturi-type section that was scaled down 10 times for the purpose of measurements by ultra-fast X-ray imaging (Coutier-Delgosha et al. 2009). Cavitation in the original size scale section (Stutz and Reboud in Exp Fluids 23:191-198, 1997, Exp Fluids 29:545-552 2000) always displays unsteady cloud separation. However, when the geometry was scaled down, the cavitation became quasi steady although some oscillations still existed. To investigate this phenomenon more in detail, experiments were conducted in six geometrically similar Venturi test sections where either width or height or both were scaled. Various types of instabilities are obtained, from simple oscillations of the sheet cavity length to large vapor cloud shedding when the size of the test section is increased. It confirms that small scale has a significant influence on cavitation. Especially the height of the test section plays a major role in the dynamics of the re-entrant jet that drives the periodical shedding observed at large scale. Results suggest that the sheet cavity becomes stabile when the section is scaled down to a certain point because re-entrant jet cannot fully develop.

  10. Detection of cavitation with directional microphones placed outside piping

    International Nuclear Information System (INIS)

    Highlights: ► The frequency characteristics of cavitation noise were different for each cavitation state. ► RMS ratio of the cavitation noises downstream and upstream from an orifice increased according to development of the cavitation state, and these characteristics became clearer using the directional microphones. ► This method could judge the developed cavitation state which caused erosion. - Abstract: In this paper, to detect cavitation occurrence, we carried out cavitation noise measurements using directional microphones, and evaluated the flow-directional distribution of noises and frequency characteristics. Then we compared the RMS (root mean square) values of the directional microphone outputs obtained upstream and downstream from an orifice, and confirmed that the microphone output RMS ratio upstream and downstream from the orifice changed according to the cavitation states. Microphones had much lower sensitivity than accelerometers, but greater improvement of sensitivity was obtained by directional microphones rather with non-directional microphones. To use the microphone output RMS ratio upstream and downstream from the orifice, measurements are needed at plural locations, but a data base to judge cavitation stages is not required and the ratio could be applied to detect cavitation phenomena in an operating plant.

  11. Sound measurements to detect cavitation phenomena in reactor coolant pumps

    International Nuclear Information System (INIS)

    As the early detection of cavitation phenomena in pumps of coolant circuits by monitoring the hydraulic data of the pumps is not possible, and as an analysis of the sonic signals stimulated at the pump by cavitation is complicated by the interference of the pump-inherent noise spectrum, the analyses are first carried out on a special cavitation pipe section and are then compared with measurement on a pump. For sound sensors a quartz crystal diaphragm pressure sensor and a piezo-ceramic sensor with sound conductor are used. In order to be able to record the cavitation phenomena at the same time visually and by measurement the testing device and the pump consisted of acrylic glass resp. glass. Characteristic power density spectra as a function of the cavitation number of the cavitation charge until void formation are given. (ORU)

  12. URANS COMPUTATION OF CAVITATING FLOWS AROUND SKEWED PROPELLERS

    Institute of Scientific and Technical Information of China (English)

    LIU Yan; ZHAO Peng-fei; WANG Qiang; CHEN Zhao-hui

    2012-01-01

    Cavitating flows around skewed propellers are investigated numerically by means of the unsteady Reynolds Averaged Navier-Stokes (RANS) Equation method.The standard k-ε turbulence and the modified Z-G-B cavitation models are employed.A measured nominal wake is used for the inlet velocity boundary condition.Predicted cavitating evolution processes and tip cavity patterns are compared with experimental observations.In addition,the influence of the skew angles on the cavitation and unsteadiness performances of propellers operating in a non-uniform wake is also studied Results show that the modified Z-G-B cavitation model performs better to simulate the cavitating flow cases studied in this paper.Comparisons demonstrate that the skewed propeller with a skew angle of 20° is the best choice for a given stern wake with a assigned thrust and the minimum force fluctuations.

  13. Negative capillary-pressure-induced cavitation probability in nanochannels

    International Nuclear Information System (INIS)

    The capillarity-induced negative pressure of water flow has been investigated in nanochannels of a rectangular cross section by using computational fluid dynamics (CFD) simulation. As a consequent effect of negative pressure, the cavitation probability has been analyzed numerically. The numerical relation between the critical radius of cavitation (Rc) and geometrical characteristics of channels shows that cavitation does not occur in channels of uniform cross section (UCS), since 2Rc is larger than the smallest dimension of the channel. However, it may occur in channels of non-uniform cross section (NUCS), except for planar or high aspect ratio channels. The inequality in height and width is favorable for the absence of cavitation. The findings can also be applied to channels of elliptical or circular cross section. The results show the influence of geometrical characteristics of channels on the cavitation probability, which is important to engineer the channel geometrical structure in order to avoid undesirable filling problem 'cavitation' during the flow process.

  14. Simulations of Steady Cavitating Flow in a Small Francis Turbine

    Directory of Open Access Journals (Sweden)

    Ahmed Laouari

    2016-01-01

    Full Text Available The turbulent flow through a small horizontal Francis turbine is solved by means of Ansys-CFX at different operating points, with the determination of the hydrodynamic performance and the best efficiency point. The flow structures at different regimes reveal a large flow eddy in the runner and a swirl in the draft tube. The use of the mixture model for the cavity/liquid two-phase flow allowed studying the influence of cavitation on the hydrodynamic performance and revealed cavitation pockets near the trailing edge of the runner and a cavitation vortex rope in the draft tube. By maintaining a constant dimensionless head and a distributor vane opening while gradually increasing the cavitation number, the output power and efficiency reached a critical point and then had begun to stabilize. The cavitation number corresponding to the safety margin of cavitation is also predicted for this hydraulic turbine.

  15. Cavitation erosion behavior of nickel-aluminum bronze weldment

    Institute of Scientific and Technical Information of China (English)

    李小亚; 闫永贵; 许振明; 李建国

    2003-01-01

    Cavitation erosion behavior of nickel-aluminum bronze(NAB)weldment in 3.5% NaCl aqueous solution was studied by magnetostrictive vibratory device for cavitation erosion.The results show that cavitation erosion resistance of the weld zone(WZ)of the weldment is superior to that of the base metal.SEM observation of eroded specimens reveals that the phases undergoing selective attack by the stress of cavitation erosion at the early stage of cavitation erosion are:martensite in the WZ,α phase in the heat-affected zone(HAZ)and eutectoidal phase in the base metal; the microcracks causing cavitation damage initiate at the phase boundaries.

  16. Comminution of Mica by Cavitation Abrasive Water Jet

    Institute of Scientific and Technical Information of China (English)

    GUO Chu-wen; LIU Lin-sheng; HAN Dong-tai; LI Ai-min; ZHANG Dong-hai

    2003-01-01

    The comminution of mica with an abrasive water jet is mainly based on three knids of effects, that is, high-speed collision, cavitating effect and shearing effect. Cavitation abrasive water jet was applied for the comminution of mica because cavitation abrasive water jet can make full use of the three effects mentioned above. Besides high speed impacting among particles,cavitation and shearing were also enhanced due to the divergent angle at the outlet of the cavitation nozzle.A JME-200CX transmission electron microscope was used for observing the size distribution of particles.Variance analysis on the experimental results indicates that the effect of cavitation is much more significant than that of collision.The effect of pressure on comminution results becomes less with the decrease of the particle size.

  17. NUMERICAL INVESTIGATION OF CAVITATION PERFORMANCE OF SHIP PROPELLERS

    Institute of Scientific and Technical Information of China (English)

    ZHU Zhi-feng; FANG Shi-liang

    2012-01-01

    The cavitation performance of propellers is studied based on viscous multiphase flow theories.With a hybrid grid based on Navier-Stokes (N-S) and bubble dynamics equations,some recent validation results are presented in this paper in the predictions of the thrust,the torque and the vapor volume fraction on the back side of propeller blade for a uniform inflow.The numerical predictions of the hydrodynamic performance and the sheet cavitation under several operating conditions for two propellers agree with the corresponding measured data in general.The thrust and the torque are plotted with respect to the advance rate and the cavitation number.The cavitation performance breakdown is closely related to the strong sheet cavitation around propellers.The models with parameters modified are shown to predict the propeller cavitation well.

  18. Enhancement of heat and mass transfer by cavitation

    Science.gov (United States)

    Zhang, Y. N.; Zhang, Y. N.; Du, X. Z.; Xian, H. Z.

    2015-01-01

    In this paper, a brief summary of effects of cavitation on the heat and mass transfer are given. The fundamental studies of cavitation bubbles, including its nonlinearity, rectified heat and mass diffusion, are initially introduced. Then selected topics of cavitation enhanced heat and mass transfer were discussed in details including whales stranding caused by active sonar activity, pool boiling heat transfer, oscillating heat pipe and high intensity focused ultrasound treatment.

  19. A neural-wavelet methodology for pump cavitation detection

    International Nuclear Information System (INIS)

    Cavitation occurs when the local absolute static pressure of a fluid drops below vapor pressure. Bubbles appear and collapse, creating a high pressure pulse where the pressure recovers above the vapor pressure. The collapse manifests itself with noise and vibration, which may also cause serious structural damage. Additionally, the hydraulic effect of pump cavitation makes the pump performance drop below its expected values, producing lower head and flow. Therefore, it is required to develop a non-intrusive, reliable and low cost methodology to detect incipient cavitation before it causes severe consequences. Valve suppression method has been applied to induce cavitation in a pump. This method is usually used to test net point suction head required (NPSHr) of a pump at various flow rates, reducing the suction pressure by throttling the valve on the line of pump suction. Based on the assumption that cavitation influences the pressure fluctuations, a pressure sensor is installed on the downstream of the pump discharge to collect the pressure signal. Cavitation and non-cavitation signals are collected from the pressure sensor. These signals can not be analyzed by conventional spectrum estimation, which is based on the Fourier transform. Instead, the signal features are better represented by subtle changes in the intrinsic fractal structures of the signal caused by cavitation disturbance. Wavelet coefficients are able to pick up the small pressure disturbance caused by cavitation. Also, theoretical analysis further indicates that variance of wavelet coefficients at each scale is a good measure of the disturbance. The feature vectors for each signal formed by calculating wavelet coefficients variance over time at each scale are applied to neural network as training data and testing data. A signal can thus be classified as cavitation or non-cavitation using an adequately trained neural network. The developed algorithm is proven sensitive and accurate for incipient

  20. Numerical Modeling of Unsteady Cavitating Flows around a Stationary Hydrofoil

    OpenAIRE

    Antoine Ducoin; Biao Huang; Yin Lu Young

    2012-01-01

    The objective of this paper is to evaluate the predictive capability of three popular transport equation-based cavitation models for the simulations of partial sheet cavitation and unsteady sheet/cloud cavitating flows around a stationary NACA66 hydrofoil. The 2D calculations are performed by solving the Reynolds-averaged Navier-Stokes equation using the CFD solver CFX with the k-ω SST turbulence model. The local compressibility effect is considered using a local density correction for the tu...

  1. L-Area Cavitation Tests Final Analysis - Limits Application

    International Nuclear Information System (INIS)

    The L-Area cavitation test was designed to better define the onset of cavitation in the reactor system. The onset of gas evolution in the effluent piping and pump cavitation was measured using state-of-the-art equipment to provide data with a high confidence and low uncertainty level. The limits calculated from the new data will allow an approximate two percent increase in reactor power if the reactor is effluent temperature-limited with no compromise in reactor safety

  2. Influence of cavitation on near nozzle exit spray

    OpenAIRE

    Mirshahi, M.; Yan, Y.; Nouri, J. M.

    2015-01-01

    The importance of cavitation inside multi-hole injectors for direct injection internal combustion (IC) engineshas been addressed in many previous investigations. Still, the effect of cavitation on jet spray, its stability and liquid breakup and atomisation is not yet fully understood. The current experimental work aims to address some of these issues. It focuses on the initiation and development of cavitation inside a 7x enlarged transparent model of a symmetric 6-hole spark ignition direct i...

  3. Numerical Calculation on Cavitation Pressure Pulsation in Centrifugal Pump

    OpenAIRE

    Weidong Shi; Chuan Wang; Wei Wang; Bing Pei

    2014-01-01

    In order to study the internal flow in centrifugal pump when cavitation occurs, numerical calculation of the unsteady flow field in the WP7 automobile centrifugal pump is conducted based on the Navier-Stokes equations with the RNG k-ε turbulence model and Zwart-Gerber-Belamri cavitation model. The distributions of bubble volume fraction and pressure pulsation laws in the pump are analyzed when cavitation occurs. The conclusions are as follows: the bubble volume fraction is larger on the sucti...

  4. On Catastrophe and Cavitation for Spherical Cavity

    Institute of Scientific and Technical Information of China (English)

    MingJIN; KefuHUANG; 等

    1999-01-01

    This work deals with catastrophe of a spherical cavity and cavitation of a spherical cavity for Hooke material with 1/2 Poisson's ratio.A nonlinear problem.which is the Cauchy traction problem,is solved analytically.The governing equations are written on the deformed region or on the present configuration.And the conditions are described on moving boundary.A closed form solution is found.Furthermore,a bifurcation solution in closed form is given from the trivial homogeneous solution of a solid sphere.The results indicate that there is a tangent bifurcation on the displacement-load curve for a sphere with a cavity.On the tangent bifurcation point,the cavity grows up suddenly,which is a kind of catastrophe,And there is a pitchfork bifurcation on the displacement-load curve for a solid sphere.On the pitchfork bifurcation point.there is a cavitation in the solid sphere.

  5. Preparation of graphene by jet cavitation

    International Nuclear Information System (INIS)

    Despite its bright prospects, graphene faces challenges including issues concerning mass production. Here we present a totally green approach whereby common crystal graphite can be exfoliated into graphene sheets in aqueous solution by jet cavitation. This is possible mainly because the tensile stress caused by graphite-solution interfacial reflection of compressive waves acts an intensive 'suction disk' on the graphite flakes. We confirm the presence of graphene sheets by diverse characterizations. The graphene yield by our method is estimated as ∼ 4 wt%, which could potentially be improved by further processing. The method, of a mechanical nature, is powerful compared to the traditional low-throughput micromechanical cleavage. Our work here illustrates jet cavitation as a facile, low cost, timesaving and laborsaving route, which can potentially be scaled up to mass production of graphene.

  6. Numerical description of cavitation on axisymmetric bodies

    Energy Technology Data Exchange (ETDEWEB)

    Hickox, C.E.; Hailey, C.E.; Wolfe, W.P.; Watts, H.A.; Gross, R.J.; Ingber, M.S.

    1988-01-01

    This paper reports on ongoing studies which are directed toward the development of predictive techniques for the modeling of steady cavitation on axisymmetric bodies. The primary goal of the modeling effort is the prediction of cavity shape and pressure distribution from which forces and moments can be calculated. Here we present an overview of the modeling techniques developed and compare predictions with experimental data obtained from water tunnel tests for both limited and supercavitation. 14 refs., 4 figs.

  7. Numerical Simulation of Unsteady Turbulent Cavitating Flows

    OpenAIRE

    Tepes, Paul

    2005-01-01

    Computational Fluid Dynamics (CFD) is a very important tool for the study of complex fluid flows and the design of hydraulic fluid flow machinery. At the same time, experimental analysis is very difficult to perform. Thus, for a better understanding of the behaviour of such complex flows, including turbulence, unsteadiness and cavitation, a suitable knowledge of CFD is indispensable. Generally, the specific applications of CFD codes for solving this type of engineering problems...

  8. Impact of acoustic cavitation on food emulsions.

    Science.gov (United States)

    Krasulya, Olga; Bogush, Vladimir; Trishina, Victoria; Potoroko, Irina; Khmelev, Sergey; Sivashanmugam, Palani; Anandan, Sambandam

    2016-05-01

    The work explores the experimental and theoretical aspects of emulsification capability of ultrasound to deliver stable emulsions of sunflower oil in water and meat sausages. In order to determine optimal parameters for direct ultrasonic emulsification of food emulsions, a model was developed based on the stability of emulsion droplets in acoustic cavitation field. The study is further extended to investigate the ultrasound induced changes to the inherent properties of raw materials under the experimental conditions of sono-emulsification. PMID:26603612

  9. Cavitation effects on the confinement/deconfinement transition

    Energy Technology Data Exchange (ETDEWEB)

    Buchel, Alex [Perimeter Institute for Theoretical Physics, Waterloo, Ontario N2J 2W9 (Canada); Department of Applied Mathematics, University of Western Ontario, London, Ontario N6A 5B7 (Canada); Camanho, Xián O. [Department of Particle Physics and IGFAE, University of Santiago de Compostela, E-15782 Santiago de Compostela (Spain); Edelstein, José D. [Department of Particle Physics and IGFAE, University of Santiago de Compostela, E-15782 Santiago de Compostela (Spain); Centro de Estudios Científicos CECs, Av. Arturo Prat 514, Valdivia (Chile)

    2014-06-27

    Cavitation is a process where the viscous terms in a relativistic fluid result in reducing the effective pressure, thus facilitating the nucleation of bubbles of a stable phase. The effect is particularly pronounced in the vicinity of a (weak) first-order phase transition. We use the holographic correspondence to study cavitation in a strongly coupled planar cascading gauge theory plasma close to the confinement/deconfinement phase transition. While in this particular model the shift of the deconfinement temperature due to cavitation does not exceed 5%, we speculate that cavitation might be important near the QCD critical point.

  10. High Speed Imaging of Cavitation around Dental Ultrasonic Scaler Tips.

    Directory of Open Access Journals (Sweden)

    Nina Vyas

    Full Text Available Cavitation occurs around dental ultrasonic scalers, which are used clinically for removing dental biofilm and calculus. However it is not known if this contributes to the cleaning process. Characterisation of the cavitation around ultrasonic scalers will assist in assessing its contribution and in developing new clinical devices for removing biofilm with cavitation. The aim is to use high speed camera imaging to quantify cavitation patterns around an ultrasonic scaler. A Satelec ultrasonic scaler operating at 29 kHz with three different shaped tips has been studied at medium and high operating power using high speed imaging at 15,000, 90,000 and 250,000 frames per second. The tip displacement has been recorded using scanning laser vibrometry. Cavitation occurs at the free end of the tip and increases with power while the area and width of the cavitation cloud varies for different shaped tips. The cavitation starts at the antinodes, with little or no cavitation at the node. High speed image sequences combined with scanning laser vibrometry show individual microbubbles imploding and bubble clouds lifting and moving away from the ultrasonic scaler tip, with larger tip displacement causing more cavitation.

  11. High Speed Imaging of Cavitation around Dental Ultrasonic Scaler Tips.

    Science.gov (United States)

    Vyas, Nina; Pecheva, Emilia; Dehghani, Hamid; Sammons, Rachel L; Wang, Qianxi X; Leppinen, David M; Walmsley, A Damien

    2016-01-01

    Cavitation occurs around dental ultrasonic scalers, which are used clinically for removing dental biofilm and calculus. However it is not known if this contributes to the cleaning process. Characterisation of the cavitation around ultrasonic scalers will assist in assessing its contribution and in developing new clinical devices for removing biofilm with cavitation. The aim is to use high speed camera imaging to quantify cavitation patterns around an ultrasonic scaler. A Satelec ultrasonic scaler operating at 29 kHz with three different shaped tips has been studied at medium and high operating power using high speed imaging at 15,000, 90,000 and 250,000 frames per second. The tip displacement has been recorded using scanning laser vibrometry. Cavitation occurs at the free end of the tip and increases with power while the area and width of the cavitation cloud varies for different shaped tips. The cavitation starts at the antinodes, with little or no cavitation at the node. High speed image sequences combined with scanning laser vibrometry show individual microbubbles imploding and bubble clouds lifting and moving away from the ultrasonic scaler tip, with larger tip displacement causing more cavitation. PMID:26934340

  12. Numerical investigation of cavitation performance on bulb tubular turbine

    Science.gov (United States)

    Sun, L. G.; Guo, P. C.; Zheng, X. B.; Luo, X. Q.

    2016-05-01

    The cavitation flow phenomena may occur in the bulb tubular turbine at some certain operation conditions, which even decrease the performance of units and causes insatiably noise and vibration when it goes worse. A steady cavitating flow numerical simulations study is carried out on the bulb tubular unit with the same blade pitch angle and different guide vane openings by using the commercial code ANSYS CFX in this paper. The phenomena of cavitation induction areas and development process are obtained and draws cavitation performance curves. The numerical results show that the travelling bubble cavity is the main types of cavitation development over a wide operating range of discharge and this type of cavitation begins to sensitive to the value of cavitation number when the discharge exceeding a certain valve, in this condition, it can lead to a severe free bubble formation with the gradually decrement of cavitation number. The reported cavitation performance curves results indicate that the flow blockage incident would happen because of a mount of free bubble formation in the flow passage when the cavity developed to certain extend, which caused head drop behavior and power broken dramatically and influenced the output power.

  13. Numerical simulation on the cavitation of waterjet propulsion pump

    Science.gov (United States)

    Xia, C. Z.; Cheng, L.; Shang, Y. N.; Zhou, J. R.; Yang, F.; Jin, Y.

    2016-05-01

    Waterjet propulsion system is widely used in high speed vessels with advantages of simple transmission mechanism, low noise underwater and good manoeuvrability. Compared with the propeller, waterjet propulsion can be used flow stamping to increasing cavitation resistance at high speed. But under certain conditions, such as low ship speed or high ship speed, cavitation problem still exists. If water-jet propulsion pump is run in cavitation condition for a long time, then the cavitation will cause a great deal of noise CFD is applied to analysis and predict the process of production and development of cavitation in waterjet propulsion pump. Based on the cavitation model of Zwart-Gerber-Belamri and a mixture of homogeneous flow model, commercial CFD software CFX was taken for characteristics of cavitation under the three operating conditions. Commercial software ANSYS 14.0 is used to build entity model, mesh and numerical simulation. The grid independence analysis determine the grid number of mixed flow pump model is about 1.6 million and the grid number of water-jet pump system unit is about 2.7 million. The cavitation characteristics of waterjet pump under three operating conditions are studied. The results show that the cavitation development trend is similar design and small rate of flow condition .Under the design conditions Cavitation bubbles are mainly gathered in suction surface of blade near the inlet side of the hub under the primary stage, and gradually extended to the water side in the direction of the rim with the loss of the inlet total pressure. Cavitation appears in hub before the blade rim, but the maximum value of gas content in blade rim is bigger than that in hub. Under large flow conditions, bubble along the direction of wheel hub extends to the rim gradually. Cavitation is found in the pressure surface of blade near the hub region under the critical point of cavitation nearby. When NPSHa is lower than critical point, the area covering by bubbles

  14. Cavitation effects on the confinement/deconfinement transition

    International Nuclear Information System (INIS)

    Cavitation is a process where the viscous terms in a relativistic fluid result in reducing the effective pressure, thus facilitating the nucleation of bubbles of a stable phase. The effect is particularly pronounced in the vicinity of a (weak) first-order phase transition. We use the holographic correspondence to study cavitation in a strongly coupled planar cascading gauge theory plasma close to the confinement/deconfinement phase transition. While in this particular model the shift of the deconfinement temperature due to cavitation does not exceed 5%, we speculate that cavitation might be important near the QCD critical point

  15. Rayleigh scattering on the cavitation region emerging in liquids

    CERN Document Server

    Shneider, M N

    2015-01-01

    It is shown that the scattering of laser radiation on cavitation ruptures in fluids is similar to the scattering by gas particles. When the characteristic dimensions of microscopic voids and bubbles are considerably smaller than the laser wavelength, the scattered light is in the Rayleigh regime and allows detecting cavitation in the very early stages of its inception. The simple estimates of the scattered radiation intensity and the dynamics of its changes in connection with the generation of cavitation in the test volume are obtained, allowing us to find the critical conditions for the cavitation inception.

  16. AN EXPERIMENTAL AND NUMERICAL PREDICTION OF MARINE PROPELLER NOISE UNDER CAVITATING AND NON-CAVITATING CONDITIONS

    Directory of Open Access Journals (Sweden)

    Mohammad Reza Bagheri

    2015-06-01

    Full Text Available In this study, the hydrodynamics and noise prediction of a five blade marine propeller were analyzed through numerical and experimental methods under variety operational conditions. The hydrodynamics of the propeller was studied and the characteristic curves were presented in both numerical and experimental methods. Inception and development of sheet cavitation conditions are obtained in both numerical and experimental methods. The cavitation was started and developed by either increasing the propeller rotational speed in constant pressure or decreasing pressure, while the velocity was kept constant. Good agreements are observed between numerical and experimental results, qualitatively and quantitatively. The noise of the propeller was analyzed through Computational fluid dynamics (CFD method, based on the formulation of Ffowcs Williams and Hawkings (FW-H. Similarly, the experimental results collected from hydrophones were compared with numerical simulations. Finally, the effects of reflection in cavitation tunnel were obtained by considering overall sound pressure levels in numerical and experimental results.

  17. Dynamics of Isolated Tip Vortex Cavitation

    Science.gov (United States)

    Pennings, Pepijn; Bosschers, Johan; van Terwisga, Tom

    2014-11-01

    Performance of ship propellers and comfort levels in the surroundings are limited by various forms of cavitation. Amongst these forms tip vortex cavitation is one of the first appearing forms and is expected to be mainly responsible for the emission of broadband pressure fluctuations typically occurring between the 4th to the 7th blade passing frequency (approx. 40--70 Hz). These radiated pressure pulses are likely to excite parts of the hull structure resulting in a design compromise between efficiency and comfort. Insight is needed in the mechanism of acoustic emission from the oscillations by a tip vortex cavity. In the current experimental study the tip vortex cavity from a blade with an elliptic planform and sections based on NACA 662 - 415 with meanline a = 0 . 8 is observed using high speed shadowgraphy in combination with blade force and acoustic measurements. An analytic model describing three main cavity deformation modes is verified and used to explain the origin of a cavity eigenfrequency or ``vortex singing'' phenomenon observed by Maines and Arndt (1997) on the tip vortex cavity originating from the same blade. As no hydrodynamic sound originating from the tip vortex cavity was observed it is posed that a tip flow instability is essential for ``vortex singing.'' This research was funded by the Lloyd's Register Foundation as part of the International Institute for Cavitation Research.

  18. Intensely oscillating cavitation bubble in microfluidics

    Science.gov (United States)

    Siew-Wan, Ohl; Tandiono; Klaseboer, Evert; Dave, Ow; Choo, Andre; Claus-Dieter, Ohl

    2015-12-01

    This study reports the technical breakthrough in generating intense ultrasonic cavitation in the confinement of a microfluidics channel [1], and applications that has been developed on this platform for the past few years [2,3,4,5]. Our system consists of circular disc transducers (10-20 mm in diameter), the microfluidics channels on PDMS (polydimethylsiloxane), and a driving circuitry. The cavitation bubbles are created at the gas- water interface due to strong capillary waves which are generated when the system is driven at its natural frequency (around 100 kHz) [1]. These bubbles oscillate and collapse within the channel. The bubbles are useful for sonochemistry and the generation of sonoluminescence [2]. When we add bacteria (Escherichia coli), and yeast cells (Pichia pastoris) into the microfluidics channels, the oscillating and collapsing bubbles stretch and lyse these cells [3]. Furthermore, the system is effective (DNA of the harvested intracellular content remains largely intact), and efficient (yield reaches saturation in less than 1 second). In another application, human red blood cells are added to a microchamber. Cell stretching and rapture are observed when a laser generated cavitation bubble expands and collapses next to the cell [4]. A numerical model of a liquid pocket surrounded by a membrane with surface tension which was placed next to an oscillating bubble was developed using the Boundary Element Method. The simulation results showed that the stretching of the liquid pocket occurs only when the surface tension is within a certain range.

  19. Modeling Unsteady Cavitation Effects and Dynamic Loads in Cryogenic Systems Project

    Data.gov (United States)

    National Aeronautics and Space Administration — There currently are no analytical or CFD tools that can reliably predict unsteady cavitation dynamics in liquid rocket turbopumps. Cavitation effects, particularly...

  20. Radiation induced cavitation: A possible phenomenon in liquid targets?

    Energy Technology Data Exchange (ETDEWEB)

    West, C.D.

    1998-07-01

    The proposed design of a new, short-pulse spallation neutron source includes a liquid mercury target irradiated with a 1 GeV proton beam. This paper explores the possibility that cavitation bubbles may be formed in the mercury and briefly discusses some design features that could avoid harmful effects should cavitation take place.

  1. Rudder gap cavitation: Fundamental understanding and its suppression devices

    International Nuclear Information System (INIS)

    With the increasing size and speed of cargo ships, which results in high speed flow in propeller slipstream, cavitation is frequently observed on and around the rudder system. Among the various types of cavitation on the rudder system, the rudder gap cavitation is the most difficult one to control and suppress. For the development of rudder gap cavitation suppression devices, both experimental and numerical analyses of the physical phenomenon are warranted. In the present study, experiments of the incipient cavitation and pressure measurement were carried out for typical cargo ship rudder sections with and without the suppression devices, which were suggested by the author. The experiments were simulated using computational fluid dynamics tools and the results were compared in terms of the cavitation inception and surface pressure distribution. Fundamental understanding of the rudder gap cavitation inception was obtained along with its relevance to the surface pressure distribution. It is confirmed that the gap flow blocking devices effectively suppress the rudder gap cavitation and, at the same time, augment lift.

  2. FINAL REPORT. CAVITATIONAL HYDROTHERMAL OXIDATION: A NEW REMEDIATION PROCESS

    Science.gov (United States)

    During the past year, we have continued to make substantial scientific progress on our understanding of cavitation phenomena in aqueous media and applications of cavitation to remediation processes. Our efforts have focused on three separate areas: sonoluminescence as a probe of ...

  3. Suppression of Fatigue Crack Propagation of Duralumin by Cavitation Peening

    Directory of Open Access Journals (Sweden)

    Hitoshi Soyama

    2015-08-01

    Full Text Available It was demonstrated in the present paper that cavitation peening which is one of the mechanical surface modification technique can suppress fatigue crack propagation in duralumin. The impacts produced when cavitation bubble collapses can be utilised for the mechanical surface modification technique in the same way as laser peening and shot peening, which is called “cavitation peening”. Cavitation peening employing a cavitating jet in water was used to treat the specimen made of duralumin Japanese Industrial Standards JIS A2017-T3. After introducing a notch, fatigue test was conducted by a load-controlled plate bending fatigue tester, which has been originally developed. The fatigue crack propagation behavior was evaluated and the relationship between the fatigue crack propagation rate versus stress intensity factor range was obtained. From the results, the fatigue crack propagation rate was drastically reduced by cavitation peening and the fatigue life of duralumin plate was extended 4.2 times by cavitation peening. In addition, the fatigue crack propagation can be suppressed by 88% in the stable crack propagation stage by cavitation peening.

  4. Detection of cavitation pits on steel surfaces using SEM imagery

    Science.gov (United States)

    Price, Jeffery R.; Hylton, Kathy W.; Tobin, Kenneth W., Jr.; Bingham, Philip R.; Hunn, John D.; Haines, John R.

    2003-04-01

    We describe an automated image processing approach for detecting and characterizing cavitation pits on stainless steel surfaces. The image sets to be examined have been captured by a scanning electron microscope (SEM). Each surface region is represented by a pair of SEM images, one captured before and one after the cavitation-causing process. Unfortunately, some required surface preparation steps between pre-cavitation and post-cavitation imaging can introduce artifacts and change image characteristics in such a way as to preclude simple image-to-image differencing. Furthermore, all of the images were manually captured and are subject to rotation and translation alignment errors as well as variations in focus and exposure. In the presented work, we first align the pre- and post- cavitation images using a Fourier-domain technique. Since pre-cavitation images can often contain artifacts that are very similar to pitting, we perform multi-scale pit detection on each pre- and post-cavitation image independently. Coincident regions labeled as pits in both pre- and post-cavitation images are discarded. Pit statistics are exported to a text file for further analysis. In this paper we provide background information, algorithmic details, and show some experimental results.

  5. Radiation induced cavitation: A possible phenomenon in liquid targets?

    International Nuclear Information System (INIS)

    The proposed design of a new, short-pulse spallation neutron source includes a liquid mercury target irradiated with a 1 GeV proton beam. This paper explores the possibility that cavitation bubbles may be formed in the mercury and briefly discusses some design features that could avoid harmful effects should cavitation take place

  6. Progress in numerical simulation of cavitating water jets

    Institute of Scientific and Technical Information of China (English)

    PENG Guoyi; SHMIZU Seiji

    2013-01-01

    This paper reviews recent progress made toward modeling of cavitation and numerical simulation of cavitating water jets.Properties of existing cavitation models are discussed and a compressible mixture flow method for the numerical simulation of highspeed water jets accompanied by intensive cavitation is introduced.Two-phase fluids media of cavitating flow are treated as a homogeneous bubbly mixture and the mean flow is computed by solving Reynolds-Averaged Navier-Stokes (RANS) equations for compressible fluid.The intensity of cavitation is evaluated by the gas volume fraction,which is governed by the compressibility of bubble-liquid mixture corresponding to the status of mean flow field.Numerical results of cavitating water jet issuing from an orifice nozzle are presented and its applicability to intensively cavitating jets is demonstrated.However,the effect of impact pressure caused by collapsing of bubbles is neglected,and effectively coupling of the present compressible mixture flow method with the dynamics of bubbles remains to be a challenge.

  7. Modelling collapse aggresiveness of cavitation bubbles in hydromachinery

    Czech Academy of Sciences Publication Activity Database

    Zima, Patrik; Sedlář, M.; Müller, M.

    Ann Arbor: University of Michigan, 2009. s. 21-21. [CAV2009 International Symposium on Cavitation /7./. 16.08.2009-20.08.2009, Ann Arbor] R&D Projects: GA ČR(CZ) GA101/07/1612 Institutional research plan: CEZ:AV0Z20760514 Keywords : cavitation * erosion * pumps Subject RIV: BK - Fluid Dynamics

  8. Analysis on Velocity Characteristics of Cavitation Flow Around Hydrofoil

    Institute of Scientific and Technical Information of China (English)

    LI Xiang-bin; LIU Shu-yan; WANG Guo-yu; ZHANG Bo; ZHANG Min-di

    2010-01-01

    The time-averaged velocity distributions in flows around a hydronautics hydrofoil were measured by using a digit-al particle image velocimeter (DPIV) system. The results show that the velocity distribution in the whole flow field depends on the development of cavitation structures with the decreasing of cavitation number. The high-fluctuation region with lower velocity relates to the cavitation area. The lowest velocity distribution in the cavity core becomes more uniform, and its in-fluence becomes smaller gradually as moving to downstream. The main-stream velocity distribution is even, then fluctuate and even at last. In the supercavitation stage, the fluid velocity in the cavitation region, corresponding to the front of the hydrofoil's suction surface, has a distribution close to the main stream, while the fluid velocity in other cavitation area is lower.

  9. Study of the cavitating instability on a grooved Venturi profile

    CERN Document Server

    Danlos, Amélie; Ravelet, Florent; Coutier-Delgosha, Olivier; Bakir, Farid

    2012-01-01

    Cavitation is a limiting phenomenon in many domains of fluid mechanics. Instabilities of a partial cavity developed on an hydrofoil, a converging-diverging step or in an inter-blade channel in turbomachinery, have already been investigated and described in many previous works. The aim of this study is to evaluate a passive control method of the sheet cavity. According to operating conditions, cavitation can be described by two different regimes: an unstable regime with a cloud cavitation shedding and a stable regime with only a pulsating sheet cavity. Avoiding cloud cavitation can limit structure damages since a pulsating sheet cavity is less agressive. The surface condition of a converging-diverging step, like a Venturi-type obstacle, is here studied as a solution for a passive control of the cavitation. This study discusses the effect of an organized roughness, in the shape of longitudinal grooves, on the developed sheet cavity. Analyzes conducted with Laser Doppler Velocimetry, visualisations and pressure ...

  10. Cavitating flow investigation inside centrifugal impellers for a condensate pump

    International Nuclear Information System (INIS)

    In order to investigate the effect of blade inlet angle on centrifugal pump cavitation performance, numerical simulation of cavitating turbulent flow is conducted for a condensate pump with different impellers based on SST k−ω turbulence model and a mixture cavitation model. The results indicate that for a condensate pump having meridional section with larger area at blade leading edge compared with conventional pumps, the reverse flows inside the blade-to-blade channels are not negligible. It is noted that large incidence at blade leading edge is helpful to improve the cavitation performance for the pump. The possible reason may be the growth of cavities inside the impeller has less influence on the flow in the channel between two neighboring blades. Further, uniform incidence angle along the blade leading edge is preferable for the improvement of cavitation performance.

  11. Theoretical model for cavitation erosion prediction in centrifugal pump impeller

    International Nuclear Information System (INIS)

    Cavitation is known to have great effects on pump hydraulic and mechanical characteristics. These effects are mainly described by deviation in pump performance, increasing vibration and noise level as well as erosion of blade and casing materials. In the present work, only the hydrodynamic aspect of cavitation was considered. The efforts were directed toward the study of cavitation inception, cavity mechanics and material erosion in order to clarify the macrohydrodynamic aspects of cavitation erosive wear in real machines. As a result of this study, it was found that cavitation damage can be predicted from model data. The obtained theoretical results show good agreement with the experimental results obtained in this investigation and with results of some other investigations. The application of the findings of this work will help the design engineer in predicting the erosion rate, according to the different operating conditions. (author)

  12. Cavitation characteristics of pit structure in ultrasonic field

    Institute of Scientific and Technical Information of China (English)

    BAI LiXin; XU WeiLin; ZHANG FaXing; LI NaiWen; ZHANG YiChi; HUANG DeFa

    2009-01-01

    Bubble collecting, bubble holding and micro-bubble ejecting characteristics of pit structure and the influence of cavitation bubble on the development of erosion pit are investigated by means of highspeed photography experiments. Pits tend to collect and hold wandering cavitation bubbles. The air holding phenomenon of pits can be a destination of the incubation period in the process of cavitation erosion. The holding bubble tends to eject micro-bubbles from the top of holding cavitation bubble,making the pit a source of nuclei. With bubbles being held in pits, the diameters of pits increase rapidly.But in the given experiment condition, there is a specific stable value beyond which the diameter of pits will not increase. This characteristic will be helpful in understanding and predicting the cavitation erosion process.

  13. Researches upon cavitation erosion behavior of some duplex steels

    Science.gov (United States)

    Bordeasu, I.; Popoviciu, M. O.; Mitelea, I.; Micu, L. M.; Bordeasu, C.; Ghera, C.; Iosif, A.

    2016-02-01

    This paper presents the cavitation erosion behavior of two stainless steels having a duplex structure formed by austenite and ferrite. The conclusions were obtained by using both the cavitation erosion characteristic curves and the pictures of the eroded surfaces obtained with performing optic microscopes. The researches were focused upon the optimal correlation between the cavitation erosion resistance and the rate of the two structural constituents. The tests were done with T2 facility, with ceramic crystals, which integrally respects the ASTM G32-2010 Standard. The obtained results present the cumulative effect upon cavitation erosion of the chemical composition, mechanical properties and the structural constituents. The results of the researches are of importance for the specialists which establishes the composition of the stainless steels used for manufacturing hydraulic machineries or other devices subjected to cavitation erosion.

  14. A PRESSURE-BASED ALGORITHM FOR CAVITATING FLOW COMPUTATIONS

    Institute of Scientific and Technical Information of China (English)

    ZHANG Ling-xin; ZHAO Wei-guo; SHAO Xue-ming

    2011-01-01

    A pressure-based algorithm for the prediction of cavitating flows is presented. The algorithm employs a set of equations including the Navier-Stokes equations and a cavitation model explaining the phase change between liquid and vapor. A pressure-based method is used to construct the algorithm and the coupling between pressure and velocity is considered. The pressure correction equation is derived from a new continuity equation which employs a source term related to phase change rate instead of the material derivative of density Dp/Dt.Thispressure-based algorithm allows for the computation of steady or unsteady,2-Dor 3-D cavitating flows. Two 2-D cases, flows around a flat-nose cylinder and around a NACA0015 hydrofoil, are simulated respectively, and the periodic cavitation behaviors associated with the re-entrant jets are captured. This algorithm shows good capability of computating time-dependent cavitating flows.

  15. Numerical Simulation of Viscous Cavitating Flow Around A Ship Propeller

    Institute of Scientific and Technical Information of China (English)

    ZHU Zhi-feng; FANG Shi-liang; WANG Xiao-yan; MENG Zhao-wen; LIU Ping-xiang; DU Xuan-min

    2011-01-01

    In the present study,cavitation and a ship propeller wake are reported by computed fluid dynamics based on viscous multiphase flow theory.Some recent validation results with a hybrid grid based on unsteady Navier-Stokes (N-S) and bubble dynamics equations are presented to predict velocity,pressure and vapor volume fraction in propeller wake in a uniform inflow.Numerical predictions of sheet cavitation,tip vortex cavitation and hub vortex cavitation are in agreement with the experimental data,same as numerical predictions of longitudinal and transversal evolution of the axial velocity.Blade and shaft rate frequency of propeller is well predicted by the computed results of pressure,and tip vortex is the most important to generate the pressure field within the near wake.The overall results indicate that the present approach is reliable for prediction of cavitation and propeller wake on the condition of uniform inflow.

  16. Cavitation measurements on a pump-turbine model

    Science.gov (United States)

    Schmidt, H.; Kirschner, O.; Riedelbauch, S.

    2015-12-01

    When a hydraulic turbine is operated at off-design conditions, cavitation on the runner and other machine parts can occur. Vibration, noise and erosion caused by cavitation can damage the turbine and lead to a limitation of the operational range. To avoid damage of the turbine, it is fundamental to get knowledge of the presence of cavitation. In this paper, the acoustic emissions at a pump-turbine model at different operating conditions with and without the presence of cavitation were recorded and analysed. High speed video recordings were carried out simultaneously to validate the acoustic measurements. The main goal of the investigation was to compare the acoustic emissions with the visual observations at operating conditions with cavitation on the leading edge of the turbine runner. The analysis of the recorded signals and the visual observations are in good accordance for the investigated operating points.

  17. Cavitation instability in bulk metallic glasses

    Directory of Open Access Journals (Sweden)

    Dai L.H.

    2015-01-01

    Full Text Available Recent experiments have shown that fracture surfaces of bulk metallic glasses (BMGs usually exhibit an intriguing nanoscale corrugation like fractographic feature mediated by nanoscale void formation. We attribute the onset of this nanoscale corrugation to TTZs (tension transformation zones mediated cavitation. In our recent study, the spall experiments of Zr-based BMG using a single-stage light gas gun were performed. To uncover the mechanisms of the spallation damage nucleation and evolution, the samples were designed to be subjected to dynamic tensile loadings of identical amplitude but with different durations by making use of the multi-stress pulse and the double-flyer techniques. It is clearly revealed that the macroscopic spall fracture in BMGs originates from the nucleation, growth and coalescence of micro-voids. Then, a microvoid nucleation model of BMGs based on free volume theory is proposed, which indicates that the nucleation of microvoids at the early stage of spallation in BMGs is resulted from diffusion and coalescence of free volume. Furthermore, a theoretical model of void growth in BMGs undergoing remote dynamic hydrostatic tension is developed. The critical condition of cavitation instability is obtained. It is found that dynamic void growth in BMGs can be well controlled by a dimensionless inertial number characterizing the competition between intrinsic and extrinsic time scales. To unveil the atomic-level mechanism of cavitation, a systematic molecular dynamics (MD simulation of spallation behaviour of a binary metallic glass with different impact velocities was performed. It is found that micro-void nucleation is determined TTZs while the growth is controlled by shear transformation zones (STZs at atomic scale.

  18. Cavitation instability in bulk metallic glasses

    Science.gov (United States)

    Dai, L. H.; Huang, X.; Ling, Z.

    2015-09-01

    Recent experiments have shown that fracture surfaces of bulk metallic glasses (BMGs) usually exhibit an intriguing nanoscale corrugation like fractographic feature mediated by nanoscale void formation. We attribute the onset of this nanoscale corrugation to TTZs (tension transformation zones) mediated cavitation. In our recent study, the spall experiments of Zr-based BMG using a single-stage light gas gun were performed. To uncover the mechanisms of the spallation damage nucleation and evolution, the samples were designed to be subjected to dynamic tensile loadings of identical amplitude but with different durations by making use of the multi-stress pulse and the double-flyer techniques. It is clearly revealed that the macroscopic spall fracture in BMGs originates from the nucleation, growth and coalescence of micro-voids. Then, a microvoid nucleation model of BMGs based on free volume theory is proposed, which indicates that the nucleation of microvoids at the early stage of spallation in BMGs is resulted from diffusion and coalescence of free volume. Furthermore, a theoretical model of void growth in BMGs undergoing remote dynamic hydrostatic tension is developed. The critical condition of cavitation instability is obtained. It is found that dynamic void growth in BMGs can be well controlled by a dimensionless inertial number characterizing the competition between intrinsic and extrinsic time scales. To unveil the atomic-level mechanism of cavitation, a systematic molecular dynamics (MD) simulation of spallation behaviour of a binary metallic glass with different impact velocities was performed. It is found that micro-void nucleation is determined TTZs while the growth is controlled by shear transformation zones (STZs) at atomic scale.

  19. Cavitation Erosion of Plasma -sprayed Coatings

    International Nuclear Information System (INIS)

    Tungsten Carbide, chromium carbide and chromium oxide coatings were obtained on a 304 stainless steel substrate by plasma spraying technique. The coated samples were exposed to cavitation generated in distilled water by a 20KHz ultrasonic horn. The results of investigation reveal that all the samples tested are significantly eroded even within ten minutes of exposure, indicative of a short incubation period. The eroded surfaces can be characterized as having large pits and flat smooth areas. The latter may be associated with the poor cohesive strength of the coatings, which leads to the failures between individual lamellae

  20. Synovial fluid cavitation during distraction radiography of the coxofemoral joint in dogs

    International Nuclear Information System (INIS)

    Objective - To determine risk factors for, and prevalence and short- and long-term effects of, synovial fluid cavitation during distractionradiography. Design - Multicenter prevalence survey. Animals - 6,649 purebred dogs comprising 129 breeds. Procedure - Radiographs from the PennHiP (University of Pennsylvania Hip Improvement Program) laboratory were subjectively evaluated for evidence of cavitation. Multiple logistic regression was used to determine whether sex, breed, age, weight, distraction index (DI), or examining veterinarian was associated with cavitation. Short-term effects of cavitation were assessed by comparing DI for the hip with cavitation with DI for the contralateral hip in dogs with unilateral cavitation. Long-term effects of cavitation were assessed by comparing DI before and after cavitation was detected, Results - Cavitation was detected in 279 (4.2%) of the radiographs analyzed. Male dogs, Golden Retrievers, and heavier dogs were at a decreased risk for cavitation. Irish Wolfhounds, Irish Setters, Rhodesian Ridgebacks, and Weimaraners had an increased risk for cavitation. Age and Di were not risk factors for cavitation. Mean DI was 0.08 greater in hips with cavitation than in paired hips without cavitation. Significant differences were not detected between DI before and after cavitation, but only I dogs were included in this analysis. Clinical Implications - Cavitation is rare during distraction radiography and can increase measured DI. Radiographs should be routinely examined to ensure accurate reporting of DI

  1. Effect of different design features of the reactor on hydrodynamic cavitation process

    Directory of Open Access Journals (Sweden)

    J. Ozonek

    2011-12-01

    Full Text Available Purpose: The determination of the effect of the change of inducers’ shape and surface on the cavitation process.Design/methodology/approach: Experimental studies of the effect of pressure changes in the function of the construction change of cavitation inducer on the hydrodynamic cavitation process.Findings: Selected effects of the cavitation process were discussed with variable pressures obtained by changing the geometry of cavitation inducer.Research limitations/implications: Analysis of the cavitation process in the function of geometric features of the cavitation inducer.Practical implications: The possibility of controlling the hydrodynamic cavitation process.Originality/value: The assessment of the effect of the cavitation reactor selection on the process or/and the selection of the solution for the specific conditions of the course of the cavitation process.

  2. Cavitation and grain growth during superplastic forming

    Directory of Open Access Journals (Sweden)

    M.J. Tan

    2007-09-01

    Full Text Available Purpose: The purpose of the paper is to study the cavitation and grain growth during superplastic forming.Design/methodology/approach: Superplastic alloys exhibit the extremely large elongation to failure by their high strain rate sensitivity. Cavities have widely been observed during superplastic deformation of metals and alloys and lead to the degradation of material properties such as tensile, creep, fatigue and stress-corrosion behavior. In this work, a finite element method is developed, which considers the grain growth and the effect of material damage.Findings: The effects of material parameters and deformation damage on the superplastic deformation process are numerically analyzed, and the means to control cavitation growth is discussed. The microstructural mechanism of grain growth during superplastic deformation is also studied. A new model considering the grain growth is proposed and applied to conventional superplastic materials The relationships between the strain, the strain rate, the test temperature, the initial grain size and the grain growth respectively in superplastic materials are discussed.Practical implications: The effect of variation of strain rate sensitivity (m value on the strain limit of the superplastic deformation is investigated, and the theoretically calculated values are compared with the experimental results.Originality/value: A new microstructure model based on the microstructural mechanism of superplastic deformation has been proposed. This model has been successfully applied to analyze conventional superplastic materials.

