WorldWideScience

Sample records for cavitation

  1. Cavitation

    International Nuclear Information System (INIS)

    Anon.

    1983-01-01

    Cavitation in fluid machines or flow passages can cause loss of performance or material damage due to erosion. This conference reports the results of world-wide research into all aspects of the study of cavitation. Contents include: Cavitation effects in machinery such as pumps, water turbines, propellers and positive displacement machinery; Cavitation in structures, flow passages, valves, flow meters and bearings; Cavitation erosion, noise and instability effects; Cavitation inception; Developed flows; Supercavitating flows and machines; Fundamentals; Bubble dynamics and thermodynamics of cavitation in various fluids; Test facilities and methods of cavitation research and testing; Special instrumentation for cavitation studies, and standards and recommendations for cavitation or erosion

  2. 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 cavitation,...

  3. Report of sodium cavitation

    International Nuclear Information System (INIS)

    Murai, Hitoshi; Shima, Akira; Oba, Toshisaburo; Kobayashi, Ryoji; Hashimoto, Hiroyuki

    1975-01-01

    The damage of components for LMFBRs due to sodium cavitation is serious problem. This report summarizes the following items, (1) mechanism of the incipience of sodium cavitation, (2) damage due to sodium cavitation, (3) detection method for sodium cavitation, and (4) estimation method for sodium cavitation by the comparison with water cavitation. Materials were collected from the reports on liquid metal cavitation, sodium cavitation and water cavitation published from 1965 to now. The mechanism of the incipience of sodium cavitation cavitation parameters (mean location, distributed amount or occurrence aspect and stability), experiment of causing cavitation with Venturi tube, and growth of bubbles within superheated sodium. The sodium cavitation damage was caused by magnetostriction vibration method and with Venturi tube. The state of damage was investigated with the cavitation performance of a sodium pump, and the damage was examined in view of the safety of LMFBR plants. Sodium cavitation was detected with acoustic method, radiation method, and electric method. The effect of physical property of liquid on incipient cavitation was studied. These are thermodynamic effect based on quasistatic thermal equilibrium condition and the effect of the physical property of liquid based on bubble dynamics. (Iwase, T.)

  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...

  5. Cavitation wear of pump impellers

    Directory of Open Access Journals (Sweden)

    Mirosław Szala

    2016-12-01

    Full Text Available Cavitation is a common phenomenon in pump systems, negatively influencing their operating parameters and components such as impellers and, thus, causing considerable financial losses. This paper explains the problem of cavitation and cavitation erosion. The causes of cavitation in pump systems are analyzed. A selection of centrifugal pump impellers damaged by cavitation erosion are presented and examined. The authors also discuss ways of preventing cavitation and cavitation erosion in pump systems. Finally, relevant conclusions are drawn.

  6. 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.

  7. Cavitating Flow over a Mini Hydrofoil

    International Nuclear Information System (INIS)

    Luo Xian-Wu; Ji Bin; Xu Hong-Yuan; Zhang Yao

    2012-01-01

    We consider a cavitating flow over a mini hydrofoil (foil profile: Clark-Y-11.7) having a 14 mm chord length in a cavitation tunnel at various cavitation numbers. Experimental observations show that cavitating flows over a miniature hydrofoil display several types of cavitation behavior, such as cavitation inception, sheet cavitation, cloud cavitation and super cavitation with the decreasing cavitation number. Under the same cavitation conditions, cavitation over a mini hydrofoil would be suppressed in comparison to cavitation over an ordinary hydrofoil. This cavitation scale effect is suspected to be caused by the Reynolds number. (condensed matter: structure, mechanical and thermal properties)

  8. Hydrodynamic Cavitation Reactors contd…

    Indian Academy of Sciences (India)

    First page Back Continue Last page Overview Graphics. Hydrodynamic Cavitation Reactors contd… Reservoir: 10 L capacity. Centrifugal Pump :1.5kW). Orifice plate (different configurations in terms of number and diameter of the holes). Bypass line (for controlling the inlet pressure and the flow rate into the cavitation ...

  9. Can Cavitation Be Anticipated?

    Energy Technology Data Exchange (ETDEWEB)

    Allgood, G.O.; Dress, W.B.; Hylton, J.O.; Kercel, S.W.

    1999-04-25

    The major problem with cavitation in pumps and hydraulic systems is that there is no effective (conventional) method for detecting or predicting its inception. The traditional method of recognizing cavitation in a pump is to declare the event occurring when the total head drops by some arbitrary value (typically 3%) in response to a pressure reduction at the pump inlet. However, the device is already seriously cavitating when this happens. What is actually needed is a practical method to detect impending rather than incipient cavitation. Whereas the detection of incipient cavitation requires the detection of features just after cavitation starts, the anticipation of cavitation requires the detection and identification of precursor features just before it begins. Two recent advances that make this detection possible. The first is acoustic sensors with a bandwidth of 1 MHz and a dynamic range of 80 dB that preserve the fine details of the features when subjected to coarse vibrations. The second is the application of Bayesian parameter estimation which makes it possible to separate weak signals, such as those present in cavitation precursors, from strong signals, such as pump vibration. Bayesian parameter estimation derives a model based on cavitation hydrodynamics and produces a figure of merit of how well it fits the acquired data. Applying this model to an anticipatory engine should lead to a reliable method of anticipating cavitation before it occurs. This paper reports the findings of precursor features using high-performance sensors and Bayesian analysis of weak acoustic emissions in the 100-1000kHz band from an experimental flow loop.

  10. 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.

  11. Pump cavitation background noise

    International Nuclear Information System (INIS)

    Cha, Y.S.

    1976-01-01

    Cavitation is defined as the growth and collapse of cavities associated with the change in pressure in contrast to the case of boiling where change in temperature is the dominating factor. It is commonly accepted that cavitation inception occurs when the minimum pressure in a system reaches the vapor pressure corresponding to the local temperatures of the liquid. The foregoing statement is, in fact, another way of defining incipient boiling which is usually defined as the condition where the temperature reaches the saturation temperature corresponding to the system pressure. Therefore, there is no difference between cavitation and boiling since both are associated with the growth and collapse of bubbles in a liquid. Cavitation noise may not be avoidable for an LMFBR primary pump under normal operating conditions, and will be present as background during boiling detection by acoustic methods

  12. Cavitation cloud growth

    International Nuclear Information System (INIS)

    Bonnin, J.

    1977-01-01

    The cavitation cloud growth in a pipeline submitted to a steep pressure drop (passage of a negative surge) is due to the simultaneous growth of a great number of homogeneous nuclei, thus producing a cloud of cavitation bubbles whose diameters become rapidly of the same order as their distances. Though their growth are independent at the beginning of the phenomenon, interactions take place when they become relatively close, due either to a change in the system planimetry, or to the interlocking of mass diffusion (gaseous cavitation) or heat (vaporous cavitation) boundary layers. After having examined known solutions to the problem of an unique bubble growth, and their possible use in case of interaction, the limits of the unique bubble growth are pointed out to conclude in favour of a preferential geometric limit, occuring near the minimum of the perturbation celerity in the mixture [fr

  13. 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.

  14. Cavitation guide for control valves

    International Nuclear Information System (INIS)

    Tullis, J.P.

    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

  15. 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.

  16. Cavitation in medicine.

    Science.gov (United States)

    Brennen, Christopher Earls

    2015-10-06

    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.

  17. Cavitation problems in sodium valves

    International Nuclear Information System (INIS)

    Elie, X.

    1976-01-01

    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)

  18. A Study of Cavitation Erosion

    International Nuclear Information System (INIS)

    Hiromu Isaka; Masatsugu Tsutsumi; Tadashi Shiraishi; Hiroyuki Kobayashi

    2002-01-01

    The authors performed experimental study for the purpose of the following two items from a viewpoint of cavitation erosion of a cylindrical orifice in view of a problem at the letdown orifice in PWR (Pressurized Water Reactor). 1. To get the critical cavitation parameter of the cylindrical orifice to establish the design criteria for prevention of cavitation erosion, and 2. to ascertain the erosion rate in such an eventuality that the cavitation erosion occurs with the orifice made of stainless steel with precipitation hardening (17-4-Cu hardening type stainless steel), so that we confirm the appropriateness of the design criteria. Regarding the 1. item, we carried out the cavitation tests to get the critical cavitation parameters inside and downstream of the orifice. The test results showed that the cavitation parameter at inception is independent of the length or the diameter of the orifice. Moreover, the design criteria of cavitation erosion of cylindrical orifices have been established. Regarding the 2. item, we tested the erosion rate under high-pressure conditions. The cavitation erosion actually occurred in the cylindrical orifice at the tests that was strongly resemble to the erosion occurred at the plant. It will be seldom to reproduce resemble cavitation erosion in a cylindrical orifice with the hard material used at plants. We could establish the criteria for preventing the cavitation erosion from the test results. (authors)

  19. Cavitating Hydrofoils: A Perspective

    Science.gov (United States)

    Arndt, Roger E. A.; Kawakami, Damien T.; Qin, Qiao; Song, Charles C. S.

    2004-11-01

    This paper reviews our recent research that is aimed at gaining a better understanding of the problem of unsteady cavitating flows on lifting surfaces. We have explored this issue with extensive numerical and experimental investigations. This includes the development of new numerical models of cavitating flows including the effects of dissolved incondensable gas and ventilation. Our simulations are based on a virtual single-phase cavitation model, that incorporates the assumptions of fully compressible and barotropic flow coupled with a Large-Eddy Simulation (LES) approach. This approach has proven to be capable of capturing the complex dynamical features of highly unsteady cavitating flows. Experimental data are drawn from experiments carried out at two different scales in two different water tunnels; one in the US at the Saint Anthony Falls Laboratory (SAFL) and the other at the Versuchsanstalt fur Wasserbau (VFW) in Obernach, Germany. Several foils shapes have been examined. Examples are drawn from investigations of several different type hydrofoils. The tests were designed to complement each other and to capitalize on the special features of each facility. Suuported by the National Science Foundation.

  20. Cavitation Generation and Usage Without Ultrasound: Hydrodynamic Cavitation

    Science.gov (United States)

    Gogate, Parag R.; Pandit, Aniruddha B.

    Hydrodynamic Cavitation, which was and is still looked upon as an unavoidable nuisance in the flow systems, can be a serious contender as an alternative to acoustic cavitation for harnessing the spectacular effects of cavitation in physical and chemical processing. The present chapter covers the basics of hydrodynamic cavitation including the considerations for the bubble dynamics analysis, reactor designs and recommendations for optimum operating parameters. An overview of applications in different areas of physical, chemical and biological processing on scales ranging from few grams to several hundred kilograms has also been presented. Since hydrodynamic cavitation was initially proposed as an alternative to acoustic cavitation, it is necessary to compare the efficacy of both these modes of cavitations for a variety of applications and hence comparisons have been discussed either on the basis of energy efficiency or based on the scale of operation. Overall it appears that hydrodynamic cavitation results in conditions similar to those generated using acoustic cavitation but at comparatively much larger scale of operation and with better energy efficiencies.

  1. Shock Waves in Cloud Cavitation

    OpenAIRE

    Brennen, C. E.; Reisman, G. E.; Wang, Y.-C.

    1997-01-01

    Thie paper described experimental and computational investigations of the dynamics of clouds of cavitation bubbles. Recent studies have confirmed that the interactions between bubbles as they are manifest in the dynamics of bubble clouds lead to generation of very large impulsive pressures which, in turn, cause substantial enhancement of the radiated noise and the material damage which results from this form of cavitation. The experimental program focuses on cloud cavitation formed on th...

  2. Techniques of Ultrasound Cavitation Control

    Directory of Open Access Journals (Sweden)

    S. P. Skvortsov

    2015-01-01

    Full Text Available The control methods of ultrasonic cavitation applied now within the range from 20 kHz to 80 kHz use either control of ultrasound source parameters (amplitude, acoustic power, etc. or control of one of the cavitation effects (erosion of materials, sonoluminescence, power of acoustic noise, etc.. These methods provide effective management of technological processes, however, make it impossible to relate the estimated effect with parameters of pulsations of cavitation bubbles. This is, mainly, due to influence of a number of uncontrollable parameters, in particular, such as temperature, composition of liquid, gas content, etc. as well as because of the difficulty to establish interrelation between the estimated effect and parameters of pulsations. As a result, in most cases it is difficult to compare controlled parameters of ultrasonic cavitation among themselves, and quantitative characteristics of processes become depending on the type of ultrasonic installation and conditions of their measurement.In this regard, methods to determine parameters of bubble pulsations through sounding a cavitation area by low-intensity laser radiation or to record cavitation noise sub-harmonics reflecting dynamics of changing radius of cavitation bubbles are of interest. The method of optical sounding, via the analysis of spectral components of a scattered signal recorded by a photo-detector, allows us to define a phase of the bubbles collapse with respect to the sound wave and a moving speed of the bubbles wall, as well as to estimate a cavitation index within the light beam section.The method to record sub-harmonicas of cavitation noise allows us to define parameters of pulsations, average for cavitation areas.The above methods allow us both to study mechanisms of cavitation action and to form quantitative criteria of its efficiency based on the physical processes, rather than their consequences and are convenient for arranging a feedback in the units using

  3. Shock Induced Cavitation

    Science.gov (United States)

    1991-02-01

    the explosion was provided by a 20-KV, 15-pF, 5-nil capacitor . The ex- ploding wire can be positioned anywhere in the tank - above or below the water...withstand tension, the total pressure would follow the dotted line. However, it cannot; hence, near the 35 DIAPHRAGM BULGES OUT, PROBABLY OWING TO LATE... bulged outward. It appears that this late impulse is a water hammer that takes place at cavitation closure. 6.2 PRELIMINARY ANALYSIS. Kennard has

  4. Cavitation Nuclei: Experiments and Theory

    DEFF Research Database (Denmark)

    Mørch, Knud Aage

    2009-01-01

    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....

  5. Cavitation onset caused by acceleration

    Science.gov (United States)

    Pan, Zhao; Kiyama, Akihito; Tagawa, Yoshiyuki; Daily, David J.; Thomson, Scott L.; Hurd, Randy; Truscott, Tadd T.

    2017-08-01

    Striking the top of a liquid-filled bottle can shatter the bottom. An intuitive interpretation of this event might label an impulsive force as the culprit in this fracturing phenomenon. However, high-speed photography reveals the formation and collapse of tiny bubbles near the bottom before fracture. This observation indicates that the damaging phenomenon of cavitation is at fault. Cavitation is well known for causing damage in various applications including pipes and ship propellers, making accurate prediction of cavitation onset vital in several industries. However, the conventional cavitation number as a function of velocity incorrectly predicts the cavitation onset caused by acceleration. This unexplained discrepancy leads to the derivation of an alternative dimensionless term from the equation of motion, predicting cavitation as a function of acceleration and fluid depth rather than velocity. Two independent research groups in different countries have tested this theory; separate series of experiments confirm that an alternative cavitation number, presented in this paper, defines the universal criteria for the onset of acceleration-induced cavitation.

  6. Nucleation and cavitation in parahydrogen

    International Nuclear Information System (INIS)

    Pi, Martí; Barranco, Manuel; Navarro, Jesús; Ancilotto, Francesco

    2012-01-01

    Highlights: ► We have constructed a density functional (DF) for parahydrogen between 14 and 32 K. ► The experimental equation of state and the surface tension are well reproduced. ► We have investigated nucleation and cavitations processes in the metastable phase. ► We have obtained the electron bubble explosion within the capillary model. - Abstract: We have used a density functional approach to investigate thermal homogeneous nucleation and cavitation in parahydrogen. The effect of electrons as seeds of heterogeneous cavitation in liquid parahydrogen is also discussed within the capillary model.

  7. Microleakage of Cavit, CavitW, CavitG and IRM by impedance spectroscopy.

    Science.gov (United States)

    Jacquot, B M; Panighi, M M; Steinmetz, P; G'Sell, C

    1996-07-01

    The aim of this study was to quantify the sealing ability of four temporary filling materials over 9 days using a new electrochemical technique. Fifty-two extracted human maxillary bicuspids were selected and prepared for the measurements. They were divided into four groups of 12 teeth each, in addition to two positive and two negative controls. After preparation of the endodontic access cavity the sealing ability was registered. After a randomization procedure one group was obturated with IRM, another group with Cavit, a third group with CavitW and the last group with CavitG. The sealability was measured just after obturation (time 0) and after days 1, 2, 3, 4, 7 and 9. The results showed that the IRM group was significantly more watertight than the different Cavit formulations. Throughout the experiment no significant difference was noticed between the Cavit and CavitW groups (P > 0.05). The CavitG group was significantly less watertight throughout the measurements (P < 0.05).

  8. 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.

  9. Cavitation onset of an accelerating liquid

    Science.gov (United States)

    Kiyama, Akihito; Pan, Zhao; Tagawa, Yoshiyuki; Daily Jesse, David; Thomson, Scott; Hurd, Randy; Truscott, Tadd

    2017-11-01

    Accelerating a liquid-filled container can shatter the bottom. High-speed imaging reveals cavitation bubbles collapse near the bottom just before this fracture event. To avoid the damage caused by cavitation, accurate prediction of cavitation onset is crucial. However, the conventional cavitation number, as a function of the mean velocity of the flow does not correctly predict cavitation onset in an accelerating liquid. This study derives an alternative cavitation number from the equation of motion, predicting cavitation as a function of acceleration (cf. Pan & Kiyama et al., Proc. Natl. Acad. Sci., 2017). We have conducted two separate series of experiments with a broad set of varied parameters. All the experimental results agreed with this theory, indicating that the proposed alternative cavitation number describes the universal threshold of cavitation onset within an accelerating liquid. JSPS KAKENHI Grant Numbers 26709007, 16J08521, and 17H01246.

  10. Surface mechanics design by cavitation peening

    Directory of Open Access Journals (Sweden)

    Hitoshi Soyama

    2015-07-01

    Full Text Available Although impacts at cavitation bubble collapses cause severe damage in hydraulic machineries, the cavitation impacts can be utilised for surface mechanics design such as introduction of compressive residual stress and/or improvement of fatigue strength. The peening method using the cavitation impacts was called as cavitation peening. In order to reveal the peening intensity of hydrodynamic cavitation and laser cavitation, the arc height of Almen strip and duralumin plate were measured. In the case of hydrodynamic cavitation, cavitation was generated by injecting a high speed water jet into water with a pressurised chamber and an open chamber, and the cavitating jet in air was also examined. The laser cavitation was produced by a pulse laser, and a high speed observation using a high speed video camera was carried out to clarify laser abrasion and laser cavitation with detecting noise by a hydrophone. It was concluded that the peening intensity by using the cavitating jet in water with the pressurized chamber was most aggressive, and the impact induced by the laser cavitation was larger than that of the laser abrasion at the present condition.

  11. Effect of temperature change on the sealing properties of Cavit and Cavit G.

    Science.gov (United States)

    Oppenheimer, S; Rosenberg, P A

    1979-09-01

    Sixty recently extracted intact anterior teeth were filled with Cavit G or Cavit. They were examined for dye penetration at room temperature and subjected to temperature change. Under the test conditions Cavit G and Cavit were resistant to penetration by aqueous methylene blue dye.

  12. Cavitation erosion in sodium flow, sodium cavitation tunnel testing

    International Nuclear Information System (INIS)

    Courbiere, Pierre.

    1981-04-01

    The high-volume sodium flows present in fast neutron reactors are liable to induce cavitation phenomena in various portion of the sodium lines and pumps. The absence of sufficient data in this area led the C.E.A. to undertake an erosion research program in cavitating sodium flow. This paper discusses the considerations leading to the definition and execution of sodium cavitation erosion tests, and reviews the tests run with 400 0 C sodium on various steel grades: 316, 316 L, 316 Ti (Z8CNDT17-12), Poral (Z3CND18-12), 304 L and LN2 - clad 316 L (Ni coating-clad 316 L). Acoustic detection and signal processing methods were used with an instrument package designed and implemented at the Cadarache Nuclear Research Center

  13. Influence of hydrodynamic cavitation on biological objects

    OpenAIRE

    Мальований, Мирослав Степанович; Никифоров, Володимир Валентинович; Синельніков, Олександр Дмитрович; Харламова, Олена Володимирівна; Бунько, Василь Ярославович

    2015-01-01

    Cavitation, which yet has not found a wide application in industrial technologies, is an effective method of hydro-mechanical intensification of chemical-engineering, food, pharmaceutical, biological and other processes. The effectiveness of cavitation process is enabled by cavitation crashing of the solid phase, turbulent diffusion of boundary layer of the fluid by cavitation bubbles, emergence mass transfer aspects, which are characterized by high values of mass transfer coefficients. Proce...

  14. 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.

  15. Surface decontamination by cavitation erosion

    International Nuclear Information System (INIS)

    Verry, P.; Lecoffre, Y.

    1984-01-01

    The aim of the study is to show the interest of using erosion by cavitation to remove a thin layer of matter from an irradiated surface during nuclear power plant dismantling. Several cavitation devices are tested on different surfaces to erode: aluminum, stainless steel, plexiglas, paints... The process is efficient enough to measure mass loss on materials as hard as stainless steels for a pressure of only 60 bars. Qualification tests using a nozzle feed under a 300 to 600 bar pressure are envisaged

  16. Cavitation instabilities and rotordynamic effects in turbopumps and hydroturbines turbopump and inducer cavitation, experiments and design

    CERN Document Server

    Salvetti, Maria

    2017-01-01

    The book provides a detailed approach to the physics, fluid dynamics, modeling, experimentation and numerical simulation of cavitation phenomena, with special emphasis on cavitation-induced instabilities and their implications on the design and operation of high performance turbopumps and hydraulic turbines. The first part covers the fundamentals (nucleation, dynamics, thermodynamic effects, erosion) and forms of cavitation (attached cavitation, cloud cavitation, supercavitation, vortex cavitation) relevant to hydraulic turbomachinery, illustrates modern experimental techniques for the characterization, visualization and analysis of cavitating flows, and introduces the main aspects of the hydrodynamic design and performance of axial inducers, centrifugal turbopumps and hydo-turbines. The second part focuses on the theoretical modeling, experimental analysis, and practical control of cavitation-induced fluid-dynamic and rotordynamic instabilities of hydraulic turbomachinery, with special emphasis on cavitating...

  17. Cavitation pulse extraction and centrifugal pump analysis

    Energy Technology Data Exchange (ETDEWEB)

    Luo, Hong Lind Shaoran [University of Electronic Science and Technology of China, Chengdu (China); Yu, Bo; Qing, Biao [Xihua University, Chengdu (China)

    2017-03-15

    This study extracted cavitation pulses from hydrophone signals sampled in a centrifugal pump and analyzed their characteristics. The modified and simplified Empirical mode decomposition (EMD) algorithm was proposed for extracting cavitation pulses from strong background noise. Experimental results showed that EMD can effectively suppress noise and obtain clear cavitation pulses, facilitating the identification of the number of pulses associated with the degree of cavitation. The cavitation characteristics were modeled to predict the value of incipient cavitation. Then, we proposed a method for detecting the wear of the impeller surface. That is, the information on the impeller surface of the centrifugal pump, including the roughness of the impeller surface and its wear trends, were quantified based on the net positive suction head available of incipient cavitation. The findings indicate that the proposed technique is suitable for condition monitoring of the pump.

  18. Size effects on cavitation instabilities

    DEFF Research Database (Denmark)

    Niordson, Christian Frithiof; Tvergaard, Viggo

    2006-01-01

    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 cavi...... as the void grows to a size well above the characteristic material length....

  19. In Vivo Microbubble Cavitation Imaging

    NARCIS (Netherlands)

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

    2011-01-01

    Stroke is the second cause of death and leading cause of disabilityworldwide. Less than 5% of ischemic stroke patients receive the state-of-the art treatment of a thrombolytic drug tPA, and only about 10% of these gain additional benefit from it. Ultrasound (US)-inducedmicrobubble (MB) cavitation

  20. Sonoporation from jetting cavitation bubbles

    NARCIS (Netherlands)

    Ohl, C.D.; Arora, M.; Ikink, Roy; de Jong, N.; Versluis, Michel; Delius, Michael; Lohse, Detlef

    2006-01-01

    The fluid dynamic interaction of cavitation bubbles with adherent cells on a substrate is experimentally investigated. We find that the nonspherical collapse of bubbles near to the boundary is responsible for cell detachment. High-speed photography reveals that a wall bounded flow leads to the

  1. Sonoporation from jetting cavitation bubbles

    NARCIS (Netherlands)

    C.-D. Ohl (Claus-Dieter); M. Arora (Manish); R. Ikink (Roy); N. de Jong (Nico); M. Versluis (Michel); M. Delius (Michael); D. Lohse (Detlef)

    2006-01-01

    textabstractThe fluid dynamic interaction of cavitation bubbles with adherent cells on a substrate is experimentally investigated. We find that the nonspherical collapse of bubbles near to the boundary is responsible for cell detachment. High-speed photography reveals that a wall bounded flow leads

  2. Role of cavitation in the phacoemulsification process.

    Science.gov (United States)

    Zacharias, Jaime

    2008-05-01

    To determine the role of cavitational energy as a mechanism responsible for the emulsification of the lens during phacoemulsification. Clinica Ophthalmologica Pasteur, Santiago, Chile. Cavitation and its relationship to phacoemulsification power were documented using a combination of light sources, high-speed video recording techniques, and computerized control and by monitoring environmental pressure. The suppression of cavitation from the phaco process was achieved by building an environmental hyperbaric system capable of retaining the phacoemulsification system's ability to provide irrigation, aspiration, and vacuum necessary at standard and elevated pressures. The pressure level was controlled and monitored through a computer interface alongside the simultaneous video monitoring of cavitation bubble creation changes during pressure rise or fall. Last, evaluation and measurement of phacoemulsification was performed on real cataract fragments in the presence and absence of cavitation. Cavitation around the phaco tip mainly occurred at longitudinal ultrasonic power levels of 30% or more. Cavitation bubble formation was observed during the backstroke or as the tip moved away from the lens material and collapsed during the forward displacement of the phaco tip. Cavitation at any power level was successfully suppressed when the pressure in the hyperbaric chamber increased beyond 2.0 bar (29.1 psi) above atmospheric pressure. Phacoemulsification performance in the presence or absence of cavitation was comparable. This study found strong evidence that cavitation plays no role in phacoemulsification, leaving the jackhammer effect as the only important mechanism responsible for the lens-disrupting power of phacoemulsification.

  3. Numerical Investigation Cavitation Buckets for Hydrofoil Parametrically

    Directory of Open Access Journals (Sweden)

    Mehmet Salih KARAALİOĞLU

    2015-12-01

    Full Text Available Cavitation is a general fluid mechanics phenomenon that is appeared in system such as pumps, turbines, marine propellers and hydrofoils which induces pressure and velocity fluctuation in the fluid (Brennen, 2013. Cavitation can be defined as the formation of vapour regions due to a decrease in local pressure. Undesirable consequences which can cause a fall in the performance of a system, structural failure, production of noise and vibration, material damage, are encountered due to cavitation (Uşar, 2015. In this study, cavitation was analysed using a bucket diagram. Bucket diagram represents the cavitation behaviour of a wing, fin or propeller blade in a two dimensional sense. This diagram is plotted as a function of section (hydrofoil angle of attack (α versus section cavitation number (σ. Pressure distribution can be calculated on two dimensional geometry of hydrofoil by using BEM (Boundary Element Method and cavitation bucket diagram can be computed. The cavitation inception case and partial cavitation cases have been investigated and the results of the present BEM were successfully compared with those of given in literature in the past and each other. While a constant source-dipole panel method has been used to calculate the pressure distribution at cavitation inception case, PCPAN programme that solves the sheet type of cavity on the hydrofoil by potential based panel method, has been used to calculate pressure distribution for the cases of partial cavitation. Effects of maximum hydrofoil thickness, maximum camber and location of maximum camber on cavitation have been analyzed by means of cavitation bucklet diagrams. All results are discussed in a detailed manner.

  4. 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.

  5. Hull-Propeller Interaction and Its Effect on Propeller Cavitation

    DEFF Research Database (Denmark)

    Regener, Pelle Bo

    computational effort. The boundary element method for propeller analysis includes a partially nonlinear cavitation model, which is able to predict partial sheet cavitation and supercavitation. The cavitation behaviour of the conventional propeller and the Kappel propeller from the earlier simulations...

  6. Development of a Cavitation Erosion Resistant Advanced Material System

    National Research Council Canada - National Science Library

    Kendrick, Light H; Caccese, Vincent

    2005-01-01

    .... Historically, neither of these materials has performed well in a cavitating environment. The objective of this effort was to evaluate cavitation erosion protection alternatives for a GRP composite structure used in a cavitating environment...

  7. Modeling of Cavitating Flow through Waterjet Propulsors

    Science.gov (United States)

    2015-02-18

    OCT-11 -31-DEC-14 To) 4. TITLE AND SUBTITLE Modeling of Cavitating Flow through Waterjet Propulsors 5a. CONTRACT NUMBER 5b. GRANT NUMBER N00014-12...239-18 Modeling of Cavitating Flow through Waterjet Propulsors Jules W. Lindau The Pennsylvania State University, Applied Research Laboratory, State...flow nature, waterjets are expected to maintain resistance to cavitation , are amenable to ad- vanced concepts such as thrust vectoring, should

  8. Cavitation inception from bubble nuclei

    DEFF Research Database (Denmark)

    Mørch, Knud Aage

    2015-01-01

    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....... 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....

  9. Method of similarity for cavitation

    Energy Technology Data Exchange (ETDEWEB)

    Espanet, L.; Tekatlian, A.; Barbier, D. [CEA/Cadarache, Dept. d' Etudes des Combustibles (DEC), 13 - Saint-Paul-lez-Durance (France); Gouin, H. [Aix-Marseille-3 Univ., 13 - Marseille (France). Laboratoire de Modelisation en Mecanique et Thermodynamique

    1998-07-01

    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)

  10. Breaking beer bottles with cavitation

    Science.gov (United States)

    Jung, Sunny; Fontana, Jake; Palffy-Muhoray, Peter; Shelley, Michael

    2009-03-01

    Hitting the top of a beer bottle, nearly full of water, with an open hand can cause the bottle to break, with the bottom separating from upper section. We have studied this phenomenon using a high-speed camera, and observed the formation, coalescence and collapse of bubbles. The breaking of glass is due to cavitation, typically occurring near the bottom edge. We make numerical estimates of the relevant physical parameters, and compare these with experimental observations.

  11. Method of similarity for cavitation

    International Nuclear Information System (INIS)

    Espanet, L.; Tekatlian, A.; Barbier, D.; Gouin, H.