  3. Laser-enhanced cavitation during high intensity focused ultrasound: An in vivo study

    Science.gov (United States)

    Cui, Huizhong; Zhang, Ti; Yang, Xinmai

    2013-04-01

    Laser-enhanced cavitation during high intensity focused ultrasound (HIFU) was studied in vivo using a small animal model. Laser light was employed to illuminate the sample concurrently with HIFU radiation. The resulting cavitation was detected with a passive cavitation detector. The in vivo measurements were made under different combinations of HIFU treatment depths, laser wavelengths, and HIFU durations. The results demonstrated that concurrent light illumination during HIFU has the potential to enhance cavitation effect by reducing cavitation threshold in vivo.

  4. Multiphase flow and cavitation - Comparison of Flow in Rectangular and Circular Nozzle

    OpenAIRE

    Jablonská Jana; Bojko Marian

    2015-01-01

    The paper describes the experimental measurement of cavitation domain at multiphase turbulent flows in rectangular and circular nozzle. The flowing medium is water. Both nozzles were measured at maximum flow range without saturation of circuit by air (without cavitation and with cavitation). Subsequently, the article describes the changes in the sizes of cavitation domain during multiphase flow if the circuit is saturated by the known amount of air. In the article the sizes of cavitation doma...

  5. Characterization of the cavitating flow in converging-diverging nozzle based on experimental investigations

    Directory of Open Access Journals (Sweden)

    Rudolf Pavel

    2014-03-01

    Full Text Available Cavitation phenomena occuring in converging-diverging nozzle (Venturi tube are described in the paper. A closed test circuit with possibility to control both flow rate and static pressure level were used. Loss coefficient was evaluated for different sigma numbers resulting in full „static“ characterization of the nozzle. Visualizations of the cavitation pattern development were acquired and matched with evolution of the loss coefficient. Three cavitation regimes are described: partial cavitation, fully developed cavitation, supercavitation.

  6. Observations of impeller tip cavitation in an axial flow pump

    International Nuclear Information System (INIS)

    As the suction head of an axial-flow pump is reduced its performance is degraded by cavitation phenomena. Cavitation may occur in the inlet region or, in some instances, in the stator blades, however the most usual source is the impeller blading, specifically the tip section. Practical difficulties in cavitation testing and in obtaining data from the vicinity of rotating impeller have reduced the availability of consistent information on cavitation effects. The state of knowledge is such that quite fundamental effects may still be overlooked. Furthermore, even if the suction head is not reduced, cavitation resulting from increased blade loading may jeopardize performance. As the pump is throttled up its characteristic the pressures in the suction peak region may drop below the vapor pressure resulting in strong local cavitation. It is usual in the testing of axial pumps to discriminate between the effects of inlet and discharge throttling by plotting performance characteristics as a function of both of these variables. The purpose of the present investigation is not the systematic study of these variables over the whole range but rather the detailed photographic investigation of cavitation patterns in order to elucidate physical phenomena not previously observed or understood

  7. NUMERICAL PREDICTION OF BLADE FREQUENCY NOISE OF CAVITATING PROPELLER

    Institute of Scientific and Technical Information of China (English)

    YE Jin-ming; XIONG Ying; LI Fang; WANG Zhan-zhi

    2012-01-01

    The blade frequency noise of a cavitating propeller in a uniform flow is analyzed in the time domain.The unsteady loading (of a dipole source) and the sheet cavity volume (of a monopole source) on the propeller surface are calculated by a potential-based surface panel method.Then the time-dependent pressure and the cavity volume data are used as the input for the Fowcs Williams-Hawkings formulation to predict the acoustics pressure.The integration of the noise source is performed over the true blade surface rather than the ideal blade surface without thickness.The noise characteristics of the cavitating propeller are discussed.With the sheet cavitation,the thickness (cavitation) noise is larger than the loading noise and is the dominant noise source.The noise directivity is not as clear as that of the noise under a non-cavitation condition.The cavitation noise is attenuated more slowly than the non-cavitation noise.

  8. Use of hydrodynamic cavitation in (waste)water treatment.

    Science.gov (United States)

    Dular, Matevž; Griessler-Bulc, Tjaša; Gutierrez-Aguirre, Ion; Heath, Ester; Kosjek, Tina; Krivograd Klemenčič, Aleksandra; Oder, Martina; Petkovšek, Martin; Rački, Nejc; Ravnikar, Maja; Šarc, Andrej; Širok, Brane; Zupanc, Mojca; Žitnik, Miha; Kompare, Boris

    2016-03-01

    The use of acoustic cavitation for water and wastewater treatment (cleaning) is a well known procedure. Yet, the use of hydrodynamic cavitation as a sole technique or in combination with other techniques such as ultrasound has only recently been suggested and employed. In the first part of this paper a general overview of techniques that employ hydrodynamic cavitation for cleaning of water and wastewater is presented. In the second part of the paper the focus is on our own most recent work using hydrodynamic cavitation for removal of pharmaceuticals (clofibric acid, ibuprofen, ketoprofen, naproxen, diclofenac, carbamazepine), toxic cyanobacteria (Microcystis aeruginosa), green microalgae (Chlorella vulgaris), bacteria (Legionella pneumophila) and viruses (Rotavirus) from water and wastewater. As will be shown, hydrodynamic cavitation, like acoustic, can manifest itself in many different forms each having its own distinctive properties and mechanisms. This was until now neglected, which eventually led to poor performance of the technique. We will show that a different type of hydrodynamic cavitation (different removal mechanism) is required for successful removal of different pollutants. The path to use hydrodynamic cavitation as a routine water cleaning method is still long, but recent results have already shown great potential for optimisation, which could lead to a low energy tool for water and wastewater cleaning. PMID:26515938

  9. Mechanical heart valve cavitation in patients with bileaflet valves.

    Science.gov (United States)

    Johansen, Peter; Andersen, Tina S; Hasenkam, J Michael; Nygaard, Hans; Paulsen, Peter K

    2014-01-01

    Today, the quality of mechanical heart valves is quite high, and implantation has become a routine clinical procedure with a low operative mortality (valves are thought of having higher cavitation potential than bileaflet valves due to higher closing velocities. However, the thromboembolic potential seems to be the same. Further studies are therefore needed to investigate the cavitation potential of bileaflet valves in vivo. The post processing of HFPF have shown difficulties when applied on bileaflet vavles due to asynchronous closure of the two leaflets. The aim of this study was therefore to isolate the pressure signature from each leaflet closure and perform cavitation analyses on each component. Six patients were included in the study (St. Jude Medical (n=3) and CarboMedics (n=3); all aortic bileaflet mechanical heart valves). HFPFs were recorded intraoperatively through a hydrophone at the aortic root. The pressure signature relating to the first and second leaflet closure was isolated and cavitation parameters were calculated (RMS after 50 kHz highpass filtering and signal energy). Data were averaged over 30 heart cycles. For all patients both the RMS value and signal energy of the second leaflet closure were higher than for the first leaflet closure. This indicates that the second leaflet closure is most prone to cause cavitation. Therefore, quantifying cavitation based on the HFPF related to the second leaflet closure may suggest that the cavitation potential for bileaflet valves in vivo may be higher than previous studies have suggested. PMID:25571278

  10. EXPERIMENTAL INVESTIGATION OF CAVITATION IN A SUDDEN EXPANSION PIPE

    Institute of Scientific and Technical Information of China (English)

    ZHANG Jian-min; YANG Qing; WANG Yu-rong; XU Wei-lin; CHEN Jian-gang

    2011-01-01

    For sudden expansion pipes, experiments were carried out to study the cavitation inception for various enlargement ratios in high speed flows.The flow velocity of the prototype reaches 50 m/s in laboratory.The relationship between the expansion ratio and the incipient cavitation number is obtained.The scale and velocity effects are revealed.It is shown that Keller's revised formula should be modified to calculate the incipient cavitation number when the forecasted velocity of the flows in the prototype exceeds the experimental velocity.

  11. Cryogenic Cavitating Flow in 2D Laval Nozzle

    Institute of Scientific and Technical Information of China (English)

    Naoki Tani; Toshio Nagashima

    2003-01-01

    Cavitation is one of the troublesome problems in rocket turbo pumps, and since most of high-efficiency rocket propellants are cryogenic fluids, so called "thermodynamic effect" becomes more evident than in water. In the present study, numerical and experimental study of liquid nitrogen cavitation in 2D Laval nozzle was carried out,so that the influence of thermodynamic effect was examined. It was revealed that temperature and cavitation have strong inter-relationship with each other in thermo-sensitive cryogenic fluids.

  12. Effects of cavitation on high-pressure atomization

    Science.gov (United States)

    Dabiri Satari, Sadegh

    2009-12-01

    Although disintegration and breakup of a liquid jet emerging from a nozzle has been studied for a long time, the effects of nozzle internal flow and specifically cavitation on the breakup of liquid jets have not been well understood. In the orifice of liquid injectors at high pressure, cavitation occurs behind the sharp corners, where a strong pressure drop is present due to quick change in the flow direction. In addition, a high level of shear stress is present inside the boundary layer. Therefore, it is important to understand the influence of the shear on the cavitation. There are two main questions to be answered: What is the effect of the shear stress on the cavitation inception? And, how does the shear stress influence the cavitation bubble dynamics? In order to answer the above questions, the laminar flow of a liquid through the orifice of an atomizer is studied by means of numerical solution of Navier-Stokes equations. The total-stress criterion for cavitation is applied to find the regions where cavitation is likely to occur and compared with those of the traditional pressure criterion. Results show that the viscous stress has significant effects on cavitation inception. Cavitation bubble dynamics is also affected by the presence of shear strain or normal strain in the flow. Interaction between a single cavitation bubble and strained flow is considered in the next part. As a result of interaction between the shear flow and the bubble, two re-entrant jets are observed on two sides of the bubble during the collapse phase. Re-entrant jets with enough strength could breakup the bubble into smaller bubbles. Finally, four sources of disturbances are proposed that could be responsible for the improvement of atomization due to cavitation. Three of these sources are monopoles, quadrupoles and the vorticity generated during the bubble growth and collapse. It is shown that the monopole sources have the strongest contribution to the disturbances at the orifice exit

  13. Ultrasound-induced inertial cavitation from gas-stabilizing nanoparticles

    Science.gov (United States)

    Kwan, J. J.; Graham, S.; Myers, R.; Carlisle, R.; Stride, E.; Coussios, C. C.

    2015-08-01

    The understanding of cavitation from nanoparticles has been hindered by the inability to control nanobubble size. We present a method to manufacture nanoparticles with a tunable single hemispherical depression (nanocups) of mean diameter 90, 260, or 650 nm entrapping a nanobubble. A modified Rayleigh-Plesset crevice model predicts the inertial cavitation threshold as a function of cavity size and frequency, and is verified experimentally. The ability to tune cavitation nanonuclei and predict their behavior will be useful for applications ranging from cancer therapy to ultrasonic cleaning.

  14. Localization in an acoustic cavitation cloud

    CERN Document Server

    Miao, Boya

    2016-01-01

    Using a nonlinear sound wave equation for a bubbly liquid in conjunction with an equation for bubble pulsation, we predict and experimentally demonstrate the appearance of a gap in the frequency spectrum of a sound wave propagating in a cavitation cloud comprising bubbles. For bubbles with an ambient radius of 100 {\\mu}m, the calculations revealed that this gap corresponds to the phenomenon of sound wave localization. For bubbles with an ambient radius of 120 {\\mu}m, this spectral gap relates to a forbidden band of the sound wave. In the experiment, we observed the predicted gap in the frequency spectrum in soda water; however, in tap water, no spectral gap was present because the bubbles were much smaller than 100 {\\mu}m.

  15. Specific decontamination methods: water nozzle, cavitation erosion

    International Nuclear Information System (INIS)

    The erosion and decontamination tests carried out in the framework of this study, allowed to specify the fields favourable to the use of the high pressure jet taking into account the determinant parameters that are the pressure and the target-nozzle distance. The previous spraying of gels with chemical reagents (sulfuric acid anf hydrazine) allows to get better decontamination factors. Then, the feasibility study of a decontamination method by cavitation erosion is presented. Gelled compounds for decontamination have been developed; their decontamination quality has been evaluated by comparative contamination tests in laboratory and decontamination tests of samples of materials used in nuclear industry; this last method is adapted to remote handling devices and produces a low quantity of secondary effluents, so it allows to clean high contaminated installation on the site without additional exposure of the personnel

  16. Cavitation damage in blood clots under HIFU

    Science.gov (United States)

    Weiss, Hope; Ahadi, Golnaz; Hoelscher, Thilo; Szeri, Andrew

    2010-11-01

    High Intensity Focused Ultrasound (HIFU) has been shown to accelerate thrombolysis, the dissolution of blood clots, in vitro and in vivo, for treatment of ischemic stroke. Cavitation in sonothrombolysis is thought to play an important role, although the mechanisms are not fully understood. The damage to a blood clot associated with bubble collapses in a HIFU field is studied. The region of damage caused by a bubble collapse on the fibrin network of the blood clot exposed to HIFU is estimated, and compared with experimental assessment of the damage. The mechanical damage to the network caused by a bubble is probed using two independent approaches, a strain based method and an energy based method. Immunoflourescent fibrin staining is used to assess the region of damage experimentally.

  17. Design method of water jet pump towards high cavitation performances

    Science.gov (United States)

    Cao, L. L.; Che, B. X.; Hu, L. J.; Wu, D. Z.

    2016-05-01

    As one of the crucial components for power supply, the propulsion system is of great significance to the advance speed, noise performances, stabilities and other associated critical performances of underwater vehicles. Developing towards much higher advance speed, the underwater vehicles make more critical demands on the performances of the propulsion system. Basically, the increased advance speed requires the significantly raised rotation speed of the propulsion system, which would result in the deteriorated cavitation performances and consequently limit the thrust and efficiency of the whole system. Compared with the traditional propeller, the water jet pump offers more favourite cavitation, propulsion efficiency and other associated performances. The present research focuses on the cavitation performances of the waterjet pump blade profile in expectation of enlarging its advantages in high-speed vehicle propulsion. Based on the specifications of a certain underwater vehicle, the design method of the waterjet blade with high cavitation performances was investigated in terms of numerical simulation.

  18. Experimental study of the cavitation erosion in centrifugal pump impeller

    International Nuclear Information System (INIS)

    Research on cavitation damage scale effects show that the damage rate is increased with size and velocity. It seems that for constant velocity there is no clear trend for the variation of erosion with cavitation number. Research on the time effects on damage rate show similarity between cavitation and impingement erosion. The cumulative weight loss versus time curve is of a ''S'' shaped type characterized by an incubation period followed by a period of increasing erosion rate, then a maximum erosion rate, and finally a period of decreasing erosion rate. The objective of this investigation is to present a prototype cavitation erosion experiment in order to clarify the time dependency of the erosive wear

  19. Experimental study on cavitation in centrifugal pump impellers

    International Nuclear Information System (INIS)

    Investigations concerning cavitation in centrifugal impellers were carried out in a closed circuit. The value of net positive suction head (NPSH) at different head drops and at breakdown were used to verify the affinity laws

  20. Cavitation bubbles collapse characteristics behind a convex body

    Institute of Scientific and Technical Information of China (English)

    李瑶; 许唯临; 张亚磊; 张敬威; 陈春祺; 阿蓉

    2013-01-01

    Cavitation bubbles behind a convex body were experimentally studied by a high speed camera and a hydrophone synch- ronously. The experiments were conducted in a circulating water tunnel with five various contraction ratios:b=0.497,b=0.6,b=0.697,b=0.751, andb=0.799. The distributions of the cavitation bubble collapse positions behind the five different convex bodies were obtained by combining the images taken by the high speed camera. According to the collapse positions, it was found that no cavitation bubble was collapsed in the region near the wall until the ratio of the water head loss over the convex body height was larger than 20, which can be used to predict if the cavitation damage would occur in the tunnel with orifice energy dissipaters.

  1. Influence of cavitation on near nozzle exit spray

    Science.gov (United States)

    Mirshahi, M.; Yan, Y.; Nouri, J. M.

    2015-12-01

    The importance of cavitation inside multi-hole injectors for direct injection internal combustion (IC) engineshas been addressed in many previous investigations. Still, the effect of cavitation on jet spray, its stability and liquid breakup and atomisation is not yet fully understood. The current experimental work aims to address some of these issues. It focuses on the initiation and development of cavitation inside a 7× enlarged transparent model of a symmetric 6-hole spark ignition direct injection (SIDI) injector and quantifies the effect of cavitation on near-nozzle spray cone angle and stability utilising high speed Mie scattering visualisation. The regions studied include the full length of the nozzle and its exitjet spray wherethe primary breakup takes place.

  2. Cavitation Performance of a Centrifugal Pump with Water and Mercury

    Science.gov (United States)

    Hammitt, F. G.; Barton, R. K.; Cramer, V. F.; Robinson, M. J.

    1961-01-01

    The cavitation performance of a given centrifugal pump with water (hot and cold) and mercury is compared. It is found that there are significant scale effects with all fluids tested, with the Thoma cavitation parameter decreasing in all cases for increased pump speed or fluid Reynolds' number. The data for a fixed flow coefficient fall into a single curve when plotted against pump speed (or fluid velocity), rather than against Reynolds' number. Conversely, the Thoma parameter for a given Reynolds' number is approximately twice as large for mercury as for water. The direction of this variation is as predicted from consideration of the cavitation thermodynamic parameters which vary by a factor of 10(exp 7) between these fluids. No difference in cavitation performance between hot and cold water (approximately 160 F and 80 F) was observed, However, the thermodynamic parameters vary only by a factor of 5.

  3. Optimization of centrifugal pump cavitation performance based on CFD

    Science.gov (United States)

    Xie, S. F.; Wang, Y.; Liu, Z. C.; Zhu, Z. T.; Ning, C.; Zhao, L. F.

    2015-01-01

    In order to further improve the cavitation performance of a centrifugal pump, slots on impeller blade near inlet were studied and six groups of hydraulic model were designed. Base on cavitating flow feature inside a centrifugal pump, bubble growth and implosion are calculated from the Rayleigh-Plesset equation which describes the dynamic behavior of spherical bubble and RNG κ-epsilon model was employed to simulate and analyze the internal two-phase flow of the model pump under the same conditions. The simulation results show that slots on blade near inlet could improve the cavitation performance and cavitation performance improvement of the second group was more obvious. Under the same conditions, the pressure on the back of blade near inlet was higher than the pressure on the back of unmodified blade near inlet, and energy distribution in the flow channel between the two blades was more uniform with a small change of head.

  4. Hign-speed penetration of projectile with cavitator into sand

    Science.gov (United States)

    Daurskikh, Anna; Veldanov, Vladislav

    2011-06-01

    Cavitators are used in underwater projectiles design to form a cavern in which projectile could move with no or significantly reduced drag. An investigation of possible application of this structural element for penetration into porous media was conducted. High-speed impact of a conical-shaped head projectile with cavitator was studied in terms of its influence on penetration capacity and projectile stability in sand for impact velocity about 1500 m/s. Cavitators were manufactured of steel with different strength moduli, and thus two penetration regimes (with eroding/non-eroding cavitator) were compared. Numerical simulations showing wave propagation in target and projectile were performed in AUTODYN with Johnson-Cook model for projectile and granular model for sand.

  5. DISCOVERY AND ANALYSIS ON CAVITATION IN PIEZOELECTRIC PUMPS

    Institute of Scientific and Technical Information of China (English)

    Zhang Jianhui; Xia Qixiao; Lai Dehua; Onuki Akiyoshi; Hong Zhen

    2004-01-01

    The contributing factors for the cavitation in piezoelectric pumps are analyzed,theoretically, and the device fitting for observing and recording is set up. With it the experiments are carried out to observe the emergence and the flowing of the cavitations in the piezoelectric pumps. According to the statistic and the analysis to the data of the experiments, the peculiar features are discovered. These features are composed of balls-amassing, center-more, and flow-out.

  6. Simulations of Steady Cavitating Flow in a Small Francis Turbine

    OpenAIRE

    Laouari, Ahmed; Ghenaiet, Adel

    2016-01-01

    The turbulent flow through a small horizontal Francis turbine is solved by means of Ansys-CFX at different operating points, with the determination of the hydrodynamic performance and the best efficiency point. The flow structures at different regimes reveal a large flow eddy in the runner and a swirl in the draft tube. The use of the mixture model for the cavity/liquid two-phase flow allowed studying the influence of cavitation on the hydrodynamic performance and revealed cavitation pockets ...

  7. BIODIESEL PRODUCTION FROM WASTE COOKING OIL USING HYDRODINAMIC CAVITATION

    OpenAIRE

    Muhammad Dani Supardan; Satriana; Mahlinda

    2012-01-01

    The aim of this research was to study biodiesel production from low cost feedstock of waste cooking oil (WCO) using hydrodynamic cavitation apparatus. A two-step processes esterification process and transesterification process using hydrodynamic cavitation for the production of biodiesel from WCO is presented. The first step is acid-catalyzed esteri-fication process for reducing free fatty acid (FFA) content of WCO and followed by base-catalyzed transesterification process for converting WCO ...

  8. Modelling on cavitation in a diffuser with vortex generator

    Directory of Open Access Journals (Sweden)

    Jablonská J.

    2013-04-01

    Full Text Available Based on cavitation modelling in Laval nozzle results and experience, problem with the diffuser with vortex generator was defined. The problem describes unsteady multiphase flow of water. Different cavitation models were used when modelling in Fluent, flow condition is inlet and pressure condition is outlet. Boundary conditions were specified by Energy Institute, Victor Kaplan’s Department of Fluid Engineering, Faculty of Mechanical Engineering, Brno University of Technology. Numerical modelling is compared with experiment.

  9. CFD Analysis of Cavitation Erosion Potential in Hydraulic Machinery

    Czech Academy of Sciences Publication Activity Database

    Sedlář, M.; Zima, Patrik; Müller, M.

    Brno : University of Technology, 2009 - (Rudolf, P.), s. 205-214 ISBN 978-80-214-3947-4. [IAHR International Meeting of the Workgroup on Cavitation and Dynamic Problems in Hydraulic Machinery and Systems /3./. Brno (CZ), 14.10.2009-16.10.2009] R&D Projects: GA ČR(CZ) GA101/07/1612 Institutional research plan: CEZ:AV0Z20760514 Keywords : cavitation erosion * bubble dynamics * CFD analysis Subject RIV: BK - Fluid Dynamics

  10. Modeling of Unsteady Sheet Cavitation on Marine Propeller Blades

    OpenAIRE

    Spyros A. Kinnas; HanSeong Lee; Yin L. Young

    2003-01-01

    Unsteady sheet cavitation is very common on marine propulsor blades. The authors summarize a lifting-surface and a surface-panel model to solve for the unsteady cavitating flow around a propeller that is subject to nonaxisymmetric inflow. The time-dependent extent and thickness of the cavity were determined by using an iterative method. The cavity detachment was determined by applying the smooth detachment criterion in an iterative manner. A nonzeroradius developed vortex cavity model was uti...

  11. Research on the characteristics of quasi-steady cavitation in a centrifugal pump

    Science.gov (United States)

    Lu, J. X.; Yuan, S. Q.; Li, X. J.; Si, Q. R.; Luo, Y.

    2015-01-01

    With the pressure decreasing, the process of cavitation in a centrifugal pump could be summarized as incipient cavitation, quasi-steady cavitation and unsteady cavitation. Quasi-steady cavitation is the condition that is between the incipient cavitation and unsteady cavitation in a centrifugal pump. Under this condition, the intensity of cavitation is relatively weak, and the head of the pump almost remains unchanged, but the cavitation exists, causing damage to the impeller by pitting and erosion. So it is important to investigate the quasi-steady cavitation. In this paper, both the numerical and experimental methods had been carried out to investigate the characteristics of quasi-steady cavitation. The internal flow in the pump, the performance of cavitation and the inlet and outlet pressure pulsation of the pump measured through experimental method have been studied under different NPSHa conditions. It was found that the head decreases about 0.77%-1.38% from non-cavitation condition and it could be regarded as the quasi-steady cavitation. Little change has been found from the internal flow between non-cavitation condition and quasi-steady cavitation condition. The period of inlet pressure pulsation changes from the time that the blade passes by to the period of shaft rotating with the development of cavitation. The dominant frequency of the inlet pressure pulsation is two times of shaft frequency whose amplitudes decrease firstly and then increase to a peak value, followed by a decrease to a low value in quasi-steady cavitation conditions. The dominant frequency of the outlet pressure pulsation is blade passing frequency whose amplitudes increase firstly and then decrease gradually with the decrease of NPSHa.

  12. Cavitation erosion resistance of microarc oxidation coating on aluminium alloy

    Energy Technology Data Exchange (ETDEWEB)

    Cheng, Feng [School of Mechanical Engineering, Southeast University, Nanjing, 211189 (China); Jiang, Shuyun, E-mail: jiangshy@seu.edu.cn [School of Mechanical Engineering, Southeast University, Nanjing, 211189 (China); Liang, Jun [State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou, 730000 (China)

    2013-09-01

    Two ceramic coatings are prepared on 2124 aluminum alloy by microarc oxidation (MAO) technology. To explore the cavitation erosion resistance of the MAO coating, cavitation tests were performed by using a rotating-disk test rig. The mass losses, surface morphologies, chemical compositions and the phase constituents of the samples after cavitation tests were examined by using digital balance, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD), respectively. The results indicate that the MAO coatings can extend the incubation period of aluminum alloy, and thus enhance the cavitation erosion resistance as compared to the untreated aluminum alloy samples. After duration of 63 h cavitation test, a lot of erosion pits and the particles in various shapes can be observed on the surfaces of the aluminum alloy samples, while only a few erosion pits are observed on the MAO coatings. Moreover, the mean depths of erosion on the MAO coatings are lower in the first 30 h and are independent on erosion time. The results show that the cavitation erosion of MAO coating is governed by water mechanical impaction, resulting from the effects of brittle fracture of the MAO coating.

  13. Numerical investigation of cavitation flow in journal bearing geometry

    Science.gov (United States)

    Riedel, M.; Schmidt, M.; Stücke, P.

    2013-04-01

    The appearance of cavitation is still a problem in technical and industrial applications. Especially in automotive internal combustion engines, hydrodynamic journal bearings are used due to their favourable wearing quality and operating characteristics. Cavitation flows inside the bearings reduces the load capacity and leads to a risk of material damages. Therefore an understanding of the complex flow phenomena inside the bearing is necessary for the design development of hydrodynamic journal bearings. Experimental investigations in the fluid domain of the journal bearing are difficult to realize founded by the small dimensions of the bearing. In the recent years more and more the advantages of the computational fluid dynamics (CFD) are used to investigate the detail of the cavitation flows. The analysis in the paper is carried out in a two-step approach. At first an experimental investigation of journal bearing including cavitation is selected from the literature. The complex numerical model validated with the experimental measured data. In a second step, typically design parameters, such as a groove and feed hole, which are necessary to distribute the oil supply across the gap were added into the model. The paper reflects on the influence of the used design parameters and the variation of the additional supply flow rate through the feed hole regarding to cavitation effects in the bearing. Detailed pictures of the three-dimensional flow structures and the cavitation regions inside the flow film of the bearing are presented.

  14. Multi-resolution analysis of passive cavitation detector signals

    International Nuclear Information System (INIS)

    Passive cavitation detectors are widely used for measuring acoustic emissions from cavitating bubbles. Acoustic emissions related to the dynamics of oscillating bubbles contain complex time and frequency domain information. Signal processing techniques traditionally used to analyse transient and stationary signals may be of limited value when analysing such acoustic emissions. This paper describes a multi-resolution approach developed for processing acoustic emissions data. The technique consists of the combination of a discrete wavelet transform and of the statistical and spectral analysis to extract cavitation features. These features include broadband emissions and harmonic, sub-harmonic and ultra-harmonic information. The implementation of the technique on experimental datasets demonstrates that this approach provides detailed information about key features of the acoustic signal, especially in complex situations where different types of cavitation occur simultaneously. Furthermore, statistical metrics used in this technique can provide a quantitative means for classifying signatures of cavitation, particularly the broadband segment of the spectrum created by inertial cavitation, which constitutes novel work

  15. Promotion of Cultural Heritage in Batangas and Cavite

    Directory of Open Access Journals (Sweden)

    Dr. Dexter R. Buted

    2014-06-01

    Full Text Available – The study aimed to identify the commonly visited cultural heritage sites in Batangas and Cavite; to assess the cultural heritage sites in Batangas and Cavite in terms of physical, social and economic aspects; and to determine existing promotional patterns of Batangas and Cavite. Descriptive type of research was utilized in the study. Results showed that the most visited cultural heritage attraction in Taal, Batangas was Basilica of St. Martin de Tours while in Maragondon, Cavite the most visited was Andres Bonifacio Trial House . Blogs, Websites and Facebook are mostly used by the municipality of Taal in promoting their cultural heritage sites. While Cavite sticks to always using leaflets/flyers, brochures as their promotional materials. Cultural heritage sites in both Taal and Maragondon were perceived to have positive results in the assessments based on different aspects such as physical, social and economic aspects. The promotional materials of Taal and Maragondon are often used. A proposed plan of action was made to promote cultural attraction in Maragondon, Cavite and Taal, Batangas.

  16. CAVITATION CONTROL BY AERATION AND ITS COMPRESSIBLE CHARACTERISTICS

    Institute of Scientific and Technical Information of China (English)

    DONG Zhi-yong; SU Pei-lan

    2006-01-01

    This paper presents an experimental investigation and a theoretical analysis of cavitation control by aeration and its compressible characteristics at the flow velocity V=20m/s-50m/s. Pressure waveforms with and without aeration in cavitation region were measured. The variation of compression ratio with air concentration was described, and the relation between the least air concentration to prevent cavitation erosion and flow velocity proposed based on our experimental study. The experimental results show that aeration remarkably increases the pressure in cavitation region, and the corresponding pressure wave exhibits a compression wave/shock wave. The pressure increase in cavitation region of high-velocity flow with aeration is due to the fact that the compression waves/shock wave after the flow is aerated. The compression ratio increases with air concentration rising. The relation between flow velocity and least air concentration to prevent cavitation erosion follows a semi-cubical parabola. Also, the speed of sound and Mach number of high-velocity aerated flow were analyzed.

  17. Numerical investigation of cavitation flow in journal bearing geometry

    Directory of Open Access Journals (Sweden)

    Stücke P.

    2013-04-01

    Full Text Available The appearance of cavitation is still a problem in technical and industrial applications. Especially in automotive internal combustion engines, hydrodynamic journal bearings are used due to their favourable wearing quality and operating characteristics. Cavitation flows inside the bearings reduces the load capacity and leads to a risk of material damages. Therefore an understanding of the complex flow phenomena inside the bearing is necessary for the design development of hydrodynamic journal bearings. Experimental investigations in the fluid domain of the journal bearing are difficult to realize founded by the small dimensions of the bearing. In the recent years more and more the advantages of the computational fluid dynamics (CFD are used to investigate the detail of the cavitation flows. The analysis in the paper is carried out in a two-step approach. At first an experimental investigation of journal bearing including cavitation is selected from the literature. The complex numerical model validated with the experimental measured data. In a second step, typically design parameters, such as a groove and feed hole, which are necessary to distribute the oil supply across the gap were added into the model. The paper reflects on the influence of the used design parameters and the variation of the additional supply flow rate through the feed hole regarding to cavitation effects in the bearing. Detailed pictures of the three-dimensional flow structures and the cavitation regions inside the flow film of the bearing are presented.

  18. Experience with control valve cavitation problems and their solutions

    International Nuclear Information System (INIS)

    Pressure reduction in control valves can induce cavitation, which has three effects on the control valve. Firstly, it modifies or changes the hydraulic performance of the control valve. Since control valves are designed for noncavitating conditions, the result is usually reduced stability of the control valve or, in extreme cavitating conditions known as supercavitation, the valve may limit the flow rate and thus be undersized. Secondly, cavitation can cause material damage to valve parts, trim, or valve body, or erodes downstream piping; consequently, the valve or piping leaks. Thirdly, cavitation causes noise and vibration, which may cause major damage or destruction to equipment such as valve positioners, actuators, pipe supports and sometimes to other downstream valves. The purpose of this paper is twofold: (1) It describes the I.S.A. valve sizing equations and how they relate to cavitation. (2) It describes experiences with these three problems, and discusses corrective actions and practical approaches to their solution. This paper discusses thirteen cavitation experiences

  19. Researches upon the cavitation erosion behaviour of austenite steels

    Science.gov (United States)

    Bordeasu, I.; Popoviciu, M. O.; Mitelea, I.; Salcianu, L. C.; Bordeasu, D.; Duma, S. T.; Iosif, A.

    2016-02-01

    Paper analyzes the cavitation erosion behavior of two stainless steels with 100% austenitic structure but differing by the chemical composition and the values of mechanical properties. The research is based on the MDE(t) and MDER(t) characteristic curves. We studied supplementary the aspect of the eroded areas by other to different means: observations with performing optical microscopes and roughness measurements. The tests were done in the T2 vibratory facility in the Cavitation Laboratory of the Timisoara Polytechnic University. The principal purpose of the study is the identification of the elements influencing significantly the cavitation erosion resistance. It was established the effect of the principal chemical components (determining the proportion of the structural components in conformity the Schaffler diagram) upon the cavitation erosion resistance. The results of the researches present the influence of the proportion of unstable austenite upon cavitation erosion resistance. The stainless steel with the great proportion of unstable austenite has the best behavior. The obtained conclusion are important for the metallurgists which realizes the stainless steels used for manufacturing the runners of hydraulic machineries (turbines and pumps) with increased resistance to cavitation attack.

  20. Application of computational fluid dynamics on cavitation in journal bearings

    Directory of Open Access Journals (Sweden)

    Riedel Marco

    2014-03-01

    Full Text Available Journal bearings are applied in internal combustion engines due to their favourable wearing quality and operating characteristics. Under certain operating conditions damage of the journal bearing can occur caused by cavitation. The cavitation reduces the load capacity and leads to material erosion. Experimental investigations of cavitating flows in dimension of real journal bearing are difficult to realize or almost impossible caused by the small gap and transient flow conditions. Therefore numerical simulation is a very helpful engineering tool to research the cavitation behaviour. The CFD-Code OpenFOAM is used to analyse the flow field inside the bearing. The numerical cavitation model based on a bubble dynamic approach and requires necessary initial parameter for the calculation, such as nuclei bubble diameter, the number of nuclei and two empirical constants. The first part of this paper shows the influence of these parameters on the solution. For the adjustment of the parameters an experiment of Jakobsson et.al. [1] was used to validate the numerical flow model. The parameters have been varied according to the method Design of Experiments (DoE. With a defined model equation the parameters determined, to identify the parameter for CFD-calculations in comparison to the experimental values. The second part of the paper presents investigations on different geometrical changes in the bearing geometry. The effect of these geometrical changes on cavitation was compared with experimental results from Wollfarth [2] and Garner et.al. [3].

  1. Controlling the cavitation phenomenon of evolution on a butterfly valve

    International Nuclear Information System (INIS)

    Development of the phenomenon of cavitation in cavitation behavior requires knowledge of both plant and equipment working in the facility. This paper presents a diagram of cavitational behavior for a butterfly valve with a diameter of 100 mm at various openings, which was experimentally built. We proposed seven stages of evolution of the phenomenon of cavitation in the case of a butterfly valve. All these phases are characterized by pressure drop, noise and vibration at various flow rates and flow sections through the valve. The level of noise and vibration for the seven stages of development of the phenomenon of cavitation were measured simultaneously. The experimental measurements were comprised in a knowledge database used in training of a neural network of a neural flow controller that maintains flow rate constantly in the facility by changing the opening butterfly valve. A fuzzy position controller is used to access the valve open. This is the method proposed to provide operational supervision outside the cavitation for a butterfly valve.

  2. A piezoelectric polymer cavitation sensor installed in an emulsion generation microchannel device and an evaluation of cavitation state

    Science.gov (United States)

    Kanda, Takefumi; Yabumoto, Masaki; Suzumori, Koichi

    2016-07-01

    In previous works, ultrasonic emulsification was realized using small microchannel devices oscillated by piezoelectric transducers. By using the devices, the emulsification in the flow process was also realized. In these devices, the driving frequency was higher than 2 MHz. This value is higher than the maximum audible field. On the other hand, the frequency is too high to utilize the cavitation effect. This is because the cavitation threshold depends on the frequency. The aim of this study is to confirm the cavitation state in the microchannel device using a piezoelectric polymer sensor. A micropatterned cavitation detection sensor has been fabricated by a photolithography technique and evaluated in a high-intensity ultrasound field. The emulsification state in the microchannel device has been evaluated using the fabricated sensor.

  3. Predicting the Inception Cavitation of a Reversible Pump- Turbine in Pump Mode

    Science.gov (United States)

    Tao, Ran; Xiao, Ruofu; Zhu, Di; Liu, Weichao

    2015-12-01

    Inception cavitation is a crucial indicator for reversible pump-turbines especially in pump mode. In actual applications, it is difficult to use CFD for the inception cavitation character. In this study, CFD simulation is conducted to find a proper way to evaluate the inception cavitation, different levels of vapor volume fraction in the impeller is predicted based on the tested results. Results show that the prediction of the location and scale of cavitation is accurate. The predicted cavitation number also matches the experimental data well. The vapor volume fraction levels from 0.0001% to 0.001% are recommended as the criterion of inception cavitation.

  4. Evaluation of Turbulence Models Performance in Predicting Incipient Cavitation in an Enlarged Step-Nozzle

    Science.gov (United States)

    Naseri, H.; Koukouvinis, P.; Gavaises, M.

    2015-12-01

    Predictive capability of RANS and LES models to calculate incipient cavitation of water in a step nozzle is assessed. The RANS models namely, Realizable k-ε, SST k-ω and Reynolds Stress Model did not predict any cavitation, due to the limitation of RANS models to predict the low pressure vortex cores. LES WALE model was able to predict the cavitation by capturing the shear layer instability and vortex shedding. The performance of a barotropic cavitation model and Rayleigh-Plesset-based cavitation models was compared using WALE model. Although the phase change formulation is different in these models, the predicted cavitation and flow field were not significantly different.

  5. Specialists' meeting on cavitation criteria for designing mechanisms working in sodium: Application to pumps. Summary report

    International Nuclear Information System (INIS)

    The purpose of the meeting was to provide a forum for discussions and exchanges of views on cavitation phenomena in sodium, cavitation tests on pump models in water and sodium, application of test results to LMFBR plants, impact on sodium pump design. Topics of interest were also detection methods for cavitation during tests and cavitation problems in electro-magnetic pumps. Two categories of papers were presented: national position papers and specialised topical papers. The main topics discussed, in three sessions were the following: National papers on cavitation; cavitation tests, performance, measuring methods and results; application of test results and implications on the future programmes

  6. Method to calculate characteristics of cavitating propeller; Cavitation wo okoshiteiru propeller no ichiseino keisanho

    Energy Technology Data Exchange (ETDEWEB)

    Maita, S.; Nakashima, A.; Ando, J.; Nakatake, K. [Kyushu University, Fukuoka (Japan)

    1998-09-04

    Based on a simple surface panel method named SQCM, we develop a method to calculate nonlinear cavity on 2-D wing by introducing the four kinds of cavity models, i.e. closed model, semi-closed model, open model and supercavitating model. This method gives pressure distribution, lift and drag of the wing. Then, by combining the QCM program, the concept of the equivalent 2-D wing and the present cavity calculation method, we obtain the characteristics of two cavitating propellers. Comparisons between calculated results and experimental ones confirm the usefulness of our method. 11 refs., 15 figs., 1 tab.

  7. On thermonuclear processes in cavitation bubbles

    International Nuclear Information System (INIS)

    The theoretical and experimental foundations of so-called bubble nuclear fusion are reviewed. In the nuclear fusion process, a spherical cavitation cluster ∼10−2 m in diameter is produced of spherical bubbles at the center of a cylindrical chamber filled with deuterated acetone using a focused acoustic field having a resonant frequency of about 20 kHz. The acoustically-forced bubbles effectuate volume oscillations with sharp collapses during the compression stage. At the final stages of collapse, the bubble cluster emits 2.5 MeV D-D fusion neutron pulses at a rate of ∼2000 per second. The neutron yield is ∼105 s−1. In parallel, tritium nuclei are produced at the same yield. It is shown numerically that, for bubbles having sufficient molecular mass, spherical shock waves develop in the center of the cluster and that these spherical shock waves (microshocks) produce converging shocks within the interior bubbles, which focus energy on the centers of the bubbles. When these shock waves reflect from the centers of the bubbles, extreme conditions of temperature (∼108 K) and density (∼104 kg m−3) arise in a (nano)spherical region (∼10−7 m in size) that last for ∼10−12 s, during which time about ten D-D fusion neutrons and tritium nuclei are produced in the region. A paradoxical result in our experiments is that it is bubble cluster (not streamer) cavitation and the sufficiently high molecular mass of (and hence the low sound speed in) D-acetone (C3D6O) vapor (as compared, for example, to deuterated water D2O) which are necessary conditions for the formation of convergent spherical microshock waves in central cluster bubbles. It is these waves that allow the energy to be sufficiently focused in the nanospherical regions near the bubble centers for fusion events to occur. The criticism to which the concept of 'bubble fusion' has been subjected in the literature, in particular, most recently in Uspekhi Fizicheskikh Nauk (Physics

  8. Modelling of flow with cavitation in centrifugal pump

    International Nuclear Information System (INIS)

    The paper concerns flow modelling in centrifugal pump with special consideration of cavitation phenomena. Cavitation occurs when local pressure drops below the saturation pressure according to the temperature of the flow. Vapour bubbles are created and then they flow through the areas with higher pressure. The bubbles collapse rapidly generating pressure wave, noise and vibration. Working under cavitation condition is very dangerous to a pump and can significantly shorten its lifetime. The investigated centrifugal pump consists of three two-flow rotors and stators working on a single shaft. The modelling process started with grid independence study. When the grid was chosen, the pump performance curve was obtained using the single phase fluid model. Next, using the results from pump performance curve calculations, the cavitation characteristic was obtained. The constant capacity was held when the pressure at the inlet was reduced. The two – phase model was used with Zwart cavitation model. The results indicate that the pump work in safe range of parameters. The analysis also provides wide range of information about the areas of vapour appearance. The most endangered regions are leading edges of rotor. When pressure at the inlet drops to about one third of pressure that calculations started from the cavitation cloud appears in whole rotor. The intense of vapour bubbles creation is greater near the shroud of the pump, rather than near the hub. As cavitation is strongly unsteady phenomena, the transient calculations were performed to check if the results are close to those obtained using the steady state type. The differences are not significant.

  9. Modelling of flow with cavitation in centrifugal pump

    Science.gov (United States)

    Homa, D.; Wróblewski, W.

    2014-08-01

    The paper concerns flow modelling in centrifugal pump with special consideration of cavitation phenomena. Cavitation occurs when local pressure drops below the saturation pressure according to the temperature of the flow. Vapour bubbles are created and then they flow through the areas with higher pressure. The bubbles collapse rapidly generating pressure wave, noise and vibration. Working under cavitation condition is very dangerous to a pump and can significantly shorten its lifetime. The investigated centrifugal pump consists of three two-flow rotors and stators working on a single shaft. The modelling process started with grid independence study. When the grid was chosen, the pump performance curve was obtained using the single phase fluid model. Next, using the results from pump performance curve calculations, the cavitation characteristic was obtained. The constant capacity was held when the pressure at the inlet was reduced. The two - phase model was used with Zwart cavitation model. The results indicate that the pump work in safe range of parameters. The analysis also provides wide range of information about the areas of vapour appearance. The most endangered regions are leading edges of rotor. When pressure at the inlet drops to about one third of pressure that calculations started from the cavitation cloud appears in whole rotor. The intense of vapour bubbles creation is greater near the shroud of the pump, rather than near the hub. As cavitation is strongly unsteady phenomena, the transient calculations were performed to check if the results are close to those obtained using the steady state type. The differences are not significant.

  10. The Specialist Committee on Cavitation Induced Pressures, Final Report and Recommendations to the 23rd ITTC

    DEFF Research Database (Denmark)

    Friesch, J.; Kim, K.-H.; Andersen, Poul;

    2002-01-01

    General Technical Conclusions Propeller-excited hull pressure fluctuations are strongly influenced by intermittence of sheet cavitation, the dynamics of tip vortex cavitation, and the statistical properties of the cavitation. On modern propellers, tip vortex cavitation may be even more important...... than sheet cavitation for hull pressure fluctuation. The influence of turbulence and blade surface roughness on cavitation-induced pressure fluctuations is still not quantifiable. Both experimental and numerical procedures for predicting propeller excitation need to be validated using results of...... at full and model scale should be accompanied by propeller cavitation viewing and hull-surface vibration measurements. Calculations are done mostly with vortex-lattice or panel methods, and in most cases only sheet cavitation is included. With the propeller and cavity flows obtained, hull...

  11. Attached cavitation at a small diameter ultrasonic horn tip

    Science.gov (United States)

    Žnidarčič, Anton; Mettin, Robert; Cairós, Carlos; Dular, Matevž

    2014-02-01

    Ultrasonic horn transducers are frequently used in applications of acoustic cavitation in liquids, for instance, for cell disruption or sonochemical reactions. They are operated typically in the frequency range up to about 50 kHz and have tip diameters from some mm to several cm. It has been observed that if the horn tip is sufficiently small and driven at high amplitude, cavitation is very strong, and the tip can be covered entirely by the gas/vapor phase for longer time intervals. A peculiar dynamics of the attached cavity can emerge with expansion and collapse at a self-generated frequency in the subharmonic range, i.e., below the acoustic driving frequency. Here, we present a systematic study of the cavitation dynamics in water at a 20 kHz horn tip of 3 mm diameter. The system was investigated by high-speed imaging with simultaneous recording of the acoustic emissions. Measurements were performed under variation of acoustic power, air saturation, viscosity, surface tension, and temperature of the liquid. Our findings show that the liquid properties play no significant role in the dynamics of the attached cavitation at the small ultrasonic horn. Also the variation of the experimental geometry, within a certain range, did not change the dynamics. We believe that the main two reasons for the peculiar dynamics of cavitation on a small ultrasonic horn are the higher energy density on a small tip and the inability of the big tip to "wash" away the gaseous bubbles. Calculation of the somewhat adapted Strouhal number revealed that, similar to the hydrodynamic cavitation, values which are relatively low characterize slow cavitation structure dynamics. In cases where the cavitation follows the driving frequency this value lies much higher - probably at Str > 20. In the spirit to distinguish the observed phenomenon with other cavitation dynamics at ultrasonic transducer surfaces, we suggest to term the observed phenomenon of attached cavities partly covering the full horn

  12. Cavitating flow during water hammer using a generalized interface vaporous cavitation model

    Science.gov (United States)

    Sadafi, Mohamadhosein; Riasi, Alireza; Nourbakhsh, Seyed Ahmad

    2012-10-01

    In a transient flow simulation, column separation may occur when the calculated pressure head decreases to the saturated vapor pressure head in a computational grid. Abrupt valve closure or pump failure can result in a fast transient flow with column separation, potentially causing problems such as pipe failure, hydraulic equipment damage, cavitation or corrosion. This paper reports a numerical study of water hammer with column separation in a simple reservoir-pipeline-valve system and pumping station. The governing equations for two-phase transient flow in pipes are solved based on the method of characteristics (MOC) using a generalized interface vaporous cavitating model (GIVCM). The numerical results were compared with the experimental data for validation purposes, and the comparison indicated that the GIVCM describes the experimental results more accurately than the discrete vapor cavity model (DVCM). In particular, the GIVCM correlated better with the experimental data than the DVCM in terms of timing and pressure magnitude. The effects of geometric and hydraulic parameters on flow behavior in a pumping station with column separation were also investigated in this study.

  13. Preventing hydrogen embrittlement in stainless steel by means of compressive stress induced by cavitation peening

    OpenAIRE

    Osamu Takakuwa; Hitoshi Soyama

    2015-01-01

    In this paper, it has been demonstrated that compressive residual stress induced by cavitation peening which is one of the mechanical surface modification techniques can reduce invasion of the surface of austenitic stainless steel by hydrogen. Cavitation peening was done with employing a cavitating jet in air. The specimens were prepared with different processing time of cavitation peening. Then, stress measurement was performed using an X-ray diffraction analysis. After that, the surface was...

  14. Experimental investigation of the local wave speed in a draft tube with cavitation vortex rope

    OpenAIRE

    Landry, C; Favrel, A; Müller, A.; Nicolet, C.; Yamamoto, K.; Avellan, F.

    2014-01-01

    Hydraulic machines operating in a wider range are subjected to cavitation developments inducing undesirable pressure pulsations which could lead to potential instability of the power plant. The occurrence of pulsating cavitation volumes in the runner and the draft tube is considered as a mass source of the system and is depending on the cavitation compliance. This dynamic parameter represents the cavitation volume variation with the respect to a variation of pressure and defines implicitly th...

  15. Recent developments in cavitation mechanisms a guide for scientists and engineers

    CERN Document Server

    Washio, Seiichi

    2014-01-01

    How does cavitation start? Presently, the nucleus theory provides the answer to this fundamental question. However the idea of nuclei contains inaccuracies that cannot be rationalized. Recent Developments in Cavitation Mechanisms discusses the uncertainties surrounding the nucleus theory, and proposes another theory of cavitation mechanism. Characteristically, the new theory is based on recent discoveries of cavity generation phenomena in separating flows. This book consists of chapters that introduce topics such as unsoundness of cavitation nuclei, and phenomena of cavity generation on walls

  16. Numerical simulation of bubble chaotic motion in a cavitating water jet

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    A computational fluid dynamics (CFD) method is developed to investigate the radical motion of single cavitating bubble in the oscillating pressure field of a cavitating water jet. Regarding water as a compressible fluid, the simulation is performed at different oscillating frequencies. It is found that the bubble motion presents obvious nonlinear feature, and bifurcation and chaos appear on some conditions. The results manifest the indetermination of the cavitating bubble motion in the oscillating pressure field of the cavitating water jet.

  17. Link between in-nozzle cavitation and jet spray in a gasoline multi-hole injector

    OpenAIRE

    Gavaises, E.; Mirshahi, M.; Nouri, J. M.; Yan, Y.

    2013-01-01

    The importance of cavitation inside multi-hole injectors has been addressed in many previous investigations where the cavitation formation and its development, fuel spray characteristics and atomisation have quantified. Different types of geometrical and vortex cavitations have been previously reported inside the nozzles of multi-hole injectors with good indication of their influences on the emerging spray. However, the effect of cavitation on jet spray, its stability and liquid breakup and a...

  18. Cavitation improvement of double suction centrifugal pump HPP Fuhren

    Science.gov (United States)

    Škerlavaj, A.; Titzschkau, M.; Pavlin, R.; Vehar, F.; Mežnar, P.; Lipej, A.

    2012-11-01

    A double suction storage pump has been refurbished because of the strong cavitation which resulted in cavitation damage on blade and consequently in frequent repairs of the impeller. The analyses of the old and the new impeller were done by the computational fluid dynamics (CFD), performing transient simulations with the commercial solver Ansys CFX. In the simulations, the scale-adaptive-simulation with the curvature correction (SAS-CC) turbulence model was used. No model tests were carried out. Additionally, observations with the digital camera were made through the specially designed plexi-glass window, mounted at the lid at the suction side. The predicted pump head at the operating point agrees well with the pump characteristics measurements, performed with the direct thermodynamic method. The extent of the cavitation predicted by CFD is smaller than the observed one because the cloud cavitation was not predicted. The observations of the cavitation extent show that the impeller design is better than the old one, which was also possible to anticipate based on the CFD results.

  19. Numerical Modeling of Unsteady Cavitating Flows around a Stationary Hydrofoil

    Directory of Open Access Journals (Sweden)

    Antoine Ducoin

    2012-01-01

    Full Text Available The objective of this paper is to evaluate the predictive capability of three popular transport equation-based cavitation models for the simulations of partial sheet cavitation and unsteady sheet/cloud cavitating flows around a stationary NACA66 hydrofoil. The 2D calculations are performed by solving the Reynolds-averaged Navier-Stokes equation using the CFD solver CFX with the k-ω SST turbulence model. The local compressibility effect is considered using a local density correction for the turbulent eddy viscosity. The calculations are validated with experiments conducted in a cavitation tunnel at the French Naval Academy. The hydrofoil has a fixed angle of attack of α=6° with a Reynolds number of Re = 750,000 at different cavitation numbers σ. Without the density modification, over-prediction of the turbulent viscosity near the cavity closure reduces the cavity length and modifies the cavity shedding characteristics. The results show that it is important to capture both the mean and fluctuating values of the hydrodynamic coefficients because (1 the high amplitude of the fluctuations is critical to capturing the extremes of the loads to ensure structural safety and (2 the need to capture the frequency of the fluctuations, to avoid unwanted noise, vibrations, and accelerated fatigue issues.

  20. Measurement on the cavitating vortex shedding behind rectangular obstacles

    Energy Technology Data Exchange (ETDEWEB)

    Hegedus, F; Hos, C; Pandula, Z; Kullmann, L, E-mail: hegedusf@hds.bme.h [Department of Hydrodynamic Systems, Budapest University of Technology and Economics Muegyetem rkp. 1, Budapest 1111 (Hungary)

    2010-08-15

    Measurement results on the cavitating vortex shedding behind sharp-edged rectangular bodies are presented, intended to provide benchmark cases for the validation of unsteady cavitation models of CFD codes. Rectangular bodies of increasing aspect ratio (1, 2, 3 and 4) were used with a constant 25mm height (12.5% blockage ratio). The water velocity in the 0.2x0.05m test section of the channel was varied between 1 and 12 m/s resulting in a Reynolds number in the range of (0.4-3.5)x105. Pressure signals were measured at several locations, notably in the wake. Dominant frequencies and Strouhal numbers are reported from cavitation-free flow (classic von Karman vortex shedding) up to supercavitation as a function of the free-stream Reynolds number. The results are in good agreement with the literature in case of the square cylinder. We experienced a slight increase of the dominant Strouhal number with increasing aspect ratio. This result is somewhat inconsistent with the literature, in which a fall of the Strouhal number can be observed at side ratio 2. This may be the consequence of the different ranges of Reynolds numbers. It was also found that between the inception of cavitation and the formation of supercavitation the Strouhal number is not affected by cavitation.

  1. Research of the cavitation performance of the condensate pump

    International Nuclear Information System (INIS)

    Condensate pump is an important part of power plant circulation systems, which is used to pump condensate water. Because the condensate water pressure is very low, the first impeller of the condensate pump must have a good cavitation performance. Numerical simulation was employed to study the first impeller cavitation performance. The first impeller was set in the condensate pump barrel, and the double suction casing was kept, the parts after the double suction casing was simplified as tube. The simplicity can guarantee the inlet and outlet conditions of the impeller. Based on the RANS and SST k − ω turbulence model, CFD software was used to simulate the condensate pump at different working conditions. The numerical simulation shows that cavitation occurred at the suction side of the blades closing to the leading edge. The cavitation performance of the impeller was predicted based on the numerical calculation. Comparing with the experimental results, the numerical simulation result is smaller than that of the experiment in small flux, and the cavitation performance trend is agreed with that of the experiments

  2. Mass Transfer During Osmotic Dehydration Using Acoustic Cavitation

    Institute of Scientific and Technical Information of China (English)

    孙宝芝; 淮秀兰; 姜任秋; 刘登瀛

    2005-01-01

    An experimental study on intensifying osmotic dehydration was carried out in a state of nature and with acoustic cavitation of different cavitating intensity (0.5A, 0.TA and 0.9A) respectively, in which the material is apple slice of 5 mm thickness. The result showed that acoustic cavitation remarkably enhanced the osmotic dehydration, and the water loss was accelerated with the increase of cavitating intensity. The water diffusivity coefficients ranged from 1.8 × 10-10 m2.s-1 at 0.5A to 2.6 × 10-10 m2.s-1 at 0.9A, and solute diffusivity coefficients ranged from 3.5×10-11 m2.s-1 at 0.5A to 4.6×10-11 m2.s-1 at 0.9A. On the basis of experiments, a mathematical model was established about mass transfer during osmotic dehydration, and the numerical simulation was carried out. The calculated results agree well with experimental data, and represent the rule of mass transfer during osmotic dehydration intensified by acoustic cavitation.

  3. Analysis of cavitation and its effects on superplastic deformation

    Directory of Open Access Journals (Sweden)

    H. Tan

    2007-12-01

    Full Text Available Purpose: To study the effects of cavitation on the superplastic deformation using finite element method.Design/methodology/approach: Using consitututive equations for superplastic deformation, and taking into account the effects of grain growth and cavitation growth, Zn-Al and LY12CZ alloys are used for simulations to show effects of m values, elongation-to-failure values, percentage cavities and effects of imposed hydrostatic pressure during superplastic forming processes.Findings: During superplastic deformation, cavitation damage increases with the increase in strain. For high strain rate sensitivity, necking develops which leads to final fracture; whereas for low strain strain rate sensitivity, the final fracture is due to cavitation growth.Research limitations/implications: The effects of material parameters and deformation damage on the superplastic deformation process are numerically analyzed, and the means to control cavitation growth is discussed.Originality/value: A three dimensional viscoplastic finite element programe, taking into account of microstructural mechanisms, such as test temperature and cavity growth has been developed for superplastic deformation.

  4. Cavitation assisted delignification of wheat straw: a review.

    Science.gov (United States)

    Iskalieva, Asylzat; Yimmou, Bob Mbouyem; Gogate, Parag R; Horvath, Miklos; Horvath, Peter G; Csoka, Levente

    2012-09-01

    Wheat is grown in most of the Indian and Chinese regions and after harvesting, the remaining straw offers considerable promise as a renewable source most suitable for papermaking and as a pulping resource. Delignification of wheat straw offers ample scope for energy conservation by way of the application of the process intensification principles. The present work reviews the pretreatment techniques available for improving the effectiveness of the conventional approach for polysaccharide component separation, softening and delignification. A detailed overview of the cavitation assisted delignification process has been presented based on the earlier literature illustrations and important operational guidelines have been presented for overall low-cost and amenable energy utilization in the processes. The effectiveness of the methods has been evaluated according to yield and properties of the isolated fibers in comparison to the conventional treatment. Also the experimental results of one such non-conventional treatment scheme based on the use of hydrodynamic cavitation have been presented for the pulping of wheat straw. The effect of hydrodynamically induced cavitation on cell wall matrix and its components have been characterized using FT-IR analysis with an objective of understanding the cavitation assisted digestion mechanism on straws. It has been observed that the use of hydrodynamic cavitation does not degrade the fibrillar structure of cellulose but causes relocalisation and partial removal of lignin. Overall it appears that considerable improvement can be obtained due to the use of pretreatment or alternate techniques for delignification, which is an energy intensive step in the paper making industries. PMID:22410399

  5. Cavitation behaviour of a metastable Cr-Mn-austenite

    Energy Technology Data Exchange (ETDEWEB)

    Zylla, I.M. (Max-Planck-Institut fuer Eisenforschung GmbH, Duesseldorf (Germany)); Hougardy, H.P. (Max-Planck-Institut fuer Eisenforschung GmbH, Duesseldorf (Germany))

    1994-04-01

    The microstructures of three steels with metastable austenite with mass contents of 10-14% Cr, 10-15% Mn and 0.1-0.35% C were optimized by a simulation of the cavitation load. Results of cavitation tests show that the microstructure should be fine grained, to avoid the arise of cracks in the early stages. The materials were pretreated by a thermomechanical treatment. Criteria for a selection were the mechanical properties and the microstructure. According to the results a steel with mass contents of 13% Cr, 10% Mn and 0.35% C (X 35 CrMn 13 10) should have the best cavitation resistance. In this steel a deformation of 400 C produces a dislocation network that forces a transformation of austenite to very fine martensite plates during cavitation and gives a smooth abrasion. The cavitation resistance of steel X 35 CrMn 13 10 in a pretreated condition is in the range of published values of a Stellite 6B, but the production of the steel is more versatile and less expensive than that of a Stellite. (orig.)

  6. EFFECTS OF ENTRAINED AIR MANNER ON CAVITATION DAMAGE*

    Institute of Scientific and Technical Information of China (English)

    WU Jian-hua; LUO Chao

    2011-01-01

    Early in 1953 the experiments by Peterka proved that air entrainment has effects on decreasing cavitation damage. This technology has been widely used in the release works of high dams since the inception of air entrainment in the Grand Goulee Dam in 1960. Behavior, mechanism and application of air entrainment for cavitation damage control have been investigated for over half century. However, severe cavitation damage happened due to complex mechanism of air entrainment. The effects of air entrainment are related to many factors, including geometric parameters, hydraulic parameters and entrained air manners. In the present work an experimental set-up for air entrainment was specially designed, the behavior of reducing cavitation damage was experimentally investigated in the three aspects of entrained air pressure, air tube aera and air tube number. The results show that magnitude of reduction of cavitation damage is closely related to the entrained air tube number as well as entrained air pressure, air tube aera, and that the effect through three air tubes is larger than that through single air tube although the entrained air tubes have the same sum of tube aera, that is, 1 + 1 + 1 > 3. Therefore, it is important to design an effective manner of air entrainment.

  7. Prediction of EMP cavitation threshold from other than sodium testing

    International Nuclear Information System (INIS)

    An experimental study has been performed to predict the cavitation threshold of electromagnetic pumps from measurements on test models using water and alcohol. Cavitation tests were carried out using water and alcohol test loop on subscale ducts of transparent acrylic resin with reference to an actual pump (1.1m3/min). These data were compared to those obtained from the in-sodium tests on the actual pump. The investigation revealed that the value of Thoma's dimensionless parameter: σ applied to the test model for water and alcohol is quite higher than that of corresponding σ on the actual pump. To minimize the incipient cavitation safety margin, more accurate prediction must be required. In view of this, the authors proposed the dimensionless parameter: σT=σ/W-bare where W-bare denotes the Weber number. This parameter was confirmed to predict the cavitation threshold of electromagnetic pumps with much more accuracy than ever before. It can also be adopted to predict cavitation threshold of other FBR components. (author)

  8. Research of the cavitation performance of the condensate pump

    Science.gov (United States)

    Li, H. F.; Pan, Z. B.; He, M. H.; Ji, K.; Zhou, W. C.; Min, S. M.

    2013-12-01

    Condensate pump is an important part of power plant circulation systems, which is used to pump condensate water. Because the condensate water pressure is very low, the first impeller of the condensate pump must have a good cavitation performance. Numerical simulation was employed to study the first impeller cavitation performance. The first impeller was set in the condensate pump barrel, and the double suction casing was kept, the parts after the double suction casing was simplified as tube. The simplicity can guarantee the inlet and outlet conditions of the impeller. Based on the RANS and SST k - ω turbulence model, CFD software was used to simulate the condensate pump at different working conditions. The numerical simulation shows that cavitation occurred at the suction side of the blades closing to the leading edge. The cavitation performance of the impeller was predicted based on the numerical calculation. Comparing with the experimental results, the numerical simulation result is smaller than that of the experiment in small flux, and the cavitation performance trend is agreed with that of the experiments.

  9. Numerical analysis for cavitation flow of marine propeller

    Science.gov (United States)

    Tauviqirrahman, Mohammad; Muchammad, Ismail, Rifky; Jamari, J.

    2015-12-01

    Concerning the environmental issue and the increase of fuel price, optimizing the fuel consumption has been recently an important subject in all industries. In marine industries one of the ways to decrease the energy consumption was by reducing the presence of cavitation on marine propeller blades. This will give a higher propulsive efficiency. This paper provides an investigation into the influence of the cavitation on a hydrodynamic performance around the propeller based on numerical method. Hydrofoil representing the blade form of propeller was of particular of interest. Two types of cavitation model were investigated with respect to the accuracy of the result and the effectiveness of the method. The results include the hydrodynamic characteristics of cavitation phenomenon like lift/drag variation with respect to the cavity extent. It was found that a high accuracy and low computational time is achieved when the cavitation model of Zwart-Gerber-Belamri is used. The interesting outcome of this study is that the results can be used as a good evaluation tool for high marine propeller performance.

  10. Cavitation performance simulation of turbine meter under different temperature water condition

    Science.gov (United States)

    Huang, Y. Z.; Zhang, B. S.; Chen, G.; Zhu, B. L.

    2015-01-01

    A cavitation thermodynamics model based on phase change, which is suitable for prediction of cavitation with thermal effects is developed. The cavitation characteristic at different temperature and cavitation number is investigated and analyzed. The initial cavitation of turbine flow meter generally occurs in the blade suction side. With the development of cavitation, the cavitation zone will appear on the front and the back end of the conditioner. In order to avoid the gather of cavitation, the design of the optimizing the blade structure should be adapted, and at the same time, the back pressure should be limited on the installation requirements. Expanding the measurement range and preventing cavitation occurs are the goal of the design and installation. The temperature effects on the cavitation of turbine flow meter is quite obvious and the increase of the temperature will delay the occurrence of cavitation. Pressure difference and the impeller torque will change obviously with the decrease of the cavitation number, which will cause the measurement error of the turbine meter.

  11. An algorithm for fast DNS cavitating flows simulations using homogeneous mixture approach

    Science.gov (United States)

    Žnidarčič, A.; Coutier-Delgosha, O.; Marquillie, M.; Dular, M.

    2015-12-01

    A new algorithm for fast DNS cavitating flows simulations is developed. The algorithm is based on Kim and Moin projection method form. Homogeneous mixture approach with transport equation for vapour volume fraction is used to model cavitation and various cavitation models can be used. Influence matrix and matrix diagonalisation technique enable fast parallel computations.

  12. Molecular mechanism for cavitation in water under tension

    CERN Document Server

    Menzl, Georg; Geiger, Philipp; Caupin, Frédéric; Abascal, Jose L F; Valeriani, Chantal; Dellago, Christoph

    2016-01-01

    Despite its relevance in biology and engineering, the molecular mechanism driving cavitation in water remains unknown. Using computer simulations, we investigate the structure and dynamics of vapor bubbles emerging from metastable water at negative pressures. We find that in the early stages of cavitation, bubbles are irregularly shaped and become more spherical as they grow. Nevertheless, the free energy of bubble formation can be perfectly reproduced in the framework of classical nucleation theory (CNT) if the curvature dependence of the surface tension is taken into account. Comparison of the observed bubble dynamics to the predictions of the macroscopic Rayleigh--Plesset (RP) equation, augmented with thermal fluctuations, demonstrates that the growth of nanoscale bubbles is governed by viscous forces. Combining the dynamical prefactor determined from the RP equation with the free energy of CNT yields an analytical expression for the cavitation rate that reproduces the simulation results very well over a w...

  13. Cavitation Erosion of Sensitized UNS S31803 Duplex Stainless Steels

    Science.gov (United States)

    Mitelea, Ion; Micu, Lavinia Mădălina; Bordeaşu, Ilare; Crăciunescu, Corneliu Marius

    2016-05-01

    During processing or use, duplex steels can be subjected to heating at high temperatures that can affect their behavior. This work aims to correlate the influence of the sensitization treatment on the ultrasonic cavitation erosion behavior of a UNS S31803 (X2CrNiMoN22-5-3) duplex stainless steel. Duplex stainless steels, formed as a result of rapid cooling after solution annealing, are sensitized at temperatures of 475 and 850 °C, respectively, leading to hardening and embrittlement due to the spinodal decomposition of the ferrite and the precipitation of secondary phases. The ultrasonic cavitation erosion experiments showed that the sensitization at 850 °C reduced the mean depth of erosion by about 11% and the mean depth of erosion rate by 28%. By contrast, the sensitization at 475 °C deteriorates the cavitation erosion resistance, increasing the erosion parameters by up to 22%, compared to the solution annealed state.

  14. Large-eddy simulation of cavitating nozzle and jet flows

    Science.gov (United States)

    Örley, F.; Trummler, T.; Hickel, S.; Mihatsch, M. S.; Schmidt, S. J.; Adams, N. A.

    2015-12-01

    We present implicit large-eddy simulations (LES) to study the primary breakup of cavitating liquid jets. The considered configuration, which consists of a rectangular nozzle geometry, adopts the setup of a reference experiment for validation. The setup is a generic reproduction of a scaled-up automotive fuel injector. Modelling of all components (i.e. gas, liquid, and vapor) is based on a barotropic two-fluid two-phase model and employs a homogenous mixture approach. The cavitating liquid model assumes thermodynamic- equilibrium. Compressibility of all phases is considered in order to capture pressure wave dynamics of collapse events. Since development of cavitation significantly affects jet break-up characteristics, we study three different operating points. We identify three main mechanisms which induce primary jet break-up: amplification of turbulent fluctuations, gas entrainment, and collapse events near the liquid-gas interface.

  15. Cavitation effects in LMFBR containment loading - a sensitivity study

    International Nuclear Information System (INIS)

    The motivation for and design of a sensitivity study into the effects of bulk cavitation of the coolant upon predicted roof loadings and vessel wall loadings and deformations are presented. The study is designed to cover simple and sophisticated models of cavitation in various geometries and with two types of energy source to represent both an explosion charge and the lower pressure expansion behavior expected in a real core disruptive accident. Effects of change of scale (from reactor to model), of coolant tensile strength, of reactor aspect ratio and design (presence or absence of an internal tank) and of reactor structural resistance (rigid or deforming outer tank) are all examined in order to provide a quantitative answer to the question 'how and to what extent does dynamic cavitation affect the containment loading process.'. (orig.)

  16. Radiographic display of carious lesions and cavitation in approximal surfaces

    DEFF Research Database (Denmark)

    Wenzel, Ann

    2014-01-01

    Abstract Background. Treatment strategies have changed with efforts on arresting carious lesions suspected to have an intact surface sparing operative treatment for cavitated lesions. Radiography is still the most recommended adjunct method in the diagnosis of clinically inaccessible approximal...... depth and clinical cavitation in approximal surfaces, a threshold for operative treatment decision has been suggested when a lesion is observed radiographically more than one-third into dentine. However, the results from previous studies are contradictory and the majority of studies are ∼25 years old...... radiography is, thus, still state-of-the-art as an adjunct in diagnosing carious lesions in clinically inaccessible approximal surfaces. The risk for cavitation is related to lesion depth, but new studies are needed in both child and adult populations to validate current thresholds for the operative treatment...

  17. Influence of ultrasonic cavitation on passive film of stainless steel.

    Science.gov (United States)

    Wang, Bao-Cheng; Zhu, Jin-hua

    2008-03-01

    The electrochemical behaviors of passive film of stainless steel 0Cr13Ni5Mo under the condition of static state (quiescence) and ultrasonic cavitation in the HCl solution have been studied by means of polarization curve, electrochemical impedance spectroscopy (EIS) and capacitance potential measurement. The results indicate that the passive film shows a multi layer structure distribution, and presents a p-type semiconductor property under the condition of quiescence. The stability of passive film decreases, the semiconducting property changes to an n-type semiconductor in the presence of cavitation. The amount of transition electrons from valence band because of cavitation is related to the height of Fermi level of passive film semiconductor. PMID:17584517

  18. Cavitation Rates in Water with Dissolved Gas and Other Impurities

    Institute of Scientific and Technical Information of China (English)

    Patrik Zima; Frantisek Marsík; Milan Sedlár

    2003-01-01

    Our objective is a better understanding of the role of physical properties of real fluids in the thermodynamics of cavitation in impure water. An extension to the classical homogenous nucleation theory suitable for mixtures is presented in attempt to address the discrepancy between the theoretical predictions and practical observations of cavitation rates in water at normal temperatures.The extension takes into account the non—equilibrium (dissipative) effects involved in nuclei formation through a substance dependent correction coefficient to be determined experimentally.The theory of thermodynamic fluctuations is applied to derive the work of formation of a bubble nucleus.The value of the correction coefficient is estimated using preliminary experimental data from a convergent-divergent nozzle. An application of the results to the numerical prediction of the cavitation zones in a radial-flow water pump is shown.

  19. Cavitation Erosion of Cermet-Coated Aluminium Bronzes

    Directory of Open Access Journals (Sweden)

    Ion Mitelea

    2016-03-01

    Full Text Available The cavitation erosion resistance of CuAl10Ni5Fe2.5Mn1 following plasma spraying with Al2O3·30(Ni20Al powder and laser re-melting was analyzed in view of possible improvements of the lifetime of components used in hydraulic environments. The cavitation erosion resistance was substantially improved compared with the one of the base material. The thickness of the re-melted layer was in the range of several hundred micrometers, with a surface microhardness increasing from 250 to 420 HV 0.2. Compositional, structural, and microstructural explorations showed that the microstructure of the re-melted and homogenized layer, consisting of a cubic Al2O3 matrix with dispersed Ni-based solid solution is associated with the hardness increase and consequently with the improvement of the cavitation erosion resistance.

  20. Analysis of cavitation inception and desinence behind surface irregularities

    Science.gov (United States)

    Amromin, Eduard

    2016-07-01

    Cavities behind a surface irregularity appear in vortices drifting downstream of it. Cavitation can occur there substantially earlier than over smooth surfaces of the same bodies. Cavitation inception and desinence behind surface irregularities have been intensively studied in the course of water tunnel experiments several decades ago, but no corresponding quantitative theoretical (numerical) analysis was reported. This numerical study is aimed at elaboration of a general approach to the prediction of cavitation desinence numbers for various irregularities over various surfaces and on determination of the major factors influencing these numbers in both computations and experiments. The developed multi-level computational method employs diverse models for flow zones of diverse scale. The viscous-inviscid interaction approach is used for the flow around irregularities submerged (or partially submerged) in the turbulent boundary layer. Combinations of the semi-empirical and asymptotic analyses are used for vortices and cavities in their cores. The computational method is validated with various known experimental data.

  1. Cavitation Erosion of Sensitized UNS S31803 Duplex Stainless Steels

    Science.gov (United States)

    Mitelea, Ion; Micu, Lavinia Mădălina; Bordeaşu, Ilare; Crăciunescu, Corneliu Marius

    2016-04-01

    During processing or use, duplex steels can be subjected to heating at high temperatures that can affect their behavior. This work aims to correlate the influence of the sensitization treatment on the ultrasonic cavitation erosion behavior of a UNS S31803 (X2CrNiMoN22-5-3) duplex stainless steel. Duplex stainless steels, formed as a result of rapid cooling after solution annealing, are sensitized at temperatures of 475 and 850 °C, respectively, leading to hardening and embrittlement due to the spinodal decomposition of the ferrite and the precipitation of secondary phases. The ultrasonic cavitation erosion experiments showed that the sensitization at 850 °C reduced the mean depth of erosion by about 11% and the mean depth of erosion rate by 28%. By contrast, the sensitization at 475 °C deteriorates the cavitation erosion resistance, increasing the erosion parameters by up to 22%, compared to the solution annealed state.

  2. Birth and growth of cavitation bubbles within water under tension

    CERN Document Server

    Vincent, Olivier; Quinto-Su, Pedro A; Ohl, Claus-Dieter

    2011-01-01

    Water under tension, such as the water rising in tree vessels, is in a metastable state. Water cavitates spontaneously when the tension is high enough, as observed at equilibrium in the water filled holes of a drying hydrogel, called artifical trees. Here, in order to understand the dynamics of cavitation in tensed water, we directly trigger cavitation events, taking advantage of the disturbance generated by a focused laser pulse. We find that the inception of a bubble progresses in two stages. The first stage is ultra-fast, lasting less than microseconds, during which a bubble with a finite volume suddenly appears. This event relaxes the water tension, that we can therefore estimate. A second, slower stage follows when water diffuses into the surrounding medium.

  3. PREFACE: 9th International Symposium on Cavitation (CAV2015)

    Science.gov (United States)

    Farhat, M.; Müller, A.

    2015-12-01

    It is our pleasure and privilege to welcome all the participants of the 9th International Symposium on Cavitation (CAV2015) to Lausanne. Since its initiation in 1986 in Sendai, Japan, the CAV symposium has grown to become the world's foremost event dedicated to cavitation. Hosted by EPFL (Ecole Polytechnique Fédérale de Lausanne) and staged at the SwissTech Convention Center, CAV2015 is a unique opportunity to exchange with leading scientists and industry experts about the latest advances in theoretical modelling, numerical simulation and experimentation related to cavitation phenomena with a special emphasis on practical applications. The topics covered by CAV2015 include cavitation in ¬fluid machinery and fuel systems, bubble dynamics, cavitation erosion, advanced numerical simulation, sonochemistery, biomedicine and experimental techniques. CAV2015 will also host an exhibition of leading providers of state of the art measurement equipment, including high-speed imaging systems, non-intrusive velocimetry, pressure sensors, as well as numerical solvers. We have accepted over 190 papers, which will be presented in four parallel sessions. The proceedings will appear in the open access Journal of Physics: Conference Series (JPCS), which is part of the IOP Conference Series. All published papers are fully citable and upon publication will be free to download in perpetuity. We would like to thank all the reviewers for their great help during the selection process. We will also propose six plenary speakers to highlight cavitation issues in different fields. Finally, we would like to warmly thank our sponsors for their valuable support and the local Organizing Committee for the efforts in setting up this important event. We look forward to seeing you in Lausanne!

  4. Possibility of Metal Processing Using Ultrasonic Cavitation Jet

    Science.gov (United States)

    Aoyagi, Ryoji; Fujiwara, Ryuichi; Niita, Tokuo

    2001-05-01

    Utilizing a high-intensity ultrasonic cavitation, a processing experiment was conducted with the aim of performing volumetric flow adjustment of a fuel jet nozzle to be used for a small engine, which cannot be carried out by a method such as machining. At the bottom of the nozzle used for the experiment, which is in the shape of a cup, a nozzle hole with a diameter of 0.15 mm is drilled. In this experiment, we make adjustments in the volumetric flow by grinding and removing the machining burr with the aid of the processing power of ultrasonic cavitation. The processing effect is highly dependent on the ultrasonic cavitation intensity. In the experiment, the processing reservoir was filled with pressurized highly deaerated water to increase the processing force by allowing cavitation with high intensity to be generated. The processing principle is to utilize the effect of a cavitation jet flow passing through the nozzle hole. To restrain the intake of the bubbles into the flow circuits during the pressure reduction cycle of the vibrator, the water flow was discharged into a pressure reduction reservoir. By allowing the horn tip with a diameter of 6 mm at a frequency of 28 kHz to approach the sample, followed by high-intensity ultrasonic irradiation, powerful cavitation was generated. As a result of the evaluation of the processing efficiency made based on the volumetric flow increase and microscopic observation of the nozzle, burrs smaller than 10 μm were almost entirely removed within 15 min of initial irradiation, resulting in a volumetric flow increase of more than 0.4%/min. However, in the case of burrs of more than 10 μm, no force that could remove the burrs was found. It was surprising for the burrs to generate deformation rather than to be removed.

  5. Model test and CFD calculation of a cavitating bulb turbine

    Energy Technology Data Exchange (ETDEWEB)

    Necker, J; Aschenbrenner, T, E-mail: joerg.necker@voith.co [Voith Hydro Holding GmbH and Co. KG Alexanderstrasse 11, 89522 Heidenheim (Germany)

    2010-08-15

    The flow in a horizontal shaft bulb turbine is calculated as a two-phase flow with a commercial Computational Fluid Dynamics (CFD-)-code including cavitation model. The results are compared with experimental results achieved at a closed loop test rig for model turbines. On the model test rig, for a certain operating point (i.e. volume flow, net head, blade angle, guide vane opening) the pressure behind the turbine is lowered (i.e. the Thoma-coefficient {sigma} is lowered) and the efficiency of the turbine is recorded. The measured values can be depicted in a so-called {sigma}-break curve or {eta}- {sigma}-diagram. Usually, the efficiency is independent of the Thoma-coefficient up to a certain value. When lowering the Thoma-coefficient below this value the efficiency will drop rapidly. Visual observations of the different cavitation conditions complete the experiment. In analogy, several calculations are done for different Thoma-coefficients {sigma}and the corresponding hydraulic losses of the runner are evaluated quantitatively. For a low {sigma}-value showing in the experiment significant efficiency loss, the the change of volume flow in the experiment was simulated. Besides, the fraction of water vapour as an indication of the size of the cavitation cavity is analyzed qualitatively. The experimentally and the numerically obtained results are compared and show a good agreement. Especially the drop in efficiency can be calculated with satisfying accuracy. This drop in efficiency is of high practical importance since it is one criterion to determine the admissible cavitation in a bulb-turbine. The visual impression of the cavitation in the CFD-analysis is well in accordance with the observed cavitation bubbles recorded on sketches and/or photographs.

  6. Cavitation erosion: Using the target material as a pressure sensor

    Science.gov (United States)

    Roy, Samir Chandra; Franc, Jean-Pierre; Fivel, Marc

    2015-10-01

    Numerical prediction of mass loss due to cavitation erosion requires the knowledge of the hydrodynamic impact loads generated by cavitation bubble collapses. Experimental measurements of such impact loads using conventional pressure sensors are not reliable (if not impossible) due to the micron size and the very small duration of the loading. In this paper, a new method to estimate these loading conditions is proposed based on cavitation pitting tests and an iterative inverse finite element modeling. The principle of the method is as follows. First, numerous pits corresponding to localized plastically deformed regions are identified from a cavitation test performed in a dedicated tunnel. Then each pit is numerically reproduced by finite element simulations of the material response to a representative Gaussian pressure field supposed to mimic a single bubble collapse. This gives the size and pressure distribution of the bubble impacts. The prime objective of this study is to find out if the target material itself could be used as a pressure sensor or not, i.e., if the cavitation pits left on the surface of the tested specimen could provide the characteristics of the cavitating flow in terms of pressure fields independently of the target material. Pitting tests were done on three materials, namely, 7075 Aluminum alloy (Al-7075), 2205 duplex stainless steel (A-2205), and Nickel-Aluminum Bronze (NAB) at three different flow conditions and the impact loads have been estimated for each identified pit. Very interestingly, a statistical analysis shows that the estimated impact loads are material independent at all flow conditions, provided the material properties are characterized properly. It is also shown that for some materials, the constitutive parameters obtained from compression tests are not satisfactory.

  7. Cavitation in ultrasound and shockwave therapy

    Science.gov (United States)

    Colonius, Tim

    2014-11-01

    Acoustic waves, especially high-intensity ultrasound and shock waves, are used for medical imaging and intra- and extra-corporeal manipulation of cells, tissue, and urinary calculi. Waves are currently used to treat kidney stone disease, plantar fasciitis, and bone nonunion, and they are being investigated as a technique to ablate cancer tumors and mediate drug delivery. In many applications, acoustic waves induce the expansion and collapse of preexisting or newly cavitating bubbles whose presence can either mediate the generation of localized stresses or lead to collateral damage, depending on how effectively they can be controlled. We describe efforts aimed at simulating the collapse of bubbles, both individually and in clusters, with the aim to characterize the induced mechanical stresses and strains. To simulate collapse of one or a few bubbles, compressible Euler and Navier-Stokes simulations of multi-component materials are performed with WENO-based shock and interface capturing schemes. Repetitive insonification generates numerous bubbles that are difficult to resolve numerically. Such clouds are also important in traditional engineering applications such as caveating hydrofoils. Models that incorporate the dynamics of an unresolved dispersed phase consisting of the bubble cloud are also developed. The results of several model problems including bubble collapse near rigid surfaces, bubble collapse near compliant surfaces and in small capillaries are analyzed. The results are processed to determine the potential for micron-sized preexisting gas bubbles to damage capillaries. The translation of the fundamental fluid dynamics into improvements in the design and clinical application of shockwave lithotripters will be discussed. NIH Grant PO1-DK043881.

  8. Real-time visualization of joint cavitation.

    Directory of Open Access Journals (Sweden)

    Gregory N Kawchuk

    Full Text Available Cracking sounds emitted from human synovial joints have been attributed historically to the sudden collapse of a cavitation bubble formed as articular surfaces are separated. Unfortunately, bubble collapse as the source of joint cracking is inconsistent with many physical phenomena that define the joint cracking phenomenon. Here we present direct evidence from real-time magnetic resonance imaging that the mechanism of joint cracking is related to cavity formation rather than bubble collapse. In this study, ten metacarpophalangeal joints were studied by inserting the finger of interest into a flexible tube tightened around a length of cable used to provide long-axis traction. Before and after traction, static 3D T1-weighted magnetic resonance images were acquired. During traction, rapid cine magnetic resonance images were obtained from the joint midline at a rate of 3.2 frames per second until the cracking event occurred. As traction forces increased, real-time cine magnetic resonance imaging demonstrated rapid cavity inception at the time of joint separation and sound production after which the resulting cavity remained visible. Our results offer direct experimental evidence that joint cracking is associated with cavity inception rather than collapse of a pre-existing bubble. These observations are consistent with tribonucleation, a known process where opposing surfaces resist separation until a critical point where they then separate rapidly creating sustained gas cavities. Observed previously in vitro, this is the first in-vivo macroscopic demonstration of tribonucleation and as such, provides a new theoretical framework to investigate health outcomes associated with joint cracking.

  9. Cavitation Bubble Nucleation by Energetic Particles

    Energy Technology Data Exchange (ETDEWEB)

    West, C.D.

    1998-12-01

    In the early sixties, experimental measurements using a bubble chamber confirmed quantitatively the thermal spike theory of bubble nucleation by energetic particles: the energy of the slow, heavy alpha decay recoils used in those experiments matched the calculated bubble nucleation energy to within a few percent. It was a triumph, but was soon to be followed by a puzzle. Within a couple of years, experiments on similar liquids, but well below their normal boiling points, placed under tensile stress showed that the calculated bubble nucleation energy was an order of magnitude less than the recoil energy. Why should the theory work so well in the one case and so badly in the other? How did the liquid, or the recoil particle, "know" the difference between the two experiments? Another mathematical model of the same physical process, introduced in 1967, showed qualitatively why different analyses would be needed for liquids with high and low vapor pressures under positive or negative pressures. But, the quantitative agreement between the calculated nucleation energy and the recoil energy was still poor--the former being smaller by a factor of two to three. In this report, the 1967 analysis is extended and refined: the qualitative understanding of the difference between positive and negative pressure nucleation, "boiling" and "cavitation" respectively, is retained, and agreement between the negative pressure calculated to be needed for nucleation and the energy calculated to be available is much improved. A plot of the calculated negative pressure needed to induce bubble formation against the measured value now has a slope of 1.0, although there is still considerable scatter in the individual points.

  10. Characterization of Axial Inducer Cavitation Instabilities via High Speed Video Recordings

    Science.gov (United States)

    Arellano, Patrick; Peneda, Marinelle; Ferguson, Thomas; Zoladz, Thomas

    2011-01-01

    Sub-scale water tests were undertaken to assess the viability of utilizing high resolution, high frame-rate digital video recordings of a liquid rocket engine turbopump axial inducer to characterize cavitation instabilities. These high speed video (HSV) images of various cavitation phenomena, including higher order cavitation, rotating cavitation, alternating blade cavitation, and asymmetric cavitation, as well as non-cavitating flows for comparison, were recorded from various orientations through an acrylic tunnel using one and two cameras at digital recording rates ranging from 6,000 to 15,700 frames per second. The physical characteristics of these cavitation forms, including the mechanisms that define the cavitation frequency, were identified. Additionally, these images showed how the cavitation forms changed and transitioned from one type (tip vortex) to another (sheet cavitation) as the inducer boundary conditions (inlet pressures) were changed. Image processing techniques were developed which tracked the formation and collapse of cavitating fluid in a specified target area, both in the temporal and frequency domains, in order to characterize the cavitation instability frequency. The accuracy of the analysis techniques was found to be very dependent on target size for higher order cavitation, but much less so for the other phenomena. Tunnel-mounted piezoelectric, dynamic pressure transducers were present throughout these tests and were used as references in correlating the results obtained by image processing. Results showed good agreement between image processing and dynamic pressure spectral data. The test set-up, test program, and test results including H-Q and suction performance, dynamic environment and cavitation characterization, and image processing techniques and results will be discussed.

  11. Visualization of unsteady behavior of cavitation in circular cylindrical orifice with abruptly expanding part

    International Nuclear Information System (INIS)

    Cavitation problems in plant's piping system have been investigated on the basis of high-speed observation. Cavitation is one of the important factors with potential damage in piping system at nuclear power plant. In a power plant, there is cavitation occurrence to be expected in some local places such as an orifice, a valve and a pressure reducer. We have investigated about unsteady behavior and impact of cavitation in a long orifice with an abruptly expanding pipe. In this study, some detailed cavitation behaviors are observed by varying cavitating condition in the orifice throat and downstream of the orifice. High-speed behaviors of cavitation are observed by means of a high-speed video camera with a laser sheet in order to observe the inside of the circular orifice. Then images are analyzed using a frame difference method. As a result, we observe a series of cavitation developing process with decrease in cavitation number such as 1: cavitation inception occurs at the inlet of orifice, 2: cavitation develops in the throat of the orifice, 3: large-scale cavitation clouds appear downstream of the orifice, 4: liquid jet appears when the pressure downstream of the orifice decrease to about vapor pressure. Cavitation clouds in a circular cylindrical orifice with abruptly expanding part show some unsteadiness even in the steady operating condition. Cavitation clouds also show a large-scale shedding behavior in the transition stage to a liquid jet condition. In addition, we observe that the interface instability of a liquid jet downstream of the orifice depends on the cavitation instability in the orifice throat. (author)

  12. Inhibition of nonlinear acoustic cavitation dynamics in liquid CO2

    Science.gov (United States)

    van Iersel, Maikel M.; Cornel, Jeroen; Benes, Nieck E.; Keurentjes, Jos T. F.

    2007-02-01

    The authors present a model to study ultrasound-induced cavitation dynamics in liquid carbon dioxide (CO2), which includes descriptions for momentum, mass, and energy transport. To assist in the interpretation of these results, numerical simulations are presented for an argon cavity in water. For aqueous systems, inertia effects and force accumulation lead to a nonlinear radial motion, resulting in an almost adiabatic compression of the cavity interior. The simulations for liquid CO2 suggest that transport limitations impede nonlinear cavitation dynamics and the corresponding temperature rise. Consequently, in liquid CO2 the ultrasound-induced formation of radicals appears improbable.

  13. Cavitation Erosion of P110 Steel in Different Drilling Muds

    Directory of Open Access Journals (Sweden)

    Kmieć M.

    2016-06-01

    Full Text Available The P110 steel specimens were subjected to ultrasonic cavitation erosion in different compositions of drilling muds and surfactant additive. The test procedure was based on ASTM-G-32 standard recommendations. API 5CT-P110 steel is used for pipes in oil and gas industry. The harsh environment and high velocity of flows poses corrosive and erosive threat on materials used there. The composition of drilling fluid influences its rheological properties and thus intensity of cavitation erosion. The erosion curves based on weight loss were measured.

  14. Detection of cystic structures using pulsed ultrasonically induced resonant cavitation

    Science.gov (United States)

    Bar-Cohen, Yoseph (Inventor); Kovach, John S. (Inventor)

    2002-01-01

    Apparatus and method for early detection of cystic structures indicative of ovarian and breast cancers uses ultrasonic wave energy at a unique resonance frequency for inducing cavitation in cystic fluid characteristic of cystic structures in the ovaries associated with ovarian cancer, and in cystic structures in the breast associated with breast cancer. Induced cavitation bubbles in the cystic fluid implode, creating implosion waves which are detected by ultrasonic receiving transducers attached to the abdomen of the patient. Triangulation of the ultrasonic receiving transducers enables the received signals to be processed and analyzed to identify the location and structure of the cyst.

  15. Cavitation Inception on Microparticles: A Self-Propelled Particle Accelerator

    DEFF Research Database (Denmark)

    Arora, M.; Ohl, C.-D.; Mørch, Knud Aage

    2004-01-01

    Corrugated, hydrophilic particles with diameters between 30 and 150 mum are found to cause cavitation inception at their surfaces when they are exposed to a short, intensive tensile stress wave. The growing cavity accelerates the particle into translatory motion until the tensile stress decreases......, and subsequently the particle separates from the cavity. The cavity growth and particle detachment are modeled by considering the momentum of the particle and the displaced liquid. The analysis suggests that all particles which cause cavitation are accelerated into translatory motion, and separate...

  16. Effect of centrifugal pump impeller shapes on cavitation erosion

    International Nuclear Information System (INIS)

    The cavitation erosion test and suction performance test for five types of centrifugal pump impellers with different blade inlet angles and different position of blade inlet edges are carried out by using the open-type pump test loop and painting method. The relationship among the shape of impellers, flow rate, pump running time and position, degree of cavitation erosion inside impellers are made clear under the state of 3% pump head dropping. The experimental results are discussed with the internal flow pattern and inlet reverse flow occurred in the pump

  17. Plasma and cavitation dynamics during pulsed laser microsurgery in vivo

    CERN Document Server

    Hutson, M Shane

    2007-01-01

    We compare the plasma and cavitation dynamics underlying pulsed laser microsurgery in water and in fruit fly embryos (in vivo) - specifically for nanosecond pulses at 355 and 532 nm. We find two key differences. First, the plasma-formation thresholds are lower in vivo - especially at 355 nm - due to the presence of endogenous chromophores that serve as additional sources for plasma seed electrons. Second, the biological matrix constrains the growth of laser-induced cavitation bubbles. Both effects reduce the disrupted region in vivo when compared to extrapolations from measurements in water.

  18. Mechanism of noise generation by cavitation in hydraulic relief valve

    Science.gov (United States)

    Okita, K.; Miyamoto, Y.; Kataoka, T.; Takagi, S.; Kato, H.

    2015-12-01

    In order to clarify the mechanism of noise generation in a hydraulic relief valve, oil cavitating flows in a half cut model of the valve were observed by means of a high-speed camera and were simulated numerically. As the result of image analysis, the fluctuation of cavitation volume is corresponding to the pressure fluctuation of downstream, and the both fluctuations take peaks at frequencies from 1.5 to 2.5 kHz depending on the back pressure. In addition, as the back pressure increases, the frequency of the pressure fluctuation increases and the peak value decreases. These phenomena were also qualitatively reproduced in the numerical simulation.

  19. Sediment and Cavitation Erosion Studies through Dam Tunnels

    Directory of Open Access Journals (Sweden)

    Muhammad Abid

    2016-01-01

    Full Text Available This paper presents results of sediment and cavitation erosion through Tunnel 2 and Tunnel 3 of Tarbela Dam in Pakistan. Main bend and main branch of Tunnel 2 and outlet 1 and outlet 3 of Tunnel 3 are concluded to be critical for cavitation and sediment erosion. Studies are also performed for increased sediments flow rate, concluding 5 kg/sec as the critical value for sudden increase in erosion rate density. Erosion rate is concluded to be the function of sediment flow rate and head condition. Particulate mass presently observed is reasonably low, hence presently not affecting the velocity and the flow field.

  20. Mapping of cavitational activity in a pilot plant dyeing equipment.

    Science.gov (United States)

    Actis Grande, G; Giansetti, M; Pezzin, A; Rovero, G; Sicardi, S

    2015-11-01

    A large number of papers of the literature quote dyeing intensification based on the application of ultrasound (US) in the dyeing liquor. Mass transfer mechanisms are described and quantified, nevertheless these experimental results in general refer to small laboratory apparatuses with a capacity of a few hundred millilitres and extremely high volumetric energy intensity. With the strategy of overcoming the scale-up inaccuracy consequent to the technological application of ultrasounds, a dyeing pilot-plant prototype of suitable liquor capacity (about 40 L) and properly simulating several liquor to textile hydraulic relationships was designed by including US transducers with different geometries. Optimal dyeing may be obtained by optimising the distance between transducer and textile material, the liquid height being a non-negligible operating parameter. Hence, mapping the cavitation energy in the machinery is expected to provide basic data on the intensity and distribution of the ultrasonic field in the aqueous liquor. A flat ultrasonic transducer (absorbed electrical power of 600 W), equipped with eight devices emitting at 25 kHz, was mounted horizontally at the equipment bottom. Considering industrial scale dyeing, liquor and textile substrate are reciprocally displaced to achieve a uniform colouration. In this technology a non uniform US field could affect the dyeing evenness to a large extent; hence, mapping the cavitation energy distribution in the machinery is expected to provide fundamental data and define optimal operating conditions. Local values of the cavitation intensity were recorded by using a carefully calibrated Ultrasonic Energy Meter, which is able to measure the power per unit surface generated by the cavitation implosion of bubbles. More than 200 measurements were recorded to define the map at each horizontal plane positioned at a different distance from the US transducer; tap water was heated at the same temperature used for dyeing tests (60

  1. Prediction of Performance of a Cavitating Propeller in Oblique Inflow

    Science.gov (United States)

    Tian, Ye; Kinnas, Spyros A.

    2015-12-01

    A cavitating propeller subject to an oblique inflow in a cavitating tunnel is simulated using potential flow methods coupled with a Reynolds-averaged Navier-Stokes (RANS) solver. The propeller is mainly modelled using a panel method, while the inflow to the propeller is evaluated by coupling a Vortex-Lattice Method (VLM) with the RANS solver. The effects of the tunnel wall are incorporated into the calculated effective inflow to the propeller. The predicted propeller forces and cavity pattern are correlated with experiment. The fully wetted open water characteristics of the propeller predicted by the panel method are presented as well.