    1998-01-01

    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. Cavitation on hydrofoils with sinusoidal leading edge

    Science.gov (United States)

    Johari, H.

    2015-12-01

    Cavitation characteristics of hydrofoils with sinusoidal leading edge were examined experimentally at a Reynolds number of 7.2 × 105. The hydrofoils had an underlying NACA 634-021 profile and an aspect ratio of 4.3. The sinusoidal leading edge geometries included three amplitudes of 2.5%, 5%, and 12% and two wavelengths of 25% and 50% of the mean chord length. Results revealed that cavitation on the leading edge-modified hydrofoils existed in pockets behind the troughs whereas the baseline hydrofoil produced cavitation along its entire span. Moreover, cavitation on the modified hydrofoils appeared at consistently lower angles of attack than on the baseline hydrofoil.

  13. Temperature measurements in cavitation bubbles

    Science.gov (United States)

    Coutier-Delgosha, Olivier

    2016-11-01

    Cavitation is usually a nearly isothermal process in the liquid phase, but in some specific flow conditions like hot water or cryogenic fluids, significant temperature variations are detected. In addition, a large temperature increase happens inside the cavitation bubbles at the very end of their collapse, due to the fast compression of the gas at the bubble core, which is almost adiabatic. This process is of primary interest in various biomedical and pharmaceutical applications, where the mechanisms of bubble collapse plays a major role. To investigate the amplitude and the spatial distribution of these temperature variations inside and outside the cavitation bubbles, a system based on cold wires has been developed. They have been tested in a configuration of a single bubble obtained by submitting a small air bubble to a large amplitude pressure wave. Some promising results have been obtained after the initial validation tests. This work is funded by the Office of Naval Research Global under Grant N62909-16-1-2116, Dr. Salahuddin Ahmed & Ki-Han Kim program managers.

  14. Laser-induced cavitation based micropump

    NARCIS (Netherlands)

    Dijkink, R.J.; Ohl, C.D.

    2008-01-01

    Lab-on-a-chip devices are in strong demand as versatile and robust pumping techniques. Here, we present a cavitation based technique, which is able to pump a volume of 4000 m3 within 75 s against an estimated pressure head of 3 bar. The single cavitation event is created by focusing a laser pulse in

  15. Comparison of Different Mathematical Models of Cavitation

    Directory of Open Access Journals (Sweden)

    Dorota HOMA

    2014-12-01

    Full Text Available Cavitation occurs during the flow when local pressure drops to the saturation pressure according to the temperature of the flow. It includes both evaporation and condensation of the vapor bubbles, which occur alternately with high frequency. Cavitation can be very dangerous, especially for pumps, because it leads to break of flow continuity, noise, vibration, erosion of blades and change in pump’s characteristics. Therefore it is very important for pump designers and users to avoid working in cavitation conditions. Simulation of flow can be very useful in that and can indicate if there is risk of cavitating flow occurrence. As this is a multiphase flow and quite complicated phenomena, there are a few mathematical models describing it. The aim of this paper is to make a short review of them and describe their approach to model cavitation. It is desirable to know differences between them to model this phenomenon properly.

  16. Reflections on cavitation nuclei in water

    DEFF Research Database (Denmark)

    Mørch, Knud Aage

    2007-01-01

    to explaining why the tensile strength of water varies so dramatically between the experiments reported. A model for calculation of the critical pressure of skin-covered free gas bubbles as well as that of interfacial gaseous nuclei covered by a skin is presented. This model is able to bridge the apparently......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...... pressure, the possibility of stabilization of free gas bubbles by a skin has been documented, but only within a range of bubble sizes that makes them responsible for tensile strengths up to about 1.5 bar, and values reaching almost 300 bar have been measured. However, cavitation nuclei can also be harbored...

  17. Superhigh Temperatures and Acoustic Cavitation

    CERN Document Server

    Belyaev, V B; Miller, M B; Sermyagin, A V; Topolnikov, A S

    2003-01-01

    The experimental results on thermonuclear synthesis under acoustic cavitation have been analyzed with the account of the latest data and their discussion. The analysis testifies that this avenue of research is a very promising one. The numerical calculations of the D(d, n)^{3}He reaction rate in the deuterated acetone (C_{3}D_{6}O) under the influence of ultrasound depending on T environment temperature within the range T=249-295 K have been carried out within the framework of hydrodynamic model. The results show that it is possible to improve substantially the effect/background relationship in experiments by decreasing the fluid temperature twenty-thirty degrees below zero.

  18. 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.

  19. Enterobacter Asburiae Pneumonia with Cavitation

    International Nuclear Information System (INIS)

    Cha, Seung Woo; Heo, Jeong Nam; Park, Choong Ki; Choi, Yo Won; Jeon, Seok Chol

    2013-01-01

    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 β-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. An Anticipatory Model of Cavitation

    Energy Technology Data Exchange (ETDEWEB)

    Allgood, G.O.; Dress, W.B., Jr.; Hylton, J.O.; Kercel, S.W.

    1999-04-05

    The Anticipatory System (AS) formalism developed by Robert Rosen provides some insight into the problem of embedding intelligent behavior in machines. AS emulates the anticipatory behavior of biological systems. AS bases its behavior on its expectations about the near future and those expectations are modified as the system gains experience. The expectation is based on an internal model that is drawn from an appeal to physical reality. To be adaptive, the model must be able to update itself. To be practical, the model must run faster than real-time. The need for a physical model and the requirement that the model execute at extreme speeds, has held back the application of AS to practical problems. Two recent advances make it possible to consider the use of AS for practical intelligent sensors. First, advances in transducer technology make it possible to obtain previously unavailable data from which a model can be derived. For example, acoustic emissions (AE) can be fed into a Bayesian system identifier that enables the separation of a weak characterizing signal, such as the signature of pump cavitation precursors, from a strong masking signal, such as a pump vibration feature. The second advance is the development of extremely fast, but inexpensive, digital signal processing hardware on which it is possible to run an adaptive Bayesian-derived model faster than real-time. This paper reports the investigation of an AS using a model of cavitation based on hydrodynamic principles and Bayesian analysis of data from high-performance AE sensors.

  1. Experimental and numerical studies on super-cavitating flow of axisymmetric cavitators

    Directory of Open Access Journals (Sweden)

    Byoung-Kwon Ahn

    2010-03-01

    Full Text Available Recently underwater systems moving at high speed such as a super-cavitating torpedo have been studied for their practical advantage of the dramatic drag reduction. In this study we are focusing our attention on super-cavitating flows around axisymmetric cavitators. A numerical method based on inviscid flow is developed and the results for several shapes of the cavitator are presented. First using a potential based boundary element method, we find the shape of the cavitator yielding a sufficiently large enough cavity to surround the body. Second, numerical predictions of supercavity are validated by comparing with experimental observations carried out in a high speed cavitation tunnel at Chungnam National University (CNU CT.

  2. Basic study on vortex cavitation inception

    International Nuclear Information System (INIS)

    Ezure, Toshiki; Sato, Hiroyuki; Kimura, Nobuyuki; Kamide, Hideki

    2008-12-01

    In the FaCT Project for Commercialized Fast Reactor Cycle Systems, a compact reactor vessel and 2 loops system are investigated in terms of economical improvement of a sodium cooled fast reactor. In order to certificate the issues in thermal hydraulics, 1/10th scaled model water tests have been performed. In the flow visualization of the 1/10th scaled model tests, vortex cavitations were observed at the inlet of Hot Leg pipes. In order to estimate the occurrence of this type of cavitation in the reactor, cavitation number will be used. In the reactor design, cover gas in a reactor vessel is pressurized up to 0.25MPa. This results in higher velocity at the onset condition of the cavitation as compared to the open-air water experiment. In addition, viscosity of the sodium at 550degC is nearly 1/3rd of that of water at room temperature. These differences may affect the flow pattern and the inception of vortex cavitation. These factors will bring some difficulties in the estimation using the cavitation number. Thus, the effects of pressure and viscosity on the inception of vortex cavitations were examined in basic water experiments. As the results, it was found that the onset value of cavitation coefficient became higher with the increase of the pressure. In addition, it also appeared that the onset value of cavitation coefficient became higher under lower viscosity. However, this difference of onset value due to the viscosity became smaller with the increase of pressure, and was negligible under the same pressure in the real reactor. (author)

  3. Size-effects on cavitation instabilities

    DEFF Research Database (Denmark)

    Niordson, Christian Frithiof; Tvergaard, Viggo

    2005-01-01

    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...

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

    Directory of Open Access Journals (Sweden)

    Ch. Suryanarayana

    2010-12-01

    Full Text Available 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.

  5. 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.

  6. Bacterial microleakage of Cavit, IRM, and TERM.

    Science.gov (United States)

    Deveaux, E; Hildelbert, P; Neut, C; Boniface, B; Romond, C

    1992-11-01

    In this in vitro study, a model system was developed and tested to evaluate the sealing ability of temporary restorative materials used in endodontic access preparations. The materials studied, Cavit, IRM, and TERM, were tested on 40 premolars against a known bacterial species, Streptococcus sanguis. The leakage of bacterial cells was checked 4 and 8 days after initial immersion in the culture. Thermocycling was introduced on the fourth day. After 8 days the cement thicknesses were measured after the teeth had been longitudinally sectioned. Before and after thermocycling, IRM was less leakproof than Cavit (p Cavit, whereas TERM remained leakproof. The thicknesses were as follows: Cavit, 3.73 mm; IRM, 3.45 mm; and TERM, 5.49 mm. There was no statistically significant relationship between thickness and tightness.

  7. Cavitation in pumps, pipes and valves

    International Nuclear Information System (INIS)

    Young, Ronald.

    1990-01-01

    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)

  8. Assessment of Cavitation Erosion with a Multiphase Reynolds-Averaged Navier-Stokes Method

    NARCIS (Netherlands)

    Li, Z.R.

    2012-01-01

    Cavitation erosion is one of the remarkable catastrophic consequences of cavitation. Predicting the cavitation aggressiveness quantitatively and predicting the most probable location of cavitation erosion are complex problems that currently still motivate an important amount of basic and applied

  9. Using cavitation for delignification of wood.

    Science.gov (United States)

    Baxi, Pranav B; Pandit, Aniruddha B

    2012-04-01

    The Kraft process is the most widely used chemical process for the removal of lignin and other polymers from wood to obtain cellulosic pulp fibres. In the present study, the effect of cavitation (growth and violent collapse of vapour bubbles in a liquid) on delignification of wood was investigated. Steam was introduced in the reactor in order to study the effect of steam driven hybrid cavitation on delignification. The results obtained were subjected to kinetic analysis. The rates of delignification obtained using hydrodynamic cavitation were about 4-5 orders of magnitude greater than those obtained using acoustic cavitation (rate constants for delignification were 9.78×10(-6) and 6.8×10(-1)min(-1) for acoustic and hydrodynamic cavitation, respectively). The energy imparted by the pump in the hydrodynamic cavitation reactor was much higher than that imparted by the acoustic devices and this was considered to be the cause of the higher delignification rates. Copyright © 2012 Elsevier Ltd. All rights reserved.

  10. Cavitation Measurement during Sonic and Ultrasonic Activated Irrigation

    NARCIS (Netherlands)

    Macedo, Ricardo; Verhaagen, Bram; Rivas, David Fernandez; Versluis, Michel; Wesselink, Paul; van der Sluis, Luc

    Introduction: The aims of this study were to quantify and to visualize the possible occurrence of transient cavitation (bubble formation and implosion) during sonic and ultrasonic (UAI) activated irrigation. Methods: The amount of cavitation generated around several endodontic instruments was

  11. Real-Time Two-Dimensional Imaging of Microbubble Cavitation

    NARCIS (Netherlands)

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

    2011-01-01

    Ultrasound cavitation of microbubble contrast agents has a potentialfor 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

  12. 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...

  13. 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.

    . Experimental results indicated that cavitation and/or turbulent fluid shear dominantly originating from cavitation are effective tools for sea water disinfection as more than 80% of the zooplankton present in the sea water were killed. It was also observed...

  14. Feedback loop process for controlling inertial cavitation: experimental evidence

    Science.gov (United States)

    Inserra, Claude; Sabraoui, Abbas; Reslan, Lina; Bera, Jean-Christophe; Gilles, Bruno; Mestas, Jean-Louis

    2011-09-01

    Applications involving cavitation mechanisms, such as sonoporation, are irreproducible in the case of a fixed-intensity sonication, due to the non-stationary behavior of cavitation. We then propose to work at a fixed-cavitation level instead of under fixed-intensity sonication conditions. For this purpose a regulated cavitation generator has been developed in a stationary wave field configuration, which allows regulation of the cavitation level during sonication by modulating the applied acoustic intensity with a feedback loop based on acoustic cavitation measurements. The cavitation level indicator was quantified by the broadband spectrum noise level relative to inertial cavitation events. This generated inertial cavitation was characterized by both acoustic and chemical measurements, quantifying hydroxyl radicals produced by water sonolysis. While the cavitation level is obtained with a 40% standard deviation for fixed applied acoustic intensities in the range [0.01 3.44] W/cm2, the regulated generator reproduces the cavitation level with a standard deviation of 3%. The results show that the hydroxyl radical production is better correlated with the cavitation level setting than with the applied acoustic intensity, highlighting the fact that broadband noise is a good indicator of inertial cavitation, with greatest interest for cavitation monitoring. In summary, the regulated device generates a cavitation level that is reproducible, repeatable and stable in time. This system produces reproducible effects that allow consideration of biological applications such as sonoporation to be independent of the experimental ultrasound device, as confirmed by transfection efficiency and cell cytotoxicity studies. Thus, this feedback loop process presents interesting perspectives for monitoring and controlling in-vivo cavitation.

  15. Vizualization of the cavitating jet using flashlamp for illumination

    Science.gov (United States)

    Mlkvik, Marek; Olšiak, Róbert; Knížat, Branislav

    2012-04-01

    The contribution deals with the ways of the illumination of the cavitating jet for the purposes of the visualization. The cavitation is induced by the fluid flow through the orifice with the diameter of 0,3mm. Region of the cavitating jet is illuminated by a different light sources. Goal of this paper is to compare the quality and the informative value of the obtained visual data. In addition, complicated structure of the cavitating jet is also shown and described.

  16. Mechanics modelling of fern cavitation catapult

    Science.gov (United States)

    Kang, Jingtian; Li, Kai; Tan, Huifeng; Wang, Changguo; Cai, Shengqiang

    2017-12-01

    Cavitation is often regarded as a failure mode in soft materials. An intriguing phenomenon has been recently discovered that fern sporangium can take advantage of drying-induced cavitation instability in annulus cells to disperse spores at an extraordinarily high acceleration. Briefly, the decrease of environmental humidity causes continuous bending of the sporangium and growth of cavities inside the annulus cells, with the elastic energy accumulated in sporangium walls. When the humidity is lower than a critical value, the cavities suddenly expand dramatically inside the cells, causing a quick release of the elastic energy stored in the annular structure. As a result, like a catapult, the sporangium snaps back and ejects the seeds at a high speed. Motivated by the observation, in this article, we study cavitation instability in a similar structure as the sporangium. To simplify the problem, in our model, the mechanics of cells in the sporangium are described by the polymer gel model, while the sporangium wall is modelled as a hyperelastic material. When the environmental humidity is lower than a critical value, through energetic analyses, we can predict the cavitation catapult phenomenon using the model. We hope that our study in this article can provide useful insights into the bio-inspired design of structures which can take advantage of cavitation instability in soft materials.

  17. Drag Reducing and Cavitation Resistant Coatings

    Energy Technology Data Exchange (ETDEWEB)

    Pease, Leonard F.

    2016-12-28

    Client, Green Building Systems (GBS), presented PNNL a coating reported to reduce drag and prevent cavitation damage on marine vessels, turbines and pumps. The composition of the coating remains proprietary but has as constituents including silicon oxides, aliphatic carbon chains, and fluorine rich particles. The coating is spray applied to surfaces. Prior GBS testing and experiments suggest reduction of both drag and cavitation on industrial scale propellers, but the underlying mechanism for these effects remains unclear. Yet, the application is compelling because even modest reductions in drag to marine vessels and cavitation to propellers and turbines present a significant economic and environmental opportunity. To discern among possible mechanisms, PNNL considered possible mechanisms with the client, executed multiple experiments, and completed one theoretical analysis (see appendix). The remainder of this report first considers image analysis to gain insight into drag reduction mechanisms and then exposes the coating to cavitation to explore its response to an intensely cavitating environment. Although further efforts may be warranted to confirm mechanisms, this report presents a first investigation into these coatings within the scope and resources of the technology assistance program (TAP).

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

    International Nuclear Information System (INIS)

    Courbiere, P.

    2002-01-01

    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)

  19. 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.

  20. Cavitation research from an intetrnational perspective

    International Nuclear Information System (INIS)

    Arndt, R E A

    2012-01-01

    This paper reviews some current research at the Saint Anthony Falls Laboratory from the perspective of the experience gained from cooperative research in other laboratories that the author has had the opportunity to participate in for several decades. Examples are drawn from the author's experience with collaborative efforts in China, Germany, Japan, Netherlands, Norway, and the US. Emphasis is placed on the progress in our understanding of the physics of cavitation as influenced by water quality, i.e. the strength of the water as influenced by the concentration of free and dissolved gas and complex fluid dynamic factors such as turbulence. The shift from experimental research to studies involving an integrated experimental/numerical approach is also underscored. Examples are drawn from early studies of inception and acoustics, vortex cavitation and more recent research on sheet/cloud cavitation and supercavitation. Some thoughts on new directions are also presented.

  1. Fundamental studies on cavitation melt processing

    Science.gov (United States)

    Tzanakis, I.; Hodnett, M.; Lebon, G. S. B.; Eskin, D. G.; Pericleous, K.

    2016-05-01

    The application of ultrasound to industrial casting processes has attracted research interest during the last 50 years. However, the transfer and scale-up of this advanced and promising technology to industry has been hindered by difficulties in treating large volumes of liquid metal due to the lack of understanding of certain fundamentals. In the current study experimental results on ultrasonic processing in deionised water and in liquid aluminium (Al) are reported. Cavitation activity was determined in both liquid environments and acoustic pressures were successfully measured using an advanced high-temperature cavitometer sensor. Results showed that highest cavitation intensity in the liquid bulk is achieved at lower amplitudes of the sonotrode tip than the maximum available, suggesting nonlinearity in energy transfer to the liquid, while the location of the sonotrode is seen to substantially affect cavitation activity within the liquid. Estimation of real-time acoustic pressures distributed inside a crucible with liquid Al was performed for the first time.

  2. Analyses of cavitation instabilities in ductile metals

    DEFF Research Database (Denmark)

    Tvergaard, Viggo

    2007-01-01

    , and also tests for a thin ductile metal layer bonding two ceramic blocks have indicated rapid void growth. Analyses for these material configurations are discussed here. When the void radius is very small, a nonlocal plasticity model is needed to account for observed size-effects, and recent analyses......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. This has been...

  3. Towards numerical prediction of cavitation erosion.

    Science.gov (United States)

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

    2015-10-06

    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.

  4. The Impact of Manifold-to-Orifice Turning Angle on Sharp-Edge Orifice Flow Characteristics in both Cavitation and Non-Cavitation Turbulent Flow Regimes (Preprint)

    National Research Council Canada - National Science Library

    Nurick, W. H; Ohanian, T; Talley, D. G; Strakey, P. A

    2007-01-01

    .... This paper deals with predicting the initiation of cavitation, cavitation impacts on Cc, and non-cavitation impacts on Cd from L/D of 5 sharp-edge orifices with both single angle and compound angle directional flow...

  5. Experimental investigation of hydrodynamic cavitation through orifices of different geometries

    Directory of Open Access Journals (Sweden)

    Rudolf Pavel

    2017-01-01

    Full Text Available Hydrodynamic cavitation in single and multihole orifices was experimentally investigated to assess their hydraulic characteristics: loss coefficients, inception cavitation number, cavitation number for transition to supercavitation. Significant difference for singlehole and multihole orifices was observed in terms of the measured loss coefficient. It is significantly more effective to use multihole orifices, where energy dissipation is much lower.It was found that using scaling factor given by ratio of orifice thickness suggests linear behaviour of both loss coefficient and inception cavitation number. Orifices seem to be convenient choice as flow constriction devices inducing cavitation due to their simplicity.

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

    Directory of Open Access Journals (Sweden)

    Hou-lin Liu

    2014-03-01

    Full Text Available 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 numerical 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 declining the condensation coefficient, which is the most effective way.

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

    Directory of Open Access Journals (Sweden)

    Liu Hou-lin

    2014-03-01

    Full Text Available 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.

  8. Seasonality of cavitation and frost fatigue in Acer mono Maxim.

    Science.gov (United States)

    Zhang, Wen; Feng, Feng; Tyree, Melvin T

    2017-12-08

    Although cavitation is common in plants, it is unknown whether the cavitation resistance of xylem is seasonally constant or variable. We tested the changes in cavitation resistance of Acer mono before and after a controlled cavitation-refilling and freeze-thaw cycles for a whole year. Cavitation resistance was determined from 'vulnerability curves' showing the percent loss of conductivity versus xylem tension. Cavitation fatigue was defined as a reduction of cavitation resistance following a cavitation-refilling cycle, whereas frost fatigue was caused by a freeze-thaw cycle. A. mono developed seasonal changes in native embolisms; values were relatively high during winter but relatively low and constant throughout the growing season. Cavitation fatigue occurred and changed seasonally during the 12-month cycle; the greatest fatigue response occurred during summer and the weakest during winter, and the transitions occurred during spring and autumn. A. mono was highly resistant to frost damage during the relatively mild winter months; however, a quite different situation occurred during the growing season, as the seasonal trend of frost fatigue was strikingly similar to that of cavitation fatigue. Seasonality changes in cavitation resistance may be caused by seasonal changes in the mechanical properties of the pit membranes. © 2017 John Wiley & Sons Ltd.

  9. International Symposium of Cavitation and Multiphase Flow (ISCM 2014)

    International Nuclear Information System (INIS)

    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

  10. Effects of cavitation on performance of automotive torque converter

    Directory of Open Access Journals (Sweden)

    Jaewon Ju

    2016-06-01

    Full Text Available Cavitation is a phenomenon whereby vapor bubbles of a flowing liquid are formed in a local region where the pressure of the liquid is below its vapor pressure. It is well known that cavitation in torque converters occurs frequently when a car with an automatic transmission makes an abrupt start. Cavitation is closely related to a performance drop and noise generation at a specific operating condition in a car and a torque converter itself. This study addressed the relation between cavitation and performance in an automotive torque converter in a quantitative and qualitative manner using numerical simulations. The cavitation was calculated at various operating conditions using a commercial flow solver with the homogeneous cavitation model, and the torque converter performance was compared with the experimental data. Numerical results well match to the data and indicate that the cavitation causes significant performance drop, as the pump speed increases or both speed ratio and reference pressure decrease.

  11. 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.

  12. 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

  13. Influence of cavitation bubble growth by rectified diffusion on cavitation-enhanced HIFU

    Science.gov (United States)

    Okita, Kohei; Sugiyama, Kazuyasu; Takagi, Shu; Matsumoto, Yoichiro

    2017-11-01

    Cavitation is becoming increasingly important in therapeutic ultrasound applications such as diagnostic, tumor ablation and lithotripsy. Mass transfer through gas-liquid interface due to rectified diffusion is important role in an initial stage of cavitation bubble growth. In the present study, influences of the rectified diffusion on cavitation-enhanced high-intensity focused ultrasound (HIFU) was investigated numerically. Firstly, the mass transfer rate of gas from the surrounding medium to the bubble was examined as function of the initial bubble radius and the driving pressure amplitude. As the result, the pressure required to bubble growth was decreases with increasing the initial bubble radius. Next, the cavitation-enhanced HIFU, which generates cavitation bubbles by high-intensity burst and induces the localized heating owing to cavitation bubble oscillation by low-intensity continuous waves, was reproduced by the present simulation. The heating region obtained by the simulation is agree to the treatment region of an in vitro experiment. Additionally, the simulation result shows that the localized heating is enhanced by the increase of the equilibrium bubble size due to the rectified diffusion. This work was supported by JSPS KAKENHI Grant Numbers JP26420125,JP17K06170.

  14. Measuring cavitation and its cleaning effect

    NARCIS (Netherlands)

    Verhaagen, B.; Fernandez Rivas, David

    2016-01-01

    The advantages and limitations of techniques for measuring the presence and amount of cavitation, and for quantifying the removal of contaminants, are provided. After reviewing chemical, physical, and biological studies, a universal cause for the cleaning effects of bubbles cannot yet be concluded.

  15. On cavitation instabilities with interacting voids

    DEFF Research Database (Denmark)

    Tvergaard, Viggo

    2012-01-01

    voids so far apart that the radius of the plastic zone around each void is less than 1% of the current spacing between the voids, can still affect each others at the occurrence of a cavitation instability such that one void stops growing while the other grows in an unstable manner. On the other hand...

  16. Mesoscale spatial variability in seawater cavitation thresholds

    Science.gov (United States)

    Mel'nikov, N. P.; Elistratov, V. P.

    2017-03-01

    The paper presents the spatial variability of cavitation thresholds and some hydrological and hydrochemical parameters of seawater in the interfrontal zone of the Pacific Subarctic Front, in the Drake Passage, and in the equatorial part of the Pacific Ocean, measured in the near-surface layer to a depth of 70 m.

  17. Relating xylem cavitation to transpiration in cotton

    Science.gov (United States)

    Acoustic emmisions (AEs) from xylem cavitation events are characteristic of transpiration processes. Even though a body of work employing AE exists with a large number of species, cotton and other agronomically important crops have either not been investigated, or limited information exists. A few s...

  18. Modelling cavitating flow around underwater missiles

    Directory of Open Access Journals (Sweden)

    Fabien Petitpas

    2011-12-01

    Full Text Available The diffuse interface model of Saurel et al. (2008 is used for the computation of compressible cavitating flows around underwater missiles. Such systems use gas injection and natural cavitation to reduce drag effects. Consequently material interfaces appear separating liquid and gas. These interfaces may have a really complex dynamics such that only a few formulations are able to predict their evolution. Contrarily to front tracking or interface reconstruction method the interfaces are computed as diffused numerical zones, that are captured in a routinely manner, as is done usually with gas dynamics solvers for shocks and contact discontinuity. With the present approach, a single set of partial differential equations is solved everywhere, with a single numerical scheme. This leads to very efficient solvers. The algorithm derived in Saurel et al. (2009 is used to compute cavitation pockets around solid bodies. It is first validated against experiments done in cavitation tunnel at CNU. Then it is used to compute flows around high speed underwater systems (Shkval-like missile. Performance data are then computed showing method ability to predict forces acting on the system.

  19. The flow of a liquid with cavitation

    Czech Academy of Sciences Publication Activity Database

    Straškraba, Ivan; Vitásek, Emil

    2010-01-01

    Roč. 8, č. 4 (2010), s. 668-681 ISSN 1548-5390 R&D Projects: GA ČR GA201/08/0315 Institutional research plan: CEZ:AV0Z10190503 Keywords : fluid flow with cavitation * special solutions Subject RIV: BA - General Mathematics

  20. Cavitation for improved sludge conversion into biogas

    NARCIS (Netherlands)

    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

  1. Classification of lubricants according to cavitation criteria

    NARCIS (Netherlands)

    Meged, Y.; Meged, Y.; Venner, Cornelis H.; ten Napel, 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

  2. The making of a cavitation children's book

    Science.gov (United States)

    Henry de Frahan, Marc; Patterson, Brandon; Lazar, Erika

    2016-11-01

    Engaging young children in science is particularly important to future scientific endeavors. From thunderstorms to the waterpark, children are constantly exposed to the wonders of fluid dynamics. Among fluid phenomena, bubbles have always fascinated children. Yet some of the most exciting aspects of bubbles, such as cavitation, are scarcely known to non-experts. To introduce cavitation to a five year old audience, we wrote "Brooke Bubble Breaks Things", a children's book about the adventures of a cavitation bubble learning about all the things she could break. In this talk, we discuss how a children's book is made by walking through the steps involved in creating the book from concept to publication. We focus on strategies for successfully communicating a technical message while balancing entertainment and fidelity to nature. To provide parents, teachers, and young inquiring minds with a detailed explanation of the physics and applications of cavitation, we also created a website with detailed explanations, animations, and links to further information. We aim to convince the fluids community that writing picture books is an intellectually stimulating and fun way of communicating fluids principles and applications to children. ArtsEngine Microgrant at the University of Michigan.

  3. Measurement of cavitation induced wall shear stress

    NARCIS (Netherlands)

    Dijkink, R.J.; Ohl, C.D.

    2008-01-01

    The wall shear stress from cavitation bubbles collapsing close to a rigid boundary is measured with a constant temperature anemometer. The bubble is created with focused laser light, and its dynamics is observed with high-speed photography. By correlating the frames, a hydrophone signal, and the

  4. Optical Measurements of Cavitation in Tribological Contacts

    Science.gov (United States)

    Tang, Tian; Morris, Nick; Coupland, Jeremy

    2015-12-01

    The paper describes the use of a white light interformeter to measure the cavitation bubble and oil film thickness in a tribological contact and compares the results to theory. It is found that oil film thickness is best predicted by the theory proposed by Coyne and Elrod.

  5. Instability of the cavitating flow in a venturi reactor

    International Nuclear Information System (INIS)

    Sayyaadi, Hoseyn

    2010-01-01

    The instability characteristics of cavitating flow were experimentally investigated in a venturi tube in a recirculating flow loop. The fluctuation process of cavitation flow in the venturi was observed using high-speed photography. The sequential images were analyzed using the light intensity comparison technique and the cavitation length for each image was evaluated. The temporal cavitation length fluctuation vectors were determined at the specified operating condition (the cavitation number and operating pressure). The frequency components of oscillation were obtained using the fast Fourier transform (FFT) method. The effects of cavitation number and operating pressure on the Strouhal numbers and amplitudes of fluctuations were obtained. It was found that cavitation number has a major effect on the fluctuation characteristics of the cavitating flow in comparison with the effect of operating pressure. It was observed that at lower cavitation numbers, periodic separation, shedding and collapsing of the cloud-like cavities are observed together with the re-entrant jet motion. At higher cavitation numbers, the simple fluctuation mode with a sinusoidal pattern is observed.