  2. An Approach in Modeling Cavitating Flows with Gravity Effect

    Institute of Scientific and Technical Information of China (English)

    ZhangtongXIE; YoushengHE

    1997-01-01

    Numerical investigations on submerged cavitating slender axisymmetric bodies with gravity effect are conducted in this paper,The developed cavity shape and the hydrodynamic characteristics on cavitating axisymmetric bodies are calculated.While these cavities originate from both the shoulder and the tail of bodies,we focus our main attention on the cavities originated from the shoulder,The boundary element method is used to solve the potential flow problem,and a new iteration method named Adaptive Modified Newton Iteration is developed to determine the cavity shape.

  3. Prediction of Non-Cavitation Propeller Noise in Time Domain

    Institute of Scientific and Technical Information of China (English)

    YE Jin-ming; XIONG Ying; XIAO Chang-run; BI Yi

    2011-01-01

    The blade frequency noise of non-cavitation propeller in a uniform flow is analyzed in time domain.The unsteady loading (dipole source) on the blade surface is calculated by a potential-based surface panel method.Then the timedependent pressure data is used as the input for Ffowcs Williams-Hawkings formulation to predict the acoustics pressure.The integration of noise source is performed over the true blade surface rather than the nothickness blade surface,and the effect of hub can be considered.The noise characteristics of the non-cavitation propeller and the numerical discretization forms are discussed.

  4. Quantitative assessment of reactive oxygen species generation by cavitation incepted efficiently using nonlinear propagation effect

    Science.gov (United States)

    Yasuda, Jun; Yoshizawa, Shin; Umemura, Shin-ichiro

    2015-10-01

    Sonodynamic treatment is a treatment method that uses chemical bio-effect of cavitation bubbles. Reactive oxygen species that can kill cancerous tissue is induced by such chemical effect of cavitation bubbles and it is important to generate them efficiently for effective sonodynamic treatment. Cavitation cloud can be formed by an effect of nonlinear propagation and focus and in this study, it was experimentally investigated if cavitation cloud was useful for efficient generation of reactive oxygen species. As a result, it was demonstrated that cavitation cloud would be useful for efficient generation of reactive oxygen species.

  5. Cavitation performance and flow characteristic in a centrifugal pump with inlet guide vanes

    Science.gov (United States)

    Tan, L.; Zha, L.; Cao, S. L.; Wang, Y. C.; Gui, S. B.

    2015-01-01

    The influence of prewhirl regulation by inlet guide vanes (IGVs) on cavitation performance and flow characteristic in a centrifugal pump is investigated. At the impeller inlet, the streamlines are regulated by the IGVs, and the axial velocity distribution is also influenced by the IGVs. Due to the total pressure loss on the IGVs, the cavitation performance of the centrifugal pump degrades. The cavitation area in impeller with IGVs is larger than one without IGVs. The specify values of total pressure loss between the suction pipe inlet and impeller inlet for three cavitation conditions show that the IGVs will generate additional pressure loss, which is related to the IGVs angles and cavitation conditions.

  6. Computational theory of cavitating flows for hydraulic turbomachinery with consideration of influence of water quality

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    Previously it was assumed that the pressure within the cavity or on the cavity surface remained constant and the vapor pressure of clean water at 20°C and 0 m altitude was utilized as the computational boundary for cavitating flows in hydraulic turbomachinery. Cavitation was confused with vaporization, and the effect of water quality on cavitation pressure characteristics was not taken into account. In recent years, lots of experiments of cavitation pressure characteristics of different water qualities including different sand concentrations of sand water and different altitudes of clean water have been performed by the authors, and the important influences of water quality on cavitation pressure characteristic have been validated. Thus the water quality should be involved in the cavitating flows computation. In the present paper, the effect of water quality on the cavitation pressure characteristic is analyzed and the computational method and theory of cavitating flows for hydraulic turbomachinery that considers the influence of water quality are proposed. The theory is suitable for both the potential flow method and the two-phase flow method for cavitating flows simulation. Finally, the validation results for cavitating flows in a hydraulic tur- bine indicate the significant influences of water quality on the cavitating flow performance.

  7. Cavitational hydrothermal oxidation: A new remediation process. 1998 annual progress report

    International Nuclear Information System (INIS)

    'The primary goal is to develop a quantitative understanding of cavitation phenomena in aqueous media and the development of applications of cavitation to remediation processes. Efforts have focused on three separate areas: sonoluminescence as a probe of conditions created during cavitational collapse in aqueous media, the use of cavitation for remediation of contaminated water, and an addition of the use of ultrasound in the synthesis of novel heterogeneous catalysts for hydrodehalogenation of halocarbons under mild conditions. This report summarizes work after one year of a three year project. In order to gain further understanding of the conditions present during cavitation, the author has continued his studies of sonoluminescence. He has made recent breakthroughs in the use of emission spectroscopy for temperature and pressure measurement of cavitation events, which he expects to publish shortly. He has been able to measure for the first time the temperature of cavitation in water during multi-bubble cavitation in the presence of aromatic hydrocarbons. The emission from excited states of C2 in water gives temperatures that are consistent with adiabatic compressional heating, with maximum temperatures of 4,300 K. Prior measurements of cavitation temperatures in low vapor pressure nonaqueous media gave somewhat higher temperatures of 5,000 K. This work lays permanently to rest exotic mechanisms for cavitational chemistry, at least for cavitation fields.'

  8. Cavitational hydrothermal oxidation: A new remediation process. Annual progress report, September 1996 - August 1997

    International Nuclear Information System (INIS)

    'During the past year, the authors have continued to make substantial scientific progress on the understanding of cavitation phenomena in aqueous media and applications of cavitation to remediation processes. The efforts have focused on three separate areas: sonoluminescence as a probe of conditions created during cavitational collapse in aqueous media, the use of cavitation for remediation of contaminated water, and an addition of the use of ultrasound in the synthesis of novel heterogeneous catalysts for hydrodehalogenation of halocarbons under mild conditions. In order to gain further understanding of the conditions present during cavitation, the author has continued his studies of sonoluminescence. He has made recent breakthroughs in the use of emission spectroscopy for temperature and pressure measurement of cavitation events, which he expects to publish shortly. He has been able to measure for the first time the temperature of cavitation in water during multi-bubble cavitation in the presence of aromatic hydrocarbons. The emission from excited states of C2 in water gives temperatures that are consistent with adiabatic compressional heating, with maximum temperatures of 4,300 K. Prior measurements of cavitation temperatures in low vapor pressure nonaqueous media gave somewhat higher temperatures of 5,000 K. This work lays permanently to rest exotic mechanisms for cavitational chemistry, at least for cavitation fields.'

  9. Precise spatial control of cavitation erosion in a vessel phantom by using an ultrasonic standing wave.

    Science.gov (United States)

    Shi, Aiwei; Huang, Peixuan; Guo, Shifang; Zhao, Lu; Jia, Yingjie; Zong, Yujin; Wan, Mingxi

    2016-07-01

    In atherosclerotic inducement in animal models, the conventionally used balloon injury is invasive, produces excessive vessel injuries at unpredictable locations and is inconvenient in arterioles. Fortunately, cavitation erosion, which plays an important role in therapeutic ultrasound in blood vessels, has the potential to induce atherosclerosis noninvasively at predictable sites. In this study, precise spatial control of cavitation erosion for superficial lesions in a vessel phantom was realised by using an ultrasonic standing wave (USW) with the participation of cavitation nuclei and medium-intensity ultrasound pulses. The superficial vessel erosions were restricted between adjacent pressure nodes, which were 0.87mm apart in the USW field of 1MHz. The erosion positions could be shifted along the vessel by nodal modulation under a submillimetre-scale accuracy without moving the ultrasound transducers. Moreover, the cavitation erosion of the proximal or distal wall could be determined by the types of cavitation nuclei and their corresponding cavitation pulses, i.e., phase-change microbubbles with cavitation pulses of 5MHz and SonoVue microbubbles with cavitation pulses of 1MHz. Effects of acoustic parameters of the cavitation pulses on the cavitation erosions were investigated. The flow conditions in the experiments were considered and discussed. Compared to only using travelling waves, the proposed method in this paper improves the controllability of the cavitation erosion and reduces the erosion depth, providing a more suitable approach for vessel endothelial injury while avoiding haemorrhage. PMID:26964937

  10. Effect of Primary Factor on Cavitation Resistance of Some Austenitic Metals

    Institute of Scientific and Technical Information of China (English)

    WANG Zai-you; ZHU Jin-hua

    2003-01-01

    The cavitation resistance of six kinds of austenitic metals was investigated using a rotating disc rig. The research results show that cavitation resistance of the austenitic metals is obviously raised due to cavitation-induced martensite and greatly influenced by mechanism of martensitic transformation. The cavitation resistance of two stress-induced martensite Fe-Mn-Si-Cr shape memory alloys is much better than that of three strain-induced martensite austenitic stainless steels. The Fe-Mn-Si-Cr shape memory alloys possess excellent cavitation resistance mainly because of their excellent elasticity in local small-zone. The first principal factor for cavitation resistance of metastable austenitic metals is unloaded rebounding depth, and the second one is energy dissipation resulted from cavitation-induced martensite.

  11. Ultrasonic cavitation erosion of gas nitrided Ti-6Al-4V alloys.

    Science.gov (United States)

    Mitelea, I; Dimian, E; Bordeaşu, I; Crăciunescu, C

    2014-07-01

    Ultrasonic cavitation erosion experiments were performed on Ti-6Al-4V alloys samples in annealed, nitrided and nitrided and subsequently heat treated state. The protective oxide layer formed as a result of annealing and heat treatment after nitriding is eliminated after less than 30 min cavitation time, while the nitride layer lasts up to 90 min cavitation time. Once the protective layer is removed, the cavitation process develops by grain boundary erosion, leading to the expulsion of grains from the surface. The gas nitrided Ti-6Al-4V alloy, forming a TixN surface layer, proved to be a better solution to improve the cavitation erosion resistance, compared to the annealed and nitrided and heat treated state, respectively. The analysis of the mean depth of erosion rate at 165 min cavitation time showed an improvement of the cavitation erosion resistance of the nitrided samples of up to 77% higher compared to the one of the annealed samples. PMID:24500067

  12. Numerical simulation of high-speed cavitating flows in submerged water jet

    Science.gov (United States)

    Peng, G.; Shimizu, S.

    2013-12-01

    Properties of existing cavitation models are discussed and a compressible mixture flow method based a simplified estimation of bubble cavitation is then presented for numerical simulation of high-speed water jets accompanied by intensive cavitation. Two-phase fluid media of cavitating flow are treated as a mixture of liquid and bubbles, and the mean flow is computed by solving RANS equations for compressible fluids considering the effect of bubble expansion a/o contraction. The intensity of cavitation is evaluated by the gas volume fraction, which is governed by the compressibility of bubble-liquid mixture corresponding to the status of mean flow field. Numerical results of cavitating water jet issuing from a submerged nozzle are presented and its applicability to intensively cavitating jets is demonstrated.

  13. Numerical simulation of high-speed cavitating flows in submerged water jet

    International Nuclear Information System (INIS)

    Properties of existing cavitation models are discussed and a compressible mixture flow method based a simplified estimation of bubble cavitation is then presented for numerical simulation of high-speed water jets accompanied by intensive cavitation. Two-phase fluid media of cavitating flow are treated as a mixture of liquid and bubbles, and the mean flow is computed by solving RANS equations for compressible fluids considering the effect of bubble expansion a/o contraction. The intensity of cavitation is evaluated by the gas volume fraction, which is governed by the compressibility of bubble-liquid mixture corresponding to the status of mean flow field. Numerical results of cavitating water jet issuing from a submerged nozzle are presented and its applicability to intensively cavitating jets is demonstrated

  14. Numerical simulation and experimental visualization of the separated cavitating boundary layer over NACA2412

    Directory of Open Access Journals (Sweden)

    Kozák Jiří

    2015-01-01

    Full Text Available Cavitation is physical phenomenon of crucial impact on the operation range and service lifetime of the hydraulic machines (pumps, turbines, valves etc.. Experimental measurement of cavitation is expensive and time consuming process, while some important characteristic of the flow are difficult to measure due to the nature of the phenomenon. Current possibilities of computational fluid dynamics provide a way for deeper understanding of cavitation which is important for many applications in the hydraulic machines industry such as expanding operation range or extending lifetime of the hydraulic machines. Simplified model consists of NACA 2412 hydrofoil with 8 degrees angle of attack fixed in between the walls of cavitation tunnel. Present investigation focuses on comparison of vapor volume fractions obtained by 3D CFD simulations and high speed visualization of the real cavitation phenomena. Several operating regimes corresponding to different cavitation numbers are studied with aim to assess the dynamics of the separated cavitating sheets/clouds

  15. A numerical model for the evolution of internal structure of cavitation cloud

    Science.gov (United States)

    Du, Tezhuan; Wang, Yiwei; Liao, Lijuan; Huang, Chenguang

    2016-07-01

    Bubble size distributions in cloud cavitation are important in cavitating flows. In this study, a numerical model was developed to study the evolution of the internal structure of cloud cavitation. The model includes (1) an evolution equation of bubble number density, which considers the bubble breakup effect and (2) the multiphase Reynolds-averaged Navier-Stokes equations with a modified cavitation model for background cavitating flows. The proposed model was validated with a flow over a projectile. Results show that the numerical model can predict the evolution of the internal structure of cloud cavitation. Comparisons of the proposed model and Singhal model were discussed. The effects of re-entrant jet and bubble number density on cavitating flows were also investigated.

  16. Parallel Computing of the Underwater Explosion Cavitation Effects on Full-scale Ship Structures

    Institute of Scientific and Technical Information of China (English)

    Zhi Zong; Yanjie Zhao; Fan Ye; Haitao Li; Gang Chen

    2012-01-01

    Abstract:As well as shock wave and bubble pulse loading,cavitation also has very significant influences on the dynamic response of surface ships and other near-surface marine structures to underwater explosive loadings.In this paper,the acoustic-structure coupling method embedded in ABAQUS is adopted to do numerical analysis of underwater explosion considering cavitation.Both the shape of bulk cavitation region and local cavitation region are obtained,and they are in good agreement with analytical results.The duration of reloading is several times longer than that of a shock wave.In the end,both the single computation and parallel computation of the cavitation effect on the dynamic responses of a full-scale ship are presented,which proved that reloading caused by cavitation is non-ignorable.All these results are helpful in understanding underwater explosion cavitation effects.

  17. On the importance of initial volume of eroded material for cavitation erosion curve

    Directory of Open Access Journals (Sweden)

    M. Szkodo

    2006-08-01

    Full Text Available Purpose: Cavitation erosion is a surface degradation mechanism which occurs most frequently in fluid-flowmachines operating in cavitation conditions. To find way to prediction the cavitation erosion progress, simplemathematical model was proposed.Design/methodology/approach: The model assumes that curve of cumulative volume loss as a function of timeapproaches initial volume of eroded material. This principle causes dependence of cavitation erosion curve notonly from mechanical properties of eroded material and cavitation loading but also from dimensions of initialvolume i.e. eroded area of material and even height of cross-section of eroded initial volume of material.Findings: Assessment of cavitation erosion resistant of material upon the base of cavitation erosion curve hasto take into account this influence. In the paper the influence of these parameters on the cavitation erosioncurve was discussed.Research limitations/implications: Future research concerning cavitation erosion resistance of materials oughtto takes into account influence of initial volume of eroded material for cavitation erosion curve. Reportedresearch ought to be completed and full cavitation curves (volume loss in time for different initial volume oferoded material must be done.Practical implications: Existing standards have recommended assessment of cavitation erosion resistance ofmaterials by comparison of their erosion curves (volume loss in time and volume loss rate of erosion. For thisreason one should strive to explanation all factors influencing on the cavitation erosion curve.Originality/value: The work proposes a mathematical model which permits to define the influence of initialvolume of eroded material on the cavitation erosion curve.

  18. Quantitative assessment of reactive oxygen sonochemically generated by cavitation bubbles

    Science.gov (United States)

    Yasuda, Jun; Miyashita, Takuya; Taguchi, Kei; Yoshizawa, Shin; Umemura, Shin-ichiro

    2015-07-01

    Acoustic cavitation bubbles can induce not only a thermal bioeffect but also a chemical bioeffect. When cavitation bubbles collapse and oscillate violently, they produce reactive oxygen species (ROS) that cause irreversible changes to the tissue. A sonosensitizer can promote such ROS generation. A treatment method using a sonosensitizer is called sonodynamic treatment. Rose bengal (RB) is one of the sonosensitizers whose in vivo and in vitro studies have been reported. In sonodynamic treatment, it is important to produce ROS at a high efficiency. For the efficient generation of ROS, a triggered high-intensity focused ultrasound (HIFU) sequence has been proposed. In this study, cavitation bubbles were generated in a chamber where RB solution was sealed, and a high-speed camera captured the behavior of these cavitation bubbles. The amount of ROS was also quantified by a potassium iodide (KI) method and compared with high-speed camera pictures to investigate the effectiveness of the triggered HIFU sequence. As a result, ROS could be obtained efficiently by this sequence.

  19. Experimental research of multiphase flow with cavitation in the nozzle

    Science.gov (United States)

    Kozubkova, Milada; Bojko, Marian; Jablonska, Jana; Homa, Dorota; Tůma, Jiří

    2016-03-01

    The paper deals with the problems of cavitation in water flow in the nozzle. The area of research is divided into two directions (experimental and numerical research). During the experimental research the equipment with the nozzle is under the measurement and basic physical quantities such as pressure and volume flow rate are recorded. In the following phase measuring of noise which is generated during flow through the nozzle in the area of cavitation is measured at various operating conditions of the pump. In the second part the appropriate multiphase mathematical model including the consideration of cavitation is defined. Boundary conditions for numerical simulation are defined on the basis of experimental measurements. Undissolved air in the flow is taken into account to obtain pressure distribution in accordance to measured one. Results of the numerical simulation are presented by means of basic current quantities such as pressure, velocity and volume fractions of each phase. The conclusions obtained from experimental research of cavitation were applied to modify the multiphase mathematical model.

  20. A cavitation model based on Eulerian stochastic fields

    International Nuclear Information System (INIS)

    Non-linear phenomena can often be described using probability density functions (pdf) and pdf transport models. Traditionally the simulation of pdf transport requires Monte-Carlo codes based on Lagrangian ''particles'' or prescribed pdf assumptions including binning techniques. Recently, in the field of combustion, a novel formulation called the stochastic-field method solving pdf transport based on Eulerian fields has been proposed which eliminates the necessity to mix Eulerian and Lagrangian techniques or prescribed pdf assumptions. In the present work, for the first time the stochastic-field method is applied to multi-phase flow and in particular to cavitating flow. To validate the proposed stochastic-field cavitation model, two applications are considered. Firstly, sheet cavitation is simulated in a Venturi-type nozzle. The second application is an innovative fluidic diode which exhibits coolant flashing. Agreement with experimental results is obtained for both applications with a fixed set of model constants. The stochastic-field cavitation model captures the wide range of pdf shapes present at different locations

  1. Numerical Investigation of Cavitation Improvement for a Francis Turbine

    Science.gov (United States)

    Yao, Zhifeng; Xiao, Ruofu; Wang, Fujun; Yang, Wei

    2015-12-01

    Cavitation in hydraulic machine is undesired due to its negative effects on performances. To improve cavitation performance of a Francis turbine without the change of the best efficiency point, a model runner geometry optimization was carried out. Firstly, the runner outlet diameter was appropriately increased to reduce the flow velocity at runner outlet region. Then, to avoid the change of the flow rate at the best efficiency point, the blade shapes were carefully adjusted by decreasing the blade outlet angles and increasing the blade wrap angles. A large number of the modified runners were tested by computational fluid dynamic (CFD) method. Finally the most appropriate one was selected, which has the runner outlet diameter 10% larger, the blade outlet angles 3 degrees smaller and the blade wrap angles 5 degrees larger. The results showed that the critical cavitation coefficient of the model runner decreased at every unit rotational speed after the optimization, and the effect was much remarkable at relative high flow rate. Besides, by analysing the internal flow field, it was found that the zone of the low pressure on pressure surface of the optimized turbine blades was reduced, the backflow and vortex rope in draft tube were reduced, and the cavitation zone was reduced obviously.

  2. Analysis of cavitation effect for water purifier using electrolysis

    Science.gov (United States)

    Shin, Dong Ho; Ko, Han Seo; Lee, Seung Ho

    2015-11-01

    Water is a limited and vital resource, so it should not be wasted by pollution. A development of new water purification technology is urgent nowadays since the original and biological treatments are not sufficient. The microbubble-aided method was investigated for removal of algal in this study since it overcomes demerits of the existing purification technologies. Thus, the cavitation effect in a venturi-type tube using the electrolysis was analyzed. Ruthenium-coated titanium plates were used as electrodes. Optimum electrode interval and applied power were determined for the electrolysis. Then, the optimized electrodes were installed in the venturi-type tube for generating cavitation. The cavitation effect could be enhanced without any byproduct by the bubbly flow induced by the electrolysis. The optimum mass flow rate and current were determined for the cavitation with the electrolysis. Finally, the visualization techniques were used to count the cell number of algal and microbubbles for the confirmation of the performance. As a result, the energy saving and high efficient water purifier was fabricated in this study. This work was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Korean government (MEST) (No. 2013R1A2A2A01068653).

  3. Experimental research of multiphase flow with cavitation in the nozzle

    Directory of Open Access Journals (Sweden)

    Kozubkova Milada

    2016-01-01

    Full Text Available The paper deals with the problems of cavitation in water flow in the nozzle. The area of research is divided into two directions (experimental and numerical research. During the experimental research the equipment with the nozzle is under the measurement and basic physical quantities such as pressure and volume flow rate are recorded. In the following phase measuring of noise which is generated during flow through the nozzle in the area of cavitation is measured at various operating conditions of the pump. In the second part the appropriate multiphase mathematical model including the consideration of cavitation is defined. Boundary conditions for numerical simulation are defined on the basis of experimental measurements. Undissolved air in the flow is taken into account to obtain pressure distribution in accordance to measured one. Results of the numerical simulation are presented by means of basic current quantities such as pressure, velocity and volume fractions of each phase. The conclusions obtained from experimental research of cavitation were applied to modify the multiphase mathematical model.

  4. Modeling of Cavitation Flow on NACA 0015 Hydrofoil

    OpenAIRE

    Štigler, Jaroslav; Svozil, Jan

    2009-01-01

    This paper is concerning with simulations of cavitation flow around the NACA 0015 hydrofoil. The problem is solved as the multi-phase and single-phase model of flow, for two different impact angles and for two different densities of computational net. The attention is focused on the comparison of single-phase and multi-phase results.

  5. Numerical and Experimental Investigation of Cavitation Erosion Potential

    Czech Academy of Sciences Publication Activity Database

    Sedlář, M.; Zima, Patrik; Müller, M.

    Dresden : FZD & ANSYS, 2009. s. 1-24. [ANSYS & FZD Short Course and Workshop Multiphase Flows Simulation, Experiment and Application /7./. 26.05.2009-28.05.2009, Dresden-Rossendorf] R&D Projects: GA ČR(CZ) GA101/07/1612 Institutional research plan: CEZ:AV0Z20760514 Keywords : cavitation * erosion * pumps Subject RIV: BK - Fluid Dynamics

  6. Orifice plate cavitation mechanism and its influencing factors

    Institute of Scientific and Technical Information of China (English)

    Wan-zheng AI; Tian-ming DING

    2010-01-01

    The orifice plate energy dissipater is an economic and highly efficient dissipater.However,there is a risk of cavitaion around the orifice plate flow.In order to provide references for engineering practice,we examined the cavitation mechanism around the orifice plate and its influencing factors by utilizing mathematical analysis methods to analyze the flow conditions around the orifice plate in view of gas bubble dynamics.Through the research presented in this paper,the following can be observed:The critical radius and the critical pressure of the gas nucleus in orifice plate flow increase with its initial state parameter τ0;the development speed of bubbles stabilizes at a certain value after experiencing a peak value and a small valley value;and the orifice plate cavitation is closely related to the distribution of the gas nucleus in flow.For computing the orifice plate cavitation number,we ought to take into account the effects of pressure fluctuation.The development time of the gas nucleus from the initial radius to the critical radius is about10-7-10-5 s;therefore,the gas nucleus has sufficient time to develop into bubbles in the negative half-cycle of flow fluctuation.The orifice critical cavitation number is closely related to the orifice plate size,and especially closely related with the ratio of the orifice plate radius to the tunnel radius.The approximate formula for the critical cavitation number of the square orifice plate that only considers the main influencing factor was obtained by model experiments.

  7. Inertial cavitation initiated by polytetrafluoroethylene nanoparticles under pulsed ultrasound stimulation.

    Science.gov (United States)

    Jin, Qiaofeng; Kang, Shih-Tsung; Chang, Yuan-Chih; Zheng, Hairong; Yeh, Chih-Kuang

    2016-09-01

    Nanoscale gas bubbles residing on a macroscale hydrophobic surface have a surprising long lifetime (on the order of days) and can serve as cavitation nuclei for initiating inertial cavitation (IC). Whether interfacial nanobubbles (NBs) reside on the infinite surface of a hydrophobic nanoparticle (NP) and could serve as cavitation nuclei is unknown, but this would be very meaningful for the development of sonosensitive NPs. To address this problem, we investigated the IC activity of polytetrafluoroethylene (PTFE) NPs, which are regarded as benchmark superhydrophobic NPs due to their low surface energy caused by the presence of fluorocarbon. Both a passive cavitation detection system and terephthalic dosimetry was applied to quantify the intensity of IC. The IC intensities of the suspension with PTFE NPs were 10.30 and 48.41 times stronger than those of deionized water for peak negative pressures of 2 and 5MPa, respectively. However, the IC activities were nearly completely inhibited when the suspension was degassed or ethanol was used to suspend PTFE NPs, and they were recovered when suspended in saturated water, which may indicates the presence of interfacial NBs on PTFE NPs surfaces. Importantly, these PTFE NPs could sustainably initiate IC for excitation by a sequence of at least 6000 pulses, whereas lipid microbubbles were completely depleted after the application of no more than 50 pulses under the same conditions. The terephthalic dosimetry has shown that much higher hydroxyl yields were achieved when PTFE NPs were present as cavitation nuclei when using ultrasound parameters that otherwise did not produce significant amounts of free radicals. These results show that superhydrophobic NPs may be an outstanding candidate for use in IC-related applications. PMID:27150739

  8. Influence of Thermodynamic Effect on Blade Load in a Cavitating Inducer

    Directory of Open Access Journals (Sweden)

    Kengo Kikuta

    2010-01-01

    Full Text Available Distribution of the blade load is one of the design parameters for a cavitating inducer. For experimental investigation of the thermodynamic effect on the blade load, we conducted experiments in both cold water and liquid nitrogen. The thermodynamic effect on cavitation notably appears in this cryogenic fluid although it can be disregarded in cold water. In these experiments, the pressure rise along the blade tip was measured. In water, the pressure increased almost linearly from the leading edge to the trailing edge at higher cavitation number. After that, with a decrease of cavitation number, pressure rise occurred only near the trailing edge. On the other hand, in liquid nitrogen, the pressure distribution was similar to that in water at a higher cavitation number, even if the cavitation number as a cavitation parameter decreased. Because the cavitation growth is suppressed by the thermodynamic effect, the distribution of the blade load does not change even at lower cavitation number. By contrast, the pressure distribution in liquid nitrogen has the same tendency as that in water if the cavity length at the blade tip is taken as a cavitation indication. From these results, it was found that the shift of the blade load to the trailing edge depended on the increase of cavity length, and that the distribution of blade load was indicated only by the cavity length independent of the thermodynamic effect.

  9. Detection of cavitation vortex in hydraulic turbines using acoustic techniques

    International Nuclear Information System (INIS)

    Cavitation phenomena are known for their destructive capacity in hydraulic machineries and are caused by the pressure decrease followed by an implosion when the cavitation bubbles find an adverse pressure gradient. A helical vortex appears in the turbine diffuser cone at partial flow rate operation and can be cavitating in its core. Cavity volumes and vortex frequencies vary with the under-pressure level. If the vortex frequency comes close to one of the eigen frequencies of the turbine, a resonance phenomenon may occur, the unsteady fluctuations can be amplified and lead to important turbine and hydraulic circuit damage. Conventional cavitation vortex detection techniques are based on passive devices (pressure sensors or accelerometers). Limited sensor bandwidths and low frequency response limit the vortex detection and characterization information provided by the passive techniques. In order to go beyond these techniques and develop a new active one that will remove these drawbacks, previous work in the field has shown that techniques based on acoustic signals using adapted signal content to a particular hydraulic situation, can be more robust and accurate. The cavitation vortex effects in the water flow profile downstream hydraulic turbines runner are responsible for signal content modifications. Basic signal techniques use narrow band signals traveling inside the flow from an emitting transducer to a receiving one (active sensors). Emissions of wide band signals in the flow during the apparition and development of the vortex embeds changes in the received signals. Signal processing methods are used to estimate the cavitation apparition and evolution. Tests done in a reduced scale facility showed that due to the increasing flow rate, the signal -- vortex interaction is seen as modifications on the received signal's high order statistics and bandwidth. Wide band acoustic transducers have a higher dynamic range over mechanical elements; the system

  10. Localization of incipient tip vortex cavitation using ray based matched field inversion method

    Science.gov (United States)

    Kim, Dongho; Seong, Woojae; Choo, Youngmin; Lee, Jeunghoon

    2015-10-01

    Cavitation of marine propeller is one of the main contributing factors of broadband radiated ship noise. In this research, an algorithm for the source localization of incipient vortex cavitation is suggested. Incipient cavitation is modeled as monopole type source and matched-field inversion method is applied to find the source position by comparing the spatial correlation between measured and replicated pressure fields at the receiver array. The accuracy of source localization is improved by broadband matched-field inversion technique that enhances correlation by incoherently averaging correlations of individual frequencies. Suggested localization algorithm is verified through known virtual source and model test conducted in Samsung ship model basin cavitation tunnel. It is found that suggested localization algorithm enables efficient localization of incipient tip vortex cavitation using a few pressure data measured on the outer hull above the propeller and practically applicable to the typically performed model scale experiment in a cavitation tunnel at the early design stage.

  11. Study of unsteady cavitation flow of a pump-turbine at pump mode

    International Nuclear Information System (INIS)

    Three dimensional, unsteady, cavitating flows in a pump-turbine at pump mode were numerically studied using SST k-ω turbulence model and the mixture model. The unsteady cavitating flow and pressure fluctuations at different positions were analysed with two openings of guide vanes. Calculation results are in good agreement with experimental data. Results show that the opening of guide vanes has great effect on the cavitation phenomenon. The cavitating region gradually decreases with the increase of the relative opening, and it locates at the inlet of the suction side. The amplitude of the pressure fluctuation reduces as the cavitating region decreases. The numerical study of unsteady cavitating flow can provide a basic understanding for the improvement of stable operation of a pump-turbine

  12. Cavitation Simulation on Conventional and Highly-Skewed Propellers in the Behind Condition

    DEFF Research Database (Denmark)

    Shin, Keun Woo; Andersen, Poul; Mikkelsen, Robert Flemming

    2011-01-01

    the study of implementing a HEM cavitation model for computing unsteady cavitation patterns in behind-hull condition with respect to blade angles and cavity extent on the complicated geometry of a conventional/highly-skewed propeller. In the computations, the efficiency of the non-homogeneously loaded......The cavitating flows around conventional and highly-skewed propellers in the behind-hull condition are simulated by an in-house RANS solver, EllipSys (Sørensen 2003), with the cavitation model, based on the homogeneous equilibrium modeling (HEM) approach and a vapor transport equation...... in the propeller plane is applied by using a non-homogenously loaded actuator disk (Mikkelsen et al 2007) placed in a plane upstream of the propeller. The variation of the computed cavitation profile with respect to the blade angle is compared with that from the cavitation tunnel test. The present work describes...

  13. Cavitation erosion in blocked flow with a ducted ice-class propeller

    Energy Technology Data Exchange (ETDEWEB)

    Doucet, J.M.; Bose, N.; Walker, D. [Memorial Univ. of Newfoundland, St. John`s, Newfoundland (Canada). Ocean Engineering Research Centre; Jones, S.J. [National Research Council of Canada, St. John`s, Newfoundland (Canada). Inst. for Marine Dynamics

    1996-12-31

    Ships that operate in ice often encounter momentary increased propeller cavitation because ice pieces block the flow into the propeller. For ducted propellers, this additional cavitation is more significant than it is for open propellers; ice pieces may become lodged against and within the duct and subject the propeller to longer periods of increased cavitation due to the blocked flow. Associated with this blocked flow is the possibility of cavitation erosion on the propeller. An erosion study, using paint films, was conducted in a cavitation tunnel with a model propeller of the type fitted to the Canadian Marine Drilling Ltd. vessel MV Robert LeMeur. A simulated ice blockage was installed ahead of the propeller model and within the duct. Tests were carried out over a range of advance coefficients for various test conditions. The resulting types of cavitation were documented, the erosion patterns were photographed and comparisons between each test were made.

  14. Outlet Conditions Causing Cavitation in the Invert of an Open Channel

    Institute of Scientific and Technical Information of China (English)

    1999-01-01

    This paper experimentally analyzes the causes of cavitation damage in the in vert of an open channel. Results show that cavitation in the invert is mainly du e to the maximum boundary shear occurring at the downstream tangential point of the invert, and the critical hydraulic condition causing cavitation occurs when the dimensionless parameter η=q/(Gh3/2) is equal to 0.015. An improved configuration of the invert is then developed.

  15. Memory effect and redistribution of cavitation nuclei in a thin liquid layer.

    Science.gov (United States)

    Bai, Lixin; Lin, Weijun; Wu, Pengfei; Deng, Jingjun; Li, Chao; Xu, Delong; Wang, Dong; Chen, Lishuo

    2016-09-01

    Temporal evolution and spatial distribution of acoustic cavitation structures in a thin liquid layer were investigated experimentally with high-speed photography. The inception and disappearance processes of cavitation bubble cloud revealed that the metastable cavitaton structures formed in the thin liquid layer caused a long-term "memory effect". A factor which weakens the memory effect was identified. The distribution of cavitation nuclei was investigated by changing the temporal decay of the memory effect. PMID:27150763

  16. Histotripsy-Induced Cavitation Cloud Initiation Thresholds in Tissues of Different Mechanical Properties

    OpenAIRE

    Vlaisavljevich, Eli; Maxwell, Adam; Warnez, Matthew; Johnsen, Eric; Cain, Charles A.; Xu, Zhen

    2014-01-01

    Histotripsy is an ultrasound ablation method that depends on the initiation and maintenance of a cavitation bubble cloud to fractionate soft tissue. This paper studies how tissue properties impact the pressure threshold to initiate the cavitation bubble cloud. Our previous study showed that shock scattering off one or more initial bubbles, expanded to sufficient size in the focus, plays an important role in initiating a dense cavitation cloud. In this process, the shock scattering causes the ...

  17. Numerical Computation of Shock Waves in a Spherical Cloud of Cavitation Bubbles

    OpenAIRE

    Wang, Yi-Chun; Brennen, Christopher E.

    1999-01-01

    The nonlinear dynamics of a spherical cloud of cavitation bubbles have been simulated numerically in order to learn more about the physical phenomena occurring in cloud cavitation. A finite cloud of nuclei is subject to a decrease in the ambient pressure which causes the cloud to cavitate. A subsequent pressure recovery then causes the cloud to collapse. This is typical of the transient behavior exhibited by a bubble cloud as it passes a body or the blade of a ship propeller. The simulati...

  18. Changes in cell morphology due to plasma membrane wounding by acoustic cavitation

    OpenAIRE

    Schlicher, Robyn K.; Hutcheson, Joshua D.; Radhakrishna, Harish; Apkarian, Robert P.; Prausnitz, Mark R.

    2010-01-01

    Acoustic cavitation-mediated wounding (i.e., sonoporation) has great potential to improve medical and laboratory applications requiring intracellular uptake of exogenous molecules; however, the field lacks detailed understanding of cavitation-induced morphological changes in cells and their relative importance. Here, we present an in-depth study of the effects of acoustic cavitation on cells using electron and confocal microscopy coupled with quantitative flow cytometry. High resolution image...

  19. Hydro-acoustic excitation at low frequencies of industrial pipe systems by cavitating butterfly valves

    International Nuclear Information System (INIS)

    Cavitating valves induce important vibrations at low frequencies in pipe systems. In this note a model is developed in order to characterize the hydro-acoustic behavior of the cavitating valves. This model is based on the transfer matrix theory. This theory can be deduced from the linearization of the Navier-Stokes equations. The experimental identification and validation of the model is made by testing a cavitating butterfly valve. (author). 5 figs., 7 refs

  20. Experimental Investigation and Passive Flow Control of a Cavitating Centrifugal Pump

    OpenAIRE

    Spyridon D. Kyparissis; Dionissios P. Margaris

    2012-01-01

    Passive flow control techniques are used to improve the flow field and efficiency of centrifugal pumps and turbomachines, in general. An important phenomenon that mechanical engineers have to take into account is cavitation. It leads to the decrease of the pump performance and total head. In the present experimental study, a centrifugal pump is investigated in cavitating conditions. A passive flow control is realized using three different blade leading edge angles in order to reduce the cavit...

  1. Cavitation preventing device in a nuclear power plant

    International Nuclear Information System (INIS)

    Purpose: To prevent the generation of cavitation upon loss of feedwater flow rate in BWR nuclear power plant by reliably and rapidly tripping a recycling pump. Constitution: Two phase streams from a nuclear reactor are divided into main steams and saturated water in a steam drum. The deviation between the corresponding flow rate of the main steams and the feedwater flow rate of the feedwater pump sending condensates to the steam drum, as well as the continuing period of the deviation are monitored. Then, if it is detected that both of the deviation and the continuing period thereof exceed specified levels, the recycling pump feeding the saturated water to the reactor is tripped. In this way, the recycling pump can be tripped rapidly and reliably upon loss of feedwater flow rate, whereby the generation of the cavitation can be prevented and the normal operation of the nuclear power plant can be insured. (Moriyama, K.)

  2. Pitting damage in metals by mercury cavitation with MIMTM

    International Nuclear Information System (INIS)

    In the liquid mercury target for the spallation neutron source, pressure waves occurs owing to the high-intense proton beam bombardment. The pressure waves induces the cavitation in the interface between the mercury and the target vessel through the propagation process. Erosion damage composed of micro-pits clusters is formed by the micro-jets and shock waves emitted from cavitation bubble collapse. In this paper, researches for damage structure of the material that was examined using the electroMagnetic IMpact Testing Machine (MIMTM) form the viewpoint of high-speed deformation. The result showed that the 200 ∼ 300 m/s of collision velocity for micro-jet impacting which was estimated from the numerical simulation is reasonable value. (J.P.N.)

  3. Cavitation nuclei in water exposed to transient pressures

    DEFF Research Database (Denmark)

    Andersen, Anders Peter; Mørch, Knud Aage

    2015-01-01

    extended period of time prior to testing is known to increase the tensile strength of water, but little information is available on how it is affected by compression pulses of short duration. This is addressed by imposing compression pulses of approximately 1 ms duration and a peak intensity of a few bar......A model of skin-stabilized interfacial cavitation nuclei and their response to tensile and compressive stressing is presented. The model is evaluated in relation to experimental tensile strength results for water at rest at the bottom of an open water-filled container at atmospheric pressure and...... room temperature. These results are obtained by recording the initial growth of cavities generated by a short tensile pulse applied to the bottom of the container. It is found that the cavitation nuclei shift their tensile strength depending on their pressure history. Static pressurization for an...

  4. Partial Averaged Navier-Stokes approach for cavitating flow

    Science.gov (United States)

    Zhang, L.; Zhang, Y. N.

    2015-01-01

    Partial Averaged Navier Stokes (PANS) is a numerical approach developed for studying practical engineering problems (e.g. cavitating flow inside hydroturbines) with a resonance cost and accuracy. One of the advantages of PANS is that it is suitable for any filter width, leading a bridging method from traditional Reynolds Averaged Navier-Stokes (RANS) to direct numerical simulations by choosing appropriate parameters. Comparing with RANS, the PANS model will inherit many physical nature from parent RANS but further resolve more scales of motion in great details, leading to PANS superior to RANS. As an important step for PANS approach, one need to identify appropriate physical filter-width control parameters e.g. ratios of unresolved-to-total kinetic energy and dissipation. In present paper, recent studies of cavitating flow based on PANS approach are introduced with a focus on the influences of filter-width control parameters on the simulation results.

  5. Modeling of Unsteady Sheet Cavitation on Marine Propeller Blades

    Directory of Open Access Journals (Sweden)

    Spyros A. Kinnas

    2003-01-01

    Full Text Available Unsteady sheet cavitation is very common on marine propulsor blades. The authors summarize a lifting-surface and a surface-panel model to solve for the unsteady cavitating flow around a propeller that is subject to nonaxisymmetric inflow. The time-dependent extent and thickness of the cavity were determined by using an iterative method. The cavity detachment was determined by applying the smooth detachment criterion in an iterative manner. A nonzeroradius developed vortex cavity model was utilized at the tip of the blade, and the trailing wake geometry was determined using a fully unsteady wake-alignment process. Comparisons of predictions by the two models and measurements from several experiments are given.

  6. Cavitation Inception on Microparticles: A Self-Propelled Particle Accelerator

    OpenAIRE

    Arora, Manish; Ohl, Claus-Dieter; Morch, Knud Aage

    2004-01-01

    Corrugated, hydrophilic particles with diameters between 30 and 150   μm are found to cause cavitation inception at their surfaces when they are exposed to a short, intensive tensile stress wave. The growing cavity accelerates the particle into translatory motion until the tensile stress decreases, and subsequently the particle separates from the cavity. The cavity growth and particle detachment are modeled by considering the momentum of the particle and the displaced liquid. The analysis sug...

  7. Classical nucleation theory for cavitation processes in water

    Czech Academy of Sciences Publication Activity Database

    Němec, Tomáš; Maršík, František

    Antalya : HEFAT, 2010 - (Meyer, J.), s. 2035-2040 ISBN 978-1-86854-818-7. [International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics (HEFAT2010) /7./. Antalya (TR), 19.07.2010-21.07.2010] R&D Projects: GA ČR(CZ) GA106/08/0557; GA ČR GAP101/10/1819 Institutional research plan: CEZ:AV0Z20760514 Keywords : cavitation * classical nucleation theory * water Subject RIV: BJ - Thermodynamics

  8. Numerical Optimization of converging diverging miniature cavitating nozzles

    Science.gov (United States)

    Chavan, Kanchan; Bhingole, B.; Raut, J.; Pandit, A. B.

    2015-12-01

    The work focuses on the numerical optimization of converging diverging cavitating nozzles through nozzle dimensions and wall shape. The objective is to develop design rules for the geometry of cavitating nozzles for desired end-use. Two main aspects of nozzle design which affects the cavitation have been studied i.e. end dimensions of the geometry (i.e. angle and/or curvature of the inlet, outlet and the throat and the lengths of the converging and diverging sections) and wall curvatures(concave or convex). Angle of convergence at the inlet was found to control the cavity growth whereas angle of divergence of the exit controls the collapse of cavity. CFD simulations were carried out for the straight line converging and diverging sections by varying converging and diverging angles to study its effect on the collapse pressure generated by the cavity. Optimized geometry configurations were obtained on the basis of maximum Cavitational Efficacy Ratio (CER)i.e. cavity collapse pressure generated for a given permanent pressure drop across the system. With increasing capabilities in machining and fabrication, it is possible to exploit the effect of wall curvature to create nozzles with further increase in the CER. Effect of wall curvature has been studied for the straight, concave and convex shapes. Curvature has been varied and effect of concave and convex wall curvatures vis-à-vis straight walls studied for fixed converging and diverging angles.It is concluded that concave converging-diverging nozzles with converging angle of 20° and diverging angle of 5° with the radius of curvature 0.03 m and 0.1530 m respectively gives maximum CER. Preliminary experiments using optimized geometry are indicating similar trends and are currently being carried out. Refinements of the CFD technique using two phase flow simulations are planned.

  9. Processing of Microalgae: Acoustic Cavitation and Hydrothermal Conversion

    Science.gov (United States)

    Greenly, Justin Michael

    The production of energy dense fuels from renewable algal biomass feedstocks -- if sustainably developed at a sufficiently large scale -- may reduce the consumption of petroleum from fossil fuels and provide many environmental benefits. Achieving economic feasibility has several technical engineering challenges that arise from dilute concentration of growing algae in aqueous media, small cell sizes, and durable cell walls. For microalgae to be a sustainable source of biofuels and co-products, efficient fractionation and conversion of the cellular contents is necessary. Research was carried out to address two processing options for efficient microalgae biofuel production: 1. Ultrasonic cavitation for cell disruption and 2. Hydrothermal conversion of a model algal triglyceride. 1. Ultrasonic cell disruption, which relies on cavitating bubbles in the suspension to produce damaging shock waves, was investigated experimentally over a range of concentrations and species types. A few seconds of high intensity sonication at fixed frequency yielded significant cell disruption, even for the more durable cells. At longer exposure times, effectiveness was seen to decline and was attributed, using acoustic measurements, to ultrasonic power attenuation in the ensuing cloud of cavitating bubbles. Processing at higher cell concentrations slowed cell disintegration marginally, but increased the effectiveness of dissipating ultrasonic energy. A theoretical study effectively predicted optimal conditions for a variety of parameters that were inaccessible in this experimental investigation. In that study, single bubble collapse was modeled to identify operating conditions that would increase cavitation, and thus cell disruption. Simulations were conducted by varying frequency and pressure amplitude of the ultrasound wave, and initial bubble size. The simulation results indicated that low frequency, high sound wave amplitudes, and small initial bubble size generate the highest shock

  10. Aspergillus infection in pulmonary cavitating lesions with right atrial myxoma.

    Science.gov (United States)

    Sharma, Divyesh; Dorgan, Eileen; Douglas, Hannah; Trouton, Tom; McMullan, Ronan; Parissis, Haralabos

    2014-11-01

    Cardiac myxomas are rare primary tumors with varied clinical presentations that may pose a diagnostic challenge. Here, we describe the case of a 21-year-old man with multiple cavitating lung lesions with aspergillosis and underlying right atrial myxoma, who presented with hemoptysis and weight loss. He was successfully treated with right atrial myxoma resection and antifungal agents, with no recurrence or complications after one year of follow-up. PMID:24887845

  11. A CFD STUDY OF CAVITATION IN REAL SIZE DIESEL INJECTORS

    OpenAIRE

    PATOUNA, STAVROULA

    2012-01-01

    In Diesel engines, the internal flow characteristics in the fuel injection nozzles, such as the turbulence level and distribution, the cavitation pattern and the velocity profile affect significantly the air-fuel mixture in the spray and subsequently the combustion process. Since the possibility to observe experimentally and measure the flow inside real size Diesel injectors is very limited, Computational Fluid Dynamics (CFD) calculations are generally used to obtain the relevant informati...

  12. Dynamics of cavitations induced by tandem shock waves in water

    Czech Academy of Sciences Publication Activity Database

    Hoffer, Petr; Šunka, Pavel; Stelmashuk, Vitaliy

    Cancun, Mexico: Institute of Physics (IOP)., 2009, PA4-5-8. (ICPIG). ISBN 978-1-61567-694-1. [International Conference on Phenomena in Ionized Gases 2009/29th./. Cancún (MX), 12.07.2009-17.07.2009] R&D Projects: GA ČR GA202/09/1151 Institutional research plan: CEZ:AV0Z20430508 Keywords : shock wave * cavitation * corona * discharge * plasma Subject RIV: BL - Plasma and Gas Discharge Physics

  13. Hydrodynamics, Acoustics and Scaling of Traveling Bubble Cavitation

    OpenAIRE

    Kuhn de Chizelle, Yan P.

    1994-01-01

    Recent observations of the geometries of growing and collapsing bubbles over axisymmetric headforms have revealed the complexity of the "microfluidmechanics" associated with these flows (Hamilton et al., 1982, Briançon Marjollet and Franc, 1990, Ceccio and Brennen, 1991). Among the complex features observed were bubble to bubble interaction, cavitation noise generation and bubble interaction with the boundary layer which leads to the shearing of the underside of the bubble and ...

  14. Cavitation and bubble dynamics: the Kelvin impulse and its applications.

    Science.gov (United States)

    Blake, John R; Leppinen, David M; Wang, Qianxi

    2015-10-01

    Cavitation and bubble dynamics have a wide range of practical applications in a range of disciplines, including hydraulic, mechanical and naval engineering, oil exploration, clinical medicine and sonochemistry. However, this paper focuses on how a fundamental concept, the Kelvin impulse, can provide practical insights into engineering and industrial design problems. The pathway is provided through physical insight, idealized experiments and enhancing the accuracy and interpretation of the computation. In 1966, Benjamin and Ellis made a number of important statements relating to the use of the Kelvin impulse in cavitation and bubble dynamics, one of these being 'One should always reason in terms of the Kelvin impulse, not in terms of the fluid momentum…'. We revisit part of this paper, developing the Kelvin impulse from first principles, using it, not only as a check on advanced computations (for which it was first used!), but also to provide greater physical insights into cavitation bubble dynamics near boundaries (rigid, potential free surface, two-fluid interface, flexible surface and axisymmetric stagnation point flow) and to provide predictions on different types of bubble collapse behaviour, later compared against experiments. The paper concludes with two recent studies involving (i) the direction of the jet formation in a cavitation bubble close to a rigid boundary in the presence of high-intensity ultrasound propagated parallel to the surface and (ii) the study of a 'paradigm bubble model' for the collapse of a translating spherical bubble, sometimes leading to a constant velocity high-speed jet, known as the Longuet-Higgins jet. PMID:26442141

  15. Cavitation Erosion in Hydraulic Turbine Components and Mitigation by Coatings: Current Status and Future Needs

    Science.gov (United States)

    Singh, Raghuvir; Tiwari, S. K.; Mishra, Suman K.

    2012-07-01

    Cavitation erosion is a frequently observed phenomenon in underwater engineering materials and is the primary reason for component failure. The damage due to cavitation erosion is not yet fully understood, as it is influenced by several parameters, such as hydrodynamics, component design, environment, and material chemistry. This article gives an overview of the current state of understanding of cavitation erosion of materials used in hydroturbines, coatings and coating methodologies for combating cavitation erosion, and methods to characterize cavitation erosion. No single material property fully characterizes the resistance to cavitation erosion. The combination of ultimate resilience, hardness, and toughness rather may be useful to estimate the cavitation erosion resistance of material. Improved hydrodynamic design and appropriate surface engineering practices reduce damage due to cavitation erosion. The coatings suggested for combating the cavitation erosion encompasses carbides (WC Cr2C3, Cr3C2, 20CrC-80WC), cermets of different compositions (e.g., 56W2C/Ni/Cr, 41WC/Ni/Cr/Co), intermetallic composites, intermetallic matrix composites with TiC reinforcement, composite nitrides such as TiAlN and elastomers. A few of them have also been used commercially. Thermal spraying, arc plasma spraying, and high velocity oxy-fuel (HVOF) processes have been used commercially to apply the coatings. Boronizing, laser surface hardening and cladding, chemical vapor deposition, physical vapor deposition, and plasma nitriding have been tried for surface treatments at laboratory levels and have shown promise to be used on actual components.

  16. Quantitative evaluation of erosive cavitation pressure field from pits in material: fact or myth?

    Science.gov (United States)

    Choi, J.-K.; Chahine, G. L.

    2015-12-01

    Material pitting in a cavitating flow has been used for a long time as an indicator of the vague ‘cavitation intensity’ concept. Periodically, some researchers suggest pitting tests as a “simple” means to provide quantitative measurements of the amplitude of the impulsive pressures in the cavitation field, especially when combined with Tabor's formula or with simple finite element computations with static loads. This paper examines the viability of such a method using fully coupled bubble dynamics and material response, and strongly concludes that the commonly accepted idea is a myth, as different loading scenarios with the same amplitude of the cavitation impulsive pressure result in different pit aspect ratios.

  17. Numerical Study of Cavitation in Francis Turbine of a Small Hydro Power Plant

    Directory of Open Access Journals (Sweden)

    Pankaj Gohil

    2016-01-01

    Full Text Available Cavitation is undesirable phenomena and more prone in reaction turbines. It is one of the challenges in any hydro power plant which cause vibration, degradation of performance and the damage to the hydraulic turbine components. Under the present study, an attempt has been made to carry out a numerical analysis to investigate the cavitation effect in a Francis turbine. Three dimensional numerical study approach of unsteady and SST turbulence model are considered for the numerical analysis under multiphase flow such as cavitating flow. The performance parameters and cavitating flow under different operating conditions have been predicted using commercial CFX code. Three different operating conditions under cavitation and without cavitation with part load and overload conditions of the turbine for a plant sigma factor are investigated. The results are presented in the form of efficiency, pressure fluctuation, vortex rope and vapor volume fraction. It has been observed that variation in efficiency and vapor volume fraction is found to be nominal between cavitation and without cavitation conditionsat rated discharge and rated head. Turbine efficiency loss and vapor bubbles formation towards suction side of the runner blade are found to be maximum under overload condition. However, the pressure pulsation has been found maximum under part load condition in the draft tube. The simulation results are found to be in good agreement with model test results for efficiency. The locations of cavitating zone observed wellwith the result of previous studies.

  18. Effect of free-air nuclei on fully developed individual bubble cavitation

    International Nuclear Information System (INIS)

    Fully developed individual-bubble cavitation was studied. Nuclei population and pressure distribution at the boundary of a cavitating converging-diverging test section were measured. It was shown that some cavitation tests can only yield valid results if the free air content of the water is known. During the initial stages of bubble growth the wall pressure in the cavitation region is lower than the vapor pressure. Wall pressure rises later. For a given cavitation number and flow velocity, the pressure distribution depends on the number of expanding bubbles on the hydrofoil. Minimum pressure coefficient depends only on the cavitation number, the flow velocity and the number of expanding bubbles present. Bubbles generate pressure pulses at the wall; combined effect of all such pulses is to shift the wall pressure away from the value that would be obtained at the same cavitation number if no cavitation was present. The greater the number of expanding bubbles, the more the wall pressure tends to approach the vapor pressure. An important result of the work is to pin-point free air contents of water tunnel which lead to correct scaling of cavitation flows

  19. Study about the influence of cavitation on the dynamic characteristics for the sliding bearing

    Science.gov (United States)

    Zhai, L. M.; Luo, Y. Y.; Wang, Z. W.

    2015-01-01

    Sliding bearings are employed to support the rotor system and limit the vibration amplitude. In high speed rotor system, cavitation often occurs in the oil film and affects the dynamic characteristics of the sliding bearing greatly. In this paper, numerical method is adopted to simulate the cavitation in the oil film with homogeneous two-phase mixture flow using Singhal-et-al cavitation model in the commercial code FLUENT-solver. Cases without cavitation model were also calculated at the same time. Many computations with different frequency ratios were conducted. Then the rotor dynamic characteristics of the sliding bearing were retrieved. The results show that the cavitation has great influences on the pressure distribution in the oil film. As the rotational speed or whirling speed of the journal increases, the cavitation will become prominent. The dynamic coefficients of the bearing such as stiffness and damping with cavitation model considered are quite different from that without cavitation. So it is worth to pay attention to and do further study about the cavitation in the sliding bearing in the high speed rotor system.

  20. Study on cavitation influence for pump head in an axial flow pump

    Science.gov (United States)

    Hosono, K.; Kajie, Y.; Saito, S.; Miyagawa, K.

    2015-12-01

    The size of axial flow pumps used in drainage pump stations has recently decreased, and their rotation speeds have increased, causing an increase in the risk of cavitation. Therefore, to provide highly reliable pumps, it is important to understand the internal flow of pumps under cavitating conditions. In this study, high-speed camera measurements and computational fluid dynamics analysis were performed to understand the cavitation performance of an axial flow pump. The mechanism that causes the head to change as a result of cavitation under low net positive suction head values is shown to be the balance between the increasing angular momentum and the loss indicated by the changing streamlines.

  1. Advanced Simulation Capability for Turbopump Cavitation Dynamics Guided by Experimental Validation Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Numerical cavitation modeling capability is critical in the design of liquid rocket engine turbopumps, feed lines, injector manifolds and engine test facilities....

  2. Activities of cavitation studies and R and D works of sodium pumps in Japan

    International Nuclear Information System (INIS)

    PNC is now performing design studies of large FBR, making the best use of past experiences from JOYO, MONJU and related R and Ds, aiming at future effective and sound development of FBR technology and at the appropriate cooperation with utilities and manufacturers. In this paper the activities of cavitation studies and R and D works of sodium pumps as well as general review of the FBR development are presented. Such activities are concentrated on the following items: 1) In-sodium and in-water cavitation tests of JOYO primary and secondary pumps as well as cavitation damage inspection after 30,000 hours of operation. 2) In-water cavitation test of subscale mock-up pumps (1/2-1/3) for MONJU. 3) In-water cavitation test of subscale mock-up pump (1/2.5) for large FBR including incipient cavitation bubble observation. 4) Cavitation tests of FLIPs (600 2/min and 1100 1/min) and ALIP (400 1/min). 5) Approach to define more advanced cavitation criteria for electromagnetic pumps instead of applying Thoma's dimensionless parameter. In view of this, cavitation tests of a FLIP and its duct models with sodium and model fluid are conducted. 6) Studies on the impeller type optimization for large FBRs: Single suction, double suction and inducer type are comprised. 7) Design studies of single suction and double suction pumps for large FBRs. (author)

  3. Study of the generated density of cavitation inside diesel nozzle using different fuels and nozzles

    International Nuclear Information System (INIS)

    Highlights: • Compared the cavitation inside diesel nozzle using different fuels and nozzles by flow visualization experiment. • Two new parameters are put forward to analyze quantitatively the generated intensity of cavitation inside nozzle. • The influences of injection conditions on the generated intensity of cavitation are investigated by new parameters. • The generated intensity of cavitation is sensitive to the change of injection conditions. - Abstract: A comparative study using different fuels and nozzles has been conducted focusing on the generated density of cavitation inside diesel nozzle. In this paper a visualization experiment has been carried out and the new parameters are presented to compare the effect of the injection conditions (including injection pressure, the spray angle of nozzle, the length–diameter ratio of nozzle orifice and the fuel type) on the generated density of cavitation. The research results indicate that the generated density of cavitation is sensitive to the change of injection conditions. The generated density increases about 10% for every 10 MPa in injection pressure. The generated density increases with the increase of nozzle spray angle and with the decrease of length–diameter ratio. The cavitation appears early and changes fast by using the fuel with lower viscosity and higher saturated vapor pressure. The generated density of cavitation increases with the increase of saturated vapor pressure and decreases with the increase of viscosity

  4. PREDICTION OF UNSTEADY CAVITATION OF PROPELLER USING SURFACE-PANEL METHOD

    Institute of Scientific and Technical Information of China (English)

    XIONG Ying; YE Jin-ming; WANG De-xun

    2005-01-01

    This paper has predicted the range and volume of unsteady sheet cavitation of a propeller by using the surface panel method. The linearization in cavity thickness is adopted to reduce the computing time and storage space. The iteration scheme between chordwise strips has been used because the range and volume of cavitation are both unknown. The propeller cavitation range determined by the calculation method presented in this paper agrees with the observation results of cavity image at cavitation tunnel very well, and this proves the practicability of the method.

  5. Prediction of Shock-Induced Cavitation in Water

    Science.gov (United States)

    Brundage, Aaron

    2013-06-01

    Fluid-structure interaction problems that require estimating the response of thin structures within fluids to shock loading has wide applicability. For example, these problems may include underwater explosions and the dynamic response of ships and submarines; and biological applications such as Traumatic Brain Injury (TBI) and wound ballistics. In all of these applications the process of cavitation, where small cavities with dissolved gases or vapor are formed as the local pressure drops below the vapor pressure due to shock hydrodynamics, can cause significant damage to the surrounding thin structures or membranes if these bubbles collapse, generating additional shock loading. Hence, a two-phase equation of state (EOS) with three distinct regions of compression, expansion, and tension was developed to model shock-induced cavitation. This EOS was evaluated by comparing data from pressure and temperature shock Hugoniot measurements for water up to 400 kbar, and data from ultrasonic pressure measurements in tension to -0.3 kbar, to simulated responses from CTH, an Eulerian, finite volume shock code. The new EOS model showed significant improvement over pre-existing CTH models such as the SESAME EOS for capturing cavitation. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy/NNSA under contract DE-AC04-94AL85000.

  6. Forces and moments on a slender, cavitating body

    Energy Technology Data Exchange (ETDEWEB)

    Hailey, C.E.; Clark, E.L.; Buffington, R.J.

    1988-01-01

    Recently a numerical code has been developed at Sandia National Laboratories to predict the pitching moment, normal force, and axial force of a slender, supercavitating shape. The potential flow about the body and cavity is calculated using an axial distribution of source/sink elements. The cavity surface is assumed to be a constant pressure streamline, extending beyond the base of the model. Slender body approximation is used to model the crossflow for small angles of attack. A significant extension of previous work in cavitation flow is the inclusion of laminar and turbulent boundary layer solutions on the body. Predictions with this code, for axial force at zero angle of attack, show good agreement with experiments. There are virtually no published data availble with which to benchmark the pitching moment and normal force predictions. An experiment was designed to measure forces and moments on a supercavitation shape. The primary reason for the test was to obtain much needed data to benchmark the hydrodynamic force and moment predictions. Since the numerical prediction is for super cavitating shapes at very small cavitation numbers, the experiment was designed to be a ventilated cavity test. This paper describes the experimental procedure used to measure the pitching moment, axial and normal forces, and base pressure on a slender body with a ventilated cavity. Limited results are presented for pitching moment and normal force. 5 refs., 7 figs.

  7. X-ray Diagnostics for Cavitating Nozzle Flow

    Science.gov (United States)

    Duke, Daniel J.; Swantek, Andrew B.; Kastengren, Alan L.; Powell, Christopher F.

    2015-12-01

    Cavitation plays a critical role in the internal flow of nozzles such as those used in direct fuel injection systems. However, quantifying the vapor fraction in the nozzle is difficult. The gas-liquid interfaces refract and multiply scatter visible light, making quantitative extinction measurements difficult. X-rays offer a solution to this problem, as they refract and scatter only weakly. In this paper, we report on current progress in the development of several x-ray diagnostics for cavitating nozzle flows. X-ray radiography experiments undertaken at the Advanced Photon Source at Argonne National Laboratory have provided measurements of total projected void fraction in a 500 μm submerged nozzle, which have been directly compared with numerical simulations. From this work, it has been shown that dissolved gases in the liquid also result in the formation of vapor regions, and it is difficult to separate these multiple phenomena. To address this problem, the liquid was doped with an x-ray fluorescent bromine tracer, and the dissolved air substituted with krypton. The fluorescent emission of Br and Kr at x-ray wavelengths provide a novel measurement of both the total void fraction and the dissolved gas component, allowing both cavitation and dissolved gas contributions to be measured independently. [199/200 words

  8. Cavitation in confined water: ultra-fast bubble dynamics

    Science.gov (United States)

    Vincent, Olivier; Marmottant, Philippe

    2012-02-01

    In the hydraulic vessels of trees, water can be found at negative pressure. This metastable state, corresponding to mechanical tension, is achieved by evaporation through a porous medium. It can be relaxed by cavitation, i.e. the sudden nucleation of vapor bubbles. Harmful for the tree due to the subsequent emboli of sap vessels, cavitation is on the contrary used by ferns to eject spores very swiftly. We will focus here on the dynamics of the cavitation bubble, which is of primary importance to explain the previously cited natural phenomena. We use the recently developed method of artificial tress, using transparent hydrogels as the porous medium. Our experiments, on water confined in micrometric hydrogel cavities, show an extremely fast dynamics: bubbles are nucleated at the microsecond timescale. For cavities larger than 100 microns, the bubble ``rings'' with damped oscillations at MHz frequencies, whereas for smaller cavities the oscillations become overdamped. This rich dynamics can be accounted for by a model we developed, leading to a modified Rayleigh-Plesset equation. Interestingly, this model predicts the impossibility to nucleate bubbles above a critical confinement that depends on liquid negative pressure and corresponds to approximately 100 nm for 20 MPa tensions.

  9. VOID GROWTH AND CAVITATION IN NONLINEAR VISCOELASTIC SOLIDS

    Institute of Scientific and Technical Information of China (English)

    张赟; 黄筑平

    2003-01-01

    This paper discusses the growth of a pre-existing void in a nonlinear viscoelastic material subjected to remote hydrostatic tensions with different loading rates. The constitutive relation of this viscoelastic material is the one recently proposed by the present authors, which may be considered as a generalization of the non-Gaussian statistical theory in rubber elasticity. As the first order approximation, the above constitutive relation can be reduced to the "neo-Hookean" type viscoelastic one.Investigations of the influences of the material viscosity and the loading rate on the void growth, or on the cavitation are carried out. It is found that: (1) for generalized "inverse Langevin approximation"nonlinear viscoelastic materials, the cavitation limit does not exist, but there is a certain (remote)stress level at which the void will grow rapidly; (2) for generalized "Gaussian statistics" (neo-Hookean type) viscoelastic materials, the cavitation limit exists, and is an increasing function of the loading rate.The present discussions may be of importance in understanding the material failure process under high triaxial stress.

  10. Phenol Oxidation by Combined Cavitation Water Jet and Hydrogen Peroxide

    Institute of Scientific and Technical Information of China (English)

    卢义玉; 刘勇; 夏彬伟; 左伟芹

    2012-01-01

    The paper presents results of phenol oxidized under the conditions of high temperature created during collapse of cavitation bubbles.The degradation efficiency has been greatly improved by using cavitation water jets combined with H2O2 as demonstrated in laboratory tests.Various factors affecting phenol removal ratio were ex-amined and the degradation mechanism was revealed by high performance liquid chromatography(HPLC).The re-sults showed that 99.85% of phenol was mineralized when phenol concentration was 100 mg·L-1 with pH value of 3.0,H2O2 concentration of 300 mg·L-1,confining pressure of 0.5 MPa,and pumping pressure of 20 MPa.The in-termediate products after phenol oxidation were composed of catechol,hydroquinone and p-benzoquinone.Finally,phenol was degraded into maleic acid and acetic acid.Furthermore,a dynamic model of phenol oxidation via cavi-tation water jets combined with H2O2 has been developed.

  11. Transient cavitation and acoustic emission produced by different laser lithotripters.

    Science.gov (United States)

    Zhong, P; Tong, H L; Cocks, F H; Pearle, M S; Preminger, G M

    1998-08-01

    Transient cavitation and shockwave generation produced by pulsed-dye and holmium:YAG laser lithotripters were studied using high-speed photography and acoustic emission measurements. In addition, stone phantoms were used to compare the fragmentation efficiency of various laser and electrohydraulic lithotripters. The pulsed-dye laser, with a wavelength (504 nm) strongly absorbed by most stone materials but not by water, and a short pulse duration of approximately 1 microsec, induces plasma formation on the surface of the target calculi. Subsequently, the rapid expansion of the plasma forms a cavitation bubble, which expands spherically to a maximum size and then collapses violently, leading to strong shockwave generation and microjet impingement, which comprises the primary mechanism for stone fragmentation with short-pulse lasers. In contrast, the holmium laser, with a wavelength (2100 nm) most strongly absorbed by water as well as by all stone materials and a long pulse duration of 250 to 350 microsec, produces an elongated, pear-shaped cavitation bubble at the tip of the optical fiber that forms a vapor channel to conduct the ensuing laser energy to the target stone (Moss effect). The expansion and subsequent collapse of the elongated bubble is asymmetric, resulting in weak shockwave generation and microjet impingement. Thus, stone fragmentation in holmium laser lithotripsy is caused primarily by thermal ablation (drilling effect). PMID:9726407

  12. Standard Test Method for Cavitation Erosion Using Vibratory Apparatus

    CERN Document Server

    American Society for Testing and Materials. Philadelphia

    2010-01-01

    1.1 This test method covers the production of cavitation damage on the face of a specimen vibrated at high frequency while immersed in a liquid. The vibration induces the formation and collapse of cavities in the liquid, and the collapsing cavities produce the damage to and erosion (material loss) of the specimen. 1.2 Although the mechanism for generating fluid cavitation in this method differs from that occurring in flowing systems and hydraulic machines (see 5.1), the nature of the material damage mechanism is believed to be basically similar. The method therefore offers a small-scale, relatively simple and controllable test that can be used to compare the cavitation erosion resistance of different materials, to study in detail the nature and progress of damage in a given material, or—by varying some of the test conditions—to study the effect of test variables on the damage produced. 1.3 This test method specifies standard test conditions covering the diameter, vibratory amplitude and frequency of the...

  13. Tandem shock wave cavitation enhancement for extracorporeal lithotripsy.

    Science.gov (United States)

    Loske, Achim M; Prieto, Fernando E; Fernandez, Francisco; van Cauwelaert, Javier

    2002-11-21

    Extracorporeal shock wave lithotripsy (ESWL) has been successful for more than twenty years in treating patients with kidney stones. Hundreds of underwater shock waves are generated outside the patient's body and focused on the kidney stone. Stones fracture mainly due to spalling, cavitation and layer separation. Cavitation bubbles are produced in the vicinity of the stone by the tensile phase of each shock wave. Bubbles expand, stabilize and finally collapse violently, creating stone-damaging secondary shock waves and microjets. Bubble collapse can be intensified by sending a second shock wave a few hundred microseconds after the first. A novel method of generating two piezoelectrically generated shock waves with an adjustable time delay between 50 and 950 micros is described and tested. The objective is to enhance cavitation-induced damage to kidney stones during ESWL in order to reduce treatment time. In vitro kidney stone model fragmentation efficiency and pressure measurements were compared with those for a standard ESWL system. Results indicate that fragmentation efficiency was significantly enhanced at a shock wave delay of about 400 and 250 micros using rectangular and spherical stone phantoms, respectively. The system presented here could be installed in clinical devices at relatively low cost, without the need for a second shock wave generator. PMID:12476975

  14. Cavitation Inside High-Pressure Optically Transparent Fuel Injector Nozzles

    Science.gov (United States)

    Falgout, Z.; Linne, M.

    2015-12-01

    Nozzle-orifice flow and cavitation have an important effect on primary breakup of sprays. For this reason, a number of studies in recent years have used injectors with optically transparent nozzles so that orifice flow cavitation can be examined directly. Many of these studies use injection pressures scaled down from realistic injection pressures used in modern fuel injectors, and so the geometry must be scaled up so that the Reynolds number can be matched with the industrial applications of interest. A relatively small number of studies have shown results at or near the injection pressures used in real systems. Unfortunately, neither the specifics of the design of the optical nozzle nor the design methodology used is explained in detail in these papers. Here, a methodology demonstrating how to prevent failure of a finished design made from commonly used optically transparent materials will be explained in detail, and a description of a new design for transparent nozzles which minimizes size and cost will be shown. The design methodology combines Finite Element Analysis with relevant materials science to evaluate the potential for failure of the finished assembly. Finally, test results imaging a cavitating flow at elevated pressures are presented.

  15. CAVITATION CHARACTERISTICS OF HIGH VELOCITY FLOW WITH AND WITHOUT AERATION ON THE ORDER OF 50 m/s

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Experimental study of cavitation characteristics with and without aeration was conducted at the flow velocity 50m/s in the non-circulating type water tunnel in the Hydraulics Laboratory at Zhejiang University of Technology. Variations of pressure and cavitation number with air concentration, pressure waveforms as well as cavitation erosion level of concrete specimen with and without aeration were obtained. The effects of cavitation control by aeration were analyzed.

  16. Mathematical Investigation of the Cavitation Phenomenon in the Nozzle with Partially Surface Wetting

    Directory of Open Access Journals (Sweden)

    Jablonská Jana

    2015-12-01

    Full Text Available Partially surface wetting has a great influence on friction losses in the fluid flow in both the pipeline system and the complex shape of hydraulic elements. In many hydraulic elements (valves, pump impellers, cavitation is generated, which significantly changes the hydraulic flow parameters, so the last part of the article is devoted to the mathematical solution of this phenomena and evaluates the impact of wall wetting on the size and shape of the cavitation area which appears in the nozzle and in small gaps at special conditions. If the cavitation appears e. g. near the wall of pipes, the blades of turbine or a pump, then it destroys the material surface. On the basis of this physical experiment (nozzle, a two-dimensional (2D mathematical cavitation model of Schnerr-Sauer was made and calculated shape and size of the cavitation region was compared with the experiment. Later this verified model of cavitation was used for cavitation research flow with partial surface wetting. The pressure drop and the size of the cavitation area as it flows from partially surface wetting theory was tested depending on the adhesion coefficient.

  17. Complete Inhibition Of Ultrasound Induced Cytolysis In The Presence Of Inertial Cavitation

    Science.gov (United States)

    Sostaric, Joe Z.; Miyoshi, Norio; Riesz, Peter; De Graff, William G.; Mitchell, James B.

    2006-05-01

    The investigation of ultrasound for biotechnological applications including non-invasive surgery (HIFU), drug/gene delivery to cells (sonoporation) or through the skin (sonophoresis) and ultrasound assisted bioreactors has focused mainly on the physical effects of ultrasound. The beneficial effects of ultrasound rely on a number of application-dependent mechanisms, and may include tissue heating, acoustic streaming or cavitation. Although acoustic cavitation is necessary in some systems, cavitation bubbles simultaneously result in uncontrollable cell damage and cytolysis. Thus, the development of a number of biotechnological uses of ultrasound has been hampered by the necessity to constrain exposure parameters in order to prevent the occurrence of acoustic cavitation or to at least limit the detrimental effects of cavitation. The current study shows that non-toxic concentrations of specific n-alkyl solutes completely inhibit ultrasound induced cytolysis of in vitro suspensions of human leukemia cells (HL-60). Protection of the whole cell population from cytolysis is achieved even under extreme ultrasound exposure conditions that result in cytolysis of 100 % of the cell population in the absence of the n-alkyl solutes. Furthermore, the n-alkyl solutes did not hinder the process of inertial cavitation. This method may allow utilization of beneficial effects of ultrasound and cavitation while protecting cells from cavitation induced cytolysis and thereby presents new possibilities for ultrasound in medicine and biology.

  18. Improvement of residual stress in gear using water peening by a cavitation jet technique

    Energy Technology Data Exchange (ETDEWEB)

    Ju, D.Y.; Machida, H. [Dept. of Material Science and Engineering, Saitama Inst. of Tech., Okabe, Saitama (Japan); Uchiyama, T.; Oba, R. [Advanced Science Inst., Saitama Inst. of Tech. (Japan); Kanawa, T. [Dept. of System Engineering, Graduate School of Saitama Inst. Tech. (Japan); Sunayama, Y.; Tsuda, H. [Experiment and Analysis Dept., Suzuki Motor Co., Hamamatsu-nishi (Japan)

    2002-07-01

    Cavitation impacts of ultrahigh-speed water could lead to stresses erosion and other damage on the surface of hydro machinery such as pumps, turbines and valves. On the other hand, the cavitation impacts can be used to modify the residual stress on surface of materials as a shot peening method. Recently, a technology to modify residual stress on a plate by using of cavitation tunnel and a cavitation water jet in air has been reported. A high level of compressive residual stress has been applied on surface of materials by using water cavitation jet. In the present paper, residual stress of a helical gear of SCR420H steel was measured by means of an X-ray diffraction method, before and after peening by water cavitation jet. In order to obtain high-level compressive residual stress, optimum peening time and standard distance from jet nozzle to surface of the gear were investigated by cavitation jet tests. These results prove that residual stress on gear surface can be improved by using cavitation jet technique. (orig.)

  19. Cavitation pitting and erosion of Al 6061-T6 in mineral oil and water

    Science.gov (United States)

    Rao, B. C. S.; Buckley, D. H.

    1983-01-01

    The authors are currently carrying out a study of the cavitation erosion of different bearing metals and alloys in mineral oils were studied. The variations of weight loss, the pit diameter and depth due to cavitation erosion on Al 6061-T6 in mineral oil and water are presented.

  20. Implicit large eddy simulation of unsteady cloud cavitation around a plane- convex hydrofoil

    Institute of Scientific and Technical Information of China (English)

    罗先武; 季斌

    2015-01-01

    The present paper focuses on the erosive cavitation behavior around a plane convex hydrofoil. The Zwart-Gerber-Belamri cavitation model is implemented in a library form to be used with the OpenFOAM. The implicit large eddy simulation (ILES) is app- lied to analyze the three dimensional unsteady cavitating flow around a plane convex hydrofoil. The numerical results in the cases under the hydrodynamic-conditions, which were experimentally tested at the high speed cavitation tunnel of the École Polytechnique Fédérale de Lausanne (EPFL), clearly show the sheet cavitation development, the shedding and the collapse of vapor clouds. It is noted that the cavitation evolutions including the maximum vapor length, the detachment and the oscillation frequency, are captured fairly well. Furthermore, the pressure pulses due to the cavitation development as well as the complex vortex structures are reasona- bly well predicted. Consequently, it may be concluded that the present numerical method can be used to investigate the unsteady cavitation around hydrofoils with a satisfactory accuracy.

  1. Numerical investigation of three-dimensional cloud cavitation with special emphasis on collapse induced shock dynamics

    NARCIS (Netherlands)

    Schnerr, G.H.; Sezal, I.H.; Schmidt, S.J.

    2008-01-01

    The aim of the present investigation is to model and analyze compressible three-dimensional (3D) cavitating liquid flows with special emphasis on the detection of shock formation and propagation. We recently developed the conservative finite volume method CATUM (Cavitation Technische Universität Mün

  2. Experimental study of the interaction between the spark-induced cavitation bubble and the air bubble

    Institute of Scientific and Technical Information of China (English)

    罗晶; 许唯临; 牛志攀; 罗书靖; 郑秋文

    2013-01-01

    Experiments are carried out by using high-speed photography to investigate the interaction between the spark-generated cavitation bubble and the air bubble in its surrounding fluid. Three problems are discussed in detail: the impact of the air bubble upon the development of the cavitation bubble, the evolution of the air bubble under the influence of the cavitation bubble, and the change of the fluid pressure during the development of a micro jet of the cavitation bubble. Based on the experimental results, under the condition of no air bubble present, the lifetime of the cavitation bubble from expansion to contraction increases with the increase of the maximum radius. On the other hand, when there is an air bubble present, different sized cavitation bubbles have similarity with one another generally in terms of the lifetime from expansion to contraction, which does not depend on the maximum radius. Also, with the presence of an air bubble, the lifetime of the smaller cavitation bubble is extended while that of the bigger ones reduced. Furthermore, it is shown in the experiment that the low pressure formed in the opposite direction to the cavitation bubble micro jet makes the air bubble in the low pressure area being stretched into a steplike shape.

  3. Large-eddy simulation of cavitating nozzle flow and primary jet break-up

    NARCIS (Netherlands)

    Örley, F.; Trummler, T.; Hickel, S.; Mihatsch, M.S.; Schmidt, S.J.; Adams, N.A.

    2015-01-01

    We employ a barotropic two-phase/two-fluid model to study the primary break-up of cavitating liquid jets emanating from a rectangular nozzle, which resembles a high aspect-ratio slot flow. All components (i.e., gas, liquid, and vapor) are represented by a homogeneous mixture approach. The cavitating

  4. High-speed motion picture camera experiments of cavitation in dynamically loaded journal bearings

    Science.gov (United States)

    Hamrock, B. J.; Jacobson, B. O.

    1983-01-01

    A high-speed camera was used to investigate cavitation in dynamically loaded journal bearings. The length-diameter ratio of the bearing, the speeds of the shaft and bearing, the surface material of the shaft, and the static and dynamic eccentricity of the bearing were varied. The results reveal not only the appearance of gas cavitation, but also the development of previously unsuspected vapor cavitation. It was found that gas cavitation increases with time until, after many hundreds of pressure cycles, there is a constant amount of gas kept in the cavitation zone of the bearing. The gas can have pressures of many times the atmospheric pressure. Vapor cavitation bubbles, on the other hand, collapse at pressures lower than the atmospheric pressure and cannot be transported through a high-pressure zone, nor does the amount of vapor cavitation in a bearing increase with time. Analysis is given to support the experimental findings for both gas and vapor cavitation. Previously announced in STAR as N82-20543

  5. Improvement of residual stress on SUS304 by using cavitating jet

    Energy Technology Data Exchange (ETDEWEB)

    Park, Jung Do [Dept. of Vehicle Engineering, Kyung Nam Junior College, Pusan (Korea, Republic of); Soyama, Hitoshi; Saka, Masumi; Abe, Hiroyuki [Dept. of Mechanical Engineering, Tohoku University, Sendai (Japan)

    1997-10-15

    A cavitating jet can improve fatigue life of materials, since impacts caused by cavitation bubble collapses produce a peening effect. In general, the cavitation impacts cause damages in hydraulic machinery. At an initial stage of the cavitation damage progress, the plastic deformation takes place and there is no mass loss. Then it is possible to do peening by the cavitating jet without the damage. In order to prove the peening effect, a residual stress on a surface of a stainless steel SUS304 was investigated by using a X-ray diffraction method. The stress components of the three different directions were measured changing with the exposure time of the cavitating jet, and then the principal stresses were calculated. The both principal stresses were changed from tension to compression. It can be concluded that the cavitating jet improves the residual stress on the surface of the stainless steel SUS304. The important parameters of the cavitating jet such as an optimum standoff distance were also shown.

  6. Improvement of residual stress on SUS304 by using cavitating jet

    International Nuclear Information System (INIS)

    A cavitating jet can improve fatigue life of materials, since impacts caused by cavitation bubble collapses produce a peening effect. In general, the cavitation impacts cause damages in hydraulic machinery. At an initial stage of the cavitation damage progress, the plastic deformation takes place and there is no mass loss. Then it is possible to do peening by the cavitating jet without the damage. In order to prove the peening effect, a residual stress on a surface of a stainless steel SUS304 was investigated by using a X-ray diffraction method. The stress components of the three different directions were measured changing with the exposure time of the cavitating jet, and then the principal stresses were calculated. The both principal stresses were changed from tension to compression. It can be concluded that the cavitating jet improves the residual stress on the surface of the stainless steel SUS304. The important parameters of the cavitating jet such as an optimum standoff distance were also shown.

  7. Vibration Characteristics Induced by Cavitation in a Centrifugal Pump with Slope Volute

    Directory of Open Access Journals (Sweden)

    Ning Zhang

    2015-01-01

    Full Text Available Cavitation is one of the instability sources in centrifugal pump, which would cause some unexpected results. The goal of this paper was to analyze the influence of cavitation process on different frequency bands in a centrifugal pump with slope volute. And special attention was paid to low frequency signals, which were often filtered in the reported researches. Results show that at noncavitation condition, vibration level is closely related to flow structure interior pump. At partial flow rates, especially low flow rates, vibration level increases rapidly with the onset of rotating stall. At cavitation condition, it is proved that cavitation process has a significant impact on low frequency signals. With cavitation number decreasing, vibration level first rises to a local maximum, then it drops to a local minimum, and finally it rises again. At different flow rates, vibration trends in variable frequency bands differ obviously. Critical point inferred from vibration level is much larger than that from 3% head drop, which indicates that cavitation occurs much earlier than that reflected in head curve. Also, it is noted that high frequency signals almost increase simultaneously with cavitation occurring, which can be used to detect cavitation in centrifugal pump.

  8. Cavitation damages morphology of high-strength low-alloy steel

    OpenAIRE

    Aleksić, V.; M. Dojčinović; Lj. Milović; Samardžić, I.

    2016-01-01

    This paper presents the research into behaviour of HSLA steel affected by cavitation. The parent material (PM) and simulated heat-affected zone (SHAZ) were studied. Ultrasonic vibratory cavitation test was performed in laboratory conditions (by stationary specimen method). Scanning electron microscopy (SEM) was used to observe the variations in the surface morphology that occurred within different time intervals.

  9. Cavitation damages morphology of high-strength low-alloy steel

    Directory of Open Access Journals (Sweden)

    V. Aleksić

    2016-07-01

    Full Text Available This paper presents the research into behaviour of HSLA steel affected by cavitation. The parent material (PM and simulated heat-affected zone (SHAZ were studied. Ultrasonic vibratory cavitation test was performed in laboratory conditions (by stationary specimen method. Scanning electron microscopy (SEM was used to observe the variations in the surface morphology that occurred within different time intervals.

  10. Ultrasonic cavitation erosion of nodular cast iron with ferrite-pearlite microstructure.

    Science.gov (United States)

    Mitelea, Ion; Bordeaşu, Ilare; Pelle, Marius; Crăciunescu, Corneliu

    2015-03-01

    The cavitation erosion of ductile cast iron with ferrite-pearlite microstructure was analyzed based on ultrasonic experiments performed according to ASTM G32-2010 and the resistance was compared to the C45 steel with similar hardness. The microstructural observation of the surface for different exposure times to the ultrasonic cavitation reveals the fact that the process initiates at the nodular graphite-ferrite interface and is controlled by micro-galvanic activities and mechanical factors. The cavitation erosion resistance was evaluated based on the evolution of the mean depth erosion and the mean depth erosion rate as a function of the cavitation time. The cavitation erosion rate of the cast iron is up to 1.32 times higher than the one of the C 45 steel with similar hardness. This is explained by the occurrence of stress concentrators due to the expulsion of the graphite from the metallic matrix. PMID:25465881

  11. Preventing hydrogen embrittlement in stainless steel by means of compressive stress induced by cavitation peening

    Directory of Open Access Journals (Sweden)

    Osamu Takakuwa

    2015-07-01

    Full Text Available In this paper, it has been demonstrated that compressive residual stress induced by cavitation peening which is one of the mechanical surface modification techniques can reduce invasion of the surface of austenitic stainless steel by hydrogen. Cavitation peening was done with employing a cavitating jet in air. The specimens were prepared with different processing time of cavitation peening. Then, stress measurement was performed using an X-ray diffraction analysis. After that, the surface was charged with hydrogen employing a cathodic charging method. Hydrogen content was evaluated by a thermal desorption analysis using a gas chromatography. From the obtained results, hydrogen content was reduced along with increase in compressive residual stress at surface. In particular hydrogen content became to 15% at processing time of 2 s/mm introducing compressive residual stress of 378 MPa. In short, cavitation peening can drastically prevent invasion by hydrogen.

  12. Cavitation and primary atomization in real injectors at low injection pressure condition

    Science.gov (United States)

    Dumouchel, Christophe; Leboucher, Nicolas; Lisiecki, Denis

    2013-06-01

    This experimental work investigates the influence of the geometry of GDI devices on primary atomization processes under low injection pressure and reduced back pressure. These pressure conditions ensure cavitating flows and observable atomization processes. Measurements include mass flux, structure velocity from high-speed visualizations and spray characterization with a laser diffraction technique. Super-cavitation regime and cavitation string, which have their own influence on the mass flux, develop independently in different injector regions. These regimes impact the flow pattern in the orifice and the subsequent atomization process. A possible interaction between cavitation string and super-cavitation is found to promote a hydraulic-flip-like regime and to deteriorate atomization quality. As far as the geometry of the injector is concerned, the profile of the orifice inlet and the roughness of the sac volume region are found to be important geometrical characteristics.

  13. Numerical investigation of cavitating flow behind the cone of a poppet valve in water hydraulic system

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Computational Fluid Dynamics (CFD) simulations of cavitating flow th rough water hydraulic poppet valves were performed using advanced RNG k-eps ilon turbulence model. The flow was turbulent, incompressible and unsteady, for Reyno lds numbers greater than 43 000. The working fluid was water, and the structure o f the valve was simplified as a two dimensional axisymmetric geometrical model. Flow field visualization was numerically achieved. The effects of inlet velocity , outlet pressure, opening size as well as poppet angle on cavitation intensity in the poppet valve were numerically investigated. Experimental flow visualization was conducted to capture cavitation images near the orifice in the poppet valve with 30° poppet angle using high speed video camera. The binary cavitating flo w field distribution obtained from digital processing of the original cavitation i mage showed a good agreement with the numerical result.

  14. Energy Consumption in Comminution of Mica with Cavitation Abrasive Water Jet

    Institute of Scientific and Technical Information of China (English)

    GUO Chu-wen; DONG Lu

    2007-01-01

    We have studied the efficiency of energy consumption in the comminution of mica powder with cavitation abrasive water jet technology. The energy required to create new surfaces in the comminution of mica powder with cavitation abrasive water jet was calculated, in order to estimate its efficiency of energy consumption. The particle size distribution and the specific surface area were measured by applying a JEM-200CX transmission electron microscope and an Autosorb-1 automatic surface area analyzer. The study results show that the efficiency of energy consumed in creating new surface areas is as high as 2.92%, or 4.94% with the aid of cavitation in the comminution of mica powder. This efficiency will decrease with an increase in the number of comminutions. After three comminutions, the efficiencies will become 1.91% and 2.29% for comminution without cavitation and with cavitation, respectively. The abrasive water jet technology is an effective way for comminution of mica powder.

  15. ENHANCING OSMOTIC DEHYDRATION WITH ACOUSTIC CAVITATION%声空化强化渗透脱水

    Institute of Scientific and Technical Information of China (English)

    孙宝芝; 姜任秋; 淮秀兰; 李斌; 刘登瀛

    2004-01-01

    An experimental study was carried out to enhance osmotic dehydration of fruits--apples using acoustic cavitation. The variation in water losses and dry matter gain rates of materials with solute concentration, cavitation intensity, the thickness of materials and treating time segment during osmotic dehydration was discussed, at the same time, the influence of different materials on mass transfer during osmotic dehydration using acoustic cavitation was investigated. The results showed that water losses rates of materials were remarkably increased during osmotic dehydration using acoustic cavitation, but dry matter gain rates increased very little. Meanwhile the physical mechanism of enhanced mass transfer during osmotic dehydration with acoustic cavitation was clarified on the basis of analyzing the experimental results.

  16. Experimental investigation on dynamic characteristics and strengthening mechanism of laser-induced cavitation bubbles.

    Science.gov (United States)

    Ren, X D; He, H; Tong, Y Q; Ren, Y P; Yuan, S Q; Liu, R; Zuo, C Y; Wu, K; Sui, S; Wang, D S

    2016-09-01

    The dynamic features of nanosecond laser-induced cavitation bubbles near the light alloy boundary were investigated with the high-speed photography. The shock-waves and the dynamic characteristics of the cavitation bubbles generated by the laser were detected using the hydrophone. The dynamic features and strengthening mechanism of cavitation bubbles were studied. The strengthening mechanisms of cavitation bubble were discussed when the relative distance parameter γ was within the range of 0.5-2.5. It showed that the strengthening mechanisms caused by liquid jet or shock-waves depended on γ much. The research results provided a new strengthening method based on laser-induced cavitation shotless peening (CSP). PMID:27150764

  17. CFD analysis of cloud cavitation on three tip-modified propellers with systematically varied tip geometry

    DEFF Research Database (Denmark)

    Shin, K. W.; Andersen, P.

    2015-01-01

    The blade tip loading is often reduced as an effort to restrain sheet and tip vortex cavitation in the design of marine propellers. This CFD analysis demonstrates that an excessive reduction of the tip loading can cause cloud cavitation responsible for much of noise and surface erosion. Detached...... eddy simulations (DES) are made for cavitating flows on three tip- modified propellers, of which one is a reference propeller having an experimental result from a cavitation tunnel test with a hull model, and the other two are modified from the reference propeller by altering the blade tip loading. DES...... results have been validated against the experiment in terms of sheet and cloud cavitation. In DES, non-uniform hull wake is modelled by using the inlet flow and momentum sources instead of including a hull model. A 4-bladed Kappel propeller with a smooth tip bending towards the suction side is used as the...

  18. Application of two turbulence models for computation of cavitating flows in a centrifugal pump

    International Nuclear Information System (INIS)

    To seek a better numerical method to simulate the cavitating flow field in a centrifugal pump, the applications between RNG k- ε and LES turbulence model were compared by using the Zwart-Gerber-Belamri cavitation model. It was found that both the models give almost the same results with respect to pump performance and cavitation evolutions including growth, local contraction, stability and separation in the impeller passage. But the LES model can not only capture the pump suction recirculation and the low frequency fluctuation caused by it, but also combine the changes of the shaft frequency amplitude acting on the impeller with the cavitation unstable characteristics. Thus the LES model has more advantages than RNG k- ε model in calculating the unsteady cavitating flow in a centrifugal pump

  19. A Blowdown Cryogenic Cavitation Tunnel and CFD Treatment for Flow Visualization around a Foil

    Institute of Scientific and Technical Information of China (English)

    Yutaka ITO; Kazuya SAWASAKI; Naoki TANI; Takao NAGASAKI; Toshio NAGASHIMA

    2005-01-01

    Cavitation is one of the major problems in the development of rocket engines. There have been few experimental studies to visualize cryogenic foil cavitation. Therefore a new cryogenic cavitation tunnel of blowdown type was built. The foil shape is "plano-convex". This profile was chosen because of simplicity, but also of being similar to the one for a rocket inducer impeller. Working fluids were water at room temperature,hot water and liquid nitrogen. In case of Angle of Attack (AOA)=8°, periodical cavity departure was observed in the experiments of both water at 90℃ and nitrogen at -190℃ under the same velocity 10 m/sec and the same cavitation number 0.7. The frequencies were observed to be 110 and 90 Hz, respectively, and almost coincided with those of vortex shedding from the foil. Temperature depression due to the thermodynamic effect was confirmed in both experiment and simulation especially in the cryogenic cavitation.

  20. On Rayleigh-Plesset based cavitation modelling of fluid film bearings using the Reynolds equation

    Science.gov (United States)

    Snyder, Troy A.; Braun, Minel J.; Pierson, Kristopher

    2015-12-01

    In the ‘universe’ of the general cavitation phenomena the issue of cavitation in bearings, due to its particular application and the mostly non-homogeneous working fluids associated with it, has presented a rather specialized challenge. The present paper models the phenomenon of pseudo-cavitation in fluid film bearings and offers a physics-based approach that conserves mass while solving the Reynolds (RE) and Rayleigh-Plesset (RP) equations in a coupled, fully transient environment. The RP solution calculates a time dependent void fraction synchronized with the RE transient solution, where density and viscosity are (re)calculated at every grid point of this homogeneous two-phase fluid. The growth and evolution of the cavitation zone expanse is physics-based and thus can accommodate evaporation, diffusion, or pseudocavitation as separate processes. This is a step beyond the present available cavitation models both for the RE and the Navier-Stokes equations.

  1. Numerical study on fatigue damage properties of cavitation erosion for rigid metal materials

    Institute of Scientific and Technical Information of China (English)

    Guogang Wang; Guang Ma; Dongbai Sun; Hongying Yu; Huimin Meng

    2008-01-01

    Cavitation erosion is an especially destructive and complex phenomenon. To understand its basic mechanism, the fatigue process of materials during cavitation erosion was investigated by numerical simulation technology. The loading spectrum used was generated by a spark-discharged electrode. Initiation crack life and true stress amplitude was used to explain the cavitation failure period and damage mechanism. The computational results indicated that the components of different materials exhibited various fatigue lives under the same external conditions. When the groove depth was extended, the initiation crack life decreased rapidly, while the true stress amplitude was increased simultaneously. This gave an important explanation to the accelerating material loss rate during cavitation erosion. However, when the groove depth was fixed and the length varied, the fatigue life became complex, more fluctuant than that happened in depth. The results also indicate that the fatigue effect of cavitation plays an important role in contributing to the formation and propagation of characteristic pits.

  2. Prediction of cavitation performance of a hydrofoil in water at high temperatures

    International Nuclear Information System (INIS)

    In this paper, the thermodynamic effects of cavitation based on the computational methodology of cavitation mass transfer has been considered in the prediction of cavitation performance of a hydrofoil in water at high temperature. A cavitation mass transfer model to study this phenomenon has been presented. The cavitation model was used to simulate the flow along a NACA0015 hydrofoil at different temperatures. The results were compared with experiments. From the distribution of the pressure coefficient, it can be seen that the simulation results with the improved model have the same trends and values comparing with the experiments. At low temperature, the length of the cavity area is nearly the same with experiment, but at high temperature, the calculated cavity length is slightly longer

  3. Influence of blade angle distribution along leading edge on cavitation performance of a centrifugal pump

    Science.gov (United States)

    Xu, Y.; Tan, L.; Cao, S. L.; Wang, Y. C.; Meng, G.; Qu, W. S.

    2015-01-01

    The influence of blade angle distribution along leading edge on cavitation performance of centrifugal pumps is analysed in the present paper. Three sets of blade angle distribution along leading edge for three blade inlet angles are chosen to design nine centrifugal pump impellers. The RNG k-epsilon turbulence model and the Zwart-Gerber-Belamri cavitation model are employed to simulate the cavitation flows in centrifugal pumps with different impellers and the same volute. The numerical results are compared with the experimental data, and the comparison proves that the numerical simulation can accurately predict the cavitation performance of centrifugal pumps. On the basis of the numerical simulations, the pump head variations with pump inlet pressure, and the flow details in centrifugal pump are revealed to demonstrate the influence of blade angle distribution along leading edge on cavitation performances of centrifugal pumps.