  6. Hydrodynamic cavitation in Stokes flow of anisotropic fluids.

    Science.gov (United States)

    Stieger, Tillmann; Agha, Hakam; Schoen, Martin; Mazza, Marco G; Sengupta, Anupam

    2017-05-30

    Cavitation, the nucleation of vapour in liquids, is ubiquitous in fluid dynamics, and is often implicated in a myriad of industrial and biomedical applications. Although extensively studied in isotropic liquids, corresponding investigations in anisotropic liquids are largely lacking. Here, by combining liquid crystal microfluidic experiments, nonequilibrium molecular dynamics simulations and theoretical arguments, we report flow-induced cavitation in an anisotropic fluid. The cavitation domain nucleates due to sudden pressure drop upon flow past a cylindrical obstacle within a microchannel. For an anisotropic fluid, the inception and growth of the cavitation domain ensued in the Stokes regime, while no cavitation was observed in isotropic liquids flowing under similar hydrodynamic parameters. Using simulations we identify a critical value of the Reynolds number for cavitation inception that scales inversely with the order parameter of the fluid. Strikingly, the critical Reynolds number for anisotropic fluids can be 50% lower than that of isotropic fluids.

  7. STUDY UPON THE CAVITATION PHENOMENON OF THE ROTORS

    Directory of Open Access Journals (Sweden)

    Beazit ALI

    2011-11-01

    Full Text Available The main problem of the hydrodynamics of cavitation implosion of a single bubble, consists inpressure and velocity fields determination, including the collapse velocity of the bubble wall. By analysis thetheoretic and experimental phenomenon it establish the implicit function which describes this phenomenon. Byapplication the  theorem for this implicit function it finds the criterion equation of phenomenon.Depending on operating condition various cavitation patterns can be observed on a body surface astravelling bubbles, attached sheet cavitation, shear cavitation or vortex cavitation. Leading edge attachedpartialcavitation is commonly encountered on rotor blades or on hydrofoil. It corresponds to the case for whichavapor cavity is attached in the vecinity of the leading edge and extends over a fraction of the foil surface. Itgenerally takes places at incidence angles for which a leading edge pressure peak occurs and reduced belowtheliquid vapor pressure. At the early phases of development, leading edge partial cavitation is steady.

  8. 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.

  9. Regulating Ultrasound Cavitation in order to Induce Reproducible Sonoporation

    Science.gov (United States)

    Mestas, J.-L.; Alberti, L.; El Maalouf, J.; Béra, J.-C.; Gilles, B.

    2010-03-01

    Sonoporation would be linked to cavitation, which generally appears to be a non reproducible and unstationary phenomenon. In order to obtain an acceptable trade-off between cell mortality and transfection, a regulated cavitation generator based on an acoustical cavitation measurement was developed and tested. The medium to be sonicated is placed in a sample tray. This tray is immersed in in degassed water and positioned above the face of a flat ultrasonic transducer (frequency: 445 kHz; intensity range: 0.08-1.09 W/cm2). This technical configuration was admitted to be conducive to standing-wave generation through reflection at the air/medium interface in the well thus enhancing the cavitation phenomenon. Laterally to the transducer, a homemade hydrophone was oriented to receive the acoustical signal from the bubbles. From this spectral signal recorded at intervals of 5 ms, a cavitation index was calculated as the mean of the cavitation spectrum integration in a logarithmic scale, and the excitation power is automatically corrected. The device generates stable and reproducible cavitation level for a wide range of cavitation setpoint from stable cavitation condition up to full-developed inertial cavitation. For the ultrasound intensity range used, the time delay of the response is lower than 200 ms. The cavitation regulation device was evaluated in terms of chemical bubble collapse effect. Hydroxyl radical production was measured on terephthalic acid solutions. In open loop, the results present a great variability whatever the excitation power. On the contrary the closed loop allows a great reproducibility. This device was implemented for study of sonodynamic effect. The regulation provides more reproducible results independent of cell medium and experimental conditions (temperature, pressure). Other applications of this regulated cavitation device concern internalization of different particles (Quantum Dot) molecules (SiRNA) or plasmids (GFP, DsRed) into different

  10. Unveiling the physical mechanism behind pistol shrimp cavitation

    OpenAIRE

    Koukouvinis, Phoevos; Bruecker, Christoph; Gavaises, Manolis

    2017-01-01

    Snapping shrimps use a special shaped claw to generate a cavitating high speed water jet. Cavitation formed in this way, may be used for hunting/stunning prey and communication. The present work is a novel computational effort to provide insight on the mechanisms of cavitation formation during the claw closure. The geometry of the claw used here is a simplified claw model, based on prior experimental work. Techniques, such as Immersed Boundary and Homogenous Equilibrium Model (HEM), are emplo...

  11. Outlook on marine propeller noise and cavitation modelling

    OpenAIRE

    Lidtke, Artur Konrad; Turnock, Stephen R.; Humphrey, Victor F.

    2014-01-01

    Two computational studies are presented in this paper. First, the Potsdam Propeller Test Case which is used to demonstrate the capabilities of mass transfer cavitation models, more precisely the model by Sauer and Schnerr, in tackling the problem of marine propeller cavitation. It is shown that the extents of the predicted cavitation regions agree well with the experiment but suffer from the fact that the tip vortices and the associated low pressure regions are under resolved when URANS is ut...

  12. Detached eddy simulation of unsteady cavitation and pressure fluctuation around 3-D NACA66 hydrofoil

    Directory of Open Access Journals (Sweden)

    Zhang De-Sheng

    2015-01-01

    Full Text Available The unsteady cavitating flow and pressure fluctuation around the 3-D NACA66 hydrofoil were simulated and validated based on detached eddy simulation turbulence model and a homogeneous cavitation model. Numerical results show that detached eddy simulation can predict the evolution of cavity inception, sheet cavitation growth, cloud cavitation shedding, and breakup, as well as the pressure fluctuation on the surface of hydrofoil. The sheet cavitation growth, detachment, cloud cavitation shedding are responsible for the features of the pressure fluctuation.

  13. Cavitation Erosion of Nodular Cast Iron − Microstructural Effects

    Directory of Open Access Journals (Sweden)

    Orłowicz A.W.

    2017-12-01

    Full Text Available The paper deals with susceptibility of nodular cast iron with ferritic-pearlitic matrix on cavitation erosion. Cavitation tests were carried out with the use of a cavitation erosion vibratory apparatus employing a vibration exciter operated at frequency of 20 kHz. The study allowed to determine the sequence of subsequent stages in which microstructure of cast iron in superficial regions is subject to degradation. The first features to be damaged are graphite precipitates. The ferritic matrix of the alloy turned out to be definitely less resistant to cavitation erosion compared to the pearlitic matrix component.

  14. Some Remarks on the Three Dimensionality of Hydrofoil Cavitation

    Directory of Open Access Journals (Sweden)

    Mehmet Salih KARAALİOĞLU

    2017-12-01

    Full Text Available As it is well-known that cavitation is a very important physical phenomenon that affects significantly the performance of three-dimensional hydrofoils. Prediction of cavitation on three-dimensional hydrofoils is very important in the design stage. In this study, some approaches have been verified for hydrofoil cavitation. The main aim of this paper is to compare the mid-section pressure distribution of three-dimensional cavitating rectangular hydrofoil for increasing aspect ratios, with the pressure distribution of two-dimensional cavitating hydrofoil having the same section geometry as in the three-dimensional hydrofoil. In this study, a boundary element (panel method (BEM has been applied to investigate the hydrofoil cavitation for both two- and three-dimensional cases. Two-dimensional analytical solution in case of cavitating flat-plate has also been applied for comparison. It has been shown that the pressure distributions on the mid-section of three-dimensional cavitating and non-cavitating hydrofoil for increasing aspect ratios have converged to the solutions in two-dimensional case.

  15. Are flowers vulnerable to xylem cavitation during drought?

    Science.gov (United States)

    Zhang, Feng-Ping; Brodribb, Timothy J

    2017-05-17

    Water stress is known to cause xylem cavitation in the leaves, roots and stems of plants, but little is known about the vulnerability of flowers to xylem damage during drought. This is an important gap in our understanding of how and when plants become damaged by water stress. Here we address fundamental questions about if and when flowers suffer cavitation damage, using a new technique of cavitation imaging to resolve the timing of cavitation in water-stressed flower petals compared with neighbouring leaves. Leaves and flowers from a sample of two herbaceous and two woody eudicots were exposed to a severe water stress while the spatial and temporal propagation of embolism through veins was recorded. Although in most cases water potentials inducing 50% embolism of herbaceous flower veins were more negative than neighbouring leaves, there was no significant difference between the average vulnerability of leaves and petals of herbaceous species. In both woody species, petals were more vulnerable to cavitation than leaves, in one case by more than 3 MPa. Early cavitation and subsequent damage of flowers in the two woody species would thus be expected to precede leaf damage during drought. Similar cavitation thresholds of flowers and leaves in the herb sample suggest that cavitation during water shortage in these species will occur simultaneously among aerial tissues. Species-specific differences in the cavitation thresholds of petals provide a new axis of variation that may explain contrasting flowering ecology among plant species. © 2017 The Author(s).

  16. Structural Analysis of Cavitation for Different Stainless Steels

    Directory of Open Access Journals (Sweden)

    Mădălina-Elena Mânzână

    2011-09-01

    Full Text Available The cavitation phenomenon is currently approaching all areas of technology and modern industry, where are fluid in motion. In this paper cavitational erosion was conducted on different samples of stainless steels. The cavitation were performed in magnetostrictive vibrating apparatus at Cavitation Laboratory (Polytechnic University of Timisoara. The present paper intends to identify specific structural features in stainless steels. Several investigations were done: macrostructural analysis (Olympus SZX57, scaning electron microscope (Philips SEM and X-ray diffraction (D8 ADVANCE. After quantitative and qualitative investigations structural features were put in evidence on experimental stainless steels.

  17. Cavitational micro-particles: plasma formation mechanisms

    International Nuclear Information System (INIS)

    Bica, Ioan

    2005-01-01

    Cavitational micro-particles are a class to which the micro-spheres, the micro-tubes and the octopus-shaped micro-particles belong. The cavitational micro-particles (micro-spheres, micro-tubes and octopus-shaped micro-particles) at an environmental pressure. The micro-spheres, the micro-tubes and the ligaments of the octopus-shaped micro-particles are produced in the argon plasma and are formed of vapors with low values of the molar concentration in comparison with the molar density of the gas and vapor mixture, the first one on the unstable and the last two on the stable movement of the vapors. The ligaments of the octopus-shaped micro-particles are open at the top for well-chosen values of the sub-cooling of the vapor and gas cylinders. The nitrogen in the air favors the formation of pores in the wall of the micro-spheres. In this paper we present the cavitational micro-particles, their production in the plasma and some mechanisms for their formation in the plasma. (author)

  18. Discrete Bubble Modeling for Cavitation Bubbles

    Science.gov (United States)

    Choi, Jin-Keun; Chahine, Georges; Hsiao, Chao-Tsung

    2007-03-01

    Dynaflow, Inc. has conducted extensive studies on non-spherical bubble dynamics and interactions with solid and free boundaries, vortical flow structures, and other bubbles. From these studies, emerged a simplified Surface Averaged Pressure (SAP) spherical bubble dynamics model and a Lagrangian bubble tracking scheme. In this SAP scheme, the pressure and velocity of the surrounding flow field are averaged on the bubble surface, and then used for the bubble motion and volume dynamics calculations. This model is implemented using the Fluent User Defined Function (UDF) as Discrete Bubble Model (DBM). The Bubble dynamics portion can be solved using an incompressible liquid modified Rayleigh-Plesset equation or a compressible liquid modified Gilmore equation. The Discrete Bubble Model is a very suitable tool for the studies on cavitation inception of foils and turbo machinery, bubble nuclei effects, noise from the bubbles, and can be used in many practical problems in industrial and naval applications associated with flows in pipes, jets, pumps, propellers, ships, and the ocean. Applications to propeller cavitation, wake signatures of waterjet propelled ships, bubble-wake interactions, modeling of cavitating jets, and bubble entrainments around a ship will be presented.

  19. Modeling Unsteady Cavitation Effects and Dynamic Loads in Cryogenic Systems, Phase II

    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. VibroCav : Hydrodynamic Vibration and Cavitation Technology

    NARCIS (Netherlands)

    Bakker, T.W.

    2012-01-01

    Vibration and cavitation can be generated in many ways and serve many useful purposes. This study describes physical aspects of useful vibration and cavitation for a broad spectrum of applications at atmospheric or elevated pressures. After a review of available devices, hydrodynamic

  1. Dental pulp reaction to Cavit temporary filling material.

    Science.gov (United States)

    Provant, D R; Adrian, J C

    1978-02-01

    Seventy-two teeth in three Macaque fasicularis monkeys were used to evaluate pulpal response to cavit. Displacement of odontoblastic nuclei was evaluated histologically at three time periods in order to identify initial, early, and final responses. There were no statistically significant differences in pulpal response between Cavit and the zinc oxide-eugenol controls when used in accordance with the manufacturer's directions.

  2. Reproducible cavitation activity in water-particle suspensions

    NARCIS (Netherlands)

    Borkent, B.M.; Arora, M.; Ohl, C.D.

    2007-01-01

    The study of cavitation inception in liquids rarely yields reproducible data, unless special control is taken on the cleanliness of the experimental environment. In this paper, an experimental technique is demonstrated which allows repeatable measurements of cavitation activity in liquid-particle

  3. Compressible Turbulent Flow Numerical Simulations of Tip Vortex Cavitation

    NARCIS (Netherlands)

    Khatami, F.; van der Weide, Edwin Theodorus Antonius; Hoeijmakers, Hendrik Willem Marie

    2015-01-01

    For an elliptic Arndt’s hydrofoil numerical simulations of vortex cavitation are presented. An equilibrium cavitation model is employed. This single-fluid model assumes local thermodynamic and mechanical equilibrium in the mixture region of the flow, is employed. Furthermore, for characterizing the

  4. Cavitation-aided grain refinement in aluminium alloys

    NARCIS (Netherlands)

    Atamanenko, T.V.

    2010-01-01

    This thesis deals with grain refinement under the influence of ultrasonic-driven cavitation in aluminium casting processes. Three major goals of this research were: (1) to identify the mechanism of the cavitation-aided grain refinement at different stages of solidification; (2) to reveal the

  5. 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.

  6. Hydrodynamic cavitation: a bottom-up approach to liquid aeration

    NARCIS (Netherlands)

    Raut, J.S.; Stoyanov, S.D.; Duggal, C.; Pelan, E.G.; Arnaudov, L.N.; Naik, V.M.

    2012-01-01

    We report the use of hydrodynamic cavitation as a novel, bottom-up method for continuous creation of foams comprising of air microbubbles in aqueous systems containing surface active ingredients, like proteins or particles. The hydrodynamic cavitation was created using a converging-diverging nozzle.

  7. A THERMODYNAMIC CAVITATION MODEL APPLICABLE TO HIGH TEMPERATURE FLOW

    Directory of Open Access Journals (Sweden)

    De-Min Liu

    2011-01-01

    Full Text Available Cavitation is not only related with pressure, but also affected by temperature. Under high temperature, temperature depression of liquids is caused by latent heat of vaporization. The cavitation characteristics under such condition are different from those under room temperature. The paper focuses on thermodynamic cavitation based on the Rayleigh-Plesset equation and modifies the mass transfer equation with fully consideration of the thermodynamic effects and physical properties. To validate the modified model, the external and internal flow fields, such as hydrofoil NACA0015 and nozzle, are calculated, respectively. The hydrofoil NACA0015's cavitation characteristic is calculated by the modified model at different temperatures. The pressure coefficient is found in accordance with the experimental data. The nozzle cavitation under the thermodynamic condition is calculated and compared with the experiment.

  8. Non-cavitating propeller noise modeling and inversion

    Science.gov (United States)

    Kim, Dongho; Lee, Keunhwa; Seong, Woojae

    2014-12-01

    Marine propeller is the dominant exciter of the hull surface above it causing high level of noise and vibration in the ship structure. Recent successful developments have led to non-cavitating propeller designs and thus present focus is the non-cavitating characteristics of propeller such as hydrodynamic noise and its induced hull excitation. In this paper, analytic source model of propeller non-cavitating noise, described by longitudinal quadrupoles and dipoles, is suggested based on the propeller hydrodynamics. To find the source unknown parameters, the multi-parameter inversion technique is adopted using the pressure data obtained from the model scale experiment and pressure field replicas calculated by boundary element method. The inversion results show that the proposed source model is appropriate in modeling non-cavitating propeller noise. The result of this study can be utilized in the prediction of propeller non-cavitating noise and hull excitation at various stages in design and analysis.

  9. 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.

  10. Retrograde root filling with amalgam and Cavit.

    Science.gov (United States)

    Finne, K; Nord, P G; Persson, G; Lennartsson, B

    1977-04-01

    In a 3-year review of 218 teeth with retrograde root filling with amalgam orCavit, the results obtained with the former proved significantly better than those obtained with the latter. The difference seemed to be due to a better obliteration of the canal by amalgam. The obliterating effect of amalgam probably eliminates the need for revision of incomplete othograde root filling, for example, in cases with a post in the root canal. Irrespective of type of filling materials, the results were less good in cases with marginal bone loss.

  11. Numerical 3D analysis of cloud cavitation shedding frequency on a circular leading edge hydrofoil with a barotropic cavitation model

    Science.gov (United States)

    Blume, M.; Skoda, R.

    2015-12-01

    A compressible density-based time-explicit low Mach number consistent viscous flow solver is utilised in combination with a barotropic cavitation model for the analysis of cloud cavitation on a circular leading edge (CLE) hydrofoil. For 5° angle of attack, cloud structure and shedding frequency for different cavitation numbers are compared to experimental data. A strong grid sensitivity is found in particular for high cavitation numbers. On a fine grid, a very good agreement with validation data is achieved even without explicit turbulence model. The neglect of viscous effects as well as a two-dimensional set-up lead to a less realistic prediction of cloud structures and frequencies. Comparative simulations with the Sauer-Schnerr cavitation model and modified pre-factors of the mass transfer terms underestimate the measured shedding frequency.

  12. Experimental investigation of the flow-induced vibration of hydrofoils in cavitating flows

    Science.gov (United States)

    Wang, Guoyu; Wu, Qin; Huang, Biao; Gao, Yuan

    2015-12-01

    The objective of this paper is to investigate the correlation between fluid induced vibration and unsteady cavitation behaviours. Experimental results are presented for a modified NACA66 hydrofoil, which is fixed at α=8°. The high-speed camera is synchronized with a single point Laser Doppler Vibrometer to analyze the transient cavitating flow structures and the corresponding structural vibration characteristics. The results showed that, with the decreasing of the cavitation number, the cavitating flows in a water tunnel display several types of cavitation patterns, such as incipient cavitation, sheet cavitation and cloud cavitation. The cavity shedding frequency reduces with the decrease of the cavitation number. As for the cloud cavitation regime, the trend of the vibration velocity goes up with the growth of the attached cavity, accompanied with small amplitude fluctuations. Then the collapse and shedding of the large-scale cloud cavities leads to substantial increase of the vibration velocity fluctuations.

  13. Transition of cavitating flow to supercavitation within Venturi nozzle – hysteresis investigation

    OpenAIRE

    Jiří Kozák; Pavel Rudolf; Rostislav Huzlík; Martin Hudec; Radomír Chovanec; Ondřej Urban; Blahoslav Maršálek; Eliška Maršálková; František Pochylý; David Štefan

    2017-01-01

    Cavitation is usually considered as undesirable phenomena. On the other hand, it can be utilized in many applications. One of the technical applications is using cavitation in water treatment, where hydrodynamic cavitation seems to be effective way how to reduce cyanobacteria within large bulks of water. The main scope of this paper is investigation of the cavitation within Venturi nozzle during the transition from fully developed cavitation to supercavitation regime and vice versa. Dynamics ...

  14. Numerical research on unsteady cavitating flow over a hydrofoil

    Science.gov (United States)

    Homa, D.; Wróblewski, W.

    2016-10-01

    Cavitation is a widely known phenomenon in pumps and water turbines installations. It can lead to significant damage of blades and walls of the rotor therefore it is crucial during pump designing and exploitation to avoid working in flow conditions, that enabled cavitation to occur. Nowadays numerical simulations of flow can provide valuable information concerning pressure and velocity distribution and can indicate if there is a risk of cavitating flow appearance. There are a few mathematical models which describe cavitating flow. In the paper Schnerr & Sauer model was chosen for simulation. Aim of the paper is to verify its utility in case of different cavitating flow regimes over Clark-Y hydrofoil. After performing the grid independence study four different cavitation regimes were investigated. The vapour areas appearance, their shapes and changes in time were observed. The assumption of isothermal, two - phase flow was made. The calculations were performed using OpenFOAM and were compared to the available measurements data. The presented results concerned sheet and cloud cavitation regimes.

  15. Detecting cavitation in vivo from shock-wave therapy devices

    Science.gov (United States)

    Matula, Thomas J.; Yu, Jinfei; Bailey, Michael R.

    2005-04-01

    Extracorporeal shock-wave therapy (ESWT) has been used as a treatment for plantar faciitis, lateral epicondylitis, shoulder tendonitis, non-unions, and other indications where conservative treatments have been unsuccessful. However, in many areas, the efficacy of SW treatment has not been well established, and the mechanism of action, particularly the role of cavitation, is not well understood. Research indicates cavitation plays an important role in other ultrasound therapies, such as lithotripsy and focused ultrasound surgery, and in some instances, cavitation has been used as a means to monitor or detect a biological effect. Although ESWT can generate cavitation easily in vitro, it is unknown whether or not cavitation is a significant factor in vivo. The purpose of this investigation is to use diagnostic ultrasound to detect and monitor cavitation generated by ESWT devices in vivo. Diagnostic images are collected at various times during and after treatment. The images are then post-processed with image-processing algorithms to enhance the contrast between bubbles and surrounding tissue. The ultimate goal of this research is to utilize cavitation as a means for optimizing shock wave parameters such as amplitude and pulse repetition frequency. [Work supported by APL internal funds and NIH DK43881 and DK55674.

  16. Numerical investigation of tip clearance cavitation in Kaplan runners

    Science.gov (United States)

    Nikiforova, K.; Semenov, G.; Kuznetsov, I.; Spiridonov, E.

    2016-11-01

    There is a gap between the Kaplan runner blade and the shroud that makes for a special kind of cavitation: cavitation in the tip leakage flow. Two types of cavitation caused by the presence of clearance gap are known: tip vortex cavitation that appears at the core of the rolled up vortex on the blade suction side and tip clearance cavitation that appears precisely in the gap between the blade tip edge and the shroud. In the context of this work numerical investigation of the model Kaplan runner has been performed taking into account variable tip clearance for several cavitation regimes. The focus is put on investigation of structure and origination of mechanism of cavitation in the tip leakage flow. Calculations have been performed with the help of 3-D unsteady numerical model for two-phase medium. Modeling of turbulent flow in this work has been carried out using full equations of Navier-Stokes averaged by Reynolds with correction for streamline curvature and system rotation. For description of this medium (liquid-vapor) simplification of Euler approach is used; it is based on the model of interpenetrating continuums, within the bounds of this two- phase medium considered as a quasi-homogeneous mixture with the common velocity field and continuous distribution of density for both phases. As a result, engineering techniques for calculation of cavitation conditioned by existence of tip clearance in model turbine runner have been developed. The detailed visualization of the flow was carried out and vortex structure on the suction side of the blade was reproduced. The range of frequency with maximum value of pulsation was assigned and maximum energy frequency was defined; it is based on spectral analysis of the obtained data. Comparison between numerical computation results and experimental data has been also performed. The location of cavitation zone has a good agreement with experiment for all analyzed regimes.

  17. 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 (mechanism found to be a possible contributor to these adverse effects is cavitation. In vitro, cavitation has been directly demonstrated by visualization and indirectly in vivo by registering of high frequency pressure fluctuations (HFPF). Tilting disc 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.

  18. Principles and effects of acoustic cavitation - A review

    Directory of Open Access Journals (Sweden)

    Corina GÂMBUŢEANU

    2013-12-01

    Full Text Available In the recent years, food industry has shown a real interest in ultrasound use because of its effect on physical, biochemical and microbial properties of food systems. In order to better understand how the acoustic cavity effects could be best applied in food industry, a review on acoustic cavitation and its effects was done. The present paper describes in detail the basic principles underlying the effects of ultrasounds on food processing applications. It also provides theoretical background on acoustic cavitation and ultrasound production method. Moreover, harnessing mechanic, optic, chemical and biological effects of acoustic cavitation in food industry were briefly highlighted.

  19. Experimental determination of cavitation thresholds in liquid water and mercury

    International Nuclear Information System (INIS)

    Taleyarkhan, R.P.; West, C.D.; Moraga, F.

    1998-01-01

    An overview is provided on cavitation threshold measurement experiments for water and mercury. Various aspects to be considered that affect onset determination are discussed along with design specifications developed for construction of appropriate apparatus types. Both static and transient-cavitation effects were studied using radically different apparatus designs. Preliminary data are presented for cavitation thresholds for water and mercury over a range of temperatures in static and high-frequency environments. Implications and issues related to spallation neutron source target designs and operation are discussed

  20. Some experiments on cavitation damage produced by a submerged jet

    International Nuclear Information System (INIS)

    Momma, T.; Lichtarowicz, A.

    1993-01-01

    Cavitation erosion produced by a submerged jet can be utilized for cleaning surface contamination. This paper describes some results obtained from experiments at the University of Nottingham conducted on cavitating jets and their effects on surfaces. Some effects of cavitation on submerged jets were examined. High speed photography was used to show the structure of the jet. All stages of damage to soft aluminum specimens from plastically deformed indentations down to large concentric erosion rings were observed. The amount of erosion depended on the configuration of the set up and on the flow parameters. Early stages of erosion can be used for cleaning

  1. Cavitation and Electrochemical Characteristics in Seawater by Water Cavitation Peening of 5083-O al Alloy for Ships

    Science.gov (United States)

    Hyun, Koangyong; Kim, Seong-Jong

    Aluminum (Al) alloy ships are vulnerable to both damage from chlorine ions in seawater environments and cavitation-erosion due to fast relative motion of metal and liquid resulting from lightweight and high-speed vessels moving through seawater. These corrosive processes cause damage to the hulls of ships, resulting in large economic losses. Recently, cavitation peening technology to improve the durability of a material has been in development. The technology works by forming compressive residual stress on the surface layer of the material in order to improve fatigue strength and fatigue life. In this study, we performed a water cavitation peening (WCP) on a 5083-O Al alloy for ships by applying an ultrasonic piezoelectric effect and cavitation effect, as described in ASTM-G32. From these experiments, we determined an optimum WCP duration, 2.5min, for sufficient cavitation resistance characteristics. This timing improved cavitation resistance by 48.68% compared to the untreated condition. A comprehensive comparison of all of results revealed that the optimum WCP duration was 3min with respect to the point of cavitation and corrosion resistance.

  2. The role of mechanical properties in cavitation erosion resistance. [parameters affecting metal fatigue under cavitation flow conditions

    Science.gov (United States)

    Gould, G. C.

    1974-01-01

    Methods for determining the correlations of erosion resistance and mechanical properties of materials are discussed. The most common method of testing cavitation erosion resistance of materials is the vibratory cavitation probe. The instrument and its operation are described. The use of the whirling arm device is considered as a second method. Metallographic investigations of the earliest stages of cavitation erosion damage of metallic materials was conducted. The materials show plastic deformation occurring during the incubation period and increasing until cracks form and metal fragments are lost. The parameters of the work done to cause material fractures are identified. The reactions obtained with specific materials are reported.

  3. Cavitation in liquid cryogens. 2: Hydrofoil

    Science.gov (United States)

    Hord, J.

    1973-01-01

    Boundary layer principles, along with two-phase concepts, are used to improve existing correlative theory for developed cavity data. Details concerning cavity instrumentation, data analysis, correlative techniques, and experimental and theoretical aspects of a cavitating hydrofoil are given. Both desinent and thermodynamic data, using liquid hydrogen and liquid nitrogen, are reported. The thermodynamic data indicated that stable thermodynamic equilibrium exists throughout the vaporous cryogen cavities. The improved correlative formulas were used to evaluate these data. A new correlating parameter based on consideration of mass limiting two-phase flow flux across the cavity interface, is proposed. This correlating parameter appears attractive for future correlative and predictive applications. Agreement between theory and experiment is discussed, and directions for future analysis are suggested. The front half of the cavities, developed on the hydrofoil, may be considered as parabolically shaped.

  4. Analysis of Acoustic Cavitation Surge in a Rocket Engine Turbopump

    Directory of Open Access Journals (Sweden)

    Hideaki Nanri

    2010-01-01

    Full Text Available In a liquid rocket engine, cavitation in an inducer of a turbopump sometimes causes instability phenomena when the inducer is operated at low inlet pressure. Cavitation surge (auto-oscillation, one such instability phenomenon, has been discussed mainly based on an inertia model assuming incompressible flow. When this model is used, the frequency of the cavitation surge decreases continuously as the inlet pressure of the turbopump decreases. However, we obtained an interesting experimental result in which the frequency of cavitation surge varied discontinuously. Therefore, we employed one-dimensional analysis based on an acoustic model in which the fluid is assumed to be compressible. The analytical result qualitatively corresponded with the experimental result.

  5. Experimental and numerical analysis of cavitating flow around a hydrofoil

    Directory of Open Access Journals (Sweden)

    Müller Miloš

    2012-04-01

    Full Text Available The paper describes experiments carried out in the cavitation tunnel with the rectangular test section of 150 × 150 × 500 mm and the maximum test section inlet velocity of 25 m/s. These experiments have been aimed to visualize the cavitation phenomena as well as to quantify the erosion potential using pitting tests evaluated during the incubation period for the cast-iron prismatic hydrofoil with the modified NACA profile. A bypass section installed in the tunnel has allowed to measure the nuclei content in the inlet flow to the test section using the acoustic spectrometer. The measured data have been compared with the CFD analysis of the cavitation phenomena on the hydrofoil as well as the numerically determined location and magnitude of the first calculated collapses of the cavitating bubbles with a good agreement.

  6. Optimization of centrifugal pump cavitation performance based on CFD

    International Nuclear Information System (INIS)

    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-ε 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

  7. Inverse Analysis of Cavitation Impact Phenomena on Structures

    National Research Council Canada - National Science Library

    Lambrakos, S. G; Tran, N. E

    2007-01-01

    A general methodology is presented for in situ detection of cavitation impact phenomena on structures based on inverse analysis of luminescent emissions resulting from the collapsing of bubbles onto surfaces...