  4. Application of two turbulence models for computation of cavitating flows in a centrifugal pump

    Science.gov (United States)

    He, M.; Guo, Q.; Zhou, L. J.; Wang, Z. W.; Wang, X.

    2013-12-01

    To seek a better numerical method to simulate the cavitating flow field in a centrifugal pump, the applications between RNG k- ε and LES turbulence model were compared by using the Zwart-Gerber-Belamri cavitation model. It was found that both the models give almost the same results with respect to pump performance and cavitation evolutions including growth, local contraction, stability and separation in the impeller passage. But the LES model can not only capture the pump suction recirculation and the low frequency fluctuation caused by it, but also combine the changes of the shaft frequency amplitude acting on the impeller with the cavitation unstable characteristics. Thus the LES model has more advantages than RNG k- ε model in calculating the unsteady cavitating flow in a centrifugal pump.

  5. A HOMOGENOUS-EQUILIBRIUM-MODEL BASED NUMERICAL CODE FOR CAVITATION FLOWS AND EVALUATION BY COMPUTATION CASES

    Institute of Scientific and Technical Information of China (English)

    CHEN Ying; LU Chuan-jing

    2008-01-01

    A computer code, ELANEX, including several Homogenous-Equilibrium-Model (HEM) type cavitation models, were developed, to numerically simulate natural cavitation phenomena. The effectiveness of the code was checked by cavitation flows around the disk and cylinder body for a wide range of different cavitation numbers. Cavity profiles were compared with the analytic solution of disk and empirical formulae fitted from the experiment data, and contrast between different cavitation models were fulfilled as well. The cavity length and maximal cavity diameter were found to agree well with the analytic solutions, and detailed cavity profiles were in accordance with the experimental formula. Comparison with the hemisphere headed cylinder body presented a good agreement of the pressure coefficient with the experiment data. Reasonable drag-force coefficient variation and drag-force reduction effect were obtained.

  6. Pseudopotential MRT lattice Boltzmann model for cavitation bubble collapse with high density ratio

    CERN Document Server

    Shan, Ming-Lei; Yao, Cheng; Yin, Cheng; Jiang, Xiao-Yan

    2016-01-01

    The dynamics of the cavitation bubble collapse is a fundamental issue for the bubble collapse application and prevention. In present work, the modified forcing scheme for the pseudopotential multi-relaxation-time lattice Boltzmann model developed by Li Q. et al. is adopted to develop a cavitation bubble collapse model. In the respects of coexistence curves and Laplace law verification, the improved pseudopotential multi-relaxation-time lattice Boltzmann model is investigated. The independence between the kinematic viscosity and the thermodynamic consistency, surface tension is founded. By homogeneous and heterogeneous cavitation simulation, the capability of the present model to describe the cavitation bubble development as well as the cavitation inception is verified. The bubble collapse between two parallel walls is simulated. The dynamic process of collapsing bubble is consistent with the results from experiments and simulations by other numerical method. It is demonstrated that the present pseudopotential...

  7. Detection of cavitation behavior using accelerometer and microphone outside of piping at orifice

    International Nuclear Information System (INIS)

    Cavitation induced vibration and the consequent erosion of pipes are one aspect of the potential damaging factors in the piping system. In order to prevent such trouble, it is needed to develop a detection method of cavitation. Especially, in a plant system such as nuclear power plants, it is preferable to detect them by measuring outside of pipes during plant operation. In this paper, the detection methods of cavitation using an accelerometer and a microphone were experimentally examined and compared each other. As a result: (1) Output of the accelerometer varied with the cavitation number, and it output voltage increased with development of cavitation. When cavitation occurred, a pulse shaped signal, which might be a shockwave by collapse of cavitation bubbles, was clearly detected. (2) Output distribution of the accelerometer in the flow direction became large where cavitation bubbles collapsed, and output voltage of the accelerometer downstream of the orifice was larger than that of the accelerometer upstream of the orifice. (3) The measurement results with the microphone were similar to those of the accelerometer qualitatively, pulse-shape signals were detected, and difference of output voltages between microphones upstream and downstream of the orifice were measured. In the simultaneous measurements by the accelerometer and the microphone, both sensors detected the shockwave considered to be generated at the same time with a time delay of the microphone. The sound velocity evaluated from the time delay agreed well with the sound velocity in the air. Using the characteristics of the measurement results, cavitation using a microphone without contacting pipes could be performed like an accelerometer mounted on the pipe surface, and cavitation could be detected from the distribution of output voltages in the flow direction even in pipings of a plant without data base to compare. (author)

  8. Energy distribution during cavitation bubble growth and collapse in water

    Czech Academy of Sciences Publication Activity Database

    Müller, M.; Maršík, František; Garen, W.

    Kyoto: Maruzen Co., Ltd, 2005 - (Nakahara, M.; Matubayasi, N.; Ueno, M.; Yasuoka, K.; Watanabe, K.), s. 226-231 ISBN 4-621-07596-9. [International Conference on the Properties of Water and Steam /14./. Kyoto (JP), 29.08.2004-03.09.2004] R&D Projects: GA AV ČR(CZ) IBS2076003; GA ČR(CZ) GA101/02/0364 Institutional research plan: CEZ:AV0Z20760514 Keywords : cavitation * bubble dynamics * optical measurement Subject RIV: BJ - Thermodynamics

  9. Cavitation behaviour of the SUPERSTON alloy after laser treatment

    OpenAIRE

    B. Majkowska; W. Serbiński

    2008-01-01

    Purpose: Results of laser treatment at cryogenic conditions and its influence on microstructure, microhardness and cavitation resistance of the SUPERSTON alloy are presented in this paper.Design/methodology/approach: New method of the laser remelting specimens diped in liquid nitrogen made by the CO2 laser with 4000 W laser beam power and scanning velocity 0.5 and 1.0 m/min was employed. Observation microstructure was carried out by scanning electron microscope. Hardness of cross-section of t...

  10. Method of forming cavitated objects of controlled dimension

    Science.gov (United States)

    Anderson, Paul R.; Miller, Wayne J.

    1982-01-01

    A method of controllably varying the dimensions of cavitated objects such as hollow spherical shells wherein a precursor shell is heated to a temperature above the shell softening temperature in an ambient atmosphere wherein the ratio of gases which are permeable through the shell wall at that temperature to gases which are impermeable through the shell wall is substantially greater than the corresponding ratio for gases contained within the precursor shell. As the shell expands, the partial pressures of permeable gases internally and externally of the shell approach and achieve equilibrium, so that the final shell size depends solely upon the difference in impermeable gas partial pressures and shell surface tension.

  11. Simulation of Cavitation Instability in 3-blade Inducer

    Czech Academy of Sciences Publication Activity Database

    Sedlář, M.; Maršík, František; Zima, Patrik

    Praha: ÚT AV ČR, v. v. i., 2007 - (Příhoda, J.; Kozel, K.), s. 145-148 ISBN 978-80-87012-04-8. [Conference TOPICAL PROBLEMS OF FLUID MECHANICS 2007. Praha (CZ), 28.02.2007-02.03.2007] R&D Projects: GA ČR(CZ) GA101/05/2536; GA ČR(CZ) GA101/07/1612; GA MŠk 1P04LA214 Institutional research plan: CEZ:AV0Z20760514 Keywords : cavitation * instability * inducer Subject RIV: BK - Fluid Dynamics

  12. Cavitation-induced ignition of cryogenic hydrogen-oxygen fluids

    OpenAIRE

    Osipov, V. V.; Muratov, C. B.; Ponizovskya-Devine, E.; Foygel, M.; Smelyanskiy, V. N.

    2011-01-01

    The Challenger disaster and purposeful experiments with liquid hydrogen (H2) and oxygen (Ox) tanks demonstrated that cryogenic H2/Ox fluids always self-ignite in the process of their mixing. Here we propose a cavitation-induced self-ignition mechanism that may be realized under these conditions. In one possible scenario, self-ignition is caused by the strong shock waves generated by the collapse of pure Ox vapor bubble near the surface of the Ox liquid that may initiate detonation of the gase...

  13. The mechanism of erosion of metallic materials under cavitation attack

    Science.gov (United States)

    Rao, B. C. S.; Buckley, D. H.

    1985-01-01

    The mean depth of penetration rates (MDPRs) of eight polycrystalline metallic materials, Al 6061-T6, Cu, brass, phosphor bronze, Ni, Fe, Mo, and Ti-5Al-2.5Sn exposed to cavitation attack in a viscous mineral oil with a 20 kHz ultrasonic oscillator vibrating at 50 micron amplitude are reported. The titanium alloy followed by molybdenum have large incubation periods and small MDPRs. The incubation periods correlate linearly with the inverse of hardness and the average MDPRs correlate linearly with the inverse of tensile strength of materials. The linear relationships yield better statistical parameters than geometric and exponential relationships. The surface roughness and the ratio of pit depth to pit width (h/a) increase with the duration of cavitation attack. The ratio h/a varies from 0.1 to 0.8 for different materials. Recent investigations (20) using scanning electron microscopy to study deformation and pit formation features are briefly reviewed. Investigations with single crystals indicate that the geometry of pits and erosion are dependent on their orientation.

  14. Effect of morphology of hydrophobic surfaces on cavitation kinetics

    Energy Technology Data Exchange (ETDEWEB)

    LUZAR,ALENKA; LEUNG,KEVIN

    2000-04-24

    Cavitation has been suggested to be a possible source of long range interactions between mesoscopic hydrophobic surfaces. While evaporation is predicted by thermodynamics, little is known about its kinetics. Glauber dynamics Monte Carlo simulations of a lattice gas close to liquid-gas coexistence and confined between partially drying surfaces are used to model the effect of water confinement on the dynamics of surface-induced phase transition. Specifically, they examine how kinetics of induced evaporation change as the texture of hydrophobic surfaces is varied. Evaporation rates are considerably slowed with relatively small amount of hydrophilic coverage. However, the distribution of hydrophilic patches is found to be crucial, with the homogeneous one being much more effective in slowing the formation of vapor tubes which triggers the evaporation process. They estimate the free energy barrier of vapor tube formation via transition state theory, using a constrained forward-backward umbrella sampling technique applied to the metastable, confined liquid. Furthermore, to relate simulation rates to experimental ones, they perform simulations using the mass-conserving Kawasaki algorithm. They predict evaporation time scales that range from hundreds of picoseconds in the case of mesoscopic surfaces {approximately} 10{sup 4} nm{sup 2} to tens of nanoseconds for smaller surfaces {approximately} 40 nm{sup 2}, when the two surfaces are {approximately} 10 solvent layers apart. The present study demonstrates that cavitation is kinetically viable in real systems and should be considered in studies of processes at confined geometry.

  15. Ultrasonic cavitation for obtainment of nanometric sized particles

    Science.gov (United States)

    Santos, A.; Guzmán, R.; Espinosa, J.; Estrada, J.

    2016-02-01

    This project aims to determine the possibility of obtaining nanometric size particles of aluminium oxide (Al2O3) and titanium dioxide (TiO2) from commercial micron-sized powders, through the physical principle of ultrasonic cavitation, in order to be used as supply material in coatings made through a process of thermal spray by flame. The tests are performed on a Hielscher UIP 1000hd Ultrasonics equipment, in a 20 micron wave amplitude and in times of 6, 8, 12, 18 and 24 hours. The determination of the particle size is done through image processing using ImageJ software, obtained by the technique of scanning electron microscopy (SEM); while the elemental composition of the processed samples is analyzed through the technique of energy dispersing spectroscopy (EDS). The results show that Al2O3 and TiO2 have a reduction behaviour of the particles size after being subjected to ultrasonic cavitation, however is only reached the nanometric size in the TiO2 samples.

  16. Cavitating pulmonary tuberculosis in children: correlating radiology with pathogenesis

    Energy Technology Data Exchange (ETDEWEB)

    Griffith-Richards, S.B.; Andronikou, Savvas; Przybojewski, Stefan J.; Strachan, Melanie; Vadachia, Yousuf; Kathan, David L. [Tygerberg Hospital and University of Stellenbosch, Department of Radiology (South Africa); Goussard, Pierre; Gie, Robert P. [Tygerberg Children' s Hospital and University of Stellenbosch, Department of Paediatrics, Tygerberg (South Africa)

    2007-08-15

    Cavitating pulmonary tuberculosis (PTB) is generally known as a disease of adults, with children typically having features of primary PTB. To group children with PTB and cavities according to possible pathogenesis by evaluating the clinical and radiological findings. The clinical and radiological findings in ten randomly selected children with PTB and cavitations on chest radiographs were retrospectively reviewed and evaluated. Three groups emerged: group 1 (four children) had cavities, usually single and unilateral in the classic upper lobe distribution of postprimary PTB; group 2 (three children) developed progressive primary spread of disease with extensive and bilateral pulmonary cavities; and group 3 (three children) developed cavities secondary to airway obstruction by mediastinal lymph nodes with consequent distal collapse and consolidation. Children in group 1 responded well to treatment and had unremarkable recoveries. Children in group 2 were all below 2 years of age with complicated recoveries. Children in group 3 had frequent complications resulting in one fatality. Cavities in PTB in children may arise by one of three possible mechanisms with a relatively equal incidence. A study is underway to determine the incidence of cavity formation associated with mediastinal lymphadenopathy and airway obstruction. (orig.)

  17. Cavitating pulmonary tuberculosis in children: correlating radiology with pathogenesis

    International Nuclear Information System (INIS)

    Cavitating pulmonary tuberculosis (PTB) is generally known as a disease of adults, with children typically having features of primary PTB. To group children with PTB and cavities according to possible pathogenesis by evaluating the clinical and radiological findings. The clinical and radiological findings in ten randomly selected children with PTB and cavitations on chest radiographs were retrospectively reviewed and evaluated. Three groups emerged: group 1 (four children) had cavities, usually single and unilateral in the classic upper lobe distribution of postprimary PTB; group 2 (three children) developed progressive primary spread of disease with extensive and bilateral pulmonary cavities; and group 3 (three children) developed cavities secondary to airway obstruction by mediastinal lymph nodes with consequent distal collapse and consolidation. Children in group 1 responded well to treatment and had unremarkable recoveries. Children in group 2 were all below 2 years of age with complicated recoveries. Children in group 3 had frequent complications resulting in one fatality. Cavities in PTB in children may arise by one of three possible mechanisms with a relatively equal incidence. A study is underway to determine the incidence of cavity formation associated with mediastinal lymphadenopathy and airway obstruction. (orig.)

  18. Intensification of biogas production using pretreatment based on hydrodynamic cavitation.

    Science.gov (United States)

    Patil, Pankaj N; Gogate, Parag R; Csoka, Levente; Dregelyi-Kiss, Agota; Horvath, Miklos

    2016-05-01

    The present work investigates the application of hydrodynamic cavitation (HC) for the pretreatment of wheat straw with an objective of enhancing the biogas production. The hydrodynamic cavitation reactor is based on a stator and rotor assembly. The effect of three different speeds of rotor (2300, 2500, 2700 rpm), wheat straw to water ratios (0.5%, 1% and 1.5% wt/wt) and also treatment times as 2, 4 and 6 min have been investigated in the work using the design of experiments (DOE) approach. It was observed that the methane yield of 31.8 ml was obtained with untreated wheat straw whereas 77.9 ml was obtained with HC pre-treated wheat straw confirming the favourable changes during the pre-treatment. The combined pre-treatment using KOH and HC gave maximum yield of biogas as 172.3 ml. Overall, it has been established that significant enhancement in the biogas production can be obtained due to the pretreatment using HC which can also be further intensified by combination with chemical treatment. PMID:26639635

  19. Laser surface modification of stainless steels for cavitation erosion resistance

    Science.gov (United States)

    Kwok, Chi Tat

    1999-12-01

    Austenitic stainless steel UNS S31603 (Fe -17.6Cr -11.2Ni -2.5Mo -1.4Mn -0.4Si -0.03C) has higher pitting corrosion resistance but lower cavitation erosion resistance than that of UNS S30400. This is because of its lower tendency for strain induced martensitic transformation and higher stacking fault energy as compared with those of UNS S30400. In order to improve its cavitation erosion resistance, surface modification of S31603 was performed by laser surface melting and laser surface alloying using a 2-kW CW Nd-YAG laser and a 3-kW CW CO2 laser. For laser surface melting, austenitic stainless steel UNS S30400, super duplex stainless steel UNS S32760 and martensitic stainless steel UNS S42000 were also investigated for comparison purpose. For laser surface alloying, alloying materials including various elements (Co, Cr, Ni, Mo, Mn, Si & C), alloys (AlSiFe & NiCrSiB), ceramics (Si3N 4, SiC, Cr3C2, TiC, CrB & Cr2O 3) and alloys-ceramics (Co-WC, Ni-WC, Ni-Al2O3, Ni-Cr2C3) were used to modify the surface of S31603. The alloyed surface was achieved first by flame spraying or pre-placing of the alloy powder on the S31603 surface and then followed by laser surface remelting. The cavitation erosion characteristics of laser surface modified specimens in 3.5% NaCl solution at 23°C were studied by means of a 20-kHz ultrasonic vibrator at a peak-to-peak amplitude of 30 mum. In addition, their pitting corrosion behaviour was evaluated by electrochemical techniques. The microstructures, compositions, phase changes and damage mechanisms under cavitation erosion were investigated by optical microscopy, SEM, EDAX and X-ray diffractometry. Mechanical properties such as microhardness profile were also examined. The cavitation erosion resistance Re (reciprocal of the mean depth of penetration rate) of laser surface melted S31603 was found to be improved by 22% and was attributed to the existence of tensile residual stress. Improvement on the Re of S42000 was found to be 8.5 times

  20. Cavitation and polyphase flow forum, 1975. Joint meeting of Fluids Engineering and Lubrication Division, Minneapolis, Minnesota, May 5--7, 1975

    International Nuclear Information System (INIS)

    The nine papers which comprise the 1975 Forum present a wide range of primarily experimental studies of cavitation and polyphase flows. These papers include the polyphase mechanism in froths, the cavitation collapse pressures in venturi flow, the effects of test conditions on developed cavity flow, a cavitation hypothesis for geophysical phenomena, the character and design of centrifugal pumps for cavitation performance, and the effect of fluid and magnetic and electrical fields on cavitation erosion

  1. Computation and analysis of cavitating flow in Francis-class hydraulic turbines

    Science.gov (United States)

    Leonard, Daniel J.

    Hydropower is the most proven renewable energy technology, supplying the world with 16% of its electricity. Conventional hydropower generates a vast majority of that percentage. Although a mature technology, hydroelectric generation shows great promise for expansion through new dams and plants in developing hydro countries. Moreover, in developed hydro countries, such as the United States, installing generating units in existing dams and the modern refurbishment of existing plants can greatly expand generating capabilities with little to no further impact on the environment. In addition, modern computational technology and fluid dynamics expertise has led to substantial improvements in modern turbine design and performance. Cavitation has always presented a problem in hydroturbines, causing performance breakdown, erosion, damage, vibration, and noise. While modern turbines are usually designed to be cavitation-free at their best efficiency point, due to the variable demand of the energy market it is fairly common to operate at off-design conditions. Here, cavitation and its deleterious effects are unavoidable, and hence, cavitation is a limiting factor on the design and operation of these turbines. Multiphase Computational Fluid Dynamics (CFD) has been used in recent years to model cavitating flow for a large range of problems, including turbomachinery. However, CFD of cavitating flow in hydroturbines is still in its infancy. This dissertation presents steady-periodic Reynolds-averaged Navier-Stokes simulations of a cavitating Francis-class hydroturbine at model and prototype scales. Computational results of the reduced-scale model and full-scale prototype, undergoing performance breakdown, are compared with empirical model data and prototype performance estimations based on standard industry scalings from the model data. Mesh convergence of the simulations is also displayed. Comparisons are made between the scales to display that cavitation performance breakdown

  2. A CFD Study on the Mechanisms Which Cause Cavitation in Positive Displacement Reciprocating Pumps

    Institute of Scientific and Technical Information of China (English)

    Aldo Iannetti; Matthew T. Stickland; William M. Dempster

    2015-01-01

    A transient multiphase CFD (computational fluid dynamics) model was set up to investigate the main causes which lead to cavitation in PD (positive displacement) reciprocating pumps. Many authors agree on distinguishing two different types of cavitation affecting PD pumps: flow induced cavitation and cavitation due to expansion. The flow induced cavitation affects the zones of high fluid velocity and consequent low static pressure e.g. the valve-seat volume gap while the cavitation due to expansion can be detected in zones where the decompression effects are important e.g. in the vicinity of the plunger. This second factor is a distinctive feature of PD pumps since other devices such as centrifugal pumps are only affected by the flow induced type. Unlike what has been published in the technical literature to date, where analysis of positive displacement pumps are based exclusively on experimental or analytic methods, the work presented in this paper is based entirely on a CFD approach, it discusses the appearance and the dynamics of these two phenomena throughout an entire pumping cycle pointing out the potential of CFD techniques in studying the causes of cavitation and assessing the consequent loss of performance in positive displacement pumps.

  3. Influence of the vibro-acoustic sensor position on cavitation detection in a Kaplan turbine

    International Nuclear Information System (INIS)

    Hydraulic turbines can be operated close to the limits of the operating range to meet the demand of the grid. When operated close to the limits, the risk increases that cavitation phenomena may occur at the runner and / or at the guide vanes of the turbine. Cavitation in a hydraulic turbine can cause material erosion on the runner and other turbine parts and reduce the durability of the machine leading to required outage time and related repair costs. Therefore it is important to get reliable information about the appearance of cavitation during prototype operation. In this experimental investigation the high frequency acoustic emissions and vibrations were measured at 20 operating points with different cavitation behaviour at different positions in a large prototype Kaplan turbine. The main goal was a comparison of the measured signals at different sensor positions to identify the sensitivity of the location for cavitation detection. The measured signals were analysed statistically and specific values were derived. Based on the measured signals, it is possible to confirm the cavitation limit of the examined turbine. The result of the investigation shows that the position of the sensors has a significant influence on the detection of cavitation

  4. Influence of blade tip rounding on tip leakage vortex cavitation of axial flow pump

    International Nuclear Information System (INIS)

    Tip leakage flow in axial flow pumps is mainly caused by the tip clearance, which is the main cause of tip leakage vortex cavitation and blade tip cavitation erosion. In order to improve tip clearance flow and reduce TLV cavitation, four schemes were adopted to the round blade tip. These are: no tip rounding, one time tip clearance tip rounding, two times tip clearance tip rounding, four times tip clearance tip rounding. Using SST k-ω turbulence model and Zwart cavitation model in CFX software, this simulation obtained four kinds of inner flow field results. The numerical results indicated that with the increase of r*, NPSHc gradually increased and the cavitation performance reduced. However, corner vortex was eliminated so that cavitation in gap was restrained. But TLV vorticity increased and cavitation's range here had a little expansion. Combined with the research of this paper and the different analyses of four schemes, we recommend adopting the two times of the tip clearance rounding

  5. The analytical description of high temperature tensile creep for cavitating materials subjected to time variable loads

    International Nuclear Information System (INIS)

    A phenomenological cavitation model is presented by means of which the life time as well as the creep curve equations can be calculated for cavitating materials subjected to time variable tensile loads. The model precludes the proportionality between the damage A and the damage rate (dA/dt) resp. Both are connected by the life time function tau. The latter is derived from static stress rupture tests and contains the loading conditions. From this model the life fraction rule (LFR) is derived. The model is used to calculate the creep curves of cavitating materials subjected at high temperatures to non-stationary tensile loading conditions. In the present paper the following loading procedures are considered: creep at constant load F and true stress s; creep at linear load increase ((dF/dt)=const) and creep at constant load amplitude cycling (CLAC). For these loading procedures the creep equations for cavitating and non-cavitating specimens are derived. Under comparable conditions the creep rate of cavitating materials are higher than for non-cavitating ones. (author)

  6. Numerical investigation on cavitation in pressure relief valve for coal liquefaction

    Science.gov (United States)

    Ou, G. F.; Li, W. Z.; Xiao, D. H.; Zheng, Z. J.; Dou, H. S.; Wang, C.

    2015-01-01

    The pressure relief valve for regulating the level of the high-pressure separator works under a pressure difference up to 15 MPa in the temperature of 415 °C. Severe cavitation erosion and particle impact lead to the valve disc's mass loss. In this paper, three-dimensional turbulent cavitating flows in the pressure relief valve are numerically simulated to reveal the mechanism of mass loss at valve disc. The RNG k-epsilon turbulence model and the mixture model with a mass transfer for cavitation are employed to simulate the cavitating flow in the pressure relief valve. The result shows that there is phase change in the pressure relief process and cavitation bubbles would be transported by high-velocity backflow to the head of valve disc. For the local pressure higher than the saturated vapor pressure, the bubbles collapse at the head of disc and cavitation erosion is formed at the head of the disc. By comparing the cases of opening of 40%, 50%, and 60%, backflow velocity and cavitation region in front of the disc decrease with the opening increase. Therefore, during the actual operation, the pressure relief valve should be kept to a relatively large opening.

  7. Cavitation performance prediction of mixed-flow pump based on CFD

    International Nuclear Information System (INIS)

    The computational fluid dynamics (CFD) method is used to investigate the three-dimensional cavitation flow fields in a mixed-flow pump with high specific speed. In the numerical modeling, the homogeneous mixture model and Navier-Stokes equation with RNG k−ε turbulence model are employed. At the best efficiency condition, the cavitation location on the impeller blades and the distribution situation of vapor volume fraction were analyzed, as well as the performance curve between the pump's NPSHA and efficiency were predicted. The results show that, the cavitation directly affects the pressure distribution on impeller blade surfaces, and also results in change of the pump external characteristic. Under the primary cavitation condition, Water vapors first accumulate on the suction surface of blade's leading edge, which is close to the tip. With the decrease of inlet total pressure, the cavitation region extended towards the trailing edge and water vapor fraction volume become larger gradually. When cavitation is serious, water vapors mainly accumulate on the suction surface of blade's trailing edge. The prediction curve has the same trend as the practical curve, which can reveal the mixed-flow pump cavitation within the static characteristics.

  8. Cavitation erosion behavior of Hastelloy C-276 nickel-based alloy

    Energy Technology Data Exchange (ETDEWEB)

    Li, Zhen [State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000 (China); University of Chinese Academy of Sciences, Beijing 100039 (China); Han, Jiesheng; Lu, Jinjun [State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000 (China); Chen, Jianmin, E-mail: chenjm@lzb.ac.cn [State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000 (China)

    2015-01-15

    Highlights: • Cavitation erosion behavior of Hastelloy C-276 was studied by ultrasonic apparatus. • The cavitation-induced precipitates formed in the eroded surface for Hastelloy C-276. • The selective cavitation erosion was found in Hastelloy C-276 alloy. - Abstract: The cavitation erosion behavior of Hastelloy C-276 alloy was investigated using an ultrasonic vibratory apparatus and compared with that of 316L stainless steel. The mean depth of erosion (MDE) and erosion rate (ER) curves vs. test time were attained for Hastelloy C-276 alloy. Morphology and microstructure evolution of the eroded surface were observed by scanning electron microscopy (SEM) and field emission scanning electron microscopy (FESEM) and the predominant erosion mechanism was also discussed. The results show that the MDE is about 1/6 times lower than that of the stainless steel after 9 h of testing. The incubation period of Hastelloy C-276 alloy is about 3 times longer than that of 316L stainless steel. The cavitation-induced nanometer-scaled precipitates were found in the local zones of the eroded surface for Hastelloy C-276. The selective cavitation erosion was found in Hastelloy C-276 alloy. The formation of nanometer-scaled precipitates in the eroded surface may play a significant role in the cavitation erosion resistance of Hastelloy C-276.

  9. Cavitation in semi-open centrifugal impellers for a miniature pump

    Institute of Scientific and Technical Information of China (English)

    Xianwu LUO; Shuhong LIU; Yao ZHANG; Hongyuan XU

    2008-01-01

    Cavitation in miniature pumps was investi-gated experimentally for two semi-open centrifugal impellers. Although both impellers had the same blade cross-section, one impeller had a two-dimensional blade, while the other had a leaned blade. The flows were also analyzed using a numerical model of the three-dimen-sional turbulent flow in the pumps near the peak efficiency point using the k-ε turbulence model and the VOF cavitation model. The average cavitation perform-ance of each impeller was satisfactorily predicted by the numerical simulations. The results show that the miniature pumps have similar cavitation performances as an ordinary-size pump, with the cavitation perform-ance of the semi-open impeller reduced by increased axial tip clearances. Also, both the hydraulic and cavitation performance of the semi-open impeller were improved by the leaned blade. The results also show that uniform flow upstream of the impeller inlet will improve the cavitation performance of a miniature pump.

  10. Numerical simulation of cavitation effects influenced by centrifugal pump inlet parameters

    Science.gov (United States)

    Zhao, L. F.; Wang, Y.; Ning, C.; Liu, Z. C.; Zhu, Z. T.; Xie, S. F.

    2015-01-01

    Cavitation has great influence on performance of the centrifugal pump. However, there is still no effective design to overcome this problem. Blade leading edge of centrifugal pump impeller is the initial position of cavitation. The leading edge geometry shape not only has a great influence on the cavitation inception and its development, but also a great influence on the flow state near the impeller inlet. In this paper, the numerical simulation method is adopted. Cavitation of four different models (including rectangular-shape blade model, circular-arc-shape blade model, elliptical-shape blade model and cusp-shape blade model) are simulated under the same condition by changing the NPSHA value. The influence of different blade models on cavitation performance is analyzed. The results show that the deviation between the simulated data and experimental data is within the deviation range. The head of rectangular-shape blade model and circular-arc-shape blade model are higher than those of elliptical-shape blade model and cusp-shape blade model. However, the head of rectangular-shape blade model and circular-arc-shape blade model is smaller than the latter under the low effective cavitation margin. What's more, the head of the models with trimmed blade are higher than the head of the models with untrimmed blade under the working condition but are smaller under the low effective cavitation margin.

  11. Numerical studies in a centrifugal pump with the improved blade considering cavitation

    Science.gov (United States)

    Song, P. F.; Zhang, Y. X.; Xu, C.; Zhou, X.; Zhang, J. Y.

    2015-01-01

    In this paper, a centrifugal pump with the improved blade for cavitation is studied numerically. A 3D impeller with logarithmic spiral blade profile was designed by the in-house hydraulic design code using a centrifugal pump geometric parameters, and the blade profile curve of suction side on the designed impeller is replaced by a combination of tangent line and circle arc line. The cavitation flows in the centrifugal pump with designed impeller, modified impeller and centrifugal pump spectrum impeller are respectively calculated by two-phase CFD simulation at three flow rates. The tests of the centrifugal pump have been conducted to verify numerical simulation. The effects of designed impeller and modified impeller on hydraulic efficiency, critical cavitation number, cavitation length, head drop performance and vapor cavity distribution in impeller are investigated. The results show that the modification of blade profile curve of suction side can improve the cavitation performance of an impeller and hydraulic efficiency of centrifugal pump. Compared with designed impeller, the critical cavitation number of centrifugal pump with modified impeller decrease by 26.5% under the same flow rate coefficient, and the cavitation intensity in the modified impeller is weakened effectively. The hydraulic efficiency of modified impeller also increases by 4.9%.

  12. CFD analysis of unsteady cavitation phenomena in multistage pump with inducer

    International Nuclear Information System (INIS)

    This paper presents the numerical simulation of the cavitating flow phenomena in the suction part of a radial-flow multistage water pump with a high rotational speed. The pump is equipped with an inducer. Besides the usual focus on the cavitation inception or the drop of the pump total head this CFD analysis also studies the possibility of the cavitation surge and attempts to quantify the risk of cavitation erosion for different flow conditions. The ANSYS CFX commercial CFD package was used to solve the URANS equations coupled with the Rayleigh-Plesset Model. The SST-SAS turbulence model was employed to capture unsteady phenomena inside the pump. The model for the prediction of the cavitation erosion risk is based on coupling the CFD analysis of 3D turbulent flow with the analysis of the dynamics of bubbles travelling along selected trajectories using the full Rayleigh-Plesset equation. The model assumes that the water at the pump inlet contains a known number of nuclei with a known size distribution. The erosion potential (or aggressiveness) of the collapse is estimated from the energy dissipated during the collapse. The presented CFD analysis has provided a map of regions endangered by cavitation erosion. The cavitation instability in the backflow vortices has been detected at 60% of the optimal flow coefficient close to the NPSHr value.

  13. Roughness measurement as an alternative method in evaluation of cavitation resistance of steels

    Directory of Open Access Journals (Sweden)

    Dojčinović Marina

    2013-01-01

    Full Text Available The purpose of this study was to investigate possible application of roughness measurement in evaluation of resistance of steels in conditions of cavitation effect where these materials are usually applied. Steels which belong to different classes were selected for testing. Cavitation testing was performed by using the ultrasonic vibratory cavitation test set up (stationary specimen method. Mass loss and surface degradation of investigated samples were monitored during the exposure to cavitation erosion. Mass loss was measured by an analytical balance. The morphology of the damaged surfaces with the change of the test period was analyzed using scanning electron microscopy (SEM. The surface roughness tester was used to monitor changes of surface roughness during the test and for obtaining the line profile of surface samples after cavitation tests. Cross-sections of samples were made after testing and optical microscopy was used to obtain complete information about the roughness change and compare the images with the lines of the profile obtained by the measurement of roughness. It can be concluded that the behaviour of steels under conditions of cavitation can be estimated by measuring the change in surface roughness. Conclusions adopted on the basis of roughness changes are consistent with that based on measurements of mass loss and morphology of surface damage during cavitation testing time.

  14. Cavitation phenomena in mechanical heart valves: studied by using a physical impinging rod system.

    Science.gov (United States)

    Lo, Chi-Wen; Chen, Sheng-Fu; Li, Chi-Pei; Lu, Po-Chien

    2010-10-01

    When studying mechanical heart valve cavitation, a physical model allows direct flow field and pressure measurements that are difficult to perform with actual valves, as well as separate testing of water hammer and squeeze flow effects. Movable rods of 5 and 10 mm diameter impinged same-sized stationary rods to simulate squeeze flow. A 24 mm piston within a tube simulated water hammer. Adding a 5 mm stationary rod within the tube generated both effects simultaneously. Charged-coupled device (CCD) laser displacement sensors, strobe lighting technique, laser Doppler velocimetry (LDV), particle image velocimetry (PIV) and high fidelity piezoelectric pressure transducers measured impact velocities, cavitation images, squeeze flow velocities, vortices, and pressure changes at impact, respectively. The movable rods created cavitation at critical impact velocities of 1.6 and 1.2 m/s; squeeze flow velocities were 2.8 and 4.64 m/s. The isolated water hammer created cavitation at 1.3 m/s piston speed. The combined piston and stationary rod created cavitation at an impact speed of 0.9 m/s and squeeze flow of 3.2 m/s. These results show squeeze flow alone caused cavitation, notably at lower impact velocity as contact area increased. Water hammer alone also caused cavitation with faster displacement. Both effects together were additive. The pressure change at the vortex center was only 150 mmHg, which cannot generate the magnitude of pressure drop required for cavitation bubble formation. Cavitation occurred at 3-5 m/s squeeze flow, significantly different from the 14 m/s derived by Bernoulli's equation; the temporal acceleration of unsteady flow requires further study. PMID:20490686

  15. ZERO-TENSILE STRENGTH FOR RESULT COMPARISON IN CAVITATION INCEPTION TESTS

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The tensile strength of test liquid affects the cavitation inception numbers very seriously, and the zero-tensile strength as a criterion for detection of the cavitation inception numbers can be used, in order to reduce the influence of tensile strength. The scale effect on measuring zero-tensile strength of test liquid based on hydraulic methods must be considered. it is supposed that the zero-tensile strength can be defined by use of the comparative method, which unites the classical theory of cavitation inception with the modern one based on an identical criterion.

  16. Femtosecond laser-induced cavitations in the lens of the human eye

    DEFF Research Database (Denmark)

    Kessel, Line; Nymand, Jose; Harbst, Michael;

    2007-01-01

    attempted to define the cavitation threshold in the human lens in vitro using multiphoton effects base d on radiation from a femtosecond 800 nm Ti:Sapphire laser. Cavitations were observed from pulse energy densities exceeding 16 mJ/cm2, but only after several minutes of exposure and not as a result of a...... laser effects in the len s that have a potential for therapeutic application and treatment of eye dis ease though further studies are needed to shed light on the nature of the formation of delayed cavitations....

  17. Femtosecond laser-induced cavitations in the lens of the human eye

    DEFF Research Database (Denmark)

    Kessel, Line; Nymand, Jose; Harbst, Michael;

    attempted to define the cavitation threshold in the human lens in vitro using multiphoton effects base d on radiation from a femtosecond 800 nm Ti:Sapphire laser. Cavitations were observed from pulse energy densities exceeding 16 mJ/cm2, but only after several minutes of exposure and not as a result of a...... laser effects in the len s that have a potential for therapeutic application and treatment of eye dis ease though further studies are needed to shed light on the nature of the formation of delayed cavitations....

  18. Cavitation-erosion resistance of arc ion-plated (Ti, Cr) N coatings

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The cavitation-erosion behavior of (Ti,Cr)N multi-component coatings produced by arcion-plating on grey cast iron was studied by using an ultrasonic cavitation -erosion testing appara-tus and scanning electron microscopy. The test results indicated that surface roughness of thesubstrate, surface morphology of the coating, substrate bias voltage and the thickness of the coat-ing had certain influence on the erosion rate. Arc ion-plated (Ti,Cr)N multi-component coatingsshowed better cavitation -erosion resistance than single component coatings because of highermicrohardness and good adhesion.

  19. Elastic cavitation, tube hollowing, and differential growth in plants and biological tissues

    KAUST Repository

    Goriely, A.

    2010-07-01

    Elastic cavitation is a well-known physical process by which elastic materials under stress can open cavities. Usually, cavitation is induced by applied loads on the elastic body. However, growing materials may generate stresses in the absence of applied loads and could induce cavity opening. Here, we demonstrate the possibility of spontaneous growth-induced cavitation in elastic materials and consider the implications of this phenomenon to biological tissues and in particular to the problem of schizogenous aerenchyma formation. Copyright © EPLA, 2010.

  20. The rotordynamic forces on a centrifugal pump impeller in the presence of cavitation

    Science.gov (United States)

    Franz, R.; Acosta, A. J.; Brennen, C. E.; Caughey, T. K.

    1990-01-01

    Fluid-induced rotordynamic forces on a centrifugal pump impeller whirling along a trajectory eccentric to its undeflected position in the presence of cavitation were measured using the experimental facility described by Jery (1987). The force measured is a combination of a steady radial force due to the volute asymmetries and an unsteady force due to the eccentric motion of the rotor. It was found that, compared to the noncavitation condition, a cavitation corresponding to a head loss of 3 percent had little effect upon the unsteady force. However, a lesser degree of cavitation at the design point, was found to increase the destabilizing force for a particular set of whirl ratios.

  1. Transient cavitation produced by extracorporeal shock wave lithotripsy

    Science.gov (United States)

    Cioanta, Iulian

    1998-12-01

    Two decades ago, a new medical procedure was introduced, allowing the fragmentation of kidney stones from outside the human body (noninvasively) using a shock wave device termed lithotripter ('stone crusher'). Considered as one of the most important medical inventions of this century, lithotripsy is currently used in more than 80% of urolithiasis cases. Experimental studies have shown that transient or inertial cavitation is generated by this procedure near the stones and in renal tissue. To find a correlation between the number of shocks delivered and the treatment efficiency, the acoustic emission (AE) generated by the oscillation of cavitation bubbles, and its relation with stone fragmentation and tissue damage during shock wave lithotripsy were studied. In vitro experiments were carried out to identify the correlation between the AE signals and the expansion and collapse of cavitation bubbles, which were captured by high-speed photography (20,000 frames per second). This correlation has been verified on four different electrohydraulic lithotripters, under multiple experimental conditions. The effects of tissue attenuation on AE and stone fragmentation were also studied. The in vitro results have further allowed the interpretation of AE signals from in vivo experiments with pigs. Although similar in general trend, in vivo AE signals are found to be shorter in expansion and longer in the total ringing times (including the rebound phenomenon) than for in vitro AE signals, indicating a tissue constraining effect on bubble oscillation. Based on this observation a new mechanism for renal vascular and tubular injury is proposed. In addition, changes in AE signals have been observed as the total number of shocks increases, and this dose dependence feature has allowed the determination of a threshold value for extended tissue injury at 20 kV. This result has been confirmed by histological analysis and by results of a theoretical model study of bubble oscillation in a

  2. Nucleus factory on cavitation bubble for amyloid β fibril

    Science.gov (United States)

    Nakajima, Kichitaro; Ogi, Hirotsugu; Adachi, Kanta; Noi, Kentaro; Hirao, Masahiko; Yagi, Hisashi; Goto, Yuji

    2016-02-01

    Structural evolution from monomer to fibril of amyloid β peptide is related to pathogenic mechanism of Alzheimer disease, and its acceleration is a long-running problem in drug development. This study reveals that ultrasonic cavitation bubbles behave as catalysts for nucleation of the peptide: The nucleation reaction is highly dependent on frequency and pressure of acoustic wave, and we discover an optimum acoustical condition, at which the reaction-rate constant for nucleation is increased by three-orders-of magnitudes. A theoretical model is proposed for explaining highly frequency and pressure dependent nucleation reaction, where monomers are captured on the bubble surface during its growth and highly condensed by subsequent bubble collapse, so that they are transiently exposed to high temperatures. Thus, the dual effects of local condensation and local heating contribute to dramatically enhance the nucleation reaction. Our model consistently reproduces the frequency and pressure dependences, supporting its essential applicability.

  3. Shockwave and cavitation bubble dynamics of atmospheric air

    Science.gov (United States)

    Leela, Ch.; Bagchi, S.; Tewari, Surya P.; Kiran, P. Prem

    2013-11-01

    The generation and evolution of laser induced shock waves (SWs) and the hot core plasma (HCP) created by focusing 7 ns, 532 nm laser pulses in ambient air is studied using time resolved shadowgraphic imaging technique. The dynamics of rapidly expanding plasma releasing SWs into the ambient atmosphere were studied for time delays ranging from nanoseconds to milliseconds with ns temporal resolution. The SW is observed to get detached from expanding HCP at around 3μs. Though the SWs were found to expand spherically following the Sedov-Taylor theory, the rapidly expanding HCP shows asymmetric expansion during both the expansion and cooling phase similar to that of inertial cavitation bubble (CB) dynamics. The asymmetric expansion of HCP leads to oscillation of the plasma boundary, eventually leading to collapse by forming vortices formed by the interaction of ambient air.

  4. Investigation of aluminum surface cleaning using cavitating fluid flow

    Energy Technology Data Exchange (ETDEWEB)

    Ralys, Aurimas; Striška, Vytautas; Mokšin, Vadim [Vilnius Gediminas Technical University, Faculty of Mechanics, Department of Machine Engineering, J. Basanavičiaus str.28, 03224, Vilnius (Lithuania)

    2013-12-16

    This paper investigates efficiency of specially designed atomizer used to spray water and cavitate microbubbles in water flow. Surface cleaning system was used to clean machined (grinded) aluminum surface from abrasive particles. It is established that cleaning efficiency depends on diameter of the diffuser, water pressure and distance between nozzle and metal surface. It is obtained that the best cleaning efficiency (100%) is achieved at pressure 36 bar, when diameter of diffuser is 0.4 mm and distance between nozzle and surface is 1 mm. It is also established that satisfactory cleaning efficiency (80%) is achieved not only when atomizer is placed closer to metal surface, but also at larger (120 mm) distances.

  5. Additional evidence of nuclear emissions during acoustic cavitation.

    Science.gov (United States)

    Taleyarkhan, R P; Cho, J S; West, C D; Lahey, R T; Nigmatulin, R I; Block, R C

    2004-03-01

    Time spectra of neutron and sonoluminescence emissions were measured in cavitation experiments with chilled deuterated acetone. Statistically significant neutron and gamma ray emissions were measured with a calibrated liquid-scintillation detector, and sonoluminescence emissions were measured with a photomultiplier tube. The neutron and sonoluminescence emissions were found to be time correlated over the time of significant bubble cluster dynamics. The neutron emission energy was less than 2.5 MeV and the neutron emission rate was up to approximately 4 x 10(5) n/s. Measurements of tritium production were also performed and these data implied a neutron emission rate due to D-D fusion which agreed with what was measured. In contrast, control experiments using normal acetone did not result in statistically significant tritium activity, or neutron or gamma ray emissions. PMID:15089363

  6. Precise measurement technique for the stable acoustic cavitation bubble

    Institute of Scientific and Technical Information of China (English)

    HUANG Wei; CHEN Weizhong; LIU Yanan; GAO Xianxian; JIANG Lian; XU Junfeng; ZHU Yifei

    2005-01-01

    Based on the periodic oscillation of the stable acoustic cavitation bubble, we present a precise measurement technique for the bubble evolution. This technique comprises the lighting engineering of pulsing laser beam whose phase can be digitally shifted, and the long distance microphotographics. We used a laser, an acousto-optic modulator, a pulse generator, and a long distance microscope. The evolution of a levitated bubble can be directly shown by a series of bubble's images at different phases. Numerical simulation in the framework of the Rayleigh-Plesset bubble dynamics well supported the experimental result, and the ambient radius of the bubble, an important parameter related to the mass of the gas inside the bubble, was obtained at the same time.

  7. Cavitation-induced fragmentation of an acoustically-levitated droplet

    Science.gov (United States)

    Gonzalez Avila, Silvestre Roberto; Ohl, Claus-Dieter

    2015-12-01

    In this paper we investigate the initial sequence of events that lead to the fragmentation of a millimetre sized water droplets when interacting with a focused ns-laser pulse. The experimental results show complex processes that result from the reflection of an initial shock wave from plasma generation with the soft boundary of the levitating droplet; furthermore, when the reflected waves from the walls of the droplet refocus they leave behind a trail of microbubbles that later act as cavitation inception regions. Numerical simulations of a shock wave impacting and reflecting from a soft boundary are also reported; the simulated results show that the lowest pressure inside the droplet occurs at the equatorial plane. The results of the numerical model display good agreement with the experimental results both in time and in space.

  8. Water treatment technologies for CBM water, including cavitation

    Energy Technology Data Exchange (ETDEWEB)

    Makysmentz, B.; Lyon, F.L. [Newpark Resources Inc., Calgary, AB (Canada). Newpark Environmental Water Solutions

    2006-07-01

    The reasons for treating CBM water, end uses, reverse osmosis, pretreatment for reverse osmosis, and Newpark case studies are described. CBM water can be treated to make it suitable for injection, re-use, irrigation, or surface discharge. Usually the total dissolved solids (TDS) must be reduced by ion exchange or reverse osmosis with pretreatment. The concept of reverse osmosis and three types of applicable membrane processes are described: microfiltration and ultrafiltration, nanofiltration, and electrodialysis. The technologies used for pretreatment depend on the water quality and treatment goals, e.g. coagulation, flocculation and sand media filtration, softening, ion exchange, and nanofiltration. A Newpark case study is described for a water treatment plant at Boulder, Wyoming where evaporation was replaced by cavitation technology. The suitability of various treatment methods for Alberta CBM water is discussed. 21 figs., 1 tab.

  9. Design of PFBR sodium pumps and their cavitation performance criteria

    International Nuclear Information System (INIS)

    The Prototype Fast Breeder Reactor (PFBR) currently under design in India is a 500 MWe sodium cooled reactor plant of pool design. The reactor will have four heat transport loops in the primary as well as the secondary. The total primary coolant flow is expected to be 32000 cubic metres/hr and the total pressure drop in the circuit within 80 mic. Primary sodium will be circulated by four pumps immersed in the cold sodium pool (400 deg. C) and supported from the roof structure. This paper discusses the design of the primary sodium pumps with particular reference to cavitation performance requirements. An outline of the experimental programme for the hydraulic development is also given

  10. Nucleation threshold and deactivation mechanisms of nanoscopic cavitation nuclei

    CERN Document Server

    Borkent, Bram M; Prosperetti, Andrea; Lohse, Detlef

    2009-01-01

    The acoustic nucleation threshold for bubbles trapped in cavities has theoretically been predicted within the crevice theory by Atchley & Prosperetti [J. Acoust. Soc. Am. 86, 1065-1084 (1989)]. Here, we determine this threshold experimentally, by applying a single pressure pulse to bubbles trapped in cylindrical nanoscopic pits ("artificial crevices") with radii down to 50 nm. By decreasing the minimum pressure stepwise, we observe the threshold for which the bubbles start to nucleate. The experimental results are quantitatively in excellent agreement with the theoretical predictions of Atchley & Prosperetti. In addition, we provide the mechanism which explains the deactivation of cavitation nuclei: gas diffusion together with an aspherical bubble collapse. Finally, we present superhydrophobic nuclei which cannot be deactivated, unless with a high-speed liquid jet directed into the pit.

  11. IMPROVEMENT OF BUBBLE MODEL FOR CAVITATING FLOW SIMULATIONS

    Institute of Scientific and Technical Information of China (English)

    TAMURA Y.; MATSUMOTO Y.

    2009-01-01

    In the present research,a bubble dynamics based model for cavitating flow simulations is extended to higher void fraction region for wider range of applications.The present bubble model is based on the so-called Rayleigh-Plesset equation that calculates a temporal bubble radius with the surrounding liquid pressure and is considered to be valid in an area below a certain void fraction.The solution algorithm is modified so that the Rayleigh-Plesset equation is no more solved once the bubble radius(or void fraction)reaches at a certain value till the liquid pressure recovers above the vapor pressure in order to overcome this problem.This procedure is expected to stabilize the numerical calculation.The results of simple two-dimensional flow field are presented compared with the existing bubble model.

  12. Investigation of aluminum surface cleaning using cavitating fluid flow

    International Nuclear Information System (INIS)

    This paper investigates efficiency of specially designed atomizer used to spray water and cavitate microbubbles in water flow. Surface cleaning system was used to clean machined (grinded) aluminum surface from abrasive particles. It is established that cleaning efficiency depends on diameter of the diffuser, water pressure and distance between nozzle and metal surface. It is obtained that the best cleaning efficiency (100%) is achieved at pressure 36 bar, when diameter of diffuser is 0.4 mm and distance between nozzle and surface is 1 mm. It is also established that satisfactory cleaning efficiency (80%) is achieved not only when atomizer is placed closer to metal surface, but also at larger (120 mm) distances

  13. Cavitation-induced ignition of cryogenic hydrogen-oxygen fluids

    CERN Document Server

    Osipov, V V; Ponizovskya-Devine, E; Foygel, M; Smelyanskiy, V N

    2011-01-01

    The Challenger disaster and purposeful experiments with liquid hydrogen (H2) and oxygen (Ox) tanks demonstrated that cryogenic H2/Ox fluids always self-ignite in the process of their mixing. Here we propose a cavitation-induced self-ignition mechanism that may be realized under these conditions. In one possible scenario, self-ignition is caused by the strong shock waves generated by the collapse of pure Ox vapor bubble near the surface of the Ox liquid that may initiate detonation of the gaseous H2/Ox mixture adjacent to the gas-liquid interface. This effect is further enhanced by H2/Ox combustion inside the collapsing bubble in the presence of admixed H2 gas.

  14. Implicit Large Eddy Simulation of Cavitation in Micro Channel Flows

    CERN Document Server

    Hickel, S; Schmidt, S J

    2014-01-01

    We present a numerical method for Large Eddy Simulations (LES) of compressible two-phase flows. The method is validated for the flow in a micro channel with a step-like restriction. This setup is representative for typical cavitating multi-phase flows in fuel injectors and follows an experimental study of Iben et al., 2010. While a diesel-like test fuel was used in the experiment, we solve the compressible Navier-Stokes equations with a barotropic equation of state for water and vapor and a simple phase-change model based on equilibrium assumptions. Our LES resolve all wave dynamics in the compressible fluid and the turbulence production in shear layers.

  15. Histological and Ultrastructural Effects of Ultrasound-induced Cavitation on Human Skin Adipose Tissue

    Directory of Open Access Journals (Sweden)

    Daniele Bani, MD

    2013-09-01

    Conclusions: This study further strengthens the current notion that noninvasive transcutaneous ultrasound cavitation is a promising and safe technology for localized reduction of fat and provides experimental evidence for its specific mechanism of action on the adipocytes.

  16. Enhancement and quenching of high-intensity focused ultrasound cavitation activity via short frequency sweep gaps.

    Science.gov (United States)

    Hallez, Loïc; Lee, Judy; Touyeras, Francis; Nevers, Aymeric; Ashokkumar, Muthupandian; Hihn, Jean-Yves

    2016-03-01

    This letter reports on the use of frequency sweeps to probe acoustic cavitation activity generated by high-intensity focused ultrasound (HIFU). Unprecedented enhancement and quenching of HIFU cavitation activity were observed when short frequency sweep gaps were applied in negative and positive directions, respectively. It was revealed that irrespective of the frequency gap, it is the direction and frequency sweep rate that govern the cavitation activity. These effects are related to the response of bubbles generated by the starting frequency to the direction of the frequency sweep, and the influence of the sweep rate on growth and coalescence of bubbles, which in turn affects the active bubble population. These findings are relevant for the use of HIFU in chemical and therapeutic applications, where greater control of cavitation bubble population is critical. PMID:26584998

  17. RANS simulation of cavitation and hull pressure fluctuation for marine propeller operating behind-hull condition

    Science.gov (United States)

    Paik, Kwang-Jun; Park, Hyung-Gil; Seo, Jongsoo

    2013-12-01

    Simulations of cavitation flow and hull pressure fluctuation for a marine propeller operating behind a hull using the unsteady Reynolds-Averaged Navier-Stokes equations (RANS) are presented. A full hull body submerged under the free surface is modeled in the computational domain to simulate directly the wake field of the ship at the propeller plane. Simulations are performed in design and ballast draught conditions to study the effect of cavitation number. And two propellers with slightly different geometry are simulated to validate the detectability of the numerical simulation. All simulations are performed using a commercial CFD software FLUENT. Cavitation patterns of the simulations show good agreement with the experimental results carried out in Samsung CAvitation Tunnel (SCAT). The simulation results for the hull pressure fluctuation induced by a propeller are also compared with the experimental results showing good agreement in the tendency and amplitude, especially, for the first blade frequency.

  18. Cavitation erosion resistance of 13/4 and 21-4-N steels

    Indian Academy of Sciences (India)

    Akhilesh K Chauhan

    2013-02-01

    Nitrogen strengthened austenitic stainless steel (termed as 21-4-N steel) in as cast and hot rolled conditions has been investigated as an alternative to 13/4 steel (termed as CA6NM) to overcome the problems of cavitation erosion in hydro turbine underwater parts. The cavitation erosion of 21-4-N and 13/4 steels was investigated by means of an ultrasonic vibration processor. The cavitation erosion is highly dependent on microstructure and mechanical properties. The results show that hot rolled 21-4-N steel is more cavitation erosion resistant than the 13/4 and 21-4-N steels in as cast condition. The eroded surfaces were analysed through optical microscope and scanning electron microscope for study of erosion mechanisms.

  19. Anatomical regulation of ice nucleation and cavitation helps trees to survive freezing and drought stress.

    Science.gov (United States)

    Lintunen, A; Hölttä, T; Kulmala, M

    2013-01-01

    Water in the xylem, the water transport system of plants, is vulnerable to freezing and cavitation, i.e. to phase change from liquid to ice or gaseous phase. The former is a threat in cold and the latter in dry environmental conditions. Here we show that a small xylem conduit diameter, which has previously been shown to be associated with lower cavitation pressure thus making a plant more drought resistant, is also associated with a decrease in the temperature required for ice nucleation in the xylem. Thus the susceptibility of freezing and cavitation are linked together in the xylem of plants. We explain this linkage by the regulation of the sizes of the nuclei catalysing freezing and drought cavitation. Our results offer better understanding of the similarities of adaption of plants to cold and drought stress, and offer new insights into the ability of plants to adapt to the changing environment. PMID:23778457

  20. The onset of cavitation during the collision of a sphere with a wetted surface

    KAUST Repository

    Mansoor, Mohammad M.

    2014-01-01

    We investigate the onset of cavitation during the collision of a sphere with a solid surface covered with a layer of Newtonian liquid. The conventional theory dictates cavitation to initiate during depressurization, i.e. when the sphere rebounds from the solid surface. Using synchronized dual-view high-speed imaging, we provide conclusive experimental evidence that confirms this scenario- namely-that cavitation occurs only after the sphere makes initial contact with the solid surface. Similar to previous experimental observations for spheres released above the liquid surface, bubbles are formed on the sphere surface during entry into the liquid layer. These were found to squeeze radially outwards with the liquid flow as the sphere approached the solid surface, producing an annular bubble structure unrelated to cavitation. In contrast, spheres released below the liquid surface did not exhibit these patterns. © Springer-Verlag Berlin Heidelberg 2014.

  1. Femtosecond laser-induced cavitations in the lens of the human eye

    DEFF Research Database (Denmark)

    Kessel, Line; Nymand, Jose; Harbst, Michael; Poel, Mike van der; Eskildsen, Lars; Larsen, Michael

    single laser pulse. This suggests that cavitations were caused by a process which differs ITom the single-pulse cavitations observed at higher intensities. To evaluate whether the release of gas was caused by ionization and plasma formation or by thermal effects, we introduced pauses into the pulse train......Ultrafast femtosecond lasers are used increasingly for a wide range of medicai purposes. The immediate tissue response to pulses above a certain threshold is optically or laser induced breakdown, which is often visible as gas-filled cavities that persist for some time. In the present study, we...... attempted to define the cavitation threshold in the human lens in vitro using multiphoton effects base d on radiation from a femtosecond 800 nm Ti:Sapphire laser. Cavitations were observed from pulse energy densities exceeding 16 mJ/cm2, but only after several minutes of exposure and not as a result of a...

  2. The acoustic signatures of cavitation erosion on grade DH36 steel

    Science.gov (United States)

    Armakolas, I.; Carlton, J.; Vidakovic, M.; Sun, T.; Grattan, K. T. V.

    2015-12-01

    Cavitation can cause considerable erosion to adjacent materials. Erosion is accompanied by acoustic emissions, related to crack formation and propagation inside the material. In this study a piezoelectric acoustic sensor mounted on the back of a grade DH36 steel plate is used to identify the acoustic signatures of cavitation. Cavitation is induced near the plate by means of an ultrasonic transducer (sonotrode). Various ‘non-erosive’ and erosive test rig configurations are examined and an acoustic threshold value for the onset of cavitation erosion is identified and presented. The use of a fibre Bragg grating (FBG)-based acoustic sensor developed at City University London for acoustic monitoring purposes is also examined. Acoustic signals from both sensors are analysed, by means of a fast Fourier transform, showing a very good agreement in terms of captured frequencies.

  3. Study on cavitation in centrifugal sodium pumps for FBTR and PFBR

    International Nuclear Information System (INIS)

    Fast Breeder Test Reactor (FBTR) which is expected to become critical shortly is a loop type reactor of 40 MW thermal capacity and has two primary and two secondary centrifugal pumps for heat removal. During the initial periods of reactor operation, the steam generator is bypassed and the secondary sodium pumps are required to operate at flows less than that at best efficiency point. This paper deals with the cavitation problems associated with operation at partial f lows, theoretical estimations and experimental cavitation measurements carried out on FBTR secondary sodium pumps. These investigations revealed that operation of FBTR pumps at this off design condition is free from cavitation damage. Cavitation experiments on a model pump for the development of large sodium pumps for a 500 MWe Prototype Fast Breeder Reactor (PFBR) are described in this paper

  4. Natural and laser-induced cavitation in corn stems: On the mechanisms of acoustic emissions

    Directory of Open Access Journals (Sweden)

    Gabriel Mario Bilmes

    2012-05-01

    Full Text Available Water in plant xylem is often superheated, and therefore in a meta-stable state. Under certain conditions, it may suddenly turn from the liquid to the vapor state. This cavitation process produces acoustic emissions. We report the measurement of ultrasonic acoustic emissions (UAE produced by natural and induced cavitation in corn stems. We induced cavitation and UAE in vivo, in well controlled and reproducible experiments, by irradiating the bare stem of the plants with a continuous-wave laser beam. By tracing the source of UAE, we were able to detect absorption and frequency filtering of the UAE propagating through the stem. This technique allows the unique possibility of studying localized embolism of plant conduits, and thus to test hypotheses on the hydraulic architecture of plants. Based on our results, we postulate that the source of UAE is a transient "cavity oscillation"' triggered by the disruptive effect of cavitation inception.

  5. Natural and laser-induced cavitation in corn stems: On the mechanisms of acoustic emissions

    CERN Document Server

    Fernández, E; Bilmes, G M; 10.4279/PIP.040003

    2012-01-01

    Water in plant xylem is often superheated, and therefore in a meta-stable state. Under certain conditions, it may suddenly turn from the liquid to the vapor state. This cavitation process produces acoustic emissions. We report the measurement of ultrasonic acoustic emissions (UAE) produced by natural and induced cavitation in corn stems. We induced cavitation and UAE in vivo, in well controlled and reproducible experiments, by irradiating the bare stem of the plants with a continuous-wave laser beam. By tracing the source of UAE, we were able to detect absorption and frequency filtering of the UAE propagating through the stem. This technique allows the unique possibility of studying localized embolism of plant conduits, and thus to test hypotheses on the hydraulic architecture of plants. Based on our results, we postulate that the source of UAE is a transient "cavity oscillation" triggered by the disruptive effect of cavitation inception.

  6. Cavitation as a Mechanism to Enhance Wetting in a Mercury Thermal Convection Loop

    Energy Technology Data Exchange (ETDEWEB)

    Pawel, SJ

    2001-07-17

    Type 316L stainless steel was statically tested under cavitation conditions via an ultrasonic transducer externally mounted on a tube filled with ambient mercury. During the preliminary exposure (24 h, 20 kHz, 1.5 MPa), cavitation resulted in apparent wetting of the specimens by mercury as well as general surface roughening and wastage similar to erosion damage. Subsequently, a thermal convection loop identical to those used previously to study thermal gradient mass transfer was modified to include an externally-mounted donut-shaped transducer in order to similarly produce cavitation and wetting at temperatures prototypic of those expected in the SNS target. However, a series of attempts to develop cavitation and wetting on 316L specimens in the thermal convection loop was unsuccessful.

  7. Measurements of the critical velocity of hydraulic cavitation in superfluid He-4

    International Nuclear Information System (INIS)

    In an effort to clarify the mechanism of the inception of phase transition in liquid helium, He II was made to cavitate in the flow through a glass constriction nozzle with a diameter of 0.45 mm, by using a fountain effect pump. Attainable critical velocities for incipient cavitation were obtained over a temperature range of 1.2 K to the lambda-point. It was found that the cavitation threshold was quite low, with an approximate range of 0.1 - 1.0 KPa. The result seems to show that, contrary to the hypothesis of nuclear bubbles, some kind of direct coupling between the state of flow of He II, probably superfluid turbulence, and the inception of cavitation may be responsible for the phenomena. 7 refs

  8. Numerical investigation of unsteady cavitation around a NACA 66 hydrofoil using OpenFOAM

    Science.gov (United States)

    Hidalgo, V. H.; Luo, X. W.; Escaler, X.; Ji, J.; Aguinaga, A.

    2014-03-01

    The prediction and control of cavitation damage in pumps, propellers, hydro turbines and fluid machinery in general is necessary during the design stage. The present paper deals with a numerical investigation of unsteady cloud cavitation around a NACA 66 hydrofoil. The current study is focused on understanding the dynamic pressures generated during the cavity collapses as a fundamental characteristic in cavitation erosion. A 2D and 3D unsteady flow simulation has been carried out using OpenFOAM. Then, Paraview and Python programming language have been used to characterize dynamic pressure field. Adapted Large Eddy Simulation (LES) and Zwart cavitation model have been implemented to improve the analysis of cloud motion and to visualize the bubble expansions. Additional results also confirm the correlation between cavity formation and generated pressures.

  9. Risk of initial and moderate caries lesions in primary teeth to progress to dentine cavitation

    DEFF Research Database (Denmark)

    Guedes, Renata S; Piovesan, Chaiana; Floriano, Isabela; Emmanuelli, Bruno; Braga, Mariana M; Ekstrand, Kim R; Ardenghi, Thiago M; Mendes, Fausto M

    2016-01-01

    AIM: To investigate the risk of sound surfaces, and initial and moderate caries lesions to progress to dentine cavitation in preschool children. DESIGN: A cohort study was designed with 639 children (12-59 months old) who had been examined by visual inspection during a survey in 2010. After 2 years...... lesions at baseline had higher risk of having a sound surface or a non-cavitated caries lesion progressing to cavitation when compared with caries-free children; however, this increased risk was not observed in children with only initial caries lesions. CONCLUSIONS: Initial caries lesions present a low......, 469 children were re-examined regarding the presence of dentine cavitations. The probability of progression was calculated for sound and carious (initial and moderate lesions) surfaces. Relative risk of progression and 95% confidence intervals for each condition compared with sound surfaces were...

  10. On the Effect of Cavitation on the Radial Forces and Hydrodynamic Stiffness of a Centrifugal Pump

    OpenAIRE

    Franz, R. J.; Brennen, C. E.; Acosta, A. J.; Caughey, T. K.

    1986-01-01

    The asymmetric flow within a volute exerts a radial force on a centrifugal impeller. The present paper presents experimental measurements of the radial forces on the impeller in the presence of cavitation.

  11. Experimental Investigation and Passive Flow Control of a Cavitating Centrifugal Pump

    Directory of Open Access Journals (Sweden)

    Spyridon D. Kyparissis

    2012-01-01

    Full Text Available Passive flow control techniques are used to improve the flow field and efficiency of centrifugal pumps and turbomachines, in general. An important phenomenon that mechanical engineers have to take into account is cavitation. It leads to the decrease of the pump performance and total head. In the present experimental study, a centrifugal pump is investigated in cavitating conditions. A passive flow control is realized using three different blade leading edge angles in order to reduce the cavitation development and enhance the pump performance. The experiments are carried out in a pump test rig specially designed and constructed, along with the impellers. The head drop and total efficiency curves are presented in order to examine the effect of the blade leading edge angle on the cavitation and pump performance. Finally, the vapour distribution along with the blades is illustrated for the tested blade leading edge angles.

  12. Numerical and Experimental Investigation of Cavitating Characteristics in Centrifugal Pump with Gap Impeller

    Science.gov (United States)

    Zhu, Bing; Chen, Hongxun; Wei, Qun

    2014-06-01

    This paper is to study the cavitating characteristics in a low specific speed centrifugal pump with gap structure impeller experimentally and numerically. A scalable DES numerical method is proposed and developed by introducing the von Karman scale instead of the local grid scale, which can switch at the RANS and LES region interface smoothly and reasonably. The SDES method can detect and grasp unsteady scale flow structures, which were proved by the flow around a triangular prism and the cavitation flow in a centrifugal pump. Through numerical and experimental research, it's shown that the simulated results match qualitatively with tested cavitation performances and visualization patterns, and we can conclude that the gap structure impeller has a superior feature of cavitation suppression. Its mechanism may be the guiding flow feature of the small vice blade and the pressure auto-balance effect of the gap tunnel.

  13. Numerical investigation of unsteady cavitation around a NACA 66 hydrofoil using OpenFOAM

    International Nuclear Information System (INIS)

    The prediction and control of cavitation damage in pumps, propellers, hydro turbines and fluid machinery in general is necessary during the design stage. The present paper deals with a numerical investigation of unsteady cloud cavitation around a NACA 66 hydrofoil. The current study is focused on understanding the dynamic pressures generated during the cavity collapses as a fundamental characteristic in cavitation erosion. A 2D and 3D unsteady flow simulation has been carried out using OpenFOAM. Then, Paraview and Python programming language have been used to characterize dynamic pressure field. Adapted Large Eddy Simulation (LES) and Zwart cavitation model have been implemented to improve the analysis of cloud motion and to visualize the bubble expansions. Additional results also confirm the correlation between cavity formation and generated pressures

  14. RECENT APPLICATIONS OF THE GREENSPAN AND TSCHIEGG DATA ON NEUTRON INDUCED CAVITATION THRESHOLDS

    Energy Technology Data Exchange (ETDEWEB)

    West, Colin D [ORNL

    2007-03-01

    In 1967 Greenspan and Tschiegg published a paper on radiation induced acoustic cavitation. They researched the thresholds for cavitation induced in various liquids by fast neutrons, {alpha}-decay recoils and fission fragments. It turns out that these data can be used to verify predictions of a more recent theory of radiation induced cavitation nucleation. In 1979, in a report to their sponsor (The Office of Naval Research) they published new details of their results on neutron induced cavitation thresholds, including tables of the thresholds at different temperatures for various liquids. They were also some fission fragment results, but none of the {alpha}-decay recoil data. By that time Greenspan had evidently retired while I had left the field of cavitation research and did not know of the existence of their report [which also contains the only published record of some cavitation threshold measurements made by West and Howlett at Harwell, England]. Later still, in 1982, Greenspan and Tschiegg published the graphical data--but not the tables--in a more easily accessible form. In the late 1990s I revisited the problem of calculating radiation induced cavitation thresholds. There was interest in this because the Spallation Neutron Source (SNS) project, then just beginning, planned to use a liquid mercury target to produce intense bursts of neutrons when irradiated by a pulsed, high energy proton beam. It was known that the pressure waves produced by local heating when the proton pulse struck the target could, upon reflection at the walls of the mercury container, give rise to very high, although brief, negative pressure waves in the mercury. There was concern that cavitation might result and, if it did, might lead to undesirable effects. With the encouragement of the SNS target team this author managed further to develop an earlier method of calculating the threshold for such cavitation, and the SNS project kindly provided funding to publish the work in two ORNL

  15. Focused liver ablation by cavitation in the rabbit: a potential new method of extracorporeal treatment.

    OpenAIRE

    Prat, F; Chapelon, J Y; Abou El Fadil, F; Sibille, A; Theillière, Y; Ponchon, T; Cathignol, D.

    1994-01-01

    A new device was used to achieve focused tissue ablation by shockwave induced cavitation. The device produced a half cycle of negative pressure followed by a shock wave, thus enhancing cavitation. Twenty eight New Zealand rabbits were treated. Therapeutic ultrasound was targeted at the centre of the liver under ultrasound guidance. The focal volume was scanned with a computer operated x-y-z micropositioner. The number and frequency of bursts as well as the distance between two x-y-z displacem...

  16. Numerical Study of Cavitation in Francis Turbine of a Small Hydro Power Plant

    OpenAIRE

    Pankaj Gohil; Rajeshwer Saini

    2016-01-01

    Cavitation is undesirable phenomena and more prone in reaction turbines. It is one of the challenges in any hydro power plant which cause vibration, degradation of performance and the damage to the hydraulic turbine components. Under the present study, an attempt has been made to carry out a numerical analysis to investigate the cavitation effect in a Francis turbine. Three dimensional numerical study approach of unsteady and SST turbulence model are considered for the numerical a...

  17. Hydroacoustic Modeling of a Cavitation Vortex Rope for a Francis Turbine

    OpenAIRE

    Landry, Christian

    2015-01-01

    Hydraulic machines subject to off-design operation involve the presence of cavitating flow regimes in the draft tube. The cavitation vortex rope at part load conditions is described as an excitation source for the hydraulic system, and interactions between this excitation source and system eigenfrequency may result in resonance phenomena and induce a draft tube surge and electrical power swings. To accurately predict and simulate a part load resonance, proper modeling of the draft tube is cri...

  18. Dynamics of the cavitation precessing vortex rope for Francis turbines at part load operating conditions

    OpenAIRE

    Favrel, Arthur Tristan

    2016-01-01

    The massive penetration of the existing electrical grid by renewable energy sources requires a continuous extension of the operating range of hydroelectric powerplants, which can lead to cavitation flow instabilities inducing undesirable mechanical vibrations and large fluctuations of pressure and output power, putting at risk the structural integrity of the machine and ultimately the grid stability. A typical example is the development of a cavitation precessing vortex rope at the outlet of ...

  19. Numerical simulation of steady cavitating flow of viscous fluid in a Francis hydroturbine

    Science.gov (United States)

    Panov, L. V.; Chirkov, D. V.; Cherny, S. G.; Pylev, I. M.; Sotnikov, A. A.

    2012-09-01

    Numerical technique was developed for simulation of cavitating flows through the flow passage of a hydraulic turbine. The technique is based on solution of steady 3D Navier—Stokes equations with a liquid phase transfer equation. The approch for setting boundary conditions meeting the requirements of cavitation testing standard was suggested. Four different models of evaporation and condensation were compared. Numerical simulations for turbines of different specific speed were compared with experiment.

  20. One-way-coupling simulation of cavitation accompanied by high-speed droplet impact

    Science.gov (United States)

    Kondo, Tomoki; Ando, Keita

    2016-03-01

    Erosion due to high-speed droplet impact is a crucial issue in industrial applications. The erosion is caused by the water-hammer loading on material surfaces and possibly by the reloading from collapsing cavitation bubbles that appear within the droplet. Here, we simulate the dynamics of cavitation bubbles accompanied by high-speed droplet impact against a deformable wall in order to see whether the bubble collapse is violent enough to give rise to cavitation erosion on the wall. The evolution of pressure waves in a single water (or gelatin) droplet to collide with a deformable wall at speed up to 110 m/s is inferred from simulations of multicomponent Euler flow where phase changes are not permitted. Then, we examine the dynamics of cavitation bubbles nucleated from micron/submicron-sized gas bubble nuclei that are supposed to exist inside the droplet. For simplicity, we perform Rayleigh-Plesset-type calculations in a one-way-coupling manner, namely, the bubble dynamics are determined according to the pressure variation obtained from the Euler flow simulation. In the simulation, the preexisting bubble nuclei whose size is either micron or submicron show large growth to submillimeters because tension inside the droplet is obtained through interaction of the pressure waves and the droplet interface; this supports the possibility of having cavitation due to the droplet impact. It is also found, in particular, for the case of cavitation arising from very small nuclei such as nanobubbles, that radiated pressure from the cavitation bubble collapse can overwhelm the water-hammer pressure directly created by the impact. Hence, cavitation may need to be accounted for when it comes to discussing erosion in the droplet impact problem.

  1. Cavitation Erosion Corrosion Behaviour of Manganese-nickel -aluminum Bronze in Comparison with Manganese-brass

    Institute of Scientific and Technical Information of China (English)

    Hong Yu; Yugui Zheng; Zhiming Yao

    2009-01-01

    The cavitation erosion corrosion behaviour of ZQMn 12-8-3-2 manganese-nickel-aluminum bronze and ZHMn55-3-1 manganese-brass was investigated by mass loss, electrochemical measurements (polarization curves and electrochemical impedance spectroscopy) and the cavitation damaged surfaces were observed by scanning electron microscopy (SEM). The results showed that ZQMn 12-8-3-2 had better cavitation erosion resistance than ZHMn55-3-l. After the cavitation erosion for 6 h, the cumulative mass loss of ZQMnl2-8-3-2 was about 1/3 that of ZHMn55-3-l. The corrosion current density of ZQMnl2-8-3-2 was less than that of ZHMn55-3-l under both static and cavitaiton condition. The free-corrosion potentials of ZQMnl2-8-3-2 and ZHMn55-3-l were all shifted in positive direction under cavitation condition compared to static condition. In the total cu-mulative mass loss under cavitation condition, the pure erosion played a key role for the two tested materials (74% for ZHMn55-3-l and 60% for ZQMnl2-8-3-2), and the total synergism between corrosion and erosion of ZQMnl2-8-3-2 (39%) was larger than that of ZHMn55-3-l (23%). The high cavitation erosion resistance of ZQMnl2-8-3-2 was mainly attributed to its lower stacking fault energy (SFE), the higher microhardness and work-hardening ability as well as the favorable propagation of cavitation cracks for ZQMn 12-8-3-2, i.e., parallel to the surface rather than perpendicular to the surface for ZHMn55-3-l.

  2. Histological and Ultrastructural Effects of Ultrasound-induced Cavitation on Human Skin Adipose Tissue

    OpenAIRE

    Daniele Bani, MD; Alessandro Quattrini Li, MD; Giancarlo Freschi, MD; Giulia Lo Russo, MD

    2013-01-01

    Background: In aesthetic medicine, the most promising techniques for noninvasive body sculpturing purposes are based on ultrasound-induced fat cavitation. Liporeductive ultrasound devices afford clinically relevant subcutaneous fat pad reduction without significant adverse reactions. This study aims at evaluating the histological and ultrastructural changes induced by ultrasound cavitation on the different cell components of human skin. Methods: Control and ultrasound-treated ex vivo abdom...

  3. Clinical cavitation and radiographic lesion depth in proximal surfaces in an Indian population

    DEFF Research Database (Denmark)

    Sansare, Kaustubh; Raghav, Mamta; Sontakke, Subodeh;

    2014-01-01

    Abstract Objectives. To assess the relationship between clinical cavitation and radiographic caries lesion depth in proximal surfaces of permanent posterior teeth in an Indian population. This study also assessed the clinical feasibility of applying 'western guidelines' to this population from the...... developing world. Materials and methods. Relationship between clinical cavitation and radiographic caries lesion depth in proximal surfaces in an Indian population was assessed. Proximal surfaces (n = 126) without restorations were examined on bitewing radiographs in patients with suspected caries and lesion...

  4. Contrôle temporel de la cavitation ultrasonore : Application à la thrombolyse ultrasonore extracorporelle

    OpenAIRE

    Poizat, Adrien

    2016-01-01

    Focused ultrasound can be used for therapeutic applications in the human body. In cardiovascular applications, they can destroy blood clots formed in the vascular system. In this case, thrombolysis mechanisms are related to ultrasonic cavitation, but the complex dynamics remains an obstacle to the development of a therapeutic device. In this thesis, a system for the temporal control of the pulsed cavitation activity has been developed and characterized. This device uses a focused transducer a...

  5. NON - OPERATIVE TREATMENT OF NON - CAVITATED APPROXIMAL CARIOUS LESIONS OF PERMANENT CHIDREN’S TEETH.

    OpenAIRE

    Rossiza I. Kabakchieva; Natalia H. Gateva; Hristina D. Mihaylova

    2014-01-01

    Aim: To apply and follow up in clinical conditions the success rate of microinvasive technique of infiltration with low viscosity resin ICON® (DMG) of non cavitated approximal caries lesions of permanent children's teeth for a period of one year. Material and methods: The study included 18 children aged 7-16 years. They were divided into two groups - children with medium and high caries risk. The survey include 20 teeth with approximal non-cavitated enamel lesions up to the outer third of ...

  6. On the role of cavitation in particle collection in flotation - A critical review. II

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, Z.A.; Xu, Z.H.; Finch, J.A.; Masliyah, J.H.; Chow, R.S. [Alberta Research Council, Edmonton, AB (Canada)

    2009-04-15

    Research in applying hydrodynamic cavitation to recovery of natural resources during the last decade is reviewed. The existence and formation of tiny bubbles or gas nuclei (diameter from microns down to nano sizes) in natural water were verified from both direct and in-direct measurements, providing a foundation for applying hydrodynamic cavitation to flotation systems. The interactions between tiny bubbles and fine particles in aqueous slurry were analysed. Tiny bubbles generated by hydrodynamic cavitation increased contact angle of solids and hence attachment force, bridge fine particles to form aggregates, minimize slime coating, remove oxidation layers on particle surfaces, and in hence reduce reagents consumption. Experiments revealed that the energy dissipation levels for cavity formation in a flowing liquid could be much lower than predicted, depending on the content of dissolved gases, presence of free gas nuclei and design of cavitation tubes. Application of hydrodynamic cavitation to fine and coarse particle flotation, high intensity conditioning, oil agglomeration of fine coal, and oil sands processing has confirmed the role of tiny bubbles formed by cavitation in improving recovery efficiency. Increased flotation kinetics by hydrodynamic cavitation could be attributed to a dual role: some collapsing cavity bubbles serving to break interfacial layers on particle surfaces while other cavity bubbles attaching to those freshly exposed mineral surfaces. The role of water vapor and other gases within cavity bubbles in particle-bubble attachment remains to be explored. Incorporating hydrodynamic cavitation into flotation systems to take advantage of its unique features is expected to develop the next generation of flotation machines.

  7. Collapse of spark-generated cavitation bubble near a solid wall

    Czech Academy of Sciences Publication Activity Database

    Müller, M.; Zima, Patrik

    Warwick : University of Warwick, 2011 - (Li, S.), s. 1-6 ISBN 978-0-9570404-1-0. [WIMRC International Cavitation Forum 2011 /3./. Warwick (GB), 04.07.2011-06.07.2011] R&D Projects: GA ČR GAP101/10/1428 Institutional research plan: CEZ:AV0Z20760514 Keywords : cavitation bubble collapse * spark Subject RIV: BK - Fluid Dynamics

  8. Application of cavitating jet-flow well washing method to in-situ leaching of uranium

    International Nuclear Information System (INIS)

    Well washing methods in in-situ leaching of uranium are introduced, with focus on a new method of cavitation jet well washing and its application in in-situ leaching of uranium of a deposit in Kazakhstan. Compared with the traditional well washing technologies, the cavitation jet well washing method has advantages of reducing the costs and labour intensity, and improving pumping and injecting solution volume. (authors)

  9. Vibration Characteristics Induced by Cavitation in a Centrifugal Pump with Slope Volute

    OpenAIRE

    Ning Zhang; Minguan Yang; Bo Gao; Zhong Li

    2015-01-01

    Cavitation is one of the instability sources in centrifugal pump, which would cause some unexpected results. The goal of this paper was to analyze the influence of cavitation process on different frequency bands in a centrifugal pump with slope volute. And special attention was paid to low frequency signals, which were often filtered in the reported researches. Results show that at noncavitation condition, vibration level is closely related to flow structure interior pump. At partial flow rat...

  10. Influence of Prewhirl Regulation by Inlet Guide Vanes on Cavitation Performance of a Centrifugal Pump

    OpenAIRE

    Lei Tan; Baoshan Zhu; Shuliang Cao; Yuchuan Wang; Binbin Wang

    2014-01-01

    The influence of prewhirl regulation by inlet guide vanes (IGVs) on a centrifugal pump performance is investigated experimentally and numerically. The experimental results show that IGVs can obviously change the head and increase the efficiency of the tested centrifugal pump over a wide range of flow rates. Although the cavitation performance is degraded, the variation of the cavitation critical point is less than 0.5 m. Movement of the computed three-dimensional streamlines in suction pipe a...

  11. Numerical simulation of cavitation erosion on a NACA0015 hydrofoil based on bubble collapse strength

    OpenAIRE

    Hidalgo, Victor; Luo, Xianwu; Escaler Puigoriol, Francesc Xavier; Huang, R.; Valencia, E.

    2015-01-01

    The prediction of erosion under unsteady cavitation is crucial to prevent damage in hydraulic machinery. The present investigation deals with the numerical simulation of erosive partial cavitation around a NACA0015 hydrofoil. The study presents the calculation of the bubble collapse strength, Sb , based on the bubble potential energy to identify the surface areas with highest risk of damage. The results are obtained with a numerical scheme assuming homogeneous mixture ow, implicit LES and Zwa...

  12. Cavitation erosion of laser processed Fe-Cr-Mn and Fe-Cr-Co alloys

    Directory of Open Access Journals (Sweden)

    M. Szkodo

    2008-12-01

    Full Text Available Purpose: Purpose of this paper is attempt explanation how laser beam processing influence on the cavitation performance of the Fe-Cr-Mn and Fe-Cr-Co alloys. This kind of alloys are frequently used in Polish power plants to routine repairs of damaged blades working under cavitation loading.Design/methodology/approach: Padding welds of investigated alloys were tested for three cases: after laser melting, after laser heating of the solid state and without additional processing. Cw. CO2 laser was employed as a source of radiation. The rotating disk rig was used in cavitation erosion investigations. The chemical composition, microstructure, and phase identification of the processed and subjected to cavitation loading alloys were examined using light microscopy, X-ray diffractometry and scanning electron microscopy, respectively.Findings: Phase transformation for processed and unprocessed alloys was observed. Obtained results revealed that laser processing contributes to delaying of austenite → martensite phase transformation. Kinetic of this transformation is different for investigated alloys and depends on the chemical composition and applied laser processing. Research limitations/implications: Reported research ought to be completed and full cavitation curves (volume loss in time for laser beam processed alloys must be done. Practical implications: For low intensity of cavitation loading, like in field conditions laser beam processing can increase of cavitation erosion resistance of investigated alloys due to increase of hardness.Originality/value: Confirmation that creation of the transformed and hardfacing structures by laser techniques leads in many cases to considerable changes in cavitation erosion properties of the processed materials.

  13. Effects of Leading Edge Sweep on the Cavitating Characteristics of Inducer Pumps

    OpenAIRE

    Acosta, Allan J.; Yoshinobu Tsujimoto; Yoshiki Yoshida; Seiji Azuma; Paul Cooper

    2001-01-01

    It is well known that leading edge sweep has a favorable effect on the cavitation of turbomachines. However, the mechanisms of the improvement have not been made clear. It has been shown that the lift and the drag on a cavitating swept single hydrofoil can be correlated fairly well based on the velocity component normal to the leading edge. In the present paper, such correlations for swept cascades are derived and the results are examined, neglecting the full geometrical effects of the induce...

  14. Steady flow and stability analyses of cavitation in finite blade count impeller; Yugen'yokusu no haneguruma ni shojiru cavitation no teijo nagare kaiseki to antei kaiseki

    Energy Technology Data Exchange (ETDEWEB)

    Horiguchi, H.; Tsujimoto, Y. [Osaka University, Osaka (Japan); Wahl, F. [SEP. division de SNECMA, (France); Watanabe, S. [Kyushu University, Fukuoka (Japan). Faculty of Engineering

    1999-08-25

    The seady flow and stability analyses of cavitation in flat plate cascades corresponding to 2, 3, 4 and 5 bladed impeller were carried out to find out all of the steady cavity patterns and destabilizing modes. For this purpose each blade is treated independently. In steady flow analysis the alternate blade cavitation was found only for impellers with even number of blades. It was shown that the alternate blade cavitation occurs since the local flow near the cavity closure reduces the angle of attack to the opposing blade when the cavity closure point approaches the leading edge of the opposing blade. For 2 or 4 bladed impeller, it was confirmed that there exists no additional destabilizing mode to those found in an analysis assuming inter-blade phase difference. It was shown that the modes with total cavity volume fluctuation depend on the inlet duct length while the modes without total cavity volume fluctuation are independent on the system. (author)

  15. Cavitation inception by the backscattering of pressure waves from a bubble interface

    Science.gov (United States)

    Takahira, Hiroyuki; Ogasawara, Toshiyuki; Mori, Naoto; Tanaka, Moe

    2015-10-01

    The secondary cavitation that occurs by the backscattering of focused ultrasound from a primary cavitation bubble caused by the negative pressure part of the ultrasound (Maxwell, et al., 2011) might be useful for the energy exchange due to bubble oscillations in High Intensity Focused Ultrasound (HIFU). The present study is concerned with the cavitation inception by the backscattering of ultrasound from a bubble. In the present experiment, a laser-induced bubble which is generated by a pulsed focused laser beam with high intensity is utilized as a primary cavitation bubble. After generating the bubble, focused ultrasound is emitted to the bubble. The acoustic field and the bubble motion are observed with a high-speed video camera. It is confirmed that the secondary cavitation bubble clouds are generated by the backscattering from the laser-induced bubble. The growth of cavitation bubble clouds is analyzed with the image processing method. The experimental results show that the height and width of the bubble clouds grow in stepwise during their evolution. The direct numerical simulations are also conducted for the backscattering of incident pressure waves from a bubble in order to evaluate a pressure field near the bubble. It is shown that the ratio of a bubble collapse time t0 to a characteristic time of wave propagation tS, η = t0/ts, is an important determinant for generating negative pressure region by backscattering. The minimum pressure location by the backscattering in simulations is in good agreement with the experiment.

  16. Cavitation structures formed during the rebound of a sphere from a wetted surface

    KAUST Repository

    Marston, Jeremy

    2010-09-28

    We use high-speed imaging to observe the dynamics of cavitation, caused by the impact and subsequent rebound of a sphere from a solid surface covered with a thin layer of highly viscous liquid. We note marked qualitative differences between the cavitation structures with increase in viscosity, as well as between Newtonian and non-Newtonian liquids. The patterns observed are quite unexpected and intricate, appearing in concentric ring formations around the site of impact. In all cases, we identify a distinct radius from which the primary bubbles emanate. This radius is modelled with a modified form of Hertz contact theory. Within this radius, we show that some fine cavitation structure may exist or that it may be one large cavitation bubble. For the non-Newtonian fluids, we observe foam-like structures extending radially with diminishing bubble sizes with increase in radial position. Whereas for the Newtonian fluids, the opposite trend is observed with increasing bubble size for increasing radial position. Finally, we compare our experimental observations of cavitation to the maximum tension criterion proposed by Joseph (J Fluid Mech 366:367-378, 1998) showing that this provides the lower limit for the onset of cavitation in our experiments. © 2010 Springer-Verlag.

  17. A physical model of the extreme mantis shrimp strike: kinematics and cavitation of Ninjabot

    International Nuclear Information System (INIS)

    To study the mechanical principles and fluid dynamics of ultrafast power-amplified systems, we built Ninjabot, a physical model of the extremely fast mantis shrimp (Stomatopoda). Ninjabot rotates a to-scale appendage within the environmental conditions and close to the kinematic range of mantis shrimp's rotating strike. Ninjabot is an adjustable mechanism that can repeatedly vary independent properties relevant to fast aquatic motions to help isolate their individual effects. Despite exceeding the kinematics of previously published biomimetic jumpers and reaching speeds in excess of 25 m s−1 at accelerations of 3.2 × 104 m s−2, Ninjabot can still be outstripped by the fastest mantis shrimp, Gonodactylus smithii, measured for the first time in this study. G. smithii reached 30 m s−1 at accelerations of 1.5 × 105 m s−2. While mantis shrimp produce cavitation upon impact with their prey, they do not cavitate during the forward portion of their strike despite their extreme speeds. In order to determine how closely to match Ninjabot and mantis shrimp kinematics to capture this cavitation behavior, we used Ninjabot to produce strikes of varying kinematics and to measure cavitation presence or absence. Using Akaike Information Criterion to compare statistical models that correlated cavitation with a variety of kinematic properties, we found that in rotating and accelerating biological conditions, cavitation inception is best explained only by maximum linear velocity. (paper)

  18. Application of signal processing techniques to the detection of tip vortex cavitation noise in marine propeller

    Institute of Scientific and Technical Information of China (English)

    LEE Jeung-Hoon; HAN Jae-Moon; PARK Hyung-Gil; SEO Jong-Soo

    2013-01-01

    The tip vortex cavitation and its relevant noise has been the subject of extensive researches up to now.In most cases of experimental approaches,the accurate and objective decision of cavitation inception is primary,which is the main topic of this paper.Although the conventional power spectrum is normally adopted as a signal processing tool for the analysis of cavitation noise,a faithful exploration cannot be made especially for the cavitation inception.Alternatively,the periodic occurrence of bursting noise induced from tip vortex cavitation gives a diagnostic proof that the repeating frequency of the bursting contents can be exploited as an indication of the inception.This study,hence,employed the Short-Time Fourier Transform (STFT) analysis and the Detection of Envelope Modulation On Noise (DEMON) spectrum analysis,both which are appropriate for finding such a repeating frequency.Through the acoustical measurement in a water tunnel,the two signal processing techniques show a satisfactory result in detecting the inception of tip vortex cavitation.

  19. Initiate and Maintain Cavitation by Combining High Amplitude Bursts and Continuous Ultrasound Exposure in Culture Medium

    Science.gov (United States)

    Mestas, J.-L.; Alberti, L.; Chesnais, S.; Lafon, C.; Blay, J.-Y.; Cathignol, D.

    2006-05-01

    Ultrasound can produce a variety of nonthermal bioeffects via acoustic cavitation. Most studies on cavitation effects pointed on the difficulty of initiating and controlling the cavitation phenomenon. Our objective is to obtain reproducible viability and transfection rate in the case of the application of a continuous low intensity ultrasound exposure. We propose to initiate and maintain cavitation in the medium by combining a continuous ultrasound exposure with periodical high amplitude bursts. Cells were exposed to ultrasound (444.5 kHz) transmitted through the bottom of twelve-well culture plates containing prostatic cells (AT2, 2.5 106 cells/mL), the plasmid DsRed in transfection case (200 μg/mL) and culture media. The cavitation effects were evaluated on the cell viability and transfection, determined 0 to 3 days after exposure by a flow cytometer (FACScan; total counted events: 10 000). Bursts of 1.73 W/cm2 intensity level had no effect on cells when their duration was lower than 100 ms and their frequency lower than 4 bursts/min. When combined with continuous exposure, only one burst of 1.73 W/cm2 intensity level and 50 ms duration was sufficient to activate the cavitation phenomenon in the medium.

  20. Degradation of C.I. Reactive Red 2 through photocatalysis coupled with water jet cavitation.

    Science.gov (United States)

    Wang, Xiaoning; Jia, Jinping; Wang, Yalin

    2011-01-15

    The decolorization of an azo dye, C.I. Reactive Red 2 was investigated using TiO(2) photocatalysis coupled with water jet cavitation. Experiments were performed in a 4.0 L solution under ultraviolet power of 9 W. The effects of TiO(2) loading, initial dye concentration, solution pH, geometry of cavitation tube, and the addition of anions on the degradation of the dye were evaluated. Degradation of the dye followed a pseudo-first order reaction. The photocatalysis coupled with water jet cavitation elevated degradation of the dye by about 136%, showing a synergistic effect compared to the individual photocatalysis and water jet cavitation. The enhancement of photocatalysis by water jet cavitation could be due to the deagglomeration of catalyst particles as well as the better contact between the catalyst surfaces and the reactants. Venturi tube with smaller diameter and shorter length of throat tube favored the dye decolorization. The degradation efficiency was found to increase with decreasing initial concentration and pH. The presence of NO(3)(-) and SO(4)(2-) enhanced the degradation of RR2, while Cl(-), and especially HCO(3)(-) significantly reduced dye decolorization. The results of this study indicated that the coupled photocatalysis and water jet cavitation is effective in degrading dye in wastewater and provides a promising alternative for treatment of dye wastewater at a large scale. PMID:20940086

  1. Improvement in cavitation erosion resistance of AISI 316L stainless steel by friction stir processing

    International Nuclear Information System (INIS)

    Commercial AISI 316L plates with the initial grain size of 14.8 μm were friction stir processed (FSP) with different processing parameters, resulting in two fine-grained microstructures with the grain sizes of 4.6 and 1.7 μm. The cavitation erosion behavior, before and after FSP, was evaluated in terms of incubation time, cumulative mass loss and mean depth of erosion. A separate cavitation erosion test was performed on the transverse cross section of a FSP sample to reveal the effect of grain structure. It was observed that FSP samples, depending on their grain size, are at least 3–6 times more resistant than the base material against cavitation erosion. The improvement in cavitation erosion resistance is attributed to smaller grain structure, lower fraction of twin boundaries, and favorable crystallographic orientation of grains in FSP samples. The finer the grain size, the more cavitation erosion resistance was achieved. Moreover, the microstructures of eroded surfaces were studied using a scanning electron microscope equipped with EBSD, and an atomic force microscope. The mechanisms controlling the cavitation erosion damage in friction stir processed AISI 316L are also discussed.

  2. Cavitation structures formed during the rebound of a sphere from a wetted surface

    Energy Technology Data Exchange (ETDEWEB)

    Marston, J.O. [A-STAR Institute of Chemical and Engineering Sciences, Singapore (Singapore); King Abdullah University of Science and Technology, Division of Physical Sciences and Engineering, Thuwal (Saudi Arabia); Yong, W. [National University of Singapore, Department of Chemical and Biomolecular Engineering, Singapore (Singapore); Ng, W.K. [A-STAR Institute of Chemical and Engineering Sciences, Singapore (Singapore); Tan, R.B.H. [A-STAR Institute of Chemical and Engineering Sciences, Singapore (Singapore); National University of Singapore, Department of Chemical and Biomolecular Engineering, Singapore (Singapore); Thoroddsen, S.T. [King Abdullah University of Science and Technology, Division of Physical Sciences and Engineering, Thuwal (Saudi Arabia)

    2011-03-15

    We use high-speed imaging to observe the dynamics of cavitation, caused by the impact and subsequent rebound of a sphere from a solid surface covered with a thin layer of highly viscous liquid. We note marked qualitative differences between the cavitation structures with increase in viscosity, as well as between Newtonian and non-Newtonian liquids. The patterns observed are quite unexpected and intricate, appearing in concentric ring formations around the site of impact. In all cases, we identify a distinct radius from which the primary bubbles emanate. This radius is modelled with a modified form of Hertz contact theory. Within this radius, we show that some fine cavitation structure may exist or that it may be one large cavitation bubble. For the non-Newtonian fluids, we observe foam-like structures extending radially with diminishing bubble sizes with increase in radial position. Whereas for the Newtonian fluids, the opposite trend is observed with increasing bubble size for increasing radial position. Finally, we compare our experimental observations of cavitation to the maximum tension criterion proposed by Joseph (J Fluid Mech 366:367-378, 1998) showing that this provides the lower limit for the onset of cavitation in our experiments. (orig.)

  3. A detector for monitoring the onset of cavitation during therapy-level measurements of ultrasonic power

    Science.gov (United States)

    Hodnett, M.; Zeqiri, B.