  8. Mathematical Modelling of Fluid Flow in Cone and Cavitation Formation

    Directory of Open Access Journals (Sweden)

    Milada KOZUBKOVÁ

    2011-06-01

    Full Text Available Problem of cavitation is the undesirable phenomena occuring in the fluid flow in many hydraulic application (pumps, turbines, valves, etc.. Therefore this is in the focus of interest using experimental and mathematical methods. Based on cavitation modelling in Laval nozzle results and experience [1], [2], [4], following problem described as the water flow at the outlet from turbine blade wheel was solved. Primarily the problem is simplified into modelling of water flow in cone. Profiles of axial, radial and tangential velocity are defined on inlet zone. The value of pressure is defined on the outlet. Boundary conditions were defined by main investigator of the grant project – Energy Institute, Victor Kaplan’s Department of Fluid Engineering, Faculty of Mechanical Engineering, Brno University of Technology. The value of air volume was insignificant. Cavitation was solved by Singhal model of cavitation.

  9. Cavitational synthesis of nanostructured inorganic materials for enhanced heterogeneous catalysis

    Science.gov (United States)

    Krausz, Ivo Michael

    The synthesis of nanostructured inorganic materials by hydrodynamic cavitation processing was investigated. The goal of this work was to develop a general synthesis technique for nanostructured materials with a control over crystallite size in the 1--20 nm range. Materials with crystallite sizes in this range have shown enhanced catalytic activity compared to materials with larger crystallite sizes. Several supported and unsupported inorganic materials were studied to understand the effects of cavitation on crystallite size. Cavitation processing of calcium fluoride resulted in more spherical particles, attached to one another by melted necks. This work produced the first evidence of shock wave heating of nanostructured materials by hydrodynamic cavitation processing. Hydrodynamic cavitation synthesis of various catalytic support materials indicated that their phase composition and purity could be controlled by adjustment of the processing parameters. Zirconia/alumina supports synthesized using hydro-dynamic cavitation and calcined to 1368 K retained a high purity cubic zirconia phase, whereas classically prepared samples showed a phase transformation to monoclinic zirconia. Similarly, the synthesis of alumina resulted in materials with varying Bohmite and Bayerite contents as a function of the process parameters. High temperature calcination resulted in stable alumina supports with varying amounts of delta-, and theta-alumina. Synthesis studies of palladium and silver showed modest variations in crystallite size as a function of cavitation process parameters. Calcination resulted in larger grain materials, indicating a disappearance of intergrain boundaries. Based on these results, a new synthesis method was studied involving controlled agglomeration of small silver crystallites by hydrodynamic cavitation processing, followed by deposition on alumina. The optimal pH, concentration, and processing time for controlling the silver crystallite size in the cavitation

  10. Experimental Investigation on Cavitating Flow Induced Vibration Characteristics of a Low Specific Speed Centrifugal Pump

    Directory of Open Access Journals (Sweden)

    Bo Gao

    2017-01-01

    Full Text Available Cavitating flow developing in the blade channels is detrimental to the stable operation of centrifugal pumps, so it is essential to detect cavitation and avoid the unexpected results. The present paper concentrates on cavitation induced vibration characteristics, and special attention is laid on vibration energy in low frequency band, 10–500 Hz. The correlation between cavitating evolution and the corresponding vibration energy in 10–500 Hz frequency band is discussed through visualization analysis. Results show that the varying trend of vibration energy in low frequency band is unique compared with the high frequency band. With cavitation number decreasing, vibration energy reaches a local maximum at a cavitation number much larger than the 3% head drop point; after that it decreases. The varying trend is closely associated with the corresponding cavitation status. With cavitation number decreasing, cavitation could be divided into four stages. The decreasing of vibration energy, in particular cavitation number range, is caused by the partial compressible cavitation structure. From cavitation induced vibration characteristics, vibration energy rises much earlier than the usual 3% head drop criterion, and it indicates that cavitation could be detected in advance and effectively by means of cavitation induced vibration characteristics.

  11. Hydrodynamic cavitation applied to food waste anaerobic digestion

    OpenAIRE

    Tran, David

    2016-01-01

    Innovative pre-treatment methods applied to anaerobic digestion (AD) have developed to enhance the methane yields of food waste. This study investigates hydrodynamic cavitation, which induce disintegration of biomass through microbubble formations, impact on food waste solubilisation and methane production during following AD. Two different sub-streams of food waste (before and after the digestion) pre-treated by hydrodynamic cavitation were evaluated in lab scale for its potential for implem...

  12. Stress corrosion cracking mitigation by ultrasound induced cavitation technique

    International Nuclear Information System (INIS)

    Fong, C.; Lee, Y.C.; Yeh, T.K.

    2014-01-01

    Cavitation is usually considered as a damaging mechanism under erosion corrosion condition. However, if used appropriately, cavitation can be applied as a peening technique for surface stress modification process. The aim of surface stress modification is to alter the stress state of processed surface through direct or indirect thermo-mechanical treatments to reduce cracking problems initiated from surface. Ultrasonic devices are used to generate cavitation bubbles which when collapse will produce high intensity shock waves and high velocity micro-jet streams. The cavitation impact when properly controlled will create plastically deformed compressive layers in nearby surfaces and minimize cracking susceptibility in corrosive environments. This study is to investigate the effectiveness of Ultrasound Induced Cavitation (UIC) technique in surface stress improvement. Ultrasonic cavitation treatment of SS304 stainless steel under pure water is carried out with different controlling parameters. The cavitation impact on SS304 surface is measured in terms of surface roughness, surface strain, hardness, and microstructural characteristics. The in-depth residual stress distribution and crack mitigation effect are also evaluated. Test result indicates ultrasound induced cavitation treatment only has minor effect on surface physical characteristics. The extent of compressive stress produced on top surface exceeds the yield strength and can reach a depth above 150 μm. The maximum surface strain measured is generally below 20%, which is not considered detrimental to accelerate crack initiation. Stress corrosion verification tests show UIC treatment is capable in preventing environmental assisted cracking of stainless steels in severely corrosive conditions. In view of the test results, UIC technique has demonstrated to be a low cost, low contaminating, and effective surface stress improvement technology. (author)

  13. A Study on Prediction of Cavitation for Centrifugal Pump

    OpenAIRE

    Myung Jin Kim; Hyun Bae Jin; Wui Jun Chung

    2012-01-01

    In this study, to accurately predict cavitation of a centrifugal pump, numerical analysis was compared with experimental results modeled on a small industrial centrifugal pump. In this study, numerical analysis was compared with experimental results modeled on a small industrial centrifugal pump for reliable prediction on cavitation of a centrifugal pump. To improve validity of the numerical analysis, transient analysis was conducted on the calculated domain of full-type ...

  14. Experience with control valve cavitation problems and their solutions

    International Nuclear Information System (INIS)

    Ozol, J.

    1988-01-01

    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

  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. 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].

  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. Application of computational fluid dynamics on cavitation in journal bearings

    Science.gov (United States)

    Riedel, Marco; Schmidt, Marcus; Reinke, Peter; Nobis, Matthias; Redlich, Marcel

    2014-03-01

    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].

  19. Biomedical device prototype based on small scale hydrodynamic cavitation

    Directory of Open Access Journals (Sweden)

    Morteza Ghorbani

    2018-03-01

    Full Text Available This study presents a biomedical device prototype based on small scale hydrodynamic cavitation. The application of small scale hydrodynamic cavitation and its integration to a biomedical device prototype is offered as an important alternative to other techniques, such as ultrasound therapy, and thus constitutes a local, cheap, and energy-efficient solution, for urinary stone therapy and abnormal tissue ablation (e.g., benign prostate hyperplasia (BPH. The destructive nature of bubbly, cavitating, flows was exploited, and the potential of the prototype was assessed and characterized. Bubbles generated in a small flow restrictive element (micro-orifice based on hydrodynamic cavitation were utilized for this purpose. The small bubbly, cavitating, flow generator (micro-orifice was fitted to a small flexible probe, which was actuated with a micromanipulator using fine control. This probe also houses an imaging device for visualization so that the emerging cavitating flow could be locally targeted to the desired spot. In this study, the feasibility of this alternative treatment method and its integration to a device prototype were successfully accomplished.

  20. Computing Thermal Effects of Cavitation in Cryogenic Liquids

    Science.gov (United States)

    Hosangadi, Ashvin; Ahuja, Vineet; Dash, Sanford M.

    2005-01-01

    A computer program implements a numerical model of thermal effects of cavitation in cryogenic fluids. The model and program were developed for use in designing and predicting the performances of turbopumps for cryogenic fluids. Prior numerical models used for this purpose do not account for either the variability of properties of cryogenic fluids or the thermal effects (especially, evaporative cooling) involved in cavitation. It is important to account for both because in a cryogenic fluid, the thermal effects of cavitation are substantial, and the cavitation characteristics are altered by coupling between the variable fluid properties and the phase changes involved in cavitation. The present model accounts for both thermal effects and variability of properties by incorporating a generalized representation of the properties of cryogenic fluids into a generalized compressible-fluid formulation for a cavitating pump. The model has been extensively validated for liquid nitrogen and liquid hydrogen. Using the available data on the properties of these fluids, the model has been shown to predict accurate temperature-depression values.

  1. 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.

  2. Investigation of the Methane Hydrate Formation by Cavitation Jet

    Science.gov (United States)

    Morita, H.; Nagao, J.

    2015-12-01

    Methane hydrate (hereafter called "MH") is crystalline solid compound consisting of hydrogen-bonded water molecules forming cages and methane gas molecules enclosed in the cage. When using MH as an energy resource, MH is dissociated to methane gas and water and collect only the methane gas. The optimum MH production method was the "depressurization method". Here, the production of MH means dissociating MH in the geologic layers and collecting the resultant methane gas by production systems. In the production of MH by depressurization method, MH regeneration was consider to important problem for the flow assurance of MH production system. Therefore, it is necessary to clarify the effect of flow phenomena in the pipeline on hydrate regeneration. Cavitation is one of the flow phenomena which was considered a cause of MH regeneration. Large quantity of microbubbles are produced by cavitation in a moment, therefore, it is considered to promote MH formation. In order to verify the possible of MH regeneration by cavitation, it is necessary to detailed understanding the condition of MH formation by cavitation. As a part of a Japanese National hydrate research program (MH21, funded by METI), we performed a study on MH formation using by cavitation. The primary objective of this study is to demonstrate the formation MH by using cavitation in the various temperature and pressure condition, and to clarify the condition of MH formation by using observation results.

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

    International Nuclear Information System (INIS)

    2002-01-01

    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

  4. Diagnostic Value of Conventional and Digital Radiography for Detection of Cavitated and Non-Cavitated Proximal Caries

    Directory of Open Access Journals (Sweden)

    Mahdieh Dehghani

    2017-02-01

    Full Text Available Objectives: This study aimed to assess the diagnostic value of conventional and digital radiography for detection of cavitated and non-cavitated proximal caries.Materials and Methods: Fifty extracted human premolars and molars were mounted in a silicone block. Charge-coupled device (CCD and photostimulable phosphor plate (PSP receptors and intra-oral films were exposed with 60 and 70 kVp with parallel technique. Two observers interpreted the radiographs twice with a two-week interval using a 5-point scale. Teeth were then serially sectioned in mesiodistal direction and evaluated under a stereomicroscope (gold standard. Sensitivity, specificity, positive predictive value, negative predictive value and accuracy were calculated.Results: Sensitivity of all three receptors for detection of enamel lesions was low (5.5-44.4% but it was higher for dentin lesions (42.8-62.8%; PSP with 70 kVp and 0.03s exposure time had the highest sensitivity for enamel lesions, but the difference among receptors was not statistically significant (P>0.05. Sensitivity of all three receptors for detection of non-cavitated lesions was lower than that for cavitated lesions; PSP with 60 kVp and 0.07s exposure time had higher sensitivity and lower patient radiation dose for detection of cavitated and non-cavitated lesions, but the difference was not significant (P>0.05.Conclusions: Digital radiography using PSP receptor with 70 kVp is recommended to detect initial enamel caries. For detection of non-cavitated and cavitated dentin caries, PSP with 60 kVp is more appropriate. Change in kVp did not affect the diagnostic accuracy for detection of caries, and type of receptor was a more important factor.Keywords: Dental Caries; Diagnostic Imaging; Radiography, Dental, Digital

  5. Diagnostic Value of Conventional and Digital Radiography for Detection of Cavitated and Non-Cavitated Proximal Caries.

    Science.gov (United States)

    Dehghani, Mahdieh; Barzegari, Rasool; Tabatabai, Hosein; Ghanea, Sahar

    2017-01-01

    This study aimed to assess the diagnostic value of conventional and digital radiography for detection of cavitated and non-cavitated proximal caries. Fifty extracted human premolars and molars were mounted in a silicone block. Charge-coupled device (CCD) and photostimulable phosphor plate (PSP) receptors and intra-oral films were exposed with 60 and 70 kVp with parallel technique. Two observers interpreted the radiographs twice with a two-week interval using a 5-point scale. Teeth were then serially sectioned in mesiodistal direction and evaluated under a stereomicroscope (gold standard). Sensitivity, specificity, positive predictive value, negative predictive value and accuracy were calculated. Sensitivity of all three receptors for detection of enamel lesions was low (5.5-44.4%) but it was higher for dentin lesions (42.8-62.8%); PSP with 70 kVp and 0.03s exposure time had the highest sensitivity for enamel lesions, but the difference among receptors was not statistically significant (P>0.05). Sensitivity of all three receptors for detection of non-cavitated lesions was lower than that for cavitated lesions; PSP with 60 kVp and 0.07s exposure time had higher sensitivity and lower patient radiation dose for detection of cavitated and non-cavitated lesions, but the difference was not significant (P>0.05). Digital radiography using PSP receptor with 70 kVp is recommended to detect initial enamel caries. For detection of non-cavitated and cavitated dentin caries, PSP with 60 kVp is more appropriate. Change in kVp did not affect the diagnostic accuracy for detection of caries, and type of receptor was a more important factor.

  6. Modelling of flow with cavitation in centrifugal pump

    International Nuclear Information System (INIS)

    Homa, D; Wróblewski, W

    2014-01-01

    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.

  7. Influence of water air content on cavitation erosion in distilled water

    CSIR Research Space (South Africa)

    Auret, JG

    1993-12-01

    Full Text Available in bubble collapse cushioning and reduction of cavitation damage. When the water was oversaturated with air, large air bubbles formed and cavitation damage was drastically reduced, probably due to both bubble collapse cushioning and shock wave attenuation....

  8. Research on 3D reconstruction measurement and parameter of cavitation bubble based on stereo vision

    Science.gov (United States)

    Li, Shengyong; Ai, Xiaochuan; Wu, Ronghua; Cao, Jing

    2017-02-01

    The problems caused by the cavitation bubble and caused many adverse effects on the ship propeller, hydraulic machinery and equipment. In order to research the production mechanism of cavitation bubble under different conditions, cavitation bubble zone parameter fine measurement and analysis technology is indispensable, this paper adopts a non-contact measurement method of optical autonomous construction of binocular stereo vision measurement system according to the characteristics of cavitation bubble, the texture features are not clear, transparent and difficult to obtain, 3D imaging measurement of cavitation bubble using composite dynamic lighting, and 3D reconstruction of cavitation bubble region and obtained the characteristics of more accurate parameters, test results show that the cavitation bubble characteristics of the fine technology can obtain and analyze cavitation bubble region and instability.

  9. Apparatus for Changing the Attack Angle of a Cavitator on a Supercavatating Underwater Research Model

    National Research Council Canada - National Science Library

    Nedderman, William H

    2005-01-01

    ... tilt the cavitator tilt plate to a desired angle. Power components are remotely located and accessible to an operator so as to enable an operator to vary the angle of the cavitator tilt plate while the supercavitating underwater research model...

  10. Modeling Unsteady Cavitation Effects and Dynamic Loads in Cryogenic Systems, Phase I

    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 cryogenic systems. Analysis of cavitating...

  11. Experimental Investigation on Cavitating Flow Induced Vibration Characteristics of a Low Specific Speed Centrifugal Pump

    OpenAIRE

    Bo Gao; Pengming Guo; Ning Zhang; Zhong Li; Minguan Yang

    2017-01-01

    Cavitating flow developing in the blade channels is detrimental to the stable operation of centrifugal pumps, so it is essential to detect cavitation and avoid the unexpected results. The present paper concentrates on cavitation induced vibration characteristics, and special attention is laid on vibration energy in low frequency band, 10–500 Hz. The correlation between cavitating evolution and the corresponding vibration energy in 10–500 Hz frequency band is discussed through visualization an...

  12. Numerical modeling of a two-dimensional aerated cavitation in a symmetrical venturi nozzle

    OpenAIRE

    Tomov, P; Khelladi, S; Ravelet, Florent; Sarraf, C; Bakir, F; Giroux, D

    2015-01-01

    National audience; Cavitation is a well-known physical phenomenon occurring in various technical applications. Its coupling with the aeration, is a recent technique, which allows the control of the overall effect of the cavitation. The aeration is achieved by introducing air bubbles into the flow. In order to reveal and explore the behaviour of air in the vicinity of the cavitation regions, the paper is oriented towards the physics of the colliding vapour phase in the presence of cavitation. ...

  13. 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

  14. Measurement on the cavitating vortex shedding behind rectangular obstacles

    International Nuclear Information System (INIS)

    Hegedus, F; Hos, C; Pandula, Z; Kullmann, L

    2010-01-01

    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.

  15. Numerical Calculation on Cavitation Pressure Pulsation in Centrifugal Pump

    Directory of Open Access Journals (Sweden)

    Weidong Shi

    2014-02-01

    Full Text Available 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 suction side of impeller blade near the inlet edge, which is consistent with the low-pressure region distribution. Bubble volume is determined by the growth rate and collapse rate of every bubble in the bubble group. The cavitation degree changes over time with the impeller rotation and the bubble growth and collapse coexist in the impeller flow channels. The main pulsation results from the cyclic and static coupling between the impeller and the tongue, while the fluctuating amplitude is increased by the cavitation.

  16. 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.

  17. Computation of Cavitating Flow in a Francis Hydroturbine

    Science.gov (United States)

    Leonard, Daniel; Lindau, Jay

    2013-11-01

    In an effort to improve cavitation characteristics at off-design conditions, a steady, periodic, multiphase, RANS CFD study of an actual Francis hydroturbine was conducted and compared to experimental results. It is well-known that operating hydroturbines at off-design conditions usually results in the formation of large-scale vaporous cavities. These cavities, and their subsequent collapse, reduce efficiency and cause damage and wear to surfaces. The conventional hydro community has expressed interest in increasing their turbine's operating ranges, improving their efficiencies, and reducing damage and wear to critical turbine components. In this work, mixing planes were used to couple rotating and stationary stages of the turbine which have non-multiple periodicity, and provide a coupled solution for the stay vanes, wicket gates, runner blades, and draft tube. The mixture approach is used to simulate the multiphase flow dynamics, and cavitation models were employed to govern the mass transfer between liquid and gas phases. The solution is compared with experimental results across a range of cavitation numbers which display all the major cavitation features in the machine. Unsteady computations are necessary to capture inherently unsteady cavitation phenomena, such as the precessing vortex rope, and the shedding of bubbles from the wicket gates and their subsequent impingement upon the leading edge of the runner blades. To display these features, preliminary unsteady simulations of the full machine are also presented.

  18. 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.

  19. Imaging manifestations of the cavitation in pulmonary parenchyma of SARS

    International Nuclear Information System (INIS)

    Yuan Chunwang; Zhao Dawei; Wang Wei; Jia Cuiyu; Bai Chunsheng

    2004-01-01

    Objective: To investigate the imaging appearances of cavitation in pulmonary parenchyma and the clinical features of the cases of SARS. Methods: Chest imaging films and clinical data of 180 patients with clinically confirmed SARS were analyzed retrospectively. The imaging manifestations of cavitation and the clinical features of the patients were observed and evaluated. Results: Of 180 patients, cavitations were showed in 5 (2.8%), which were all found through X-ray or CT scanning. Most of them were round or irregular, and had thick wall. The 5 patients all had been in hospital and treated with more dosage antibiotics, antivirus medicines and glucocorticoid for long time, the glucocorticoid was used for 25-65 d, and in the first 10-15 days the dosage was 160-240 mg per day. In hospitalization, one of them had been diagnosed diabetes mellitus, four had increased fasting blood sugar, the counts of white blood cells [(14.1-20.4) x 10 9 /L] increased significantly, the percent of neutrophils might increased also. Meanwhile, there was a continue increase of lactate dehydrogenase (228.00-475.00 U/L), glutamic dehydrogenase (10.08-60.00 U/L) and hydroxybutyrate dehydrogenase (190.00-444.00 U/L) in lab examination. Conclusion: SARS can cause cavitation in pulmonary parenchyma in posterior process of the disease. CT scanning can find the cavitation earlier and accurately, catching the imaging features of them is helpful in differential diagnosis, guiding therapy and estimating prognosis

  20. Cavitation erosion resistance of 13/4 and 21-4-N steels

    Indian Academy of Sciences (India)

    operating efficiency of the turbine. Considering the cost of electrical energy, even a relatively ..... During cavitation erosion, the target material is subjected to very high repeated loading by cavitation ... Due to the repeated attack by cavitation impact wave, the target material undergoes deforma- tion plastically. The hot rolled ...

  1. 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 validation of the cavitation model in EllipSys has been conducted for the cavitating flows on 2D/3D hydrofoils (Shin 2010). Prior to the cavitation simulation, the open-water characteristics of the propellers from the computation are compared with those from the propulsion test for the fully-wetted flows (Li...

  2. Fluid dynamics of acoustic and hydrodynamic cavitation in hydraulic power systems.

    Science.gov (United States)

    Ferrari, A

    2017-03-01

    Cavitation is the transition from a liquid to a vapour phase, due to a drop in pressure to the level of the vapour tension of the fluid. Two kinds of cavitation have been reviewed here: acoustic cavitation and hydrodynamic cavitation. As acoustic cavitation in engineering systems is related to the propagation of waves through a region subjected to liquid vaporization, the available expressions of the sound speed are discussed. One of the main effects of hydrodynamic cavitation in the nozzles and orifices of hydraulic power systems is a reduction in flow permeability. Different discharge coefficient formulae are analysed in this paper: the Reynolds number and the cavitation number result to be the key fluid dynamical parameters for liquid and cavitating flows, respectively. The latest advances in the characterization of different cavitation regimes in a nozzle, as the cavitation number reduces, are presented. The physical cause of choked flows is explained, and an analogy between cavitation and supersonic aerodynamic flows is proposed. The main approaches to cavitation modelling in hydraulic power systems are also reviewed: these are divided into homogeneous-mixture and two-phase models. The homogeneous-mixture models are further subdivided into barotropic and baroclinic models. The advantages and disadvantages of an implementation of the complete Rayleigh-Plesset equation are examined.

  3. Power cavitation-guided blood-brain barrier opening with focused ultrasound and microbubbles

    Science.gov (United States)

    Burgess, M. T.; Apostolakis, I.; Konofagou, E. E.

    2018-03-01

    Image-guided monitoring of microbubble-based focused ultrasound (FUS) therapies relies on the accurate localization of FUS-stimulated microbubble activity (i.e. acoustic cavitation). Passive cavitation imaging with ultrasound arrays can achieve this, but with insufficient spatial resolution. In this study, we address this limitation and perform high-resolution monitoring of acoustic cavitation-mediated blood-brain barrier (BBB) opening with a new technique called power cavitation imaging. By synchronizing the FUS transmit and passive receive acquisition, high-resolution passive cavitation imaging was achieved by using delay and sum beamforming with absolute time delays. Since the axial image resolution is now dependent on the duration of the received acoustic cavitation emission, short pulses of FUS were used to limit its duration. Image sets were acquired at high-frame rates for calculation of power cavitation images analogous to power Doppler imaging. Power cavitation imaging displays the mean intensity of acoustic cavitation over time and was correlated with areas of acoustic cavitation-induced BBB opening. Power cavitation-guided BBB opening with FUS could constitute a standalone system that may not require MRI guidance during the procedure. The same technique can be used for other acoustic cavitation-based FUS therapies, for both safety and guidance.

  4. Numerical Study on Characteristics of 3D Cavitating Hydrofoil

    Directory of Open Access Journals (Sweden)

    Cao Wei

    2015-01-01

    Full Text Available The commercial software ANSYS CFX, APDL and Workbench are applied for modeling the hydrodynamic and structural interactions and characteristics of an elastic hydrofoil by means of a two-way FSI method. The SST (Shear Stress Transport turbulence model and the simplified Rayleigh-Plesset equations are employed for the cavitating flow simulation. Both CFX and APDL solvers are set to be transient. The fluid and solid computational domains are sequentially solved to simulate the interactions between the hydrofoil and the cavitating flow. The results show that the difference in stiffness of common metal materials has trifling effects on hydrofoil performance. But variations in cavitation number and angle of attack will dramatically affect the hydrodynamic and structural interactions and characteristics.

  5. Flow Modelling for partially Cavitating Two-dimensional Hydrofoils

    DEFF Research Database (Denmark)

    Krishnaswamy, Paddy

    2001-01-01

    The present work addresses te computational analysis of partial sheet hydrofoil cavitation in two dimensions. Particular attention is given to the method of simulating the flow at the end of the cavity. A fixed-length partially cavitating panel method is used to predict the height of the re...... of the model and comparing the present calculations with numerical results. The flow around the partially cavitating hydrofoil with a re-entrant jet has also been treated with a viscous/inviscid interactive method. The viscous flow model is based on boundary layer theory applied on the compound foil......, consisting of the union of the cavity and the hydrofoil surface. The change in the flow direction in the cavity closure region is seen to have a slightly adverse effect on the viscous pressure distribution. Otherwise, it is seen that the viscous re-entrant jet solution compares favourably with experimental...

  6. Neuroaxonal Dystrophy and Cavitating Leukoencephalopathy of Chihuahua Dogs.

    Science.gov (United States)

    Degl'Innocenti, Sara; Asiag, Nimrod; Zeira, Offer; Falzone, Cristian; Cantile, Carlo

    2017-09-01

    A novel form of neuroaxonal dystrophy is described in 3 Chihuahua pups, 2 of which were from the same litter. It was characterized not only by accumulation of numerous and widely distributed axonal swellings (spheroids) but also by a severe cavitating leukoencephalopathy. The dogs presented with progressive neurological signs, including gait abnormalities and postural reaction deficits. Magnetic resonance images and gross examination at necropsy revealed dilation of lateral ventricles and cerebral atrophy, accompanied by cavitation of the subcortical white matter. Histopathologically, severe axonal degeneration with formation of large spheroids was found in the cerebral and cerebellar white matter, thalamus, and brainstem nuclei. Small-caliber spheroids were observed in the cerebral and cerebellar gray matter. The telencephalic white matter had severe myelin loss and cavitation with relative sparing of the U-fibers. Different from previously reported cases of canine neuroaxonal dystrophy, in these Chihuahuas the spheroid distribution predominantly involved the white matter with secondary severe leukoencephalopathy.

  7. Unraveling the Anomalous Grain Size Dependence of Cavitation

    Science.gov (United States)

    Wilkerson, J. W.; Ramesh, K. T.

    2016-11-01

    Experimental studies have identified an anomalous grain size dependence associated with the critical tensile pressure that a metal may sustain before catastrophic failure by cavitation processes. Here we derive the first quantitative theory (and its associated closed-form solution) capable of explaining this phenomena. The theory agrees well with experimental measurements and atomistic calculations over a very wide range of conditions. Utilizing this theory, we are able to map out three distinct regimes in which the critical tensile pressure for cavitation failure (i) increases with decreasing grain size in accordance with conventional wisdom, (ii) nonintuitively decreases with decreasing grain size, and (iii) is independent of grain size. The theory also predicts microscopic signatures of the cavitation process which agree with available data.

  8. The dynamics of cavity clusters in ultrasonic (vibratory) cavitation erosion

    DEFF Research Database (Denmark)

    Hansson, I.; Mørch, Knud Aage

    1980-01-01

    The erosion of solids caused by cavitating liquids is a result of the concerted collapse of clusters of cavities. In vibratory cavitation equipment the clusters grow and collapse adjacent to a solid surface and are typically of hemispherical or cylindrical form. In the present paper the collapse...... process of these clusters is described and the collapse equations are developed and solved. The theoretical results are compared with results from high-speed photography of the clusters and with the initial stages of cavitation erosion on metal specimens. Experimental and theoretical results show...... the ambient pressure. Therefore the collapse velocity of the individual cavities increases towards the cluster center, which explains that the erosion, being caused by the individual cavities, occurs predominantly in this region. Likewise, the pressure increase at the cluster boundary explains why materials...

  9. 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.

  10. 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.

  11. 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.

  12. 3D analyses of cavitation instabilities accounting for plastic anisotropy

    DEFF Research Database (Denmark)

    Legarth, Brian Nyvang; Tvergaard, Viggo

    2010-01-01

    Full three dimensional cell model analyses are carried out for a solid containing a single small void, in order to determine the critical stress levels for the occurrence of cavitation instabilities. The material models applied are elastic‐viscoplastic, with a small rate‐hardening exponent...... that the quasi‐static solution is well approximated. A special procedure is used to strongly reduce the loading rate a little before the instability occurs. It is found that plastic anisotropy has a significant effect on the level of the critical stress for cavitation instabilities....

  13. Cavitation instabilities between fibres in a metal matrix composite

    DEFF Research Database (Denmark)

    Tvergaard, Viggo

    2016-01-01

    induced by bonding to the ceramics that only show elastic deformation. In an MMC the stress state in the metal matrix is highly non-uniform, varying between regions where shear stresses are dominant and regions where hydrostatic tension is strong. An Al–SiC whisker composite with a periodic pattern......Short fibre reinforced metal matrix composites (MMC) are studied here to investigate the possibility that a cavitation instability can develop in the metal matrix. The high stress levels needed for a cavitation instability may occur in metal–ceramic systems due to the constraint on plastic flow...

  14. 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 from...

  15. 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.

  16. Spatial distribution of cavitation-shock-pressure around a jet-flow gate-valve

    International Nuclear Information System (INIS)

    Oba, Risaburo; Takayama, Kazuyoshi; Ito, Yukio; Miyakura, Hideto; Nozaki, Satoru; Ishige, Tadashi; Sonoda, Shuji; Sakamoto, Kenji.

    1987-01-01

    To make clear the mechanism of cavitation erosion, the spatial distribution of cavitation shock pressures were quantitatively measured by a pressure sensitive sheet in the 1/10 scale model of a jet-flow gate-valve, for various valve-openings and cavitation numbers. The dynamic pressure response of the sheet was corrected by the shock wave generated from detonation explosives. It is made clear that the erosive shock pressures are distributed in a limited part of the whole cavitation region, and the safety region without the fatal cavitation erosion is defined. (author)

  17. Effect of austempering temperature on cavitation behaviour of unalloyed ADI material

    Energy Technology Data Exchange (ETDEWEB)

    Dojcinovic, Marina [University of Belgrade, Faculty of Technology and Metallurgy, Karnegijeva 4, Belgrade (Serbia); Eric, Olivera [Innovation Centre, Faculty of Mechanical Engineering, University of Belgrade, Kraljice Marije 16, Belgrade (Serbia); Rajnovic, Dragan; Sidjanin, Leposava [Department of Production Engineering, Faculty of Technical Sciences, University of Novi Sad, Trg Dositeja Obradovića 6, Novi Sad (Serbia); Balos, Sebastian, E-mail: sebab@uns.ac.rs [Department of Production Engineering, Faculty of Technical Sciences, University of Novi Sad, Trg Dositeja Obradovića 6, Novi Sad (Serbia)

    2013-08-15

    This paper provides an in-depth study and description of cavitation damage and microstructural changes in two types of unalloyed austempered ductile iron (ADI). ADI materials used were austempered at 300 and 400 °C having ausferrite microstructure with 16 and 31.4% of retained austenite, respectively. Metallographic examination was carried out to study the morphology of their cavitation-damaged surfaces. Cavitation damage was initiated at graphite nodules as well as in the interface between a graphite nodule and an ausferrite matrix. Furthermore, microcracking and ferrite/retained austenite morphology were proved to be of great importance for cavitation resistance. Mass loss rate revealed that ADI austempered at 400 °C has a higher cavitation resistance in water than ADI austempered at 300 °C. A higher amount of retained austenite in ADI austempered at 400 °C played an important role in increasing cavitation resistance. The good cavitation behaviour of ADI austempered at 400 °C was due to the matrix hardening by stress assisted phase transformation of retained austenite into martensite (SATRAM) phenomenon, as shown by X-ray diffraction analysis. - Highlights: • Cavitation rate of two ADI materials was tested. • ADI material with a lower hardness has had a lower cavitation rate. • The main reason is microstructural transformations during cavitation. • SATRAM phenomenon increases cavitation resistance.

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

    Science.gov (United States)

    Shin, K. W.; Andersen, P.

    2015-12-01

    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 reference propeller. For the reference propeller, sheet cavitation extends over a whole chord length in the hull wake peak. As the blade gets out of the wake peak, the rear part of sheet cavity is detached in a form of cloud cavitation. For the reference propeller, the tip pitch reduction from the maximum is about 35%. When decreasing the tip pitch reduction to 10%, tip vortex cavitation is formed and cloud cavitation is significantly weakened. When increasing the tip pitch reduction to 60%, sheet cavitation slightly moves to inner radii and cloud cavitation grows larger.

  19. Statistical characteristics of suction pressure signals for a centrifugal pump under cavitating conditions

    Science.gov (United States)

    Li, Xiaojun; Yu, Benxu; Ji, Yucheng; Lu, Jiaxin; Yuan, Shouqi

    2017-02-01

    Centrifugal pumps are often used in operating conditions where they can be susceptible to premature failure. The cavitation phenomenon is a common fault in centrifugal pumps and is associated with undesired effects. Among the numerous cavitation detection methods, the measurement of suction pressure fluctuation is one of the most used methods to detect or diagnose the degree of cavitation in a centrifugal pump. In this paper, a closed loop was established to investigate the pump cavitation phenomenon, the statistical parameters for PDF (Probability Density Function), Variance and RMS (Root Mean Square) were used to analyze the relationship between the cavitation performance and the suction pressure signals during the development of cavitation. It is found that the statistical parameters used in this research are able to capture critical cavitation condition and cavitation breakdown condition, whereas difficult for the detection of incipient cavitation in the pump. At part-load conditions, the pressure fluctuations at the impeller inlet show more complexity than the best efficiency point (BEP). Amplitude of PDF values of suction pressure increased steeply when the flow rate dropped to 40 m3/h (the design flow rate was 60 m3/h). One possible reason is that the flow structure in the impeller channel promotes an increase of the cavitation intensity when the flow rate is reduced to a certain degree. This shows that it is necessary to find the relationship between the cavitation instabilities and flow instabilities when centrifugal pumps operate under part-load flow rates.

  20. Transition of cavitating flow to supercavitation within Venturi nozzle – hysteresis investigation

    Directory of Open Access Journals (Sweden)

    Jiří Kozák

    2017-01-01

    Full Text Available Cavitation is usually considered as undesirable phenomena. On the other hand, it can be utilized in many applications. One of the technical applications is using cavitation in water treatment, where hydrodynamic cavitation seems to be effective way how to reduce cyanobacteria within large bulks of water. The main scope of this paper is investigation of the cavitation within Venturi nozzle during the transition from fully developed cavitation to supercavitation regime and vice versa. Dynamics of cavitation was investigated using experimental data of pressure pulsations and analysis of high speed videos, where FFT of the pixel intensity and Proper Orthogonal Decomposition (POD of the records were done to identify dominant frequencies connected with the presence of cavitation. The methodology of the high speed (HS records semiautomated analysis using the FFT was described. Obtained results were correlated and above that the possible presence of hysteresis was discussed.

  1. Microleakage of cavit in varnish-lined, matrix-supported endodontic access preparations.

    Science.gov (United States)

    Iqbal, M K; Saad, N A

    1998-07-01

    The effect of the application of a matrix band and the use of cavity varnish on the microleakage of Cavit in endodontic access preparations was investigated. Sixty human upper premolars were divided into six groups of ten specimens each. Access cavities with proximal extensions were prepared and filled with 1, Cavit only; 2, Cavit after application of varnish; 3, Cavit with the use of a matrix band; 4, Cavit with a matrix band and varnish; 5, incremental deposition of Cavit with the use of a matrix band and varnish; and 6, gutta percha stopping. The specimens were placed in 2% methylene blue dye, thermocycled, and evaluated for both proximal and occlusal linear leakage. The experimental group in which Cavit was incrementally deposited in varnish-lined and matrix-supported cavities exhibited significantly (p < 0.05) less proximal microleakage than those groups in which cavities were filled without the application of both a matrix band and a cavity varnish.

  2. 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

  3. Interactions of inertial cavitation bubbles with stratum corneum lipid bilayers during low-frequency sonophoresis.

    Science.gov (United States)

    Tezel, Ahmet; Mitragotri, Samir

    2003-12-01

    Interactions of acoustic cavitation bubbles with biological tissues play an important role in biomedical applications of ultrasound. Acoustic cavitation plays a particularly important role in enhancing transdermal transport of macromolecules, thereby offering a noninvasive mode of drug delivery (sonophoresis). Ultrasound-enhanced transdermal transport is mediated by inertial cavitation, where collapses of cavitation bubbles microscopically disrupt the lipid bilayers of the stratum corneum. In this study, we describe a theoretical analysis of the interactions of cavitation bubbles with the stratum corneum lipid bilayers. Three modes of bubble-stratum corneum interactions including shock wave emission, microjet penetration into the stratum corneum, and impact of microjet on the stratum corneum are considered. By relating the mechanical effects of these events on the stratum corneum structure, the relationship between the number of cavitation events and collapse pressures with experimentally measured increase in skin permeability was established. Theoretical predictions were compared to experimentally measured parameters of cavitation events.

  4. Propeller Cavitation in Non-Uniform Flow and Correlation with the Near Pressure Field

    Directory of Open Access Journals (Sweden)

    Francisco Alves Pereira

    2016-11-01

    Full Text Available An experimental study is carried out in a cavitation tunnel on a propeller operating downstream of a non-uniform wake. The goal of this work is to establish quantitative correlations between the near pressure field and the cavitation pattern that takes place on the propeller blades. The pressure field is measured at the walls of the test section and in the near wake of the propeller and is combined with quantitative high-speed image recording of the cavitation pattern. Through harmonic analysis of the pressure data and image processing techniques that allow retrieving the cavitation extension and volume, we discuss the potential sources that generate the pressure fluctuations. Time correlations are unambiguously established between pressure peak fluctuations and cavitation collapse events, based on the Rayleigh collapse time. Finally, we design a model to predict the cavitation-induced pressure fluctuations from the derivation of the cavitation volume acceleration. A remarkable agreement is observed with the actual pressure field.

  5. Peripapillary intrachoroidal cavitations. The Beijing eye study.

    Directory of Open Access Journals (Sweden)

    Qi Sheng You

    Full Text Available To assess prevalence, size and location of peripapillary intrachoroidal cavitations (PICCs and their associations in a population-based sample. .The population-based Beijing Eye Study 2011 included 3468 individuals with a mean age of 64.6 ± 9.8 years (range:50-93 years. A detailed ophthalmic examination included enhanced depth imaging of the choroid by spectral-domain optical coherence tomography and fundus photography. PICCs were defined as triangular thickening of the choroid with the base at the optic disc border and a distance between Bruch's membrane and sclera of ≥ 200 μm. Parapapillary large choroidal vessels were excluded.Out of 94 subjects with high myopia (refractive error 26.5mm in right eyes, OCT images were available for 89 (94.7% participants. A PICC was detected in 15 out of these 89 highly myopic subjects (prevalence:16.9 ± 4.0% and in none of hyperopic, emmetropic or medium myopic subgroups each consisting of 100 randomly selected subjects. Mean PICC width was 4.2 ± 2.3 hours (30° of disc circumference and mean length was 1363 ± 384 μm. PICCs were located most frequently (40% at the inferior disc border. On fundus photos, a typical yellow-orange lesion was found in 8 (53% eyes with PICCs. In binary regression analysis, presence of PICCs was significantly associated with optic disc tilting (P=0.04 and presence of posterior staphylomata (P=0.046.Prevalence of PICCs in the adult Chinese population was 16.9 ± 4.0% in the highly myopic group, with no PICCs detected in non-highly myopic eyes. PICCs were located most frequently at the inferior optic disc border. Only half of the PICCs detected on OCT images showed a yellow-orange lesion on fundus photos. Presence of PICC was significantly associated only with an increased optic disc tilting and presence of posterior staphylomata, while it was not associated with axial length, refractive error or other ocular or systemic parameters.

  6. Modeling and computation of cavitation in vortical flow

    International Nuclear Information System (INIS)

    Abdel-Maksoud, M.; Haenel, D.; Lantermann, U.

    2010-01-01

    The paper presents an investigation of Euler-Lagrangian methods for cavitating two-phase flows. The Euler-Euler methods, widely used for simulations of cavitating flows in ship technology, perform well in regions of moderate flow changes but fail in zones of strong, vortical flow. Reasons are the strong approximations of cavitation models in the Euler concept. Alternatively, Euler-Lagrangian concepts enable more detailed formulations for transport, dynamics and acoustic of discrete vapor bubbles. Test calculations are performed to study the influence of different parameters in the equations of motion and in the Rayleigh-Plesset equation for bubble dynamics. Results confirm that only Lagrangian models are able to describe correctly the bubble behavior in vortices, while Eulerian results deviate strongly. Lagrangian formulations enable additionally the determination of acoustic pressure of cavitation noise. Two-way coupling between the phases is required for large regions of the vapor phase. A new coupling concept between continuous fluid flow and discrete bubble phase is developed and demonstrated for flow through a nozzle. However, the iterative coupling between the phases via volume fractions is computationally expensive and should therefore be applied only in regions where Eulerian treatment fails. A corresponding local concept for combination with an Euler-Euler method is outlined and is in progress.

  7. Relating xylem cavitation to gas exchange in cotton

    Science.gov (United States)

    Acoustic emissions (AEs) from xylem cavitation events are characteristic of transpiration processes. Though a body of work using AE exists with a large number of species, cotton and other agronomically important crops have either not been investigated, or limited information exists. The objective of...

  8. Cavitation in microscale confinement: new concept of mild brain injury.

    Science.gov (United States)

    Akhatov, Iskander; Wang, Cheng; Ziejewski, Mariusz

    2007-11-01

    The present effort is to understand the possible damages in brain caused by the cavitation bubbles generated when the impacting shock waves passing through human head. In order to build an adequate mathematical model of this phenomenon, one should be able to model inception and dynamics of cavitation in biological liquid confined in macroscale or microscale space between solids, elastic surfaces, or membranes -- biological tissues, in general. A more in-depth understanding of the outcomes from the dynamic response of brain tissue, including the location, size, and geometry of the damage site, will be of assistance to physicians in the properly interpreting the neurodiagnostic results. In the present study it is stated that in micro scale confinement bubble collapse can not cause any damage. This is due to the fact that collapse is damped by viscous dissipation in micro channels. Otherwise, the bubble inception itself may cause damage. It is shown that cavitation inception in micro scale may happen for much higher tensions than in infinite liquid. At such a strong tension substantial amount of elastic energy is stored in liquid. This energy being released during cavitation inception generates `recoil pressure' that may be high enough to damage biological tissue.

  9. Numerical modelling of unsteady 2D sheet cavitation

    NARCIS (Netherlands)

    de Lange, D.F.; de Bruin, G.J.; van Wijngaarden, L.; van Wijngaarden, L.

    1996-01-01

    Unsteady 2D sheet cavitation has been calculated by a BEM. Cubics are used to represent various quantities like the potential on the wet part of the profile, the normal velocity on the sheet, the geometry of the profile and the sheet. The growing cavity sheet, the re-entrant jet and the sheet

  10. Prediction of tip vortex cavitation for ship propellers

    NARCIS (Netherlands)

    Oprea, A.I.

    2013-01-01

    An open propeller is the conventional device providing thrust for ships. Due to its working principles, regions with low pressure are formed on its blades specifically at the leading edge and in the tip region. If this pressure is becoming lower than the vapor pressure, the cavitation phenomenon is

  11. Relationship between cavitation and water uptake in rose stems

    NARCIS (Netherlands)

    Doorn, van W.G.; Suiro, V.

    1996-01-01

    Cavitation in rose stems (Rosa hybrida L.) was assessed in both intact plants and excised flowers, by measurement of ultrasonic acoustic emissions at the stem surface and determination of the air-conductivity of 2.5-cm segments that were attached at one end to air at low pressure (0.01 MPa). On

  12. Condensation and cavitation in water and water mixtures

    Czech Academy of Sciences Publication Activity Database

    Maršík, František; Delale, C. F.; Sedlář, M.

    2003-01-01

    Roč. 24, č. 1 (2003), s. 3-16 ISSN 1231-0956 R&D Projects: GA AV ČR IBS2076003; GA ČR GA101/02/0364 Institutional research plan: CEZ:AV0Z2076919 Keywords : condensation * cavitation * water mixtures Subject RIV: BJ - Thermodynamics

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

    Science.gov (United States)

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

    2015-10-06

    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.

  14. Cavitation inception on microparticles: a self-propelled particle accelerator

    NARCIS (Netherlands)

    Arora, M.; Ohl, C.D.; 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,

  15. Transfert convectif dans les cavites poreuses soumises a un champ ...

    African Journals Online (AJOL)

    un champ magnétique transversal sur la convection naturelle bidimensionnelle en milieu poreux confiné dans une cavité horizontale. Le milieu poreux, de grande extension est chauffé isothermiquement par les côtés tandis que ses parois ...

  16. Experimental measurements of the cavitating flow after horizontal water entry

    Science.gov (United States)

    Tat Nguyen, Thang; Hai, Duong Ngoc; Quang Thai, Nguyen; Phuong, Truong Thi

    2017-10-01

    Water-entry cavitating flow is of considerable importance in underwater high-speed applications. That is because of the drag-reduction effect that concerns the presence of a cavity around moving objects. Though the study of the flow has long been carried out, little data are documented in literature so far. Besides, currently, in the case of unsteady flow, experimental measurements of some flow parameters such as the cavity pressure still encounter difficulties. Hence continuing research efforts are of important significance. The objective of this study is to investigate experimentally the unsteady cavitating flow after the horizontal water entry of projectiles. An experimental apparatus has been developed. Qualitative and quantitative optical visualizations of the flow have been carried out by using high-speed videography. Digital image processing has been applied to analyzing the recorded flow images. Based on the known correlations between the ellipsoidal super-cavity’s size and the corresponding cavitation number, the cavity pressure has been measured by utilizing the data of image processing. A comparison between the partial- and super-cavitating flow regimes is reported. The received results can be useful for the design of high-speed underwater projectiles.

  17. Pressure Transient Model of Water-Hydraulic Pipelines with Cavitation

    Directory of Open Access Journals (Sweden)

    Dan Jiang

    2018-03-01

    Full Text Available Transient pressure investigation of water-hydraulic pipelines is a challenge in the fluid transmission field, since the flow continuity equation and momentum equation are partial differential, and the vaporous cavitation has high dynamics; the frictional force caused by fluid viscosity is especially uncertain. In this study, due to the different transient pressure dynamics in upstream and downstream pipelines, the finite difference method (FDM is adopted to handle pressure transients with and without cavitation, as well as steady friction and frequency-dependent unsteady friction. Different from the traditional method of characteristics (MOC, the FDM is advantageous in terms of the simple and convenient computation. Furthermore, the mechanism of cavitation growth and collapse are captured both upstream and downstream of the water-hydraulic pipeline, i.e., the cavitation start time, the end time, the duration, the maximum volume, and the corresponding time points. By referring to the experimental results of two previous works, the comparative simulation results of two computation methods are verified in experimental water-hydraulic pipelines, which indicates that the finite difference method shows better data consistency than the MOC.

  18. Cavitation, subcooled boiling and a measuring method developed at ENEA

    International Nuclear Information System (INIS)

    Tirelli, D.

    1988-01-01

    A brief description of cavitation and subcooled boiling is reported; their effects, measuring methods, operating limits and prescribed standards are described. The whole, to better clarify the usefulness and the importance of a measuring instrument developed at ENEA, to study the above phenomena

  19. Effects of viscoelasticity on cavitation in drag reducing fluids

    Science.gov (United States)

    Ting, R. Y.

    1974-01-01

    To study cavitation inception in polymer solutions, a blow-down water tunnel with short running times was used. Tests were made using 1/4 and 1/2 inch diameter models of hemispherical-nose cylinders. To accurately detect the inception of cavitation, a reliable technique was developed using a continuously operating He-Ne gas laser. The laser beam was adjusted to grazing incidence with the model at the minimum pressure point where cavitation inception was to be expected. A sensitive photocell was placed at ninety degrees to detect the beam. As incipient cavitation occurred, the bubbles caused scattering of the laser beam which was picked up by the photocell. Static pressure near the model in the working section of the tunnel was measured using a solid-state pressure pick-up. The signals from the photocell and the pressure pick-up were recorded on an oscillograph. Velocity field visualization was achieved using one microsecond duration light pulses scattered by small polystryrene latex spheres in the flow.

  20. Sugars from woody tissue photosynthesis reduce xylem vulnerability to cavitation.

    Science.gov (United States)

    De Baerdemaeker, Niels J F; Salomón, Roberto Luis; De Roo, Linus; Steppe, Kathy

    2017-11-01

    Reassimilation of internal CO 2 via woody tissue photosynthesis has a substantial effect on tree carbon income and wood production. However, little is known about its role in xylem vulnerability to cavitation and its implications in drought-driven tree mortality. Young trees of Populus nigra were subjected to light exclusion at the branch and stem levels. After 40 d, measurements of xylem water potential, diameter variation and acoustic emission (AE) were performed in detached branches to obtain acoustic vulnerability curves to cavitation following bench-top dehydration. Acoustic vulnerability curves and derived AE 50 values (i.e. water potential at which 50% of cavitation-related acoustic emissions occur) differed significantly between light-excluded and control branches (AE 50,light-excluded  = -1.00 ± 0.13 MPa; AE 50,control  = -1.45 ± 0.09 MPa; P = 0.007) denoting higher vulnerability to cavitation in light-excluded trees. Woody tissue photosynthesis represents an alternative and immediate source of nonstructural carbohydrates (NSC) that confers lower xylem vulnerability to cavitation via sugar-mediated mechanisms. Embolism repair and xylem structural changes could not explain this observation as the amount of cumulative AE and basic wood density did not differ between treatments. We suggest that woody tissue assimilates might play a role in the synthesis of xylem surfactants for nanobubble stabilization under tension. © 2017 The Authors. New Phytologist © 2017 New Phytologist Trust.

  1. 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. Copyright © 2012 Elsevier B.V. All rights reserved.

  2. Solution to valve failures at Braidwood induced by service water cavitation

    International Nuclear Information System (INIS)

    Ozol, J.; Schipiour, B.K.; Wix, J.E.

    1994-01-01

    Control valves throttle fluid from a high pressure to a lower pressure. On water systems, this throttling process may be accompanied by cavitation, which induces valve noise, vibration, and material damage. Extensive and significant caviation erosion has been experienced the last 10 years in most service water control valve bodies, downstream flanges, and reducers at Braidwood Station. There have been 40 different and distinct cavitation-induced failures in the service water system at Braidwood Station. These failures have created significant costs and continue to be a lingering source of operational maintenance costs to the Commonwealth Edison Company, which is incurring significant financial losses. It should be noted that almost all service water control valves experience some cavitation effects. Cavitation and cavitation damage are complex and elusive phenomena for which no single, simple analytical model exists. The purpose of this paper is to explain features of service water control valve cavitation failures and some of the solutions used by Commonwealth Edison at their six nuclear stations. The paper discusses the following: (1) Braidwood's history of erosion from cavitation; (2) Erosion-corrosion considerations; (3) The Instrument Society of America's valve sizing equations and how they relate to cavitation; (4) Methods to eliminate cavitation; (5) Corrective actions and practical approaches used by Commonwealth Edison to eliminate cavitation

  3. Numerical investigations on cavitating flows with thermodynamic effects in a diffuser-type centrifugal pump

    Energy Technology Data Exchange (ETDEWEB)

    Xuelin, Tang Xue; Liyuan, Bian; Fujun, Wang; Xiaoqin, Lin; Man, Hao [China Agricultural University, Beijing (China)

    2013-06-15

    A cavitation model with thermodynamic effects for cavitating flows in a diffuser-type centrifugal pump is developed based on the bubble two-phase flow model. The proposed cavitation model includes mass, momentum, and energy transportations according to the thermodynamic mechanism of cavitation. Numerical simulations are conducted inside the entire passage of the centrifugal pump by using the proposed cavitation model and the renormalization group-based k - ε turbulent model coupled with the energy transportation equation. By using the commercial computational fluid dynamics software FLUENT 6.3, we have shown that the predicted performance characteristics of the pump, as well as the pressure, vapor, and density distributions in the impeller, agree well with that calculated by the full cavitation model. Simulation results show that cavitation initially occurs slightly behind the inlet of the blade suction surface, i.e., the area with maximum vapor concentration and minimum pressure. The predicted temperature field shows that the reduction in temperature restrains the growth of cavitating bubbles. Therefore, the thermodynamic effect should be treated as a necessary factor in cavitation models. Comparison results validate the efficiency and accuracy of the numerical technique in simulating cavitation flows in centrifugal pumps.

  4. Comparative CFD Investigation on the Performance of a New Family of Super-Cavitating Hydrofoils

    Science.gov (United States)

    Brizzolara, S.; Bonfiglio, L.

    2015-12-01

    We present a CFD characterization of a new type of super-cavitating hydrofoil section designed to have optimal performance both in super-cavitating conditions and in sub-cavitating conditions (including transitional regime). The basic concepts of the new profile family are first introduced. Lift, drag and cavity shapes at different cavitation numbers are calculated for a new foil and compared with those of conventional sub-cavitating and super-cavitating profiles. Numerical calculations confirm the superior characteristics of the new hydrofoil family, which is able to attain high lift and efficiency both in sub-cavitating and super-cavitating conditions. Numerical calculations are based on a multi-phase fully turbulent URANSE solver with a bubble dynamic cavitation model to follow the generation and evaporation of the vapor phase. The new profile family, initially devised for ultra-high speed hydrofoil crafts, may result useful for diverse applications such as super-cavitating or surface-piercing propellers or high-speed sailing boats.

  5. 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.

  6. Numerical investigations on cavitating flows with thermodynamic effects in a diffuser-type centrifugal pump

    International Nuclear Information System (INIS)

    Xuelin, Tang Xue; Liyuan, Bian; Fujun, Wang; Xiaoqin, Lin; Man, Hao

    2013-01-01

    A cavitation model with thermodynamic effects for cavitating flows in a diffuser-type centrifugal pump is developed based on the bubble two-phase flow model. The proposed cavitation model includes mass, momentum, and energy transportations according to the thermodynamic mechanism of cavitation. Numerical simulations are conducted inside the entire passage of the centrifugal pump by using the proposed cavitation model and the renormalization group-based k - ε turbulent model coupled with the energy transportation equation. By using the commercial computational fluid dynamics software FLUENT 6.3, we have shown that the predicted performance characteristics of the pump, as well as the pressure, vapor, and density distributions in the impeller, agree well with that calculated by the full cavitation model. Simulation results show that cavitation initially occurs slightly behind the inlet of the blade suction surface, i.e., the area with maximum vapor concentration and minimum pressure. The predicted temperature field shows that the reduction in temperature restrains the growth of cavitating bubbles. Therefore, the thermodynamic effect should be treated as a necessary factor in cavitation models. Comparison results validate the efficiency and accuracy of the numerical technique in simulating cavitation flows in centrifugal pumps.

  7. Ultrahigh-Speed Dynamics of Micrometer-Scale Inertial Cavitation from NanoparticlesUltrahigh-Speed Dynamics of Micrometer-Scale Inertial Cavitation from Nanoparticles

    NARCIS (Netherlands)

    Kwan, J.J.; Lajoinie, Guillaume Pierre Rene; de Jong, N.; Stride, E.; Versluis, Michel; Coussios, C.C.

    2016-01-01

    Direct imaging of cavitation from solid nanoparticles has been a challenge due to the combined nanosized length and time scales involved. We report on high-speed microscopic imaging of inertial cavitation from gas trapped on nanoparticles with a tunable hemispherical depression (nanocups) at

  8. Assessment of non-cavitated and cavitated carious lesions among 12- to 15-year-old government and private school children in Pune, Maharashtra, India.

    Science.gov (United States)

    Machale, Priyanka S; Hegde-Shetiya, Sahana; Shirahatti, Ravi; Agarwal, Deept

    2014-01-01

    The present cross-sectional study was conducted to assess and compare the mean number of non-cavitated (initial lesions, IL) and cavitated carious lesions (WHO criteria) per child in the permanent dentition and to correlate it with the plaque index among 12- to 15-year-old government and private school children. 481 schoolchildren aged 12-15 years were selected randomly by multistage random sampling from two government and two private schools. Demographic details were collected at the time of examination. Baseline plaque scores were recorded using the Silness and Löe plaque index. Immediately after brushing and drying the teeth, cavitated lesions were recorded based on WHO recommendations and non-cavitated lesions were recorded using the IL criteria of Nyvad et al and Fyffe et al. The mean number of surfaces with cavitated and non-cavitated lesions for government school children was 2.13 ± 2.98 and 3.21 ± 2.97, respectively, and 1.24 ± 1.86 and 3.08 ± 2.33 for private school children, respectively. WHO + IL surfaces among private school children were 4.33 ± 3.48 and in government school children 5.35 ± 4.45. There was a positive correlation of plaque score with IL (r = 0.63) and WHO+IL (r = 0.73). Non-cavitated lesions are about twice as common as cavitated carious lesions in school children. Government school children had a higher number of cavitated and non-cavitated carious lesions when compared with private school children.

  9. Effect of ultrasonic cavitation on measurement of sound pressure using hydrophone

    Science.gov (United States)

    Thanh Nguyen, Tam; Asakura, Yoshiyuki; Okada, Nagaya; Koda, Shinobu; Yasuda, Keiji

    2017-07-01

    Effect of ultrasonic cavitation on sound pressure at the fundamental, second harmonic, and first ultraharmonic frequencies was investigated from low to high ultrasonic intensities. The driving frequencies were 22, 304, and 488 kHz. Sound pressure was measured using a needle-type hydrophone and ultrasonic cavitation was estimated from the broadband integrated pressure (BIP). With increasing square root of electric power applied to a transducer, the sound pressure at the fundamental frequency linearly increased initially, dropped at approximately the electric power of cavitation inception, and afterward increased again. The sound pressure at the second harmonic frequency was detected just below the electric power of cavitation inception. The first ultraharmonic component appeared at around the electric power of cavitation inception at 304 and 488 kHz. However, at 22 kHz, the first ultraharmonic component appeared at a higher electric power than that of cavitation inception.

  10. Porous resins as a cavitation enhancer for low-frequency sonophoresis.

    Science.gov (United States)

    Terahara, Takaaki; Mitragotri, Samir; Langer, Robert

    2002-03-01

    The application of low-frequency ultrasound enhances drug transport through the skin, a phenomenon referred to as low-frequency sonophoresis. This enhancement is mediated through cavitation, the formation and collapse of gaseous bubbles. We hypothesized that the efficacy of low-frequency sonophoresis can be significantly enhanced by provision of nuclei for cavitation. In this study, we used two porous resins, Diaion HP20 and Diaion HP2MG (2MG), as cavitation nuclei. We measured the effect of these resins on cavitation using pitting of aluminum foil. 2MG showed a higher efficacy in enhancing cavitation compared with Diaion HP20. 2MG was also effective in enhancing transdermal mannitol transport. These results confirm that the addition of cavitation nuclei such as porous resins further increases the effect of low-frequency ultrasound on skin permeability. Copyright 2002 Wiley-Liss, Inc. and the American Pharmaceutical Association.

  11. Cavitation in liquid cryogens. 4: Combined correlations for venturi, hydrofoil, ogives, and pumps

    Science.gov (United States)

    Hord, J.

    1974-01-01

    The results of a series of experimental and analytical cavitation studies are presented. Cross-correlation is performed of the developed cavity data for a venturi, a hydrofoil and three scaled ogives. The new correlating parameter, MTWO, improves data correlation for these stationary bodies and for pumping equipment. Existing techniques for predicting the cavitating performance of pumping machinery were extended to include variations in flow coefficient, cavitation parameter, and equipment geometry. The new predictive formulations hold promise as a design tool and universal method for correlating pumping machinery performance. Application of these predictive formulas requires prescribed cavitation test data or an independent method of estimating the cavitation parameter for each pump. The latter would permit prediction of performance without testing; potential methods for evaluating the cavitation parameter prior to testing are suggested.

  12. 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.

  13. Simultaneous pressure measurement and high-speed photography study of cavitation in a dynamically loaded journal bearing

    Science.gov (United States)

    Sun, D. C.; Brewe, David E.; Abel, Philip B.

    1994-01-01

    Cavitation of the oil film in a dynamically loaded journal bearing was studied using high-speed photography and pressure measurement simultaneously. Comparison of the visual and pressure data provided considerable insight into the occurrence and nonoccurrence of cavitation. It was found that (1) for the submerged journal bearing, cavitation typically occurred in the form of one bubble with the pressure in the cavitation bubble close to the absolute zero; and (2) for cavitation-producing operating conditions, cavitation did not always occur; with the oil film then supporting a tensile stress.

  14. An experimental investigation of artificial supercavitation generated by air injection behind disk-shaped cavitators

    OpenAIRE

    Byoung-Kwon Ahn; So-Won Jeong; Ji-Hye Kim; Siyao Shao; Jiarong Hong; Roger E.A. Arndt

    2017-01-01

    In this paper, we investigated physical characteristics of an artificial supercavity generated behind an axisymmetric cavitator. Experiments for the same model were carried out at two different cavitation tunnels of the Chungnam National University and the University of Minnesota, and the results were compared and verified with each other. We measured pressures inside the cavity and observed the cavity formation by using a high-speed camera. Cavitation parameters were evaluated in considering...

  15. The Investigation of the Cavitation Phenomenon in the Laval Nozzle with Full and Partial Surface Wetting

    Directory of Open Access Journals (Sweden)

    Jablonská Jana

    2017-04-01

    Full Text Available The article deals with the cavitation phenomenon affected by full and partial wetting of the wall. For the numerical computation of flow in the Laval nozzle the Schnerr-Sauer cavitation model was tested and was used for cavitation research of flow within the nozzle considering partial surface wetting. The coefficient of wetting for various materials was determined using experimental, theoretical and numerical methods of fluid flow due to partial surface wetting.

  16. Cavitation optimization for a centrifugal pump impeller by using orthogonal design of experiment

    Science.gov (United States)

    Pei, Ji; Yin, Tingyun; Yuan, Shouqi; Wang, Wenjie; Wang, Jiabin

    2017-01-01

    Cavitation is one of the most important performance of centrifugal pumps. However, the current optimization works of centrifugal pump are mostly focusing on hydraulic efficiency only, which may result in poor cavitation performance. Therefore, it is necessary to find an appropriate solution to improve cavitation performance with acceptable efficiency. In this paper, to improve the cavitation performance of a centrifugal pump with a vaned diffuser, the influence of impeller geometric parameters on the cavitation of the pump is investigated using the orthogonal design of experiment (DOE) based on computational fluid dynamics. The impeller inlet diameter D 1, inlet incidence angle Δ β, and blade wrap angle φ are selected as the main impeller geometric parameters and the orthogonal experiment of L9(3*3) is performed. Three-dimensional steady simulations for cavitation are conducted by using constant gas mass fraction model with second-order upwind, and the predicated cavitation performance is validated by laboratory experiment. The optimization results are obtained by the range analysis method to improve cavitation performance without obvious decreasing the efficiency of the centrifugal pump. The internal flow of the pump is analyzed in order to identify the flow behavior that can affect cavitation performance. The results show that D 1 has the greatest influence on the pump cavitation and the final optimized impeller provides better flow distribution at blade leading edge. The final optimized impeller accomplishes better cavitation and hydraulic performance and the NPSHR decreases by 0.63m compared with the original one. The presented work supplies a feasible route in engineering practice to optimize a centrifugal pump impeller for better cavitation performance.

  17. 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.

  18. Cavitation nuclei in water exposed to transient pressures

    DEFF Research Database (Denmark)

    Andersen, Anders Peter; Mørch, Knud Aage

    2015-01-01

    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 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...

  19. System and method of detecting cavitation in pumps

    Science.gov (United States)

    Lu, Bin; Sharma, Santosh Kumar; Yan, Ting; Dimino, Steven A.

    2017-10-03

    A system and method for detecting cavitation in pumps for fixed and variable supply frequency applications is disclosed. The system includes a controller having a processor programmed to repeatedly receive real-time operating current data from a motor driving a pump, generate a current frequency spectrum from the current data, and analyze current data within a pair of signature frequency bands of the current frequency spectrum. The processor is further programmed to repeatedly determine fault signatures as a function of the current data within the pair of signature frequency bands, repeatedly determine fault indices based on the fault signatures and a dynamic reference signature, compare the fault indices to a reference index, and identify a cavitation condition in a pump based on a comparison between the reference index and a current fault index.

  20. Partial Averaged Navier-Stokes approach for cavitating flow

    International Nuclear Information System (INIS)

    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

  1. The acceleration of solid particles subjected to cavitation nucleation

    DEFF Research Database (Denmark)

    Borkent, B.M.; Arora, M.; Ohl, C.-D.

    2008-01-01

    The cavity -particle dynamics at cavitation inception on the surface of spherical particles suspended in water and exposed to a strong tensile stress wave is experimentally studied with high-speed photography. Particles, which serve as nucleation sites for cavitation bubbles, are set into a fast...... translatory motion during the explosive growth of the cavity. They reach velocities of ~40 ms-1 and even higher. When the volume growth of the cavity slows down, the particle detaches from the cavity through a process of neck-breaking, and the particle is shot away. The experimental observations are simulated...... with (i) a spherical cavity model and (ii) with an axisymmetric boundary element method (BEM). The input for both models is a pressure pulse, which is obtained from the observed radial cavity dynamics during an individual experiment. The model then allows us to calculate the resulting particle trajectory...

  2. Radiolucencies and cavitation in bronchioloalveolar carcinoma: CT-pathologic correlation

    International Nuclear Information System (INIS)

    Gaeta, M.; Bartiromo, G.; Caruso, R.; Blandino, A.; Scribano, E.; Pandolfo, I.

    1999-01-01

    Bronchioloalveolar carcinoma (BAC) is a polymorphic lung cancer the incidence of which is rising. The presence of intratumoral radiolucencies is an important feature of bronchioloalveolar carcinoma.The aim of this study was to present pictorially the spectrum of intratumoral radiolucencies visible in BAC. In 57 BACs studied with thin-slice CT, we identified six types of radiolucencies: (a) patent intratumoral bronchioles (air bronchiologram); (b) pseudocavitations; (c) cavitation; (d) serpentine radiolucencies; (e) internal alveologram; and (f) multiple cystic lesions. (orig.) (orig.)

  3. Improving methane production using hydrodynamic cavitation as pre-treatment

    OpenAIRE

    Abrahamsson, Louise

    2016-01-01

    To develop anaerobic digestion (AD), innovative solutions to increase methane yields in existing AD processes are needed. In particular, the adoption of low energy pre-treatments to enhance biomass biodegradability is needed to provide efficient digestion processes increasing profitability. To obtain these features, hydrodynamic cavitation has been evaluated as an innovative solutions for AD of waste activated sludge (WAS), food waste (FW), macro algae and grass, in comparison with steam expl...

  4. Sono-chemiluminescence from a single cavitation bubble in water

    International Nuclear Information System (INIS)

    Brotchie, Adam; Shchukin, Dmitry; Moehwald, Helmuth; Schneider, Julia; Pflieger, Rachel

    2012-01-01

    In summary, this study has revealed the conditions required for a single bubble to be sono-chemically active. Evidence of radical-induced processes surrounding the bubble was only observed below the SL threshold, where the bubble was not spatially stable, and did not correlate with emission from excited molecular states inside the bubble. Moreover, this work substantiates recent progress that has been made in bridging the gap between single and multi-bubble cavitation. (authors)

  5. A Numerical Study of Cavitation Inception in Complex Flow Fields

    Science.gov (United States)

    2007-12-01

    time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the...INCEPTION OF FINITE-SPAN HYDROFOIL [4] .........................................8 2.2 EFFECT OF VORTEX/VORTEX INTERACTION ON CAVITATION INCEPTION FOR...2M4001-1-ONR - p. 3 LIST OF TABLES TABLE 1. SUMMARY OF THE POWER CONSTANT IN THE SCALING LAW FOR THE NACA HYDROFOILS IN THE CASE OF A RELATIVELY

  6. The fern cavitation catapult: mechanism and design principles.

    Science.gov (United States)

    Llorens, C; Argentina, M; Rojas, N; Westbrook, J; Dumais, J; Noblin, X

    2016-01-01

    Leptosporangiate ferns have evolved an ingenious cavitation catapult to disperse their spores. The mechanism relies almost entirely on the annulus, a row of 12-25 cells, which successively: (i) stores energy by evaporation of the cells' content, (ii) triggers the catapult by internal cavitation, and (iii) controls the time scales of energy release to ensure efficient spore ejection. The confluence of these three biomechanical functions within the confines of a single structure suggests a level of sophistication that goes beyond most man-made devices where specific structures or parts rarely serve more than one function. Here, we study in detail the three phases of spore ejection in the sporangia of the fern Polypodium aureum. For each of these phases, we have written the governing equations and measured the key parameters. For the opening of the sporangium, we show that the structural design of the annulus is particularly well suited to inducing bending deformations in response to osmotic volume changes. Moreover, the measured parameters for the osmoelastic design lead to a near-optimal speed of spore ejection (approx. 10 m s(-1)). Our analysis of the trigger mechanism by cavitation points to a critical cavitation pressure of approximately -100 ± 14 bar, a value that matches the most negative pressures recorded in the xylem of plants. Finally, using high-speed imaging, we elucidated the physics leading to the sharp separation of time scales (30 versus 5000 µs) in the closing dynamics. Our results highlight the importance of the precise tuning of the parameters without which the function of the leptosporangium as a catapult would be severely compromised. © 2016 The Author(s).

  7. Cavitation Susceptibility Measurements of Ocean Lake and Laboratory Waters.

    Science.gov (United States)

    1986-05-01

    can increase with depth. ADMINISTRATIVE INFORMATION This project was supported by the Ship and Submarine Technology Program Element 62543N Propulsor ...2) QV0 2 where P,, is the vapor pressure of the liquid. It has generally been assumed that cavitation inception occurs when the local pressure falls...to or below the vapor pressure of the fluid. One of the main goals in the present investigation is to examine the validity of this assumption

  8. Comment on "Nuclear Emissions During Self-Nucleated Acoustic Cavitation"

    OpenAIRE

    Naranjo, B.

    2006-01-01

    In a recent Letter to PRL, Taleyarkhan and coauthors claim to observe DD fusion produced by acoustic cavitation. Among other evidence, they provide a proton recoil spectrum that they interpret as arising from 2.45 MeV DD fusion neutrons. My analysis concludes the spectrum is inconsistent with 2.45 MeV neutrons, cosmic background, or a PuBe source, but it is consistent with a Cf-252 source.

  9. Research on the induction motor current signature for centrifugal pump at cavitation condition

    Directory of Open Access Journals (Sweden)

    Yin Luo

    2015-11-01

    Full Text Available Cavitation is a major undesirable phenomenon for centrifugal pump because it can cause hydraulic performance deterioration, pump damage by pitting and material erosion, and structural vibration and noise. Cavitation can appear within the entire range of the operating conditions; therefore, it must be prevented by all means. Sensorless monitoring technology based on motor current signature analysis is non-intrusive and economic for monitoring motor-driven equipment. Thus, this technology is suitable for centrifugal pump systems. The motor current signature for centrifugal pump load at the cavitation condition is the basis of this technology. However, systematic research is lacking on sensorless monitoring technology based on motor current signature. As a result, the tentative exploration for motor current signature at cavitation load was conducted in this study. The results show that the stator current is still a sinusoidal alternating current strictly to the law of sine. Moreover, the root mean square of the current fluctuates because of different flow regimes in the cavitation progress and decreases because vapor density is smaller than water density when cavitation is fully formed. For the stator current spectrum, the noise level, noise distribution, rotation speed, and vane pass frequency components show features in the cavitation process. These indicator indexes change according to the stage of cavitation development. Thus, the motor current signature analysis is found to be a feasible and cost-effective method for the stages of cavitation condition.

  10. Nominal vs. Effective Wake Fields and their Influence on Propeller Cavitation Performance

    DEFF Research Database (Denmark)

    Regener, Pelle Bo; Mirsadraee, Yasaman; Andersen, Poul

    2017-01-01

    Propeller designers often need to base their design on thenominal model scale wake distribution, because the effectivefull scale distribution is not available. The effects of suchincomplete design data on cavitation performance is examinedin this paper. The behind-ship cavitation performanceof two...... flow, with a coupling ofthe two for the interaction of ship and propeller flows. Theeffect on sheet cavitation due to the different wake distributionsis examined for a typical full-form ship. Results showconsiderable differences in cavitation extent, volume, andhull pressure pulses....

  11. Advanced Simulation Capability for Turbopump Cavitation Dynamics Guided by Experimental Validation, Phase I

    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....

  12. Study on tip leakage vortex cavitating flows using a visualization method

    Science.gov (United States)

    Zhao, Yu; Jiang, Yutong; Cao, Xiaolong; Wang, Guoyu

    2018-01-01

    Experimental investigations of unsteady cavitating flows in a hydrofoil tip leakage region with different gap sizes are conducted to highlight the development of gap cavitation. The experiments were taken in a closed cavitation tunnel, during which high-speed camera had been used to capture the cavitation patterns. A new visualization method based on image processing was developed to capture time-dependent cavitation patterns. The results show that the visualization method can effectively capture the cavitation patterns in the tip region, including both the attached cavity in the gap and the tip leakage vortex (TLV) cavity near the trailing edge. Moreover, with the decrease of cavitation number, the TLV cavity develops from a rapid onset-growth-collapse process to a continuous process, and extends both upstream and downstream. The attached cavity in the gap develops gradually stretching beyond the gap and combines with the vortex cavity to form the triangle cavitating region. Furthermore, the influences of gap size on the cavitation are also discussed. The gap size has a great influence on the loss across the gap, and hence the locations of the inception attached cavity. Besides, inception locations and extending direction of the TLV cavity with different gap sizes also differ. The TLV in the case with τ = 0.061 is more likely to be jet-like compared with that in the case with τ = 0.024, and the gap size has a great influence on the TLV strength.

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

    International Nuclear Information System (INIS)

    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

  14. Investigations of effect of phase change mass transfer rate on cavitation process with homogeneous relaxation model

    Energy Technology Data Exchange (ETDEWEB)

    He, Zhixia; Zhang, Liang; Saha, Kaushik; Som, Sibendu; Duan, Lian; Wang, Qian

    2017-12-01

    The super high fuel injection pressure and micro size of nozzle orifice has been an important development trend for the fuel injection system. Accordingly, cavitation transient process, fuel compressibility, amount of noncondensable gas in the fuel and cavitation erosion have attracted more attention. Based on the fact of cavitation in itself is a kind of thermodynamic phase change process, this paper takes the perspective of the cavitation phase change mass transfer process to analyze above mentioned phenomenon. The two-phase cavitating turbulent flow simulations with VOF approach coupled with HRM cavitation model and U-RANS of standard k-ε turbulence model were performed for investigations of cavitation phase change mass transfer process. It is concluded the mass transfer time scale coefficient in the Homogenous Relaxation Model (HRM) representing mass transfer rate should tend to be as small as possible in a condition that ensured the solver stable. At very fast mass transfer rate, the phase change occurs at very thin interface between liquid and vapor phase and condensation occurs more focused and then will contribute predictably to a more serious cavitation erosion. Both the initial non-condensable gas in fuel and the fuel compressibility can accelerate the cavitation mass transfer process.

  15. Hydrodynamic cavitation as a novel approach for delignification of wheat straw for paper manufacturing.

    Science.gov (United States)

    Badve, Mandar P; Gogate, Parag R; Pandit, Aniruddha B; Csoka, Levente

    2014-01-01

    The present work deals with application of hydrodynamic cavitation for intensification of delignification of wheat straw as an essential step in the paper manufacturing process. Wheat straw was first treated with potassium hydroxide (KOH) for 48 h and subsequently alkali treated wheat straw was subjected to hydrodynamic cavitation. Hydrodynamic cavitation reactor used in the work is basically a stator and rotor assembly, where the rotor is provided with indentations and cavitational events are expected to occur on the surface of rotor as well as within the indentations. It has been observed that treatment of alkali treated wheat straw in hydrodynamic cavitation reactor for 10-15 min increases the tensile index of the synthesized paper sheets to about 50-55%, which is sufficient for paper board manufacture. The final mechanical properties of the paper can be effectively managed by controlling the processing parameters as well as the cavitational parameters. It has also been established that hydrodynamic cavitation proves to be an effective method over other standard digestion techniques of delignification in terms of electrical energy requirements as well as the required time for processing. Overall, the work is first of its kind application of hydrodynamic cavitation for enhancing the effectiveness of delignification and presents novel results of significant interest to the paper and pulp industry opening an entirely new area of application of cavitational reactors. Copyright © 2013 Elsevier B.V. All rights reserved.

  16. An Experimental Study of Cavitation Detection in a Centrifugal Pump Using Envelope Analysis

    Science.gov (United States)

    Tan, Chek Zin; Leong, M. Salman

    Cavitation represents one of the most common faults in pumps and could potentially lead to a series of failure in mechanical seal, impeller, bearing, shaft, motor, etc. In this work, an experimental rig was setup to investigate cavitation detection using vibration envelope analysis method, and measured parameters included sound, pressure and flow rate for feasibility of cavitation detection. The experiment testing included 3 operating points of the centrifugal pump (B.E.P, 90% of B.E.P and 80% of B.E.P). Suction pressure of the centrifugal pump was decreased gradually until the inception point of cavitation. Vibration measurements were undertaken at various locations including casing, bearing, suction and discharge flange of the centrifugal pump. Comparisons of envelope spectrums under cavitating and non-cavitating conditions were presented. Envelope analysis was proven useful in detecting cavitation over the 3 testing conditions. During the normal operating condition, vibration peak synchronous to rotational speed was more pronounced. It was however during cavitation condition, the half order sub-harmonic vibration component was clearly evident in the envelope spectrums undertaken at all measurement locations except at the pump bearing. The possible explanation of the strong sub-harmonic (½ of BPF) during cavitation existence in the centrifugal pump was due to insufficient time for the bubbles to collapse completely before the end of the single cycle.

  17. Fast X-ray imaging of cavitating flows

    Energy Technology Data Exchange (ETDEWEB)

    Khlifa, Ilyass; Fuzier, Sylvie; Roussette, Olivier [Arts et Metiers ParisTech, Lille (France); Vabre, Alexandre [CEA Saclay, Gif-sur-Yvette (France); Hocevar, Marko [Faculty of Mechanical Engineering, University of Ljubljana, Ljubljana (Slovenia); Fezzaa, Kamel [Argonne National Laboratory, Advanced Photon Source, Lemont, IL (United States); Coutier-Delgosha, Olivier [Virginia Tech, Kevin T. Crofton Department of Aerospace and Ocean Engineering, Blacksburg, VA (United States)

    2017-11-15

    A new method based on ultra-fast X-ray imaging was developed in this work for the investigation of the dynamics and the structures of complex two-phase flows. In this paper, cavitation was created inside a millimetric 2D Venturi-type test section, while seeding particles were injected into the flow. Thanks to the phase-contrast enhancement technique provided by the APS (Advanced Photon Source) synchrotron beam, high definition X-ray images of the complex cavitating flows were obtained. These images contain valuable information about both the liquid and the gaseous phases. By means of image processing, the two phases were separated, and velocity fields of each phase were, therefore, calculated using image cross-correlations. The local vapour volume fractions were also obtained, thanks to the local intensity levels within the recorded images. These simultaneous measurements, provided by this new technique, afford more insight into the structure and the dynamic of two-phase flows as well as the interactions between them, and hence enable to improve our understanding of their behaviour. In the case of cavitating flows inside a Venturi-type test section, the X-ray measurements demonstrate, for the first time, the presence of significant slip velocities between the phases within sheet cavities for both steady and unsteady flow configurations. (orig.)

  18. Cavitation clouds created by shock scattering from bubbles during histotripsy

    Science.gov (United States)

    Maxwell, Adam D.; Wang, Tzu-Yin; Cain, Charles A.; Fowlkes, J. Brian; Sapozhnikov, Oleg A.; Bailey, Michael R.; Xu, Zhen

    2011-01-01

    Histotripsy is a therapy that focuses short-duration, high-amplitude pulses of ultrasound to incite a localized cavitation cloud that mechanically breaks down tissue. To investigate the mechanism of cloud formation, high-speed photography was used to observe clouds generated during single histotripsy pulses. Pulses of 5−20 cycles duration were applied to a transparent tissue phantom by a 1-MHz spherically focused transducer. Clouds initiated from single cavitation bubbles that formed during the initial cycles of the pulse, and grew along the acoustic axis opposite the propagation direction. Based on these observations, we hypothesized that clouds form as a result of large negative pressure generated by the backscattering of shockwaves from a single bubble. The positive-pressure phase of the wave inverts upon scattering and superimposes on the incident negative-pressure phase to create this negative pressure and cavitation. The process repeats with each cycle of the incident wave, and the bubble cloud elongates toward the transducer. Finite-amplitude propagation distorts the incident wave such that the peak-positive pressure is much greater than the peak-negative pressure, which exaggerates the effect. The hypothesis was tested with two modified incident waves that maintained negative pressure but reduced the positive pressure amplitude. These waves suppressed cloud formation which supported the hypothesis. PMID:21973343

  19. 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...

  20. Comparison of cavitation prediction for a centrifugal pump with or without volute casing

    Energy Technology Data Exchange (ETDEWEB)

    Luo, Xianwu; Wei, Wei; Ji, Bin; Xu, Hongyuan [Tsinghua University, Beijing (China); Pan, Zaibing; Zhou, Wenchao [KSB Shanghai Pump Co., Shanghai (China)

    2013-06-15

    Cavitation may not only cause head and efficiency breakdown of hydraulic machines but also generate other unfavorable phenomena such as noise and vibration. Therefore, the accurate prediction of cavitation development is important for various pump applications. In this paper, two numerical models, namely, models A and B, are applied to simulate the turbulent cavitating flows inside a centrifugal pump to investigate the effect of calculation domain on the prediction accuracy of cavitation performance for hydraulic machines. Model A has a calculation domain with volute casing, whereas model B has a single blade-to-blade flow passage without volute casing. Steady simulations of cavitating flow in the pump have been conducted based on the shear stress transport k-ω turbulence model and the homogeneous cavitation model. Both models A and B predicted that the pump performance decreases with decreasing cavitation number. Experimental results show that model B can predict better the critical cavitation number at the best efficiency point compared with model A, which is the full flow passage model. Internal flow investigations indicate that an asymmetrical feature of cavitating flow exists when the calculation domain with volute casing is applied. The asymmetrical cavitation development in different blade-to-blade flow passages for model A results in an over-estimation of the decrease in pump performance because of the interaction between the impeller blade and the tongue of the volute casing. A simple calculation domain without volute casing is preferred for steady cavitation prediction in pumps rather than the full flow passage with volute casing because the former has better convergence, less resource requirements, and lower time consumption.

  1. Effect of geometrical parameters on submerged cavitation jet discharged from profiled central-body nozzle

    Science.gov (United States)

    Yang, Minguan; Xiao, Shengnan; Kang, Can; Wang, Yuli

    2013-05-01

    The flow characteristics of cavitation jets are essential issues among relevant studies. The physical properties of the jet are largely determined by the geometrical parameters of the nozzle. The structure and cavitation jets characteristics of the angular-nozzle and the self-resonating cavitation nozzle have been extensively studied, but little research is conducted in the central-body cavitation nozzle mainly because of its hard processing and the cavitation jet effect not satisfactory. In this paper, a novel central-body nozzle (a non-plunger central-body nozzle with square outlet) is studied to solve above problems. Submerged jets discharged from the novel central-body nozzle are simulated, employing the full cavitation model. The impact of nozzle configuration on jet properties is analyzed. The analysis results indicate that when central-body relative diameter keeps constant, there is an optimal contraction degree of nozzle's outlet, which can induce intense cavitation in the jet. The central-body relative diameter also affects jet profiles. In the case of large central-body relative diameter, most of the bubbles settle in the jet core. On the contrary, a smaller relative diameter makes bubbles concentrate in the interface between the jet and its surrounding fluid. Moreover, the shorter outlet part allows the cavitation zone further extend in both the axial and racial directions. The research results further consummate the study on the central-body nozzles and the correlation between cavitation jet and the structure, and elementarily reveal the mechanism of cavitation jet produced in a non-plunger novel central-body nozzle and the effect of the structure parameters on the cavitation jet, moreover, provide the theoretical basis for the optimal design of the nozzle.

  2. Detecting Cavitation in a Vertical Sea water Centrifugal Lift Pump Related to Iran Oil Industry Cooling Water Circulation System

    OpenAIRE

    Omid A. Zargar

    2014-01-01

    Cavitation is one of the most well-known process faults that may occur in different industrial equipment especially centrifugal pumps. Cavitation also may happen in water pumps and turbines. Sometimes cavitation has been severe enough to wear holes in the impeller and damage the vanes to such a degree that the impeller becomes very ineffective. More commonly, the pump efficiency will decrease significantly during cavitation and continue to decrease as damage to the impeller increases. Typical...

  3. Thermo-Hydrodynamic Analysis of a Plain Journal Bearing on the Basis of a New Mass Conserving Cavitation Algorithm

    NARCIS (Netherlands)

    Alakhramsing, S.; Van Ostayen, R.A.J.; Eling, R.P.T.

    2015-01-01

    Accurate prediction of cavitation is an important feature in hydrodynamic bearing modeling. Especially for thermo-hydrodynamic modeling, it is crucial to use a mass-conservative cavitation algorithm. This paper introduces a new mass-conserving Reynolds cavitation algorithm, which provides fast

  4. 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.

  5. 76 FR 55954 - Astralis Ltd., Cavit Sciences, Inc., Crystal International Travel Group, Inc., and Tasker...

    Science.gov (United States)

    2011-09-09

    ... From the Federal Register Online via the Government Publishing Office SECURITIES AND EXCHANGE COMMISSION Astralis Ltd., Cavit Sciences, Inc., Crystal International Travel Group, Inc., and Tasker Products... securities of Cavit Sciences, Inc. because it has not filed any periodic reports since the period ended...

  6. 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.

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

    NARCIS (Netherlands)

    Schnerr, Günter; 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

  8. Cavitation control on a 2D hydrofoil through a continuous tangential injection of liquid: Experimental study

    Science.gov (United States)

    Timoshevskiy, M. V.; Zapryagaev, I. I.; Pervunin, K. S.; Markovich, D. M.

    2016-10-01

    In the paper, the possibility of active control of a cavitating flow over a 2D hydrofoil that replicates a scaled-down model of high-pressure hydroturbine guide vane (GV) was tested. The flow manipulation was implemented by a continuous tangential liquid injection at different flow rates through a spanwise slot in the foil surface. In experiments, the hydrofoil was placed in the test channel at the attack angle of 9°. Different cavitation conditions were reached by varying the cavitation number and injection velocity. In order to study time dynamics and spatial patterns of partial cavities, high-speed imaging was employed. A PIV method was used to measure the mean and fluctuating velocity fields over the hydrofoil. Hydroacoustic measurements were carried out by means of a pressure transducer to identify spectral characteristics of the cavitating flow. It was found that the present control technique is able to modify the partial cavity pattern (or even totally suppress cavitation) in case of stable sheet cavitation and change the amplitude of pressure pulsations at unsteady regimes. The injection technique makes it also possible to significantly influence the spatial distributions of the mean velocity and its turbulent fluctuations over the GV section for non-cavitating flow and sheet cavitation.

  9. 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

    . But the trend of CFD applications toward 2-D and 3-D cavitating hydrofoils shows the great potential of those codes for propeller applications as well. For all numerical predictions, potential methods as well as RANS, it is important that the cavitation simulation is fully unsteady, particularly if higher...

  10. Study of ultrasonic cavitation during extraction of the peanut oil at varying frequencies.

    Science.gov (United States)

    Zhang, Lei; Zhou, Cunshan; Wang, Bei; Yagoub, Abu El-Gasim A; Ma, Haile; Zhang, Xiao; Wu, Mian

    2017-07-01

    The ultrasonic extraction of oils is a typical physical processing technology. The extraction process was monitored from the standpoint of the oil quality and efficiency of oil extraction. In this study, the ultrasonic cavitation fields were measured by polyvinylidene fluoride (PVDF) sensor. Waveform of ultrasonic cavitation fields was gained and analyzed. The extraction yield and oxidation properties were compared. The relationship between the fields and cavitation oxidation was established. Numerical calculation of oscillation cycle was done for the cavitation bubbles. Results showed that the resonance frequency, f r , of the oil extraction was 40kHz. At f r , the voltage amplitude was the highest; the time was the shortest as reaching the amplitude of the waveform. Accordingly, the cavitation effect worked most rapidly, resulting in the strongest cavitation intensity. The extraction yield and oxidation properties were closely related to the cavitation effect. It controlled the cavitation oxidation effectively from the viewpoint of chemical and physical aspects. Copyright © 2017 Elsevier B.V. All rights reserved.

  11. 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.

  12. Cavitation erosion resistance of 13/4 and 21-4-N steels

    Indian Academy of Sciences (India)

    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 ...

  13. Research on Cavitation Regions of Upstream Pumping Mechanical Seal Based on Dynamic Mesh Technique

    Directory of Open Access Journals (Sweden)

    Huilong Chen

    2014-08-01

    Full Text Available In order to study the cavitation area of the Upstream Pumping Mechanical Seal, three-dimensional microgap inner flow field of the Upstream Pumping Mechanical Seal was simulated with multiphase flow cavitation model and dynamic mesh technique based on hydrodynamic lubrication theory. Furthermore, the simulated result was compared with the experimental data. The results show that the simulated result with the Zwart-Gerber-Belamri cavitation model was much closer to the experimental data. The area of cavitation inception mainly occurred at the concave side of the spiral groove and surrounding region without spiral grooves, which was nearly covered by the inner diameter to roots of grooves; in addition, the region near the surface of the stationary ring was primary cavitation location. The area of cavitation has little relationship with the medium pressure; however, it became larger following increasing rotating speed in the range of researched operating conditions. Moreover the boundary of cavitated area was transformed from smooth to rough, which occurred in similar film thickness. When cavitation number was decreasing, which was conducive to improving the lubrication performance of sealed auxiliary, it made the sealing stability decline.

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

    DEFF Research Database (Denmark)

    Shin, K. W.; Andersen, Poul

    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...

  15. Numerical study of unsteady flows with cavitation in a high-speed micro centrifugal pump

    Science.gov (United States)

    Li, Yeqiang; Yuan, Shiwei; Lai, Huanxin

    2017-02-01

    The unsteady flows caused by the interaction between the impeller and the volute in a high-speed micro centrifugal pump are numerically studied. The internal flows of both with and without cavitations are analyzed using the CFX. The characteristics of unsteady pressure on the blade surfaces and the symmetric plane of the volute are presented and compared. The results show that the amplitudes of pressure fluctuations of critical cavitation on the blade pressure surface (PS) are bigger as compared with those at the non-cavitation condition, but on the suction surface (SS), the situation is on the contrary. When cavitation occurs, reduction of load in the impeller is a result. In the present study, such reduction of load is observed mainly on the first half of the blades. Pressure fluctuations at five monitoring points, denoted by WK1 to WK5 in the volute, are also analyzed. No matter at the critical cavitation or at the non-cavitation conditions, the monitored pressure fluctuations are at the same frequencies, which equal to the blade passing frequency (BPF) and its multiples. However, the amplitudes of the fluctuations at critical cavitation condition are considerably stronger, as compared with those for without cavitation.

  16. In-line holography for flow and cavitation visualization on hydrofoils and for nuclei measurements

    NARCIS (Netherlands)

    Renesse, R.L. van; Meulen, J.H.J. van der

    1980-01-01

    The boundary layer flow about two hydrofoils and the appearance of cavitation are investigated by means of in-line holography. Practical details on the hologram resolution and data collection time for nuclei size analysis are given. It is shown that the appearance of cavitation on the hydrofoils is

  17. Sonoporation of suspension cells with a single cavitation bubble in a microfluidic confinement

    NARCIS (Netherlands)

    le Gac, Severine; Zwaan, Ed; van den Berg, Albert; Ohl, C.D.

    2007-01-01

    We report here the sonoporation of HL60 (human promyelocytic leukemia) suspension cells in a microfluidic confinement using a single laser-induced cavitation bubble. Cavitation bubbles can induce membrane poration of cells located in their close vicinity. Membrane integrity of suspension cells

  18. Should cavitation in proximal surfaces be reported in cone beam computed tomography examination

    DEFF Research Database (Denmark)

    Sansare, K.; Singh, D.; Sontakke, S.

    2014-01-01

    Aim: A clinical study was done to assess the clinical diagnostic accuracy of cone beam computed tomography (CBCT) in detecting proximal cavitated carious lesions in order to determine whether cavitation should be reported when a CBCT examination is available. Materials and Methods: 79 adjacent...

  19. Theoretical Analysis of Thermodynamic Effect of Cavitation in Cryogenic Inducer Using Singularity Method

    Directory of Open Access Journals (Sweden)

    S. Watanabe

    2008-01-01

    Full Text Available Vapor production in cavitation extracts the latent heat of evaporation from the surrounding liquid, which decreases the local temperature, and hence the local vapor pressure in the vicinity of cavity. This is called thermodynamic/thermal effect of cavitation and leads to the good suction performance of cryogenic turbopumps. We have already established the simple analysis of partially cavitating flow with the thermodynamic effect, where the latent heat extraction and the heat transfer between the cavity and the ambient fluid are taken into account. In the present study, we carry out the analysis for cavitating inducer and compare it with the experimental data available from literatures using Freon R-114 and liquid nitrogen. It is found that the present analysis can simulate fairly well the thermodynamic effect of cavitation and some modification of the analysis considering the real fluid properties, that is, saturation characteristic, is favorable for more qualitative agreement.

  20. 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.

  1. Experimental Investigation of Cavitation Signatures in an Automotive Torque Converter Using a Microwave Telemetry Technique

    Directory of Open Access Journals (Sweden)

    C. L. Anderson

    2003-01-01

    Full Text Available A unique experimental investigation of cavitation signatures in an automotive torque converter under stall conditions is reported. A quantitative criterion is proposed for predicting early and advanced cavitation in terms of suitable nondimensional pump speeds. The dimensionless pump speed that marks early cavitation is obtained by relating this parameter to the appearance of charge-pressure–dependent pressure fluctuations in the differential pressure transducer readings. The differential pressure transducers were mounted at well-defined locations in the pump passage of a torque converter. The data were transmitted by a wireless telemetry system mounted on the pump housing. Data were received and processed by a ground-based data acquisition system. Automatic transmission fluid exhibited cavitation for charge pressures of 70–130 psi and pump speeds of 1000– 2250 rpm. Advanced cavitation was marked by operating conditions that exhibited a 2% or more torque degradation from the converter's noncavitating performance.

  2. 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.

  3. Study on cavitation effect of mechanical seals with laser-textured porous surface

    Science.gov (United States)

    Liu, T.; Chen, H. l.; Liu, Y. H.; Wang, Q.; Liu, Z. B.; Hou, D. H.

    2012-11-01

    Study on the mechanisms underlying generation of hydrodynamic pressure effect associated with laser-textured porous surface on mechanical seal, is the key to seal and lubricant properties. The theory model of mechanical seals with laser-textured porous surface (LES-MS) based on cavitation model was established. The LST-MS was calculated and analyzed by using Fluent software with full cavitation model and non-cavitation model and film thickness was predicted by the dynamic mesh technique. The results indicate that the effect of hydrodynamic pressure and cavitation are the important reasons to generate liquid film opening force on LST-MS; Cavitation effect can enhance hydrodynamic pressure effect of LST-MS; The thickness of liquid film could be well predicted with the method of dynamic mesh technique on Fluent and it becomes larger as the increasing of shaft speed and the decreasing of pressure.

  4. Study on cavitation effect of mechanical seals with laser-textured porous surface

    International Nuclear Information System (INIS)

    Liu, T; Chen, H l; Liu, Y H; Wang, Q; Liu, Z B; Hou, D H

    2012-01-01

    Study on the mechanisms underlying generation of hydrodynamic pressure effect associated with laser-textured porous surface on mechanical seal, is the key to seal and lubricant properties. The theory model of mechanical seals with laser-textured porous surface (LES-MS) based on cavitation model was established. The LST-MS was calculated and analyzed by using Fluent software with full cavitation model and non-cavitation model and film thickness was predicted by the dynamic mesh technique. The results indicate that the effect of hydrodynamic pressure and cavitation are the important reasons to generate liquid film opening force on LST-MS; Cavitation effect can enhance hydrodynamic pressure effect of LST-MS; The thickness of liquid film could be well predicted with the method of dynamic mesh technique on Fluent and it becomes larger as the increasing of shaft speed and the decreasing of pressure.

  5. Acoustic cavitation as an enhancing mechanism of low-frequency sonophoresis for transdermal drug delivery.

    Science.gov (United States)

    Ueda, Hideo; Mutoh, Mizue; Seki, Toshinobu; Kobayashi, Daisuke; Morimoto, Yasunori

    2009-05-01

    We investigated the role of acoustic cavitation on sonophoretic skin permeation of calcein, a model permeant, across excised hairless rat skin. Three different frequencies (41, 158, 445 kHz) and various intensities (60 to 300 mW/cm(2)) of ultrasound were applied. Cavitation generation in degassed and undegassed (normal) water was monitored using a commercially available cavitation meter, then compared with skin permeability from calcein solution consistent of them. In addition, the penetration of a fluorescent dye, rhodamine B, into gelatin gel as a skin alternative was observed to estimate the role of cavitation collapse in the solution at or near the skin surface. Cavitation generation in the undegassed water was dependent on the ultrasound frequency, and the rank order of the cavitation was 41 kHz>158 kHz>445 kHz. At 41 kHz, cavitation generation in degassed water was clearly lower than that in undegassed water. Calcein permeability during ultrasound application correlated well with the cavitation generation in the medium, suggesting the important role of the indirect actions of cavitation collapse which occurred in the applied solution rather than the direct action in the skin. When ultrasound (41 or 158 kHz) was applied to the gelatin gels covered with rhodamine B solution, alteration in the surface configuration, like spots, and the coincident penetration of the dye were observed only at 41 kHz, while no alteration in the surface configuration was evident at 158 kHz. These results suggest that cavitation collapses in the vicinity of the skin surface might be more important for solute penetration in addition to skin permeabilization.

  6. Radiolucencies and cavitation in bronchioloalveolar carcinoma: CT-pathologic correlation

    Energy Technology Data Exchange (ETDEWEB)

    Gaeta, M.; Bartiromo, G. [Service of Diagnostic Imaging, Piemonte Hospital, Messina (Italy); Caruso, R. [Institute of Pathology, University of Messina (Italy); Blandino, A.; Scribano, E.; Pandolfo, I. [Institute of Radiologic Sciences, University of Messina (Italy)

    1999-02-01

    Bronchioloalveolar carcinoma (BAC) is a polymorphic lung cancer the incidence of which is rising. The presence of intratumoral radiolucencies is an important feature of bronchioloalveolar carcinoma.The aim of this study was to present pictorially the spectrum of intratumoral radiolucencies visible in BAC. In 57 BACs studied with thin-slice CT, we identified six types of radiolucencies: (a) patent intratumoral bronchioles (air bronchiologram); (b) pseudocavitations; (c) cavitation; (d) serpentine radiolucencies; (e) internal alveologram; and (f) multiple cystic lesions. (orig.) (orig.) With 12 figs., 13 refs.

  7. 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. © The Author(s) 2013 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav.

  8. Modeling Cavitation in ICE Pistons Made with Isothermal Forging

    Directory of Open Access Journals (Sweden)

    V.V. Astanin

    2014-07-01

    Full Text Available Possible causes for cavitations in parts made with an Al-Si eutectic alloy AK12D (AlSi12 were explored with mathematical and physical modeling with involved acoustic emission. Pores were formed from micro-cracks, which appear during the early stages of a deformation process, with the help of micro-stresses appearing at phase boundaries (Al/Si interface due to thermal expansion. At the design stage of isothermal forgings of such products it is recommended to provide a scheme of the deformed shape, which is under uniform compression, to compensate for the inter-phase stresses.

  9. Method of forming cavitated objects of controlled dimension

    International Nuclear Information System (INIS)

    Anderson, P.R.; Miller, W.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

  10. Propeller Cavitation Noise Investigations in a Free-Field Environment.

    Science.gov (United States)

    1982-06-01

    se produire sur l’ar~te d’entr6e de la pale. Chacun de ces types de cavitation peut avoir des puissances et des spectres acoustiques divers. Un m...canisme d’entrainement des h6ices a 6t4 construit Sla P~niche de recherches acoustiques au Centre de recherches pour ia d~fense Atlantique. Cette p6niche...le son dans, le champ 6loign4 et les m6canismes de la source hydro- acoustique dans le champ proche de l’h6lice. Au moyen de doubles correlations, on a

  11. Effect of Cavitation on Surface Damage of 16.7Cr-10Ni-2Mo Stainless Steel in Marine Environment

    International Nuclear Information System (INIS)

    Chong, Sang-Ok; Han, Min-Su; Kim, Seong-Jong

    2015-01-01

    Stainless steel is generally known to have characteristics of excellent corrosion resistance and durability, but in a marine environment it can suffer from localized corrosion due to the breakdown of passivity film due to chloride ion in seawater. Furthermore, the damage behaviors are sped up under a cavitation environment because of complex damage from electrochemical corrosion and cavitation-erosion. In this study the characteristics of electrochemical corrosion and cavitation erosion behavior were evaluated on 16.7Cr-10Ni-2Mo stainless steel under a cavitation environment in natural seawater. The electrochemical experiments have been conducted at both static conditions and dynamic conditions inducing cavitation with different current density parameters. The surface morphology and damage behaviors were compared after the experiment. After the cavitation test with time variables morphological examinations on damaged specimens were analyzed by using a scanning electron microscope and a 3D microscope. the galvanostatic experiment gave a cleaner surface morphology presented with less damage depth at high current density regions. It is due to the effect of water cavitation peening under the cavitation condition. In the cavitation experiment, with amplitude of 30 μm and seawater temperature of 25 ℃, weight loss and cavitation-erosion damage depth were dramatically increased after 5 hours inducing cavitation

  12. Cavités laser auto-organisables

    Science.gov (United States)

    Dubreuil, N.; Godard, A.; Maerten, S.; Meilhac, L.; Pauliat, G.; Jonathan, J.-M.; Roosen, G.

    2002-06-01

    L'insertion d'un cristal photoréfractif à l'intérieur de la cavité d'un laser permet de fortement réduire le nombre de modes laser. Les modes enregistrent dans le cristal un hologramme qui modifie en retour leurs pertes. II en résulte une très forte sélection entre les modes et qui, sous certaines conditions, force le laser à osciller sur un seul mode. L'hologramme étant systématiquement adapté à la structure de modes émis par le laser, on parle alors de cavités laser auto-organisables. Nous présentons les résultats qui ont été obtenus sur le filtrage de modes longitudinaux dans des lasers de type quatre niveaux fonctionnant en régimes continu et impulsionnel, ainsi que dans des lasers à semi-conducteurs. En outre, nous montrons que l'insertion d'un tel cristal peut avoir comme application la stabilisation d'un mode. Le laser est alors monomode, l'inscription d'un hologramme par ce mode diminue ses pertes et étend son domaine de stabilité.

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

    International Nuclear Information System (INIS)

    Griffith-Richards, S.B.; Andronikou, Savvas; Przybojewski, Stefan J.; Strachan, Melanie; Vadachia, Yousuf; Kathan, David L.; Goussard, Pierre; Gie, Robert P.

    2007-01-01

    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.)

  14. Numerical Analysis of Tip Cavitation on Marine Propeller with Wake Alignment Using a Simple Surface Panel Method “SQCM”

    Science.gov (United States)

    Kanemaru, T.; Ando, J.

    2015-12-01

    This paper presents the calculation method of tip cavitation with wake alignment. Tip cavitation consists of tip vortex cavitation and tip super cavitation which means the undeveloped and local super cavitation around blade tip. The feature of this study is that the method applies the wake alignment model in order to express the realistic phenomena of tip cavitation and predict the pressure fluctuation more accurately. In the present method, the wake sheet is deformed according to the induced velocity vector on the vortex lines. The singularity of the potential vortex can be removed by using the Rankine Vortex model. This paper shows the calculated results regarding cavitation pattern, pressure fluctuation etc. comparing with published experimental data and calculated results without wake alignment.

  15. 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

  16. 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

  17. Investigation on Hydrodynamic Cavitation of a Restriction Orifice and Static Mixer on Crud-like Deposits

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Seong Man; Lee, Seung Won; Park, Seong Dae; Kang, Sa Rah; Seo, Han; Bang, In Cheol [Ulsan National Institute of Science and Technology, Ulsan (Korea, Republic of)

    2012-05-15

    Axial Offset Anomaly (AOA) referring to an unexpected neutron flux depression is also known as Crud Induced Power Shift (CIPS). Fuel assemblies removed from an AOA core have shown a thick porous deposition layer of crud on fuel clad surface. The deposition layer was induced by precipitation reactions of both boron species and crud during sub-cooled nucleate boiling. Therefore, to resolve the AOA issues, a fuel cleaning technology using ultrasonic cavitation has been developed by EPRI and applied to the domestic NPPs by KNF. However, the performance of crud removal during maintenance of NPPs is known to be not enough. Hydrodynamic cavitation is the process of vaporization, bubble generation and bubble implosion which occurs in a flowing liquid as a result of decrease and subsequent increase in pressure. Hydrodynamic cavitation generates shock pressure of a few tens MPa due to bubble collapse like the cavitation generated by Ultrasonics. It is well known that the cavitation can erode the metal surface. The idea of the current study is that such energetic cavitation bubble collapses could help to remove the crud from the fuel assembly. Therefore, the current study first investigates effects of hydrodynamic cavitation occurred from a single hole orifice and static mixer fundamentally

  18. An experimental study on suppressing Tip Vortex Cavitation by means of a Flexible Thread

    Science.gov (United States)

    Seo, Jeonghwa; Amini, Ali; Lee, Seung Jae; Park, Jongyeol; Yeo, Honggu; Farhat, Mohamed; Rhee, Shin Hyung

    2017-11-01

    Tip vortex cavitation (TVC) is an important issue in hydraulic machines and efforts to reduce it are required. The present study aims to mitigate the intensity of a TVC by attaching a flexible thread at the hydrofoil tip. As the test model, a hydrofoil with elliptical planform with NACA 16-020 cross section was used. Reynolds number, incidence angle, and cavitation number were varied to examine the cavitation suppression effects under different flow conditions. It is observed that the size of the cavitating core of the tip vortex is drastically reduced in comparison to the same flow conditions without the thread. The vortex roll-up and formation was disturbed by the fluctuations of the flexible string around the TVC, resulting in cavitation intensity reduction. In addition, the thread diameter and length were varied, to show that the technique was proved effective even for strings as short as half of the root chord length, which acted like a stiff thread. Our results demonstrate that there exists a critical thread length of, where the decrease in the cavitating core diameter converges. It is also found that this recipe ameliorates the desinent cavitation index of the TVC.

  19. Effect of gold nanoparticle size on acoustic cavitation using chemical dosimetry method.

    Science.gov (United States)

    Shanei, Ahmad; Shanei, Mohammad Mahdi

    2017-01-01

    When a liquid is irradiated with high intensities of ultrasound irradiation, acoustic cavitation occurs. Acoustic cavitation generates free radicals from the breakdown of water and other molecules. Cavitation can be fatal to cells and is utilized to destroy cancer tumors. The existence of particles in liquid provides nucleation sites for cavitation bubbles and leads to decrease the ultrasonic intensity threshold needed for cavitation onset. In the present investigation, the effect of gold nanoparticles with appropriate amount and size on the acoustic cavitation activity has been shown by determining hydroxyl radicals in terephthalic acid solutions containing 15, 20, 28 and 35nm gold nanoparticles sizes by using 1MHz low level ultrasound. The effect of sonication intensity in hydroxyl radical production was considered. The recorded fluorescence signal in terephthalic acid solutions containing gold nanoparticles was considerably higher than the terephthalic acid solutions without gold nanoparticles at different intensities of ultrasound irradiation. Also, the results showed that the recorded fluorescence signal intensity in terephthalic acid solution containing finer size of gold nanoparticles was lower than the terephthalic acid solutions containing larger size of gold nanoparticles. Acoustic cavitation in the presence of gold nanoparticles can be used as a way for improving therapeutic effects on the tumors. Copyright © 2016 Elsevier B.V. All rights reserved.

  20. Elastomeric impression as a diagnostic method of cavitation in proximal dentin caries in primary molars

    Directory of Open Access Journals (Sweden)

    Adriela Azevedo Souza Mariath

    2007-12-01

    Full Text Available The purpose of this study was to validate the elastomeric impression after temporary tooth separation as a method of cavitation detection in proximal caries lesions in primary molars with outer half dentin radiolucency. Fifty-one children (4-10 years old, presenting radiolucency in the outer half of the dentin at the proximal surfaces of primary molars and proximal anatomic contact with the adjacent tooth (without restoration/cavitated caries lesion were enrolled in the study. Temporary tooth separation was performed with an orthodontic rubber ring placed around the contact point during 2-3 days. Thereafter, impression of the proximal surfaces was made. The elastomeric impressions were classified as "non-cavitated" or "cavitated" surfaces. Visual inspection after tooth separation was considered as the gold standard. Examiner reliability of visual inspection after tooth separation was determined (kappa 0.92. Impression examination was repeated every 5 participants to evaluate the reproducibility of the method. The frequency of cavitated lesions was 65%, and 67% of those were inactive. Sensitivity, specificity, positive and negative predictive values were 0.88% (95%CI 0.73-0.95, 0.89% (95%CI 0.67-0.97, 0.94% (95%CI 0.79-0.98 and 0.80% (95%CI 0.58-0.92, respectively. Impression examination showed total agreement regarding cavitation. The evaluation of elastomeric impression after tooth separation is a useful clinical resource in cavitation detection for clinicians and researchers when visual inspection is doubtful.

  1. Cavitation in centrifugal pump with rotating walls of axial inlet device

    Science.gov (United States)

    Moloshnyi, O.; Sotnyk, M.

    2017-08-01

    The article deals with the analysis of cavitation processes in the flowing part of the double entry centrifugal pump. The analysis is conducted using numerical modeling of the centrifugal pump operating process in the software environment ANSYS CFX. Two models of the axial inlet device is researched. It is shaped by a cylindrical section and diffuser section in front of the impeller, which includes fairing. The walls of the axial inlet device rotate with the same speed as the pump rotor. The numerical experiment is conducted under the condition of the flow rate change and absolute pressure at the inlet. The analysis shows that the pump has the average statistical cavitation performance. The occurrence of the cavitation in the axial inlet device is after narrowing the cross-section of flow channel and at the beginning of the diffuser section. Additional sudden expansion at the outlet of the axial inlet diffuser section does not affect the cavitation characteristics of the impeller, however, improves cavitation characteristics of the axial inlet device. For considered geometric parameters of the axial inlet device the cavitation in the impeller begins earlier than in the axial inlet device. That is, the considered design of the axial inlet device will not be subjected to destruction at the ensuring operation without cavitation in the impeller.

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

    International Nuclear Information System (INIS)

    Li, Zhen; Han, Jiesheng; Lu, Jinjun; Chen, Jianmin

    2015-01-01

    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

  3. The cavitation erosion of ultrasonic sonotrode during large-scale metallic casting: Experiment and simulation.

    Science.gov (United States)

    Tian, Yang; Liu, Zhilin; Li, Xiaoqian; Zhang, Lihua; Li, Ruiqing; Jiang, Ripeng; Dong, Fang

    2018-05-01

    Ultrasonic sonotrodes play an essential role in transmitting power ultrasound into the large-scale metallic casting. However, cavitation erosion considerably impairs the in-service performance of ultrasonic sonotrodes, leading to marginal microstructural refinement. In this work, the cavitation erosion behaviour of ultrasonic sonotrodes in large-scale castings was explored using the industry-level experiments of Al alloy cylindrical ingots (i.e. 630 mm in diameter and 6000 mm in length). When introducing power ultrasound, severe cavitation erosion was found to reproducibly occur at some specific positions on ultrasonic sonotrodes. However, there is no cavitation erosion present on the ultrasonic sonotrodes that were not driven by electric generator. Vibratory examination showed cavitation erosion depended on the vibration state of ultrasonic sonotrodes. Moreover, a finite element (FE) model was developed to simulate the evolution and distribution of acoustic pressure in 3-D solidification volume. FE simulation results confirmed that significant dynamic interaction between sonotrodes and melts only happened at some specific positions corresponding to severe cavitation erosion. This work will allow for developing more advanced ultrasonic sonotrodes with better cavitation erosion-resistance, in particular for large-scale castings, from the perspectives of ultrasonic physics and mechanical design. Copyright © 2018 Elsevier B.V. All rights reserved.

  4. Effect of ultrasound on dynamics characteristic of the cavitation bubble in grinding fluids during honing process.

    Science.gov (United States)

    Guo, Ce; Zhu, Xijing

    2018-03-01

    The effect of ultrasound on generating and controlling the cavitation bubble of the grinding fluid during ultrasonic vibration honing was investigated. The grinding fluid on the surface of the honing stone was measured by utilizing the digital microscope VHX-600ESO. Based on analyzing the cavitation mechanism of the grinding fluid, the bubble dynamics model under conventional honing (CH) and ultrasonic vibration honing (UVH) was established respectively. Difference of dynamic behaviors of the bubble between the cases in UVH and CH was compared respectively, and the effects of acoustic amplitude and ultrasonic frequency on the bubble dynamics were simulated numerically using the Runge-Kutta fourth order method with variable step size adaptive control. Finally, the cavitation intensity of grinding fluids under ultrasound was measured quantitatively using acoustimeter. The results showed that the grinding fluid subjected to ultrasound can generate many bubbles and further forms numerous groups of araneose cavitation bubbles on the surface of the honing stone. The oscillation of the bubble under UVH is more intense than the case under CH, and the maximum velocity of the bubble wall under UVH is higher two magnitudes than the case under CH. For lower acoustic amplitude, the dynamic behaviors of the bubble under UVH are similar to that case under CH. As increasing acoustic amplitude, the cavitation intensity of the bubble is growing increased. Honing pressure has an inhabitation effect on cavitation effect of the grinding fluid. The perfect performance of cavitation of the grinding fluid can be obtained when the device of UVH is in the resonance. However, the cavitation intensity of the grinding fluid can be growing weakened with increasing ultrasonic frequency, when the device of UVH is in the off-resonance. The experimental results agree with the theoretical and numerical analysis, which provides a method for exploring applications of the cavitation effect in

  5. The influence of surface roughness on cloud cavitation flow around hydrofoils

    Science.gov (United States)

    Hao, Jiafeng; Zhang, Mindi; Huang, Xu

    2017-08-01

    The aim of this study is to investigate experimentally the effect of surface roughness on cloud cavitation around Clark-Y hydrofoils. High-speed video and particle image velocimetry (PIV) were used to obtain cavitation patterns images (Prog. Aerosp. Sci. 37: 551-581, 2001), as well as velocity and vorticity fields. Results are presented for cloud cavitating conditions around a Clark-Y hydrofoil fixed at angle of attack of α =8{°} for moderate Reynolds number of Re=5.6 × 105 . The results show that roughness had a great influence on the pattern, velocity and vorticity distribution of cloud cavitation. For cavitating flow around a smooth hydrofoil (A) and a rough hydrofoil (B), cloud cavitation occurred in the form of finger-like cavities and attached subulate cavities, respectively. The period of cloud cavitation around hydrofoil A was shorter than for hydrofoil B. Surface roughness had a great influence on the process of cloud cavitation. The development of cloud cavitation around hydrofoil A consisted of two stages: (1) Attached cavities developed along the surface to the trailing edge; (2) A reentrant jet developed, resulting in shedding and collapse of cluster bubbles or vortex structure. Meanwhile, its development for hydrofoil B included three stages: (1) Attached cavities developed along the surface to the trailing edge, with accumulation and rotation of bubbles at the trailing edge of the hydrofoil affecting the flow field; (2) Development of a reentrant jet resulted in the first shedding of cavities. Interaction and movement of flows from the pressure side and suction side brought liquid water from the pressure side to the suction side of the hydrofoil, finally forming a reentrant jet. The jet kept moving along the surface to the leading edge of the hydrofoil, resulting in large-scale shedding of cloud bubbles. Several vortices appeared and dissipated during the process; (3) Cavities grew and shed again.

  6. Frequency characteristics of liquid hydrogen cavitating flow over a NACA0015 hydrofoil

    Science.gov (United States)

    Zhu, Jiakai; Wang, Shunhao; Qiu, Limin; Zhi, Xiaoqin; Zhang, Xiaobin

    2018-03-01

    Large eddy simulation on unsteady cavitating flow of liquid hydrogen over a three-dimensional NACA0015 hydrofoil with the attack angle (α) of 6° are carried out to investigate the dynamic features of cavity with the existence of thermal effects. The numerical model considers the compressibility of both liquid and vapor phase, and is validated by comparing the results with the available experimental data. Special emphasis is put on analyzing the frequency characteristics of cavitation cloud. Strouhal number (St) is plotted against σ/2α (σ is cavitation number), and the water cavitation data reported by Andrt et al. are also used as a reference. It is found that the St number for LH2 cavitation is much smaller than the water, in which the thermal effects are generally not considered, at the same σ/2α value when it is greater than about 2.0, while it returns to the same level as water when σ/2α decreases to below 2.0. The reason is primarily ascribed to the thermal effects, and the detailed explanations are given based on the recognitions that the shedding mechanism of cavitation clouds is predominated by the combined action of the vortex flow and thermal effects. While, when σ/2α decreases to a critical value, the relative effect of the thermal effects on the cavitation dynamics is greatly weakened compared with the mechanism due to the vortex flow, like those in isothermal cavitation flow in traditional fluids. The results provide a deeper understanding of the cryogenic fluid cavitation flow.

  7. Numerical Prediction of Tip Vortex Cavitation for Marine Propellers in Non-uniform Wake

    Science.gov (United States)

    Zhu, Zhi-Feng; Zhou, Fang; Li, Dan

    2017-07-01

    Tip vortex cavitation is the first type of cavitation to take place around most marine propellers. But the numerical prediction of tip vortex cavitation is one of the challenges for propeller wake because of turbulence dissipation during the numerical simulation. Several parameters of computational mesh and numerical algorithm are tested by mean of the predicted length of tip vortex cavtiation to validate a developed method. The predicted length of tip vortex cavtiation is on the increase about 0.4 propeller diameters using the developed numerical method. The predicted length of tip vortex cavtiation by RNG k - ɛ model is about 3 times of that by SST k - ω model. Therefore, based on the validation of the present approach, the cavitating flows generated by two rotating propellers under a non-uniform inflow are calculated further. The distributions of axial velocity, total pressure and vapor volume fraction in the transversal planes across tip vortex region are shown to be useful in analyzing the feature of the cavitating flow. The strongest kernel of tip vortex cavitation is not at the position most close to blade tip but slightly far away from the region. During the growth of tip vortex cavitation extension, it appears short and thick, and then it becomes long and thin. The pressure fluctuations at the positions inside tip vortex region also validates the conclusion. A key finding of the study is that the grids constructed especially for tip vortex flows by using separated computational domain is capable of decreasing the turbulence dissipation and correctly capturing the feature of propeller tip vortex cavitation under uniform and non-uniform inflows. The turbulence model and advanced grids is important to predict tip vortex cavitation.

  8. The influence of surface roughness on cloud cavitation flow around hydrofoils

    Science.gov (United States)

    Hao, Jiafeng; Zhang, Mindi; Huang, Xu

    2018-02-01

    The aim of this study is to investigate experimentally the effect of surface roughness on cloud cavitation around Clark-Y hydrofoils. High-speed video and particle image velocimetry (PIV) were used to obtain cavitation patterns images (Prog. Aerosp. Sci. 37: 551-581, 2001), as well as velocity and vorticity fields. Results are presented for cloud cavitating conditions around a Clark-Y hydrofoil fixed at angle of attack of α =8{°} for moderate Reynolds number of Re=5.6 × 105. The results show that roughness had a great influence on the pattern, velocity and vorticity distribution of cloud cavitation. For cavitating flow around a smooth hydrofoil (A) and a rough hydrofoil (B), cloud cavitation occurred in the form of finger-like cavities and attached subulate cavities, respectively. The period of cloud cavitation around hydrofoil A was shorter than for hydrofoil B. Surface roughness had a great influence on the process of cloud cavitation. The development of cloud cavitation around hydrofoil A consisted of two stages: (1) Attached cavities developed along the surface to the trailing edge; (2) A reentrant jet developed, resulting in shedding and collapse of cluster bubbles or vortex structure. Meanwhile, its development for hydrofoil B included three stages: (1) Attached cavities developed along the surface to the trailing edge, with accumulation and rotation of bubbles at the trailing edge of the hydrofoil affecting the flow field; (2) Development of a reentrant jet resulted in the first shedding of cavities. Interaction and movement of flows from the pressure side and suction side brought liquid water from the pressure side to the suction side of the hydrofoil, finally forming a reentrant jet. The jet kept moving along the surface to the leading edge of the hydrofoil, resulting in large-scale shedding of cloud bubbles. Several vortices appeared and dissipated during the process; (3) Cavities grew and shed again.

  9. 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.

  10. Methods for Cavitation Prediction on Tip-Modified Propellers in Ship Wake Fields

    DEFF Research Database (Denmark)

    Shin, Keun Woo; Regener, Pelle Bo; Andersen, Poul

    2015-01-01

    Unsteady cavitation simulations on a tip-modified propellerin behind-hull condition are made by both BoundaryElement Method (BEM) and Computational FluidDynamics (CFD).As the hull geometry typically is not disclosed to thepropeller designer and thus cannot be included in thesimulation, other...... types of hullwake fields: One originating from model test measurementsand the other from a bare hull RANS simulation at thecavitation test Reynolds number. By comparing simulationresults, the different numerical approaches are evaluated foraccuracy of the unsteady cavitation prediction...... as a propellerdesign tool complementing the cavitation tunnel test....

  11. Spatio-temporal description of the cavitating flow behavior around NACA 2412 hydrofoil

    Science.gov (United States)

    Rudolf, P.; Štefan, D.; Sedlář, M.; Kozák, J.; Habán, V.; Huzlík, R.

    2015-12-01

    Spatio-temporal description of the cavitating flow around hydrofoil with 8 degrees incidence using proper orthogonal decomposition (POD) is presented. POD is a suitable tool, which provides information not only about the flow dynamics, but also about relevance of different flow structures. POD also enables to track energy transport within the domain and energy transfer among the eigenmodes of the flow field. Analysis documents change of the flow structure for decreasing cavitation number, which can be most likely attributed to sheet/cloud cavitation transition.

  12. 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.

  13. Predicting Cavitation on Marine and Hydrokinetic Turbine Blades with AeroDyn V15.04

    Energy Technology Data Exchange (ETDEWEB)

    Murray, Robynne [National Renewable Energy Laboratory (NREL), Golden, CO (United States)

    2017-09-14

    Cavitation is an important consideration in the design of marine and hydrokinetic (MHK) turbines. The National Renewable Energy Laboratory's AeroDyn performance code was originally developed for horizontal-axis wind turbines and did not have the capability to predict cavitation inception. Therefore, AeroDyn has been updated to include the ability to predict cavitation on MHK turbines based on user-specified vapor pressure and submerged depth. This report outlines a verification of the AeroDyn V15.04 performance code for MHK turbines through a comparison to publicly available performance data.

  14. Transmission of High Frequency Vibrations in Rotating Systems. Application to Cavitation Detection in Hydraulic Turbines

    Directory of Open Access Journals (Sweden)

    David Valentín

    2018-03-01

    Full Text Available One of the main causes of damage in hydraulic turbines is cavitation. While not all cavitation appearing in a turbine is of a destructive type, erosive cavitation can severely affect the structure, thus increasing maintenance costs and reducing the remaining useful life of the machine. Of all types of cavitation, the maximum erosion occurs when clouds of bubbles collapse on the runner surface (cloud cavitation. When this occurs it is associated with a substantial increase in noise, and vibrations that are propagated everywhere throughout the machine. The generation of these cavitation clouds may occur naturally or it may be the response to a periodic pressure fluctuation, like the rotor/stator interaction in a hydraulic turbine. Erosive bubble cavitation generates high-frequency vibrations that are modulated by the shedding frequency. Therefore, the methods for the detection of erosive cavitation in hydraulic turbines are based on the measurement and demodulation of high-frequency vibrations. In this paper, the feasibility of detecting erosive cavitation in hydraulic turbines is investigated experimentally in a rotating disk system, which represents a simplified hydraulic turbine structure. The test rig used consists of a rotating disk submerged in a tank of water and confined with nearby axial and radial rigid surfaces. The excitation patterns produced by cloud cavitation are reproduced with a PZT (piezoelectric patch located on the disk. These patterns include pseudo-random excitations of different frequency bands modulated by one low carrier frequency, which model the erosive cavitation characteristics. Different types of sensors have been placed in the stationary and in the rotating parts (accelerometers, acoustic emission (AE, and a microphone in order to detect the excitation pattern. The results obtained for all the sensors tested have been compared in detail for the different excitation patterns applied to the disk. With this information

  15. Cavitation dynamics and directional microbubble ejection induced by intense femtosecond laser pulses in liquids

    Science.gov (United States)

    Faccio, D.; Tamošauskas, G.; Rubino, E.; Darginavičius, J.; Papazoglou, D. G.; Tzortzakis, S.; Couairon, A.; Dubietis, A.

    2012-09-01

    We study cavitation dynamics when focusing ring-shaped femtosecond laser beams in water. This focusing geometry reduces detrimental nonlinear beam distortions and enhances energy deposition within the medium, localized at the focal spot. We observe remarkable postcollapse dynamics of elongated cavitation bubbles with high-speed ejection of microbubbles out of the laser focal region. Bubbles are ejected along the laser axis in both directions (away and towards the laser). The initial shape of the cavitation bubble is also seen to either enhance or completely suppress jet formation during collapse. In the absence of jetting, microbubble ejection occurs orthogonal to the laser propagation axis.

  16. Cavitation dynamics and directional microbubble ejection induced by intense femtosecond laser pulses in liquids.

    Science.gov (United States)

    Faccio, D; Tamošauskas, G; Rubino, E; Darginavičius, J; Papazoglou, D G; Tzortzakis, S; Couairon, A; Dubietis, A

    2012-09-01

    We study cavitation dynamics when focusing ring-shaped femtosecond laser beams in water. This focusing geometry reduces detrimental nonlinear beam distortions and enhances energy deposition within the medium, localized at the focal spot. We observe remarkable postcollapse dynamics of elongated cavitation bubbles with high-speed ejection of microbubbles out of the laser focal region. Bubbles are ejected along the laser axis in both directions (away and towards the laser). The initial shape of the cavitation bubble is also seen to either enhance or completely suppress jet formation during collapse. In the absence of jetting, microbubble ejection occurs orthogonal to the laser propagation axis.

  17. A critical pressure based panel method for prediction of unsteady loading of marine propellers under cavitation

    International Nuclear Information System (INIS)

    Liu, P.; Bose, N.; Colbourne, B.

    2002-01-01

    A simple numerical procedure is established and implemented into a time domain panel method to predict hydrodynamic performance of marine propellers with sheet cavitation. This paper describes the numerical formulations and procedures to construct this integration. Predicted hydrodynamic loads were compared with both a previous numerical model and experimental measurements for a propeller in steady flow. The current method gives a substantial improvement in thrust and torque coefficient prediction over a previous numerical method at low cavitation numbers of less than 2.0, where severe cavitation occurs. Predicted pressure coefficient distributions are also presented. (author)

  18. Shockwave and cavitation bubble dynamics of atmospheric air

    Directory of Open Access Journals (Sweden)

    Leela Ch.

    2013-11-01

    Full Text Available 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.

  19. 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.

  20. Investigations of the role of cavitation in low-frequency sonophoresis using acoustic spectroscopy.

    Science.gov (United States)

    Tezel, Ahmet; Sens, Ashley; Mitragotri, Samir

    2002-02-01

    Application of low-frequency ultrasound significantly enhances skin permeability. The enhancement of skin permeability is mediated by cavitation, oscillation, and collapse of gaseous cavities. In this article, we report detailed investigations of the occurrence of cavitation during low-frequency sonophoresis. Cavitation was monitored by recording pressure amplitudes of subharmonic emission and broadband noise at four different ultrasound frequencies in the range of 20-100 kHz and at various intensities in the range of 0-2.6 W/cm(2). Enhancement of skin conductivity, in the presence of sodium lauryl sulfate (SLS), was also measured under the same ultrasound conditions. Enhancement of skin conductivity correlated well with the amplitude of broadband noise, which suggests the role of transient cavitation in low-frequency sonophoresis. No correlation was found between the subharmonic pressure amplitude and conductivity enhancement. Copyright 2002 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 91:444-453, 2002

  1. PTAC: a computer program for pressure-transient analysis, including the effects of cavitation. [LMFBR

    Energy Technology Data Exchange (ETDEWEB)

    Kot, C A; Youngdahl, C K

    1978-09-01

    PTAC was developed to predict pressure transients in nuclear-power-plant piping systems in which the possibility of cavitation must be considered. The program performs linear or nonlinear fluid-hammer calculations, using a fixed-grid method-of-characteristics solution procedure. In addition to pipe friction and elasticity, the program can treat a variety of flow components, pipe junctions, and boundary conditions, including arbitrary pressure sources and a sodium/water reaction. Essential features of transient cavitation are modeled by a modified column-separation technique. Comparisons of calculated results with available experimental data, for a simple piping arrangement, show good agreement and provide validation of the computational cavitation model. Calculations for a variety of piping networks, containing either liquid sodium or water, demonstrate the versatility of PTAC and clearly show that neglecting cavitation leads to erroneous predictions of pressure-time histories.

  2. An experimental investigation of artificial supercavitation generated by air injection behind disk-shaped cavitators

    Directory of Open Access Journals (Sweden)

    Byoung-Kwon Ahn

    2017-03-01

    Full Text Available In this paper, we investigated physical characteristics of an artificial supercavity generated behind an axisymmetric cavitator. Experiments for the same model were carried out at two different cavitation tunnels of the Chungnam National University and the University of Minnesota, and the results were compared and verified with each other. We measured pressures inside the cavity and observed the cavity formation by using a high-speed camera. Cavitation parameters were evaluated in considering blockage effects of the tunnel, and gravitational effects on supercavity dimensions were examined. Cavity dimensions corresponding to the unbounded cavitation number were compared. In addition, we investigated how artificial supercavitation develops according to the combination of injection positions and direction.

  3. 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.

  4. Defect structures in nickel and SUS304SS formed by the collapse of cavitation bubbles

    Energy Technology Data Exchange (ETDEWEB)

    Yoshiie, T., E-mail: yoshiie@rri.kyoto-u.ac.j [Research Reactor Institute, Kyoto University, Kumatori-cho, Sennan-gun, Osaka-fu 590-0494 (Japan); Sato, K.; Xu, Q. [Research Reactor Institute, Kyoto University, Kumatori-cho, Sennan-gun, Osaka-fu 590-0494 (Japan); Komatsu, M. [Research Reactor Institute, Kyoto University, Kumatori-cho, Sennan-gun, Osaka-fu 590-0494 (Japan); Hiroshima Institute of Technology, Saeki-ku, Hiroshima-ken 731-5193 (Japan); Futakawa, M.; Naoe, T. [Research Reactor Institute, Kyoto University, Kumatori-cho, Sennan-gun, Osaka-fu 590-0494 (Japan); J-PARC Center, Japan Atomic Energy Agency, Tokai-mura, Ibaraki-ken 319-1195 (Japan); Kawai, M. [Research Reactor Institute, Kyoto University, Kumatori-cho, Sennan-gun, Osaka-fu 590-0494 (Japan); High Energy Accelerator Research Organization, Oho, Tsukuba-shi, Ibaraki-ken 305-0801 (Japan)

    2010-03-15

    A mercury target in high-power spallation neutron sources is subjected to pressure waves induced by a proton beam. The subsequent formation and collapse of cavitation bubbles lead to cavitation damage on the target vessel, especially the beam window. The cavitation damage in Ni and austenitic stainless steel SUS304SS were studied by using an electro-Magnetic IMpact Testing Machine (MIMTM) developed to simulate the damage. The existence of dislocations, stacking fault tetrahedra and vacancies was detected by positron annihilation lifetime measurements in Ni, and non-cellular dislocation structures were observed by transmission electron microscopy in Ni and SUS304SS. In addition, a high density of twins was observed in SUS304SS. These results were compared with those of high-speed compression tests using a high-speed projectile, proving that the cavitation damage caused by MIMTM corresponded to high-speed deformation.

  5. 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.

  6. The numerical study of the cavitation-structure interaction around 3D flexible hydrofoil

    Science.gov (United States)

    Shi-liang, Hu; Ying, Chen; Chuan-jing, Lu

    2015-12-01

    The closely coupled approach combined the Finite Volume Method (FVM) solver and the Finite Element Method (FEM) solver is applied to simulation the cavitation-structure interaction of a 3D cantilevered flexible hydrofoil in water tunnel. In the cavitating flow, the elastic hydrofoil would deform or vibrate in bending and twisting mode. And the motion of the foil would affect the characteristics of the cavity and the hydrodynamic load on the foil in turn. With smaller cavitation numbers (σv=2.15), the frequency spectrum of the lift on the foil would contain two frequencies which are associated to the cavity shedding and the first bend frequency of the hydrofoil. With larger cavitation number (σv=2.55), the frequency of the lift is completely dominated by the natural frequency of the foil.

  7. Numerical study on cavitating flow due to a hydrofoil near a free surface

    Directory of Open Access Journals (Sweden)

    Ping-Chen Wu

    2016-09-01

    Full Text Available A numerical strategy is proposed for a viscous uniform flow past a 2-D partially cavitating hydrofoil placed at a finite depth from the free surface. The flow was modeled by the Reynolds-averaged Navier–Stokes (RANS equations. A finite-volume method with the SIMPLE scheme and k-ε turbulence model were employed for computations. The “full cavitation model,” which included the effects of vaporization, noncondensible gases and compressibility, was incorporated in the computation of cavitating flow. The cavity shape and free surface were updated iteratively till a reasonable convergence was reached. As for the determination of the free surface, the VOF approach was adopted. The test cases show the accuracy and stability of our procedure to capture the cavitating flow near the free surface.

  8. Combined slurry and cavitation erosion resistance of surface modified SS410 stainless steel

    Science.gov (United States)

    Amarendra, H. J.; Pratap, M. S.; Karthik, S.; Punitha Kumara, M. S.; Rajath, H. C.; Ranjith, H.; Shubhatunga, S. V.

    2018-03-01

    Slurry erosion and combined slurry and cavitation erosion resistance of thermal spray coatings are studied and compared with the as-received martensitic stainless steel material. 70Ni-Cr coatings are deposited on SS 410 material through plasma thermal spray process. The synergy effect of the combined slurry and cavitation erosion resistance of plasma thermal spray coatings were investigated in a slurry pot tester in the presence of bluff bodies known as Cavitation Inducers. Results showed the combined slurry and cavitation erosion resistance of martensitic stainless steel - 410 can be improved by plasma thermal spray coating. It is observed that the plasma spray coated specimens are better erosion resistant than the as- received material, subjected to erosion test under similar conditions. As-received and the surface modified steels are mechanically characterized for its hardness, bending. Morphological studies are conducted through scanning electron microscope.

  9. RANS simulation of cavitation and hull pressure fluctuation for marine propeller operating behind-hull condition

    Directory of Open Access Journals (Sweden)

    Kwang-Jun Paik

    2013-12-01

    Full Text Available 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.

  10. Acoustic methods in sodium flow for characterising pump cavitation and noise erosion correlations

    International Nuclear Information System (INIS)

    Courbiere, E.; Defaucheux, J.; Garnaud, P.

    1982-11-01

    Under the terms of agreements between the CEA and Jeumont-Schneider on fast breeder reactor sodium pumps, joint preliminary water mockup tests were carried out at the Jeumont facility. Similar experiments were carried out on the Superphenix primary sodium pumps during water testings at the EDF facility in Gennevilliers. The purpose of these tests was to define acoustic criteria for pump cavitation and to study the similitude between the mockup and the actual pump. This paper also presents the results of cavitation erosion tests conducted under CEA research programs. Two points are covered in the conclusion. (a) The test results show that pump noise changes with the drop in hydraulic performance characteristics, and can thus be representative of caviting conditions. (b) It should be possible to develop an acoustic method capable of discriminating between erosive and non-destructive cavitation

  11. Experimental analysis of the onset and development of cavitation in a centrifugal pump

    Science.gov (United States)

    Mousmoulis, G.; Karlsen-Davies, N.; Aggidis, G.; Anagnostopoulos, J.; Papantonis, D.

    2017-04-01

    Centrifugal pumps are considered as machines of high importance in a wide range of industries, hence several strategies and methods have been developed in order to ensure their optimum performance under different operating conditions. An important mechanism that can affect pump’s steady and dynamic operation is cavitation, which appears in the low static pressure zone at the inlet of the impeller. Several researchers have studied experimentally the physics of the phenomenon in order to develop different methodologies for its safe detection. The aim of this paper is to study the onset and evolution of cavitation in a centrifugal pump with unshrouded impeller by performing of flow visualization and acoustic emission measurements. The results showed that the acoustic emission technique is able to detect the onset of cavitation, while the leakage backflow through the clearance affects the development of cavitation between the impeller blades.

  12. 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

  13. A survey of LMFBR cavitation technology in the U.S.A

    International Nuclear Information System (INIS)

    Cha, Y.S.; Huebotter, P.R.; Hopenfeld, J.

    1976-01-01

    Several experimental programmes of a basic and applied nature were established in the USA in order to develop guidelines to ensure design and operation of LMFBR hydraulic components free from cavitation and/or cavitation damage. As of March 1976, most of these experimental programs are still in progress. Each programme is briefly described. The available interium data are presented. References that are relevant are provided

  14. Hydrodynamic cavitation as a strategy to enhance the efficiency of lignocellulosic biomass pretreatment

    DEFF Research Database (Denmark)

    Terán Hilares, Ruly; Ramos, Lucas; da Silva, Silvio Silvério

    2017-01-01

    Hydrodynamic cavitation (HC) is a process technology with potential for application in different areas including environmental, food processing, and biofuels production. Although HC is an undesirable phenomenon for hydraulic equipment, the net energy released during this process is enough...... to accelerate certain chemical reactions. The application of cavitation energy to enhance the efficiency of lignocellulosic biomass pretreatment is an interesting strategy proposed for integration in biorefineries for the production of bio-based products. Moreover, the use of an HC-assisted process...

  15. Prediction of Cavitating Waterjet Propulsor Performance Using a Boundary Element Method

    Science.gov (United States)

    2007-10-01

    fast ferries. Compared to conventional propellers, waterjet propulsors provide several advantages. A comprehensive review of issues concerning the...approach Viscous Flow Analysis on a Partially Cavitating (Kerwin et al, 1987), as was recently implemented in Hydrofoil ," Journal of Ship Research, Vol. 41...Cavitating Hydrofoils ," Journal of Fluid Mechanics, Performance of Ducted Propeller," Sixth International Vol. 254, pp. 151-181, 1993. Symposium on

  16. Lamellar thickness and stretching temperature dependency of cavitation in semicrystalline polymers.

    Directory of Open Access Journals (Sweden)

    Yaotao Wang

    Full Text Available Polybutene-1 (PB-1, a typical semicrystalline polymer, in its stable form I shows a peculiar temperature dependent strain-whitening behavior when being stretched at temperatures in between room temperature and melting temperature of the crystallites where the extent of strain-whitening weakens with the increasing of stretching temperature reaching a minima value followed by an increase at higher stretching temperatures. Correspondingly, a stronger strain-hardening phenomenon was observed at higher temperatures. The strain-whitening phenomenon in semicrystalline polymers has its origin of cavitation process during stretching. In this work, the effect of crystalline lamellar thickness and stretching temperature on the cavitation process in PB-1 has been investigated by means of combined synchrotron ultrasmall-angle and wide-angle X-ray scattering techniques. Three modes of cavitation during the stretching process can be identified, namely "no cavitation" for the quenched sample with the thinnest lamellae where only shear yielding occurred, "cavitation with reorientation" for the samples stretched at lower temperatures and samples with thicker lamellae, and "cavitation without reorientation" for samples with thinner lamellae stretched at higher temperatures. The mode "cavitation with reorientation" occurs before yield point where the plate-like cavities start to be generated within the lamellar stacks with normal perpendicular to the stretching direction due to the blocky substructure of the crystalline lamellae and reorient gradually to the stretching direction after strain-hardening. The mode of "cavitation without reorientation" appears after yield point where ellipsoidal shaped cavities are generated in those lamellae stacks with normal parallel to the stretching direction followed by an improvement of their orientation at larger strains. X-ray diffraction results reveal a much improved crystalline orientation for samples with thinner lamellae

  17. Lamellar thickness and stretching temperature dependency of cavitation in semicrystalline polymers.

    Science.gov (United States)

    Wang, Yaotao; Jiang, Zhiyong; Fu, Lianlian; Lu, Ying; Men, Yongfeng

    2014-01-01

    Polybutene-1 (PB-1), a typical semicrystalline polymer, in its stable form I shows a peculiar temperature dependent strain-whitening behavior when being stretched at temperatures in between room temperature and melting temperature of the crystallites where the extent of strain-whitening weakens with the increasing of stretching temperature reaching a minima value followed by an increase at higher stretching temperatures. Correspondingly, a stronger strain-hardening phenomenon was observed at higher temperatures. The strain-whitening phenomenon in semicrystalline polymers has its origin of cavitation process during stretching. In this work, the effect of crystalline lamellar thickness and stretching temperature on the cavitation process in PB-1 has been investigated by means of combined synchrotron ultrasmall-angle and wide-angle X-ray scattering techniques. Three modes of cavitation during the stretching process can be identified, namely "no cavitation" for the quenched sample with the thinnest lamellae where only shear yielding occurred, "cavitation with reorientation" for the samples stretched at lower temperatures and samples with thicker lamellae, and "cavitation without reorientation" for samples with thinner lamellae stretched at higher temperatures. The mode "cavitation with reorientation" occurs before yield point where the plate-like cavities start to be generated within the lamellar stacks with normal perpendicular to the stretching direction due to the blocky substructure of the crystalline lamellae and reorient gradually to the stretching direction after strain-hardening. The mode of "cavitation without reorientation" appears after yield point where ellipsoidal shaped cavities are generated in those lamellae stacks with normal parallel to the stretching direction followed by an improvement of their orientation at larger strains. X-ray diffraction results reveal a much improved crystalline orientation for samples with thinner lamellae stretched at higher

  18. Vulnerability to drought-induced cavitation in poplars : synthesis and future opportunities

    OpenAIRE

    Fichot, Regis; Brignolas, Franck; Cochard, Herve; Ceulemans, Reinhart

    2015-01-01

    Abstract: Vulnerability to drought-induced cavitation is a key trait of plant water relations. Here, we summarize the available literature on vulnerability to drought-induced cavitation in poplars (Populus spp.), a genus of agronomic, ecological and scientific importance. Vulnerability curves and vulnerability parameters (including the water potential inducing 50% loss in hydraulic conductivity, P50) were collected from 37 studies published between 1991 and 2014, covering a range of 10 specie...

  19. Effect of large elastic strains on cavitation instability predictions for elastic-plastic solids

    DEFF Research Database (Denmark)

    Tvergaard, Viggo

    1999-01-01

    For an infinite solid containing a void, the cavitation instability limit is defined as the remote stress-and strain state, at which the void grows without bound, driven by the elastic energy stored in the surrounding material. Such cavitation limits have been analysed by a number of authors...... hydrostatic tension as well as for more general axisymmetric remote stress field, with an initially spherical void. Different levels of strain hardening are considered. (C) 1998 Elsevier Science Ltd. All rights reserved....

  20. One-way-coupling simulation of cavitation accompanied by high-speed droplet impact

    Energy Technology Data Exchange (ETDEWEB)

    Kondo, Tomoki; Ando, Keita, E-mail: kando@mech.keio.ac.jp [Department of Mechanical Engineering, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522 (Japan)

    2016-03-15

    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. 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.

  2. Application of modified κ-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 κ-ω model for predicting the cavitating flow in a centrifugal pump, in which the modified κ-ω model and Schnerr-Sauer cavitation model were combined with ANSYS CFX. To evaluate the modified and standard κ-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 κ-ω model showed agreement with most of the experimental data. The cavitating flow in the centrifugal pump obtained by the modified κ-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.

  3. Study of Cavitation Shedding Dynamics on a NACA0015 Hydrofoil Using X-Ray Densitometry

    Science.gov (United States)

    Ganesh, Harish; Wu, Juliana; Ceccio, Steven

    2016-11-01

    Cavitation dynamics on the NACA0015 hydrofoil at several attack angles are found to be spectrally rich, being multi-modal with abrupt changes in Strouhal number with change in cavitation number. Present study focusses on identifying the physical mechanisms responsible for the change in cavitation dynamics on a NACA0015 hydrofoil in a re-circulating water tunnel using time resolved X-ray densitometry. Time-resolved void fraction flow fields obtained using X-ray densitometry, synchronized with acoustic noise measurements using a hydrophone, are used to identify different flow features and mechanisms that are responsible for the change in the observed spectral behavior. It is shown that under higher cavitation numbers, the shedding mechanism is predominantly re-entrant liquid flow based, but as the cavitation number drops many different processes are at play. At lower cavitation numbers, the shed cavity cloud collapse arrests cavity growth and this results in altered cycle dynamics and hence the Strouhal number. In addition, propagation bubbly shock waves are also found to be a dominant mechanism of shedding for certain conditions. The multi-modal nature of the acoustic pressure signature is explained by presence of different flow features, which could be concurrent or alternating. Office of Naval Research.

  4. Numerical investigation on cavitation flow of hydrofoil and its flow noise with emphasis on turbulence models

    Science.gov (United States)

    Kim, Sanghyeon; Cheong, Cheolung; Park, Warn-Gyu

    2017-06-01

    In this study, cavitation flow of hydrofoils is numerically investigated to characterize the effects of turbulence models on cavitation-flow patterns and the corresponding radiated sound waves. The two distinct flow conditions are considered by varying the mean flow velocity and angle of attack, which are categorized under the experimentally observed unstable or stable cavitation flows. To consider the phase interchanges between the vapor and the liquid, the flow fields around the hydrofoil are analyzed by solving the unsteady compressible Reynolds-averaged Navier-Stokes equations coupled with a mass-transfer model, also referred to as the cavitation model. In the numerical solver, a preconditioning algorithm with dual-time stepping techniques is employed in generalized curvilinear coordinates. The following three types of turbulence models are employed: the laminar-flow model, standard k - ɛ turbulent model, and filter-based model. Hydro-acoustic field formed by the cavitation flow of the hydrofoil is predicted by applying the Ffowcs Williams and Hawkings equation to the predicted flow field. From the predicted results, the effects of the turbulences on the cavitation flow pattern and radiated flow noise are quantitatively assessed in terms of the void fraction, sound-pressure-propagation directivities, and spectrum.

  5. Cavitation erosion resistance of diamond-like carbon coating on stainless steel

    International Nuclear Information System (INIS)

    Cheng, Feng; Jiang, Shuyun

    2014-01-01

    Two diamond-like carbon (DLC) coatings are prepared on stainless steel 304 by cathodic arc plasma deposition technology at different substrate bias voltages and arc currents (−200 V/80 A, labeled DLC-1, and −100 V/60 A, labeled DLC-2). Cavitation tests are performed by using a rotating-disk test rig to explore the cavitation erosion resistance of the DLC coating. The mass losses, surface morphologies, chemical compositions and the phase constituents of the specimens after cavitation tests are examined by using digital balance, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD), respectively. The results indicate that the DLC-2 coatings can elongate the incubation period of stainless steel, leading to an excellent cavitation erosion resistance as compared to the untreated stainless steel specimens. After duration of 100 h cavitation test, serious damaged surfaces and plenty of scratches can be observed on the surfaces of the stainless steel specimens, while only a few grooves and tiny pits are observed on the DLC-2 coatings. It is concluded that, decreasing micro defects and increasing adhesion can reduce the delamination of DLC coating, and the erosion continues in the stainless steel substrate after DLC coating failure, and the eroded surface of the substrate is subjected to the combined action from cavitation erosion and slurry erosion.

  6. Cavitational effects in aqueous endodontic irrigants generated by near-infrared lasers.

    Science.gov (United States)

    Hmud, Raghad; Kahler, William A; George, Roy; Walsh, Laurence James

    2010-02-01

    Laser-generated pressure waves may have application for removing debris and smear layers from root canals. Past work has employed middle infrared erbium lasers. The present study examined whether near infrared 940 and 980 nm diode lasers (Biolase Ezlase and Sirona Sirolaser, respectively) could induce cavitations in aqueous media. Laser energy was delivered into a capillary tube using a 200 microm fiber, and the formation of cavitations observed with a microscope. In the first part of the study, a range of laser parameters were trialled to establish conditions which form cavitations within 5 seconds of the commencement of laser irradiation. The second part of the study compared cavitation in distilled water, aerated tap water, degassed distilled water, ozonated water, 3 and 6% hydrogen peroxide using panel setting of 2.5 W/25 Hz for the Sirolaser, and 4 W/10 Hz for the Ezlase. Both diode laser systems could induce cavitation in water-base media by the formation and implosion of water vapour. Laser power played a more important role than pulse frequency or pulse interval. Optimal laser-initiated cavitation occurred when weak (3%) peroxide solutions were used as the target irrigant, rather than water. This phenomenon has potential for enhancing debridement in endodontics. Copyright 2010 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

  7. Development of turbopump cavitation performance test facility and the test of inducer performance

    International Nuclear Information System (INIS)

    Sohn, Dong Kee; Kim, Chun Tak; Yoon, Min Soo; Cha, Bong Jun; Kim, Jin Han; Yang, Soo Seok

    2001-01-01

    A performance test facility for turbopump inducer cavitation was developed and the inducer cavitation performance tests were performed. Major components of the performance test facility are driving unit, test section, piping, water tank, and data acquisition and control system. The maximum of testing capability of this facility are as follows: flow rate - 30kg/s; pressure - 13 bar, rotational speed - 10,000rpm. This cavitation test facility is characterized by the booster pump installed at the outlet of the pump that extends the flow rate range, and by the pressure control system that makes the line pressure down to vapor pressure. The vacuum pump is used for removing the dissolved air in the water as well as the line pressure. Performance tests were carried out and preliminary data of test model inducer were obtained. The cavitation performance test and cavitation bubble flow visualization were also made. This facility is originally designed for turbopump inducer performance test and cavitation