    2004-01-01

    Acoustic cavitation occurring in the water path between a transducer and the target of a radiation force balance can provide a significant source of error during measurements of ultrasonic power. These problems can be particularly acute at physiotherapy levels (>1 W), and low frequencies (leq 1 MHz). The cavitating bubbles can absorb and scatter incident ultrasound, leading to an underestimate in the measured power. For these reasons, International Specification standards demand the use of degassed water. This imposes requirements that may actually be difficult to meet, for example, in the case of hospitals. Also, initially degassed water will rapidly re-gas, increasing the likelihood of cavitation occurring. For these reasons, NPL has developed a device that monitors acoustic emissions generated by bubble activity, for detecting the onset of cavitation during power measurements. A commercially available needle hydrophone is used to detect these emissions. The acoustic signals are then monitored using a Cavitation Detector (CD) unit, comprising an analogue electrical filter that may be tuned to detect frequency components generated by cavitating bubbles, and which provides an indication of when the measured level exceeds a pre-defined threshold. This paper describes studies to establish a suitable detection scheme, the principles of operation of the CD unit, and the performance tests carried out with a range of propagation media.

  4. A detector for monitoring the onset of cavitation during therapy-level measurements of ultrasonic power

    Energy Technology Data Exchange (ETDEWEB)

    Hodnett, M; Zeqiri, B [National Physical Laboratory, Queens Road, Teddington, Middlesex, TW11 0LW (United Kingdom)

    2004-01-01

    Acoustic cavitation occurring in the water path between a transducer and the target of a radiation force balance can provide a significant source of error during measurements of ultrasonic power. These problems can be particularly acute at physiotherapy levels (>1 W), and low frequencies ({<=} 1 MHz). The cavitating bubbles can absorb and scatter incident ultrasound, leading to an underestimate in the measured power. For these reasons, International Specification standards demand the use of degassed water. This imposes requirements that may actually be difficult to meet, for example, in the case of hospitals. Also, initially degassed water will rapidly re-gas, increasing the likelihood of cavitation occurring. For these reasons, NPL has developed a device that monitors acoustic emissions generated by bubble activity, for detecting the onset of cavitation during power measurements. A commercially available needle hydrophone is used to detect these emissions. The acoustic signals are then monitored using a Cavitation Detector (CD) unit, comprising an analogue electrical filter that may be tuned to detect frequency components generated by cavitating bubbles, and which provides an indication of when the measured level exceeds a pre-defined threshold. This paper describes studies to establish a suitable detection scheme, the principles of operation of the CD unit, and the performance tests carried out with a range of propagation media.

  5. Sound field measurement in a double layer cavitation cluster by rugged miniature needle hydrophones.

    Science.gov (United States)

    Koch, Christian

    2016-03-01

    During multi-bubble cavitation the bubbles tend to organize themselves into clusters and thus the understanding of properties and dynamics of clustering is essential for controlling technical applications of cavitation. Sound field measurements are a potential technique to provide valuable experimental information about the status of cavitation clouds. Using purpose-made, rugged, wide band, and small-sized needle hydrophones, sound field measurements in bubble clusters were performed and time-dependent sound pressure waveforms were acquired and analyzed in the frequency domain up to 20 MHz. The cavitation clusters were synchronously observed by an electron multiplying charge-coupled device (EMCCD) camera and the relation between the sound field measurements and cluster behaviour was investigated. Depending on the driving power, three ranges could be identified and characteristic properties were assigned. At low power settings no transient and no or very low stable cavitation activity can be observed. The medium range is characterized by strong pressure peaks and various bubble cluster forms. At high power a stable double layer was observed which grew with further increasing power and became quite dynamic. The sound field was irregular and the fundamental at driving frequency decreased. Between the bubble clouds completely different sound field properties were found in comparison to those in the cloud where the cavitation activity is high. In between the sound field pressure amplitude was quite small and no collapses were detected. PMID:24953962

  6. Improvement in cavitation erosion resistance of AISI 316L stainless steel by friction stir processing

    Science.gov (United States)

    Hajian, M.; Abdollah-zadeh, A.; Rezaei-Nejad, S. S.; Assadi, H.; Hadavi, S. M. M.; Chung, K.; Shokouhimehr, M.

    2014-07-01

    Commercial AISI 316L plates with the initial grain size of 14.8 μm were friction stir processed (FSP) with different processing parameters, resulting in two fine-grained microstructures with the grain sizes of 4.6 and 1.7 μm. The cavitation erosion behavior, before and after FSP, was evaluated in terms of incubation time, cumulative mass loss and mean depth of erosion. A separate cavitation erosion test was performed on the transverse cross section of a FSP sample to reveal the effect of grain structure. It was observed that FSP samples, depending on their grain size, are at least 3-6 times more resistant than the base material against cavitation erosion. The improvement in cavitation erosion resistance is attributed to smaller grain structure, lower fraction of twin boundaries, and favorable crystallographic orientation of grains in FSP samples. The finer the grain size, the more cavitation erosion resistance was achieved. Moreover, the microstructures of eroded surfaces were studied using a scanning electron microscope equipped with EBSD, and an atomic force microscope. The mechanisms controlling the cavitation erosion damage in friction stir processed AISI 316L are also discussed.

  7. Improvement in cavitation erosion resistance of AISI 316L stainless steel by friction stir processing

    Energy Technology Data Exchange (ETDEWEB)

    Hajian, M. [Department of Materials Engineering, Tarbiat Modares University, P.O. Box 14115-143, Tehran (Iran, Islamic Republic of); Abdollah-zadeh, A., E-mail: zadeh@modares.ac.ir [Department of Materials Engineering, Tarbiat Modares University, P.O. Box 14115-143, Tehran (Iran, Islamic Republic of); Rezaei-Nejad, S.S.; Assadi, H. [Department of Materials Engineering, Tarbiat Modares University, P.O. Box 14115-143, Tehran (Iran, Islamic Republic of); Hadavi, S.M.M. [Department of Materials Science and Engineering, MA University of Technology, Tehran (Iran, Islamic Republic of); Chung, K. [Department of Materials Science and Engineering, Research Institute of Advanced Materials, Engineering Research Institute, Seoul National University, Seoul (Korea, Republic of); Shokouhimehr, M. [Department of Chemical Engineering, College of Engineering, Seoul National University, Seoul 151-742 (Korea, Republic of)

    2014-07-01

    Commercial AISI 316L plates with the initial grain size of 14.8 μm were friction stir processed (FSP) with different processing parameters, resulting in two fine-grained microstructures with the grain sizes of 4.6 and 1.7 μm. The cavitation erosion behavior, before and after FSP, was evaluated in terms of incubation time, cumulative mass loss and mean depth of erosion. A separate cavitation erosion test was performed on the transverse cross section of a FSP sample to reveal the effect of grain structure. It was observed that FSP samples, depending on their grain size, are at least 3–6 times more resistant than the base material against cavitation erosion. The improvement in cavitation erosion resistance is attributed to smaller grain structure, lower fraction of twin boundaries, and favorable crystallographic orientation of grains in FSP samples. The finer the grain size, the more cavitation erosion resistance was achieved. Moreover, the microstructures of eroded surfaces were studied using a scanning electron microscope equipped with EBSD, and an atomic force microscope. The mechanisms controlling the cavitation erosion damage in friction stir processed AISI 316L are also discussed.

  8. Cavitation of a Propeller and Influence of an Wake Equalizing Duct

    Directory of Open Access Journals (Sweden)

    George Martinas

    2015-06-01

    Full Text Available The wake equalizing duct (WED is one of the most commonly used energy saving devices for improving the propulsion performance of a ship; and reducing the propeller-excited vibrations and viscous resistance forces. During the last three decades considerable research and development activities have taken into place within this context. Most of these devices are used to improve propulsive efficiency, but some of them aims to improve other performance characteristics, such as cavitations, vibration, noise, maneuverability, etc. Marine propellers are the most common propulsion systems; nevertheless, it is possible to improve its propulsive performance using additional auxiliary propulsor devices (unconventional propulsors. Two versions of an existing ship in normal version and fitted with WED device were analyzed in order to demonstrate the influence on the WED device on the propeller cavitations . It was determined that the values for the pressure coefficient is 1.98 for without WED situation and 2.029 for WED situation. The difference is not so significant that, the conclusion is that WED device did not have influence over the cavitations of the propeller. Either optimization of dimension and form of WED did not help in reducing negative effects of cavitations. Not being a study in this paperwork, to decrease the cavitations we have other choices including a sound design of the propeller biased to improve the propeller behavior in cavitations. WED is clearly not a choice.

  9. Application of modified k-ω model to predicting cavitating flow in centrifugal pump

    Directory of Open Access Journals (Sweden)

    Hou-lin LIU

    2013-07-01

    Full Text Available Considering the compressibility of the cavity in the cavitating flow, this paper presents a modified k-ω model for predicting the cavitating flow in a centrifugal pump, in which the modified k-ω model and Schnerr-Sauer cavitation model were combined with ANSYS CFX. To evaluate the modified and standard k-ω models, numerical simulations were performed with these two models, respectively, and the calculation results were compared with the experimental data. Numerical simulations were executed with three different values of the flow coefficient, and the simulation results of the modified k-ω model showed agreement with most of the experimental data. The cavitating flow in the centrifugal pump obtained by the modified k-ω model at the design flow coefficient of 0.102, was analyzed. When the cavitation number decreases, the cavity initially generates on the suction side of the blade near the leading edge and then expands to the outlet of the impeller, and the decrease of the total pressure coefficient mainly occurs upstream of the impeller passage, while the downstream remains almost unaffected by the development of cavitation.

  10. Degradation of diclofenac sodium using combined processes based on hydrodynamic cavitation and heterogeneous photocatalysis.

    Science.gov (United States)

    Bagal, Manisha V; Gogate, Parag R

    2014-05-01

    Diclofenac sodium, a widely detected pharmaceutical drug in wastewater samples, has been selected as a model pollutant for degradation using novel combined approach of hydrodynamic cavitation and heterogeneous photocatalysis. A slit venturi has been used as cavitating device in the hydrodynamic cavitation reactor. The effect of various operating parameters such as inlet fluid pressure (2-4 bar) and initial pH of the solution (4-7.5) on the extent of degradation have been studied. The maximum extent of degradation of diclofenac sodium was obtained at inlet fluid pressure of 3 bar and initial pH as 4 using hydrodynamic cavitation alone. The loadings of TiO2 and H2O2 have been optimised to maximise the extent of degradation of diclofenac sodium. Kinetic study revealed that the degradation of diclofenac sodium fitted first order kinetics over the selected range of operating protocols. It has been observed that combination of hydrodynamic cavitation with UV, UV/TiO2 and UV/TiO2/H2O2 results in enhanced extents of degradation as compared to the individual schemes. The maximum extent of degradation as 95% with 76% reduction in TOC has been observed using hydrodynamic cavitation in conjunction with UV/TiO2/H2O2 under the optimised operating conditions. The diclofenac sodium degradation byproducts have been identified using LC/MS analysis. PMID:24262760

  11. Mitigation of tip vortex cavitation by means of air injection on a Kaplan turbine scale model

    International Nuclear Information System (INIS)

    Kaplan turbines operating at full-load conditions may undergo excessive vibration, noise and cavitation. In such cases, damage by erosion associated to tip vortex cavitation can be observed at the discharge ring. This phenomenon involves design features such as (1) overhang of guide vanes; (2) blade profile; (3) gap increasing size with blade opening; (4) suction head; (5) operation point; and (6) discharge ring stiffness, among others. Tip vortex cavitation may cause erosion at the discharge ring and draft tube inlet following a wavy pattern, in which the number of vanes can be clearly identified. Injection of pressurized air above the runner blade centerline was tested as a mean to mitigate discharge ring cavitation damage on a scale model. Air entrance was observed by means of a high-speed camera in order to track the air trajectory toward its mergence with the tip vortex cavitation core. Post-processing of acceleration signals shows that the level of vibration and the RSI frequency amplitude decrease proportionally with air flow rate injected. These findings reveal the potential mitigating effect of air injection in preventing cavitation damage and will be useful in further tests to be performed on prototype, aiming at determining the optimum air flow rate, size and distribution of the injectors

  12. Effect of Tensile Stress on Cavitation Erosion and Damage of Polymer

    Science.gov (United States)

    Hibi, M.; Inaba, K.; Takahashi, K.; Kishimoto, K.; Hayabusa, K.

    2015-12-01

    Cavitation erosion tests for epoxy, unsaturated polyester, polycarbonate, and acrylic resin were conducted under various tensile stress conditions (Tensile-Cavitation test). A new testing device was designed to conduct the Tensile-Cavitation test and observe specimen surface during the experiment based on ASTM G32. When tensile stress of 1.31 MPa was loaded on epoxy resin, cracks occurred on the specimen after 0.5 hours during cavitation erosion. When no tensile stress was loaded on the epoxy resin, the damage was general cavitation erosion only. As well as the epoxy resin, unsaturated polyester resin applied tensile stress of 1.31 MPa and polycarbonate resin of 6.54 MPa indicated erosion damages and cracks. When tensile stress of 6.54 MPa was loaded on acrylic resin, the erosion damage was almost the same as the results without tensile stress. We confirmed that anti-cavitation property of epoxy resin was higher than those of acrylic and polycarbonate without tensile stress while the damage of epoxy resin was much serious than that of acrylic resins under tensile stress loadings.

  13. Time intervals of the cavitation bubble`s collapse near a free surface; Jiyu hyomen kinbo deno cavitation kiho no shukiteki hokai ni kansuru kenkyu

    Energy Technology Data Exchange (ETDEWEB)

    Mori, S.; Doihara, R. [Kyushu University, Fukuoka (Japan); Takahashi, K.; Nagayama, K. [Kyushu University, Fukuoka (Japan). Faculty of Engineering

    1998-09-25

    Cavitation bubbles induced by pulsed laser near a free surface have been investigated experimentally and numerically. The successive pressure waves from them and their vertical migrations and volume change were measured by using hydrophone and high-speed streak camera. The characteristics of the first and second rebound times due to the distance from the free surface enable us to guess the mechanisms of bubble collapse with microjet. Because our new scheme by CIP method is successfully applicable for such two-phase flow, the comparison between experimental and numerical results- is also very useful to understand the fundamental factor of the complicated phenomena of cavitation bubbles. 23 refs., 10 figs.

  14. Formation of the self-assembled structures by the ultrasonic cavitation erosion-corrosion effect on carbon steel

    OpenAIRE

    Dayun Yan; Jiadao Wang; Fengbin Liu; Kenan Rajjoub

    2015-01-01

    The cavitation erosion-corrosion effect on the metal surface always forms irregular oxide structures. In this study, we reported the formation of regular self-assembled structures of amorphous nanoparticles around the cavitation erosion pits on carbon steel upon the ultrasonic cavitation in methylene blue solution. Each self-assembled structure was composed of linearly aligned nanoparticles of about 100 nm. The formation of self-assembled structures might be due to the combined effect of corr...

  15. Analysis of the suction chamber of external gear pumps and their influence on cavitation and volumetric efficiency

    OpenAIRE

    Campo Sud, David del

    2012-01-01

    Hydraulic machines are faced with increasingly severe performance requirements. The need to design smaller and more powerful machines rotating at higher speeds in order to provide increasing efficiencies, has to face a major limitation: cavitation. A two-dimensional numerical approach, by means of Computational Fluid Dynamics (CFD), has been developed for studying the effect of cavitation in the volumetric efficiency of external gear pumps. Several cavitation models and grid de...

  16. The influence of cavitation damage upon high temperature creep under stationary and non-stationary loading conditions. Pt. 4

    International Nuclear Information System (INIS)

    The aim of the present paper is to investigate the influence of high temperature cavitation upon the creep behavior of ideally plastic materials subjected to tensile load cycling. The oscillating tensile stress is replaced by a static equivalent stress which is a function of the loading conditions. Creep equations are derived for cavitating and non-cavitating specimens respectively. The volume change for constant load amplitude cycling is calculated. The main results derived for different loading procedures are also compared. (orig./RK)

  17. Dual pulses for cavitation control in lithotripsy: Shock wave-bubble interactions and bioeffects

    Science.gov (United States)

    Sokolov, Dahlia L.

    2002-08-01

    Cavitation, the growth and collapse of gas/vapor bubbles, appears to play an important role in both stone comminution and tissue injury during shock wave lithotripsy, the clinical treatment in which focused, high amplitude shock pulses are used to comminute kidney stones. The goal of this research was to characterize in vitro cavitation activity and stone and cell damage in a novel system that uses converging dual pulses, produced by two identical, confocal lithotripters, to modify the cavitation field. The cavitation bubble dynamics were numerically calculated, and experiments were performed in a research electrohydraulic shock wave lithotripter to determine bubble size, lifetime, and pit depth created in aluminum foils by cavitation collapse. Furthermore, damage to model stones and to red blood cells was measured for both single and dual-pulses. A single shock pulse creates a ˜15 x 100 mm cloud of bubbles in water. The greatest cavitation activity and stone damage from single-pulses was found to occur 2 cm proximal to the geometric focus, F2, where the stone is normally aligned. Therefore, a 2 cm shift in stone alignment may potentially improve stone comminution and reduce tissue injury in clinical treatment. The dual-pulse lithotripter, on the other hand, generates a localized and intensified cavitation field that increased stone comminution efficiency at F2 by at least three times the maximum values achieved by single-pulses. At F2, acoustic pressure approximately doubled, as did bubble size, collapse time, and pit depth on foils. A significant reduction in comminution of stones suspended in glycerol indicates that cavitation activity, not the doubling of acoustic pressure, explains the increased comminution. On either side of F2, the second delayed pulse mitigated bubble collapse, resulting in little or no pitting on foils and reduced hemolysis, even when compared with single pulses. Numerical calculations of radial dynamics agreed with experimental findings

  18. The role of positive and negative pressure on cavitation nucleation in nanodroplet-mediated histotripsy

    Science.gov (United States)

    Vlaisavljevich, Eli; Aydin, Omer; Lin, Kuang-Wei; Yuksel Durmaz, Yasemin; Fowlkes, Brian; ElSayed, Mohamed; Xu, Zhen

    2016-01-01

    Nanodroplet-mediated histotripsy (NMH) is an ultrasound ablation technique combining histotripsy with acoustically sensitive perfluorocarbon (PFC) nanodroplets that can be selectively delivered to tumor cells for targeted tumor ablation. NMH takes advantage of the significantly reduced cavitation threshold of the nanodroplets, allowing for cavitation to be selectively generated only in regions containing nanodroplets. Understanding the physical mechanisms underlying the nanodroplet cavitation process is essential to the development of NMH. In this study, we hypothesize that cavitation nucleation is caused by the negative pressure (p-) exposed to the PFC, and the NMH cavitation threshold is therefore determined by the incident p-  of the single-cycle pulses commonly used in NMH. This paper reports the first study that separately investigates the effects of negative and positive pressure on the NMH cavitation threshold using near half-cycle ultrasound pulses with dominant negative (negative-polarity pulses) or positive (positive-polarity pulses) pressure phases. Tissue phantoms containing perfluorohexane (PFH) nanodroplets were exposed to negative-polarity and positive-polarity pulses generated by a frequency compounding transducer recently developed in our lab, and the probability of generating cavitation was measured as a function of peak negative (p-) and peak positive (p+) pressure. The results showed close agreement in the p-  cavitation threshold for PFH phantoms exposed to negative-polarity (11.4  ±  0.1 MPa) and positive-polarity (11.7  ±  0.2 MPa) pulses. The p+ at the cavitation threshold, in contrast, was measured to be significantly different for the negative-polarity (4.0  ±  0.1 MPa) and positive-polarity (42.6  ±  0.2 MPa) pulses. In the final part of this study, the experimental results were compared to the cavitation threshold predicted by classical nucleation theory (CNT), with results showing

  19. Numerical Simulation of Cavitation in a Centrifugal Pump at Low Flow Rate

    Institute of Scientific and Technical Information of China (English)

    TAN Lei; CAO Shu-Liang; WANG Yu-Ming; ZHU Bao-Shan

    2012-01-01

    Based on the full cavitation model which adopts homogeneous flow supposition and considering the compressibility effect on cavitation flow to modify the re-normalization group k-e turbulence model by the density function,a computational model is developed to simulate cavitation flow of a centrifugal pump at low flow rate.The NavierStokes equation is solved with the SIMPLEC algorithm.The calculated curves of net positive suction head available (NPSHa) HNPSHa agree well with the experimental data.The critical point of cavitation in centrifugal pump can be predicted precisely,and the NPSH critical values derived from simulation are consistent with the experimental data.Thus the veracity and reliability of this computational model are verified.Based on the result of numerical simulation,the distribution of vapor volume fraction in the impeller and pressure at the impeller inlet are analyzed.Cavities first appear on the suction side of the blade head near the front shroud.A large number of cavities block the impeller channels,which leads to the sudden drop of head at the cavitation critical point.With the reduction of NPSHa,the distribution of pressure at the impeller inlet is more uniform.%Based on the full cavitation model which adopts homogeneous Sow supposition and considering the compressibility effect on cavitation Row to modify the re-normalization group κ-ε turbulence model by the density function, a computational model is developed to simulate cavitation Bow of a centrifugal pump at low Bow rate. The Navier-Stokes equation is solved with the SIMPLEC algorithm. The calculated curves of net positive suction head available (NPSHa) Hnpshs agree well with the experimental data. The critical point of cavitation in centrifugal pump can be predicted precisely, and the NPSH critical values derived from simulation are consistent with the experimental data. Thus the veracity and reliability of this computational model are veriBed. Based on the result of numerical

  20. The use of image analysis for determination of surface deterioration level of improved alumina based materials subjected to cavitation

    Directory of Open Access Journals (Sweden)

    Dimitrijević M.M.

    2013-01-01

    Full Text Available Alumina based specimens having different content of alumina based fibers were investigated for possible application as cavitation resistant material. Cavitation damages of the alumina based specimens were tested by the modified vibratory cavitation set up. Erosion rates were measured based on the method developed for metallic samples, mass loss was measured during the experiment. Surface erosion was determined during the experiment simultaneously to mass loss measurements. Image Pro Plus Program was applied for surface analysis during testing. Results indicate that investigated material exhibit excellent mechanical properties and very good resistance to cavitation erosion. [Projekat Ministarstva nauke Republike Srbije, br. TR34011, br. TR35002 i br. III 45012

  1. Prediction of rotating stall and cavitation inception in pump turbines

    Science.gov (United States)

    Anciger, D.; Jung, A.; Aschenbrenner, T.

    2010-08-01

    The current development of modern pump storage plants aims towards a higher flexibility in operation, an extended operation range of the hydraulic machine, especially in the pumping mode, and a higher reliability. A major design target for state-of-the-art reversible Francis-type pump turbines is to find an optimal balance between pumping and generating performance. The pumping requirements are the crucial design drivers, since, even if the turbine mode performance is world class, the success of a project depends on the pump turbine delivering the required maximum pump head and starting reliably in pump mode. The proposed paper describes how advanced computational fluid dynamic (CFD) simulations can help the designer to evaluate his design with respect to hydraulic performance and dynamic phenomena occurring in pump turbines. A standard procedure today is to compute the flow by applying the Reynolds-averaged Navier-Stokes equations (RANS) on the steady-state flow in individual components or in multiple components which are coupled by mixing-plane interfaces (sometimes also called stage-interface). This standard approach gives fast turnaround times and is a good engineering tool. However, accuracy is limited due to necessary simplifications. Therefore methods are developed and evaluated which allow a more reliable prediction of the onset of rotating stall which is the operation limit of the pump under high heads and low flow rates. The behaviour a modern pump turbine design in this instability region is investigated in detail. Another important task in the design process is the proper prediction of cavitation phenomena in the runner. Predicting cavitating flows with multi-phase CFD computations is still a very challenging task. Some results of ongoing work in this field are presented and compared to single phase computations and results from model tests. The relevance and applicability of such computations is discussed. All the information gained from these kinds of

  2. Prediction of rotating stall and cavitation inception in pump turbines

    International Nuclear Information System (INIS)

    The current development of modern pump storage plants aims towards a higher flexibility in operation, an extended operation range of the hydraulic machine, especially in the pumping mode, and a higher reliability. A major design target for state-of-the-art reversible Francis-type pump turbines is to find an optimal balance between pumping and generating performance. The pumping requirements are the crucial design drivers, since, even if the turbine mode performance is world class, the success of a project depends on the pump turbine delivering the required maximum pump head and starting reliably in pump mode. The proposed paper describes how advanced computational fluid dynamic (CFD) simulations can help the designer to evaluate his design with respect to hydraulic performance and dynamic phenomena occurring in pump turbines. A standard procedure today is to compute the flow by applying the Reynolds-averaged Navier-Stokes equations (RANS) on the steady-state flow in individual components or in multiple components which are coupled by mixing-plane interfaces (sometimes also called stage-interface). This standard approach gives fast turnaround times and is a good engineering tool. However, accuracy is limited due to necessary simplifications. Therefore methods are developed and evaluated which allow a more reliable prediction of the onset of rotating stall which is the operation limit of the pump under high heads and low flow rates. The behaviour a modern pump turbine design in this instability region is investigated in detail. Another important task in the design process is the proper prediction of cavitation phenomena in the runner. Predicting cavitating flows with multi-phase CFD computations is still a very challenging task. Some results of ongoing work in this field are presented and compared to single phase computations and results from model tests. The relevance and applicability of such computations is discussed. All the information gained from these kinds of

  3. Prediction of rotating stall and cavitation inception in pump turbines

    Energy Technology Data Exchange (ETDEWEB)

    Anciger, D; Jung, A; Aschenbrenner, T, E-mail: Danijel.Anciger@voith.co [Voith Hydro Holding GmbH and Co. KG Alexanderstr. 11, 89522 Heidenheim (Germany)

    2010-08-15

    The current development of modern pump storage plants aims towards a higher flexibility in operation, an extended operation range of the hydraulic machine, especially in the pumping mode, and a higher reliability. A major design target for state-of-the-art reversible Francis-type pump turbines is to find an optimal balance between pumping and generating performance. The pumping requirements are the crucial design drivers, since, even if the turbine mode performance is world class, the success of a project depends on the pump turbine delivering the required maximum pump head and starting reliably in pump mode. The proposed paper describes how advanced computational fluid dynamic (CFD) simulations can help the designer to evaluate his design with respect to hydraulic performance and dynamic phenomena occurring in pump turbines. A standard procedure today is to compute the flow by applying the Reynolds-averaged Navier-Stokes equations (RANS) on the steady-state flow in individual components or in multiple components which are coupled by mixing-plane interfaces (sometimes also called stage-interface). This standard approach gives fast turnaround times and is a good engineering tool. However, accuracy is limited due to necessary simplifications. Therefore methods are developed and evaluated which allow a more reliable prediction of the onset of rotating stall which is the operation limit of the pump under high heads and low flow rates. The behaviour a modern pump turbine design in this instability region is investigated in detail. Another important task in the design process is the proper prediction of cavitation phenomena in the runner. Predicting cavitating flows with multi-phase CFD computations is still a very challenging task. Some results of ongoing work in this field are presented and compared to single phase computations and results from model tests. The relevance and applicability of such computations is discussed. All the information gained from these kinds of

  4. Bulk coolant cavitation in LMFBR containment loading following a whole-core explosion

    International Nuclear Information System (INIS)

    An LMFBR core undergoing an explosion transmits energy to the containment in a series of pressure waves and the containment loading is determined by their cumulative effect. These pressure waves are modified by their interaction with the coolant through which they propagate. In liquids in their normal state the main effect of the interaction is to steepen the fronts of waves leading to shock formation but in liquids which have undergone bulk cavitation the interaction is much stronger and is expected to be dissipative and dispersive. Since reflections of initial pressure waves from the core at free surfaces lead to the establishment of a state of tension and consequently of bulk cavitation over large volumes of the coolant, it is necessary to model both the induction of bulk cavitation by tension waves and the interaction of pressure waves with cavitated liquid in realistic containment loading calculations. This paper sets out the progress which has been achieved in such modelling and first indications for the effect of bulk coolant cavitation in LMFBR containment loading. A model describing the interaction between cavitation bubbles and a host liquid subject to time-varying pressure fields, including the physical process of momentum conservation, phase change, heat conduction and mass diffusion is presented and used to a) determine which of the various physical processes involved dominate the results. It is shown that if we are only interested in bulk effects momentum transfer is the chief factor for the pressures and timescales of interest. b) determine the effect of the state of purity of the liquid. The main characterising parameters are the initial radii of nucleation sites and their number density, the latter being very influential. c) identify the important differences between model water and reactor sodium as far as cavitation is concerned. These are chiefly the lower surface tension and higher concentration of initially larger nucleation sites in the

  5. Experimental investigation and numerical analysis of unsteady attached sheet-cavitating flows in a centrifugal pump

    Institute of Scientific and Technical Information of China (English)

    LIU Hou-lin; LIU Dong-xi; WANG Yong; WU Xian-fang; WANG Jian; DU Hui

    2013-01-01

    This paper studies the attached sheet cavitation in centrifugal pumps.A pump casted from Perspex is used as the test subject.The cavitation bubbles were observed in the entrance of the impeller and the drops of the head coefficients were measured under different operating conditions.A Filter-Based Model (FBM),derived from the RNG k-ε model,and a modified Zwart model are adopted in the numerical predictions of the unsteady cavitating flows in the pump.The simulations are carried out and the results are compared with experimental results for 3 different flow coefficients,from 0.077 to 0.114.Under four operating conditions,qualitative comparisons are made between experimental and numerical cavitation patterns,as visualized by a high-speed camera and described as isosurfaces of the vapour volume fraction αv =0.1.It is shown that the simulation can truly represent the development of the attached sheet cavitation in the impeller.At the same time,the curves for the drops of the head coefficients obtained from experiments and calculations are also quantitatively compared,which shows that the decline of the head coefficients at every flow coefficient is correctly captured,and the prediction accuracy is high.In addition,the detailed analysis is made on the vapour volume fraction contours on the plane of span is 0.5 and the loading distributions around the blade section at the midspan.It is shown that the FBM model and the modified Zwart model are effective for the numerical simulation of the cavitating flow in centrifugal pumps.The analysis results can also be used as the basis for the further research of the attached sheet cavitation and the improvement of centrifugal pumps.

  6. Cavitation erosion behaviour of laser processed Fe-Cr-Mn and Fe-Cr-Co alloys

    Directory of Open Access Journals (Sweden)

    M. Szkodo

    2006-08-01

    Full Text Available Purpose: Purpose of this paper is investigation of influence of the surface processing by laser method on thecavitation performance of the Fe-Cr-Mn and Fe-Cr-Co alloys. This kind of alloys are frequently used in Polishpower plants to routine repairs of damaged blades working under cavitation loading.Design/methodology/approach: Padding welds were tested for three cases: without additional processing,after laser heating of the solid state and after laser melting of the coating. Cw. CO2 laser with a beam power1000 W was used as a source of radiation. The investigated samples were subjected to cavitation loading at therotating disk facility. The microstructure, chemical composition and phase identification of the modified andsubjected to cavitation loading layers were examined using scanning electron microscopy, light microscopy, andX-ray diffractometry, respectively.Findings: Results revealed that structure refinement due to laser processing contributes to delaying ofaustenite → martensite phase transformation. Kinetic of austenite → martensite transformation is different forinvestigated alloys and depends on the chemical composition and applied laser processing.Research limitations/implications: Reported research ought to be completed and full cavitation curves(volume loss in time for processed padding welds must be done.Practical implications: Obtained results indicate that for low intensity of cavitation loading, like in fieldconditions, laser beam machining can increase of cavitation erosion resistance of investigated alloys due toincrease of hardness and structure fine degree.Originality/value: Confirmation that creation of the transformed and hardfacing structures by laser techniquesleads in many cases to considerable changes in cavitation erosion properties of the processed materials.

  7. Cavitation characteristics of multihole diesel-fuel nozzles in high-speed oil flows. Diesel kikan yo nenryo tako nozzle no abura cavitation tokusei

    Energy Technology Data Exchange (ETDEWEB)

    Yokota, M. (Shimonoseki Univ. of Fisheris, Yamaguchi (Japan)); Ito, Y. (Hachinohe Inst. of Tech., Aomori (Japan)); Aoki, H. (Xexel-Gleason U.S.A. Inc., New York (U.S.A))

    1991-07-25

    Recently, since higher velocity and higher pressure are required for diesel injection systems, cavitation behaviors in high velocity oil flows are strongly interested in such as 100 to 500 m/s for oil flow velocity and less than the cavitation factor {sigma} of 0.01. In this paper, oil cavitation characteristics at the injection part of multihole nozzles, especially on the flow characteristics, were studied systematically using fuel injection multihole nozzles for an actual use. As a result, it was clarified that subcavitation area (sub C), transition area, and supercavitation area (SC) could be existing in C{sub d}-{sigma} relation, which was similar to that specified cavitation conditions could be exisiting in the actual working area of multihole nozzles. And it was also clarified that flow coefficient C{sub d} relied on Reynolds number R{sub e} in the transition of {sigma}{ge}{sigma}{sub cr} and in {sub C} area, and mainly relied on {sigma} in SC area of {sigma}<{sigma}{sub cr}. Moreover, it was also confirmed that such tendency was similar to the one of the two-dimensional contraction of an area. 22 refs., 10 figs., 1 tab.

  8. Numerical 3D flow simulation of ultrasonic horns with attached cavitation structures and assessment of flow aggressiveness and cavitation erosion sensitive wall zones.

    Science.gov (United States)

    Mottyll, Stephan; Skoda, Romuald

    2016-07-01

    As a contribution to a better understanding of cavitation erosion mechanisms, a compressible inviscid finite volume flow solver with barotropic homogeneous liquid-vapor mixture cavitation model is applied to ultrasonic horn set-ups with and without stationary specimen, that exhibit attached cavitation at the horn tip. Void collapses and shock waves, which are closely related to cavitation erosion, are resolved. The computational results are compared to hydrophone, shadowgraphy and erosion test data. At the horn tip, vapor volume and topology, subharmonic oscillation frequency as well as the amplitude of propagating pressure waves are in good agreement with experimental data. For the evaluation of flow aggressiveness and the assessment of erosion sensitive wall zones, statistical analyses of wall loads and of the multiplicity of distinct collapses in wall-adjacent flow regions are applied to the horn tip and the stationary specimen. An a posteriori projection of load collectives, i.e. cumulative collapse rate vs. collapse pressure, onto a reference grid eliminates the grid dependency effectively for attached cavitation at the horn tip, whereas a significant grid dependency remains at the stationary specimen. The load collectives show an exponential decrease towards higher collapse pressures. Erosion sensitive wall zones are well predicted for both, horn tip and stationary specimen, and load profiles are in good qualitative agreement with measured topography profiles of eroded duplex stainless steel samples after long-term runs. For the considered amplitude and gap width according to ASTM G32-10 standard, the analysis of load collectives reveals that the distinctive erosive ring shape at the horn tip can be attributed to frequent breakdown and re-development of a small portion of the tip-attached cavity. This partial breakdown of the attached cavity repeats at each driving cycle and is associated with relatively moderate collapse peak pressures, whereas the

  9. Cavitating Lung Lesions in Chronic Thromboembolic Pulmonary Hypertension

    Directory of Open Access Journals (Sweden)

    edwin j r van beek

    2008-09-01

    Full Text Available Purpose: The aim of this study is to assess the incidence and natural history of cavitating lung lesions in chronic thromboembolic pulmonary hypertension (CTEPH, note thrombus position between patients with and without a cavity and determine whether their development is a predictor of mortality. Materials & Methods: All patients with confirmed CTEPH attending our Pulmonary Vascular Unit between February 1998 and January 2006 were identified, and a review of their notes and imaging was performed. Thrombus position, pre-disposing factors, cavity progression and mortality were noted, and comparisons made between those with and without a cavity. Results: 11 of 104 patients had a cavity (10.6%. Thrombus distribution was similar between those with and those without a cavity. Preceding infection was not proven in  most cases. 27.3% of patients with a cavity died compared to 26.8% of those without. Conclusion: Cavity formation in CTEPH is 3 times more common than in acute pulmonary embolism. Thrombus position does not predict cavity development, and the presence of a cavity may serve as an indicator of disease severity but does not appear to predict mortality.

  10. Water hammer and cavitational hammer in process plant pipe systems

    Energy Technology Data Exchange (ETDEWEB)

    Dudlik, A.; Schoenfeld, S.B.H.; Hagemann, O. [Fraunhofer-Institut fuer Umwelt-, Sicherheits- und Energietechnik UMSICHT, Oberhausen (Germany); Fahlenkamp, H. [Univ. Dortmund (Germany). Chair of Environmental Technology

    2003-05-01

    Fast acting valves are often applied for quick safety shut-down of pipelines for liquids and gases in the chemical and petrochemical industry as well as in power plants and state water supplies. The fast deceleration of the liquid leads to water hammer upstream the valve and to cavitational hammer downstream the fast closing valve. The valve characteristics given by manufacturers are usually measured at steady state flow conditions of the liquid. In comparison, the dynamic characteristics depend on the initial liquid velocity, valve closing velocity, the absolute pipe pressure and the pipe geometry. Fraunhofer UMSICHT conducts various test series examining valve dynamic characteristics in order of the dynamic analysis of pressure surges in fast closing processes. Therefore a test rig is used which consists of two pipelines of DN 50 and DN 100 with an approximate length of 230 m each. In this paper the results of performed pressure surge experiments with fast closing and opening valves will be compared to calculations of commercial software programs such as MONA, FLOWMASTER 2. Thus the calculation software for water supply, power plants oil and gas and chemical industry can be permanently improved. (orig.)

  11. Water hammer and cavitational hammer in process plant pipe systems

    International Nuclear Information System (INIS)

    Fast acting valves are often applied for quick safety shut-down of pipelines for liquids and gases in the chemical and petrochemical industry as well as in power plants and state water supplies. The fast deceleration of the liquid leads to water hammer upstream the valve and to cavitational hammer downstream the fast closing valve. The valve characteristics given by manufacturers are usually measured at steady state flow conditions of the liquid. In comparison, the dynamic characteristics depend on the initial liquid velocity, valve closing velocity, the absolute pipe pressure and the pipe geometry. Fraunhofer UMSICHT conducts various test series examining valve dynamic characteristics in order of the dynamic analysis of pressure surges in fast closing processes. Therefore a test rig is used which consists of two pipelines of DN 50 and DN 100 with an approximate length of 230 m each. In this paper the results of performed pressure surge experiments with fast closing and opening valves will be compared to calculations of commercial software programs such as MONA, FLOWMASTER 2. Thus the calculation software for water supply, power plants oil and gas and chemical industry can be permanently improved. (orig.)

  12. Evidence for liquid phase reactions during single bubble acoustic cavitation.

    Science.gov (United States)

    Troia, A; Madonna Ripa, D; Lago, S; Spagnolo, R

    2004-07-01

    We extended the recent experiment by Lepoint et al. [Sonochemistry and Sonoluminescence, NATO ASI Series, Series C 524, Kluwer Academic Publishers, Dordrecht/Boston/London, 1999, p. 285], involving a so-called single bubble sonochemistry process, to a three-phase system. We have found experimental evidence that a single cavitating bubble can activate the oxidation of I- ions after the injection of a CCl4 liquid drop in the bubble trapping apparatus. The solvent drop (CCl4 is almost water insoluble) is pushed towards the bubble position and forms a thin film on the bubble surface. When the acoustic pressure drive is increased above 100 kPa, the three-phase system gives rise to a dark filament, indicating the complexation reaction between starch (added to the water phase) and I2. I2 species is the product of surface reactions involving bubble-induced decomposition of CCl4. Further increase of the acoustic drive causes the thin CCl4 film to separate from the bubble and stops I2 production. The study of the chemical activity of this three-phase system could give new advances on dynamics of the bubble collapse. PMID:15157862

  13. Engineering design method for cavitational reactors: I. Sonochemical reactors

    Energy Technology Data Exchange (ETDEWEB)

    Gogate, P.R.; Pandit, A.B.

    2000-02-01

    High pressures and temperatures generated during the cavitation process are now considered responsible for the observed physical and chemical transformations using ultrasound irradiation. Effects of various operating parameters reported here include the frequency, the intensity of ultrasound, and the initial nuclei sizes on the bubble dynamics, and hence the magnitude of pressure generated. Rigorous solutions of the Rayleigh-Plesset equation require considerable numerical skills and the results obtained depend on various assumptions. The Rayleigh-Plesset equation was solved numerically, and the results have been empirically correlated using easily measurable global parameters in a sonochemical reactor. Liquid-phase compressibility effects were also considered. These considerations resulted in a criterion for critical ultrasound intensity, which if not considered properly can lead to overdesign or underdesign. A sound heuristic correlation, developed for the prediction of the pressure pulse generated as a function of initial nuclei sizes, frequency, and intensity of ultrasound, is valid not only over the entire range of operating parameters commonly used but also in the design procedure of sonochemical reactors with great confidence.

  14. DNS and LES of two-phase flows with cavitation

    CERN Document Server

    Hickel, Stefan

    2014-01-01

    We report on recent progress in the physical and numerical modeling of compressible two-phase flows that involve phase transition between the liquid and gaseous state of the fluid. The high-speed dynamics of cavitation bubbles is studied in well-resolved simulations (DNS) with a sharp-interface numerical model on a micro scale. The underlying assumption of the employed evaporation/condensation model is that phase change occurs in thermal non-equilibrium and that the associated timescale is larger than that of the wave dynamics. Results for the collapse of a spherical vapor bubble close to a solid wall are discussed for three different bubble-wall configurations. The major challenge for such numerical investigations is to accurately reproduce the dynamics of the interface between liquid and vapor during the entire collapse process, including the high-speed dynamics of the late stages, where compressibility of both phases plays a decisive role. Direct interface resolving simulations are intractable for real wor...

  15. Superplastic behavior and cavitation for WC-Co cemented carbides

    Energy Technology Data Exchange (ETDEWEB)

    Hosokawa, H.; Shimojima, K. [Inst. for Structural and Engineering Materials, National Inst. of Advanced Industrial Science and Technology (AIST) (Japan); Kawakami, M.; Terada, O. [Fuji Die Co. Ltd., Hadano, Kanagawa (Japan); Sano, S. [Fuji Die Co. Ltd., Tokyo (Japan); Mabuchi, M. [Dept. of Energy Science and Technology, Kyoto Univ. (Japan)

    2005-07-01

    Superplastic behavior and cavitation were investigated for WC-15 mass% Co cemented carbides with the WC grain sizes of 0.7 {mu}m (A) and 5.2 {mu}m (B), WC-10 mass% Co cemented carbide with the WC grain size of 1.5 {mu}m (C) and WC-5 mass% Co cemented carbides with the WC grain sizes of 0.5 {mu}m (D) and 2.5 {mu}m (E) by tensile tests at 1473 K. WC contiguity were 0.51, 0.31, 0.27, 0.56 and 0.49, respectively. The large elongations about 200% were obtained for the B and the C having smaller values of WC contiguity compared to the other cemented carbides. The values of cavity volume fraction for them were less for the other cemented carbides, furthermore, cavities formed at WC/WC interfaces. Therefore, it is noted that the distribution of the Co phase is important for superplasticity of the cemented carbides. (orig.)

  16. High speed observation of HIFU-induced cavitation cloud near curved rigid boundaries

    Science.gov (United States)

    Zuo, Z. G.; Wang, F. B.; Liu, S. H.; Wu, S. J.

    2015-01-01

    This paper focuses on the experimental study of the influence of surface curvature to the behaviour of HIFU-induced cavitation cloud. A Q-switched ruby pulse laser is used to induce cavitation nuclei in deionized water. A piezoelectric ultrasonic transducer (1.7 MHz) provides a focused ultrasound field to inspire the nucleus to cavitation cloud. A PZT probe type hydrophone is applied for measuring the HIFU sound field. It was observed that the motion of cavitation cloud located near the boundary is significantly influenced by the distance between cloud and boundary, as well as the curvature of the boundary. The curvature was defined by parameters λ and ξ. Convex boundary, concave boundary, and flat boundary correspond to ξ 1 and ξ = 1, respectively. Different behaviours of the cloud, including the migration of the cloud, the characteristics of oscillation, etc., were observed under different boundary curvatures by high-speed photography. Sonoluminescence of the acoustic cavitation bubble clouds were also studied to illustrate the characteristics of acoustic streaming.

  17. Cavitation performance improvement of high specific speed mixed-flow pump

    International Nuclear Information System (INIS)

    Cavitation performance improvement of large hydraulic machinery such as pump and turbine has been a hot topic for decades. During the design process of the pumps, in order to minimize size, weight and cost centrifugal and mixed-flow pump impellers are required to operate at the highest possible rotational speed. The rotational speed is limited by the phenomenon of cavitation. The hydraulic model of high-speed mixed-flow pump with large flow rate and high pumping head, which was designed based on the traditional method, always involves poor cavitation performance. In this paper, on the basis of the same hydraulic design parameters, two hydraulic models of high-speed mixed-flow pump were designed by using different methods, in order to investigate the cavitation and hydraulic performance of the two models, the method of computational fluid dynamics (CFD) was adopted for internal flow simulation of the high specific speed mixed-flow pump. Based on the results of numerical simulation, the influences of impeller parameters and three-dimensional configuration on pressure distribution of the blades' suction surfaces were analyzed. The numerical simulation results shows a better pressure distribution and lower pressure drop around the leading edge of the improved model. The research results could provide references to the design and optimization of the anti-cavitation blade.

  18. EXPERIMENTAL STUDY ON CAVITATION AND WATER-WING FOR MIDDLE-PIERS OF DISCHARGE TUNNELS

    Institute of Scientific and Technical Information of China (English)

    WU Jian-hua; CAI Chang-guang; JI Wei; RUAN Shi-ping; LUO Chao

    2005-01-01

    In construction of high dams, design of a middle-pier, placed in a discharge tunnel to divide it into two parts, is a better choice that could breakthrough the limits of the manufacture and operation of the gate due to the high head to it. However, cavitation and water-wing, a kind of flow striking the top and side walls of the tunnel, induced by the middle-pier, may take place and bring about bad effects on operation of the tunnel. The experiments of the six comparing plans were conducted, consisting of atmospheric and vacuum tank models, and the interesting areas included relationships between discharges and reservoir levels, measurements of side wall pressures, comparisons of water-wing states for the various middle-piers, estimations of the incipient cavitation numbers and the flow cavitation numbers, and analyses of cavitation characteristics for the tunnel. A kind of new bodily form of middle-pier was developed. Water-wing states were better improved and non-cavitation conditions were satisfied.

  19. Research on the method of cavitations resistance in a piezoelectric pump with 3-dimensional mesh structure

    Institute of Scientific and Technical Information of China (English)

    ZHANG Jian-hui; XIA Qi-xiao; Bai Heng-jun; NING Hong-gang; ONUKI Akiyoshi

    2006-01-01

    The volume valve piezoelectric pump has received increasing attention from many areas because of its different characteristics such as the absence of chemical pollution and electromagnetic pollution.However,when the pump is working,it produces cavitations and the air bubbles that originate from these will flow out of the pump.Cavitations occurring in the pump will bring out noise and shorten the life of the pump.Furthermore,air bubbles flowing out of the pump will hinder its application in areas such as medical treatment and health care where blood transfusion and infusion are concerned.As a solution to this disadvantage,the CR3DMS (cavitations resistance with 3-dimensional mesh structure) method is developed,which is tested and verified to be effective on not only reducing the occurrence of cavitations and eliminating cavitations' flowing out,but also restraining the emission of noise.In conclusion,the pump with CR3DMS,on the relationship between flow and driving frequency and the relationship between flow and the number of Resistant-Layers in both theory and test,are analyzed.

  20. Detailed investigation of cavitation and supercavitation around different geometries using various turbulence and mass transfer models

    Science.gov (United States)

    Pendar, M. R.; Roohi, E.

    2015-12-01

    In this paper cavitation around 3D hemispherical head-form body as well as disk and conical cavitators were studied numerically with particular emphasis on detailed comparisons of the various turbulence and mass transfer models. Dynamic and unsteady behaviors of cavitation were simulated using the large eddy simulation (LES) and k-ω SST turbulence models together with Kunz, Sauer and Zwart mass transfer models. In addition, the compressive volume of fluid (VOF) method is used to track the cavity interface. Simulation is performed under the framework of the OpenFOAM package. Discussions on the boundary layer separation, re-entrant jet, cavity cloud, vortices and pressure/volume fraction contours over a broad range of cavitation numbers, especially in very low cavitation numbers, are provided. Our numerical results compared fairly well with experimental data and a wide set of analytical relations. Our results indicate that the most accurate solutions will be obtained with the LES/ Kunz approach. Moreover, for the first time, we present a correlation between the cavity length and diameter for hemispherical head-form bodies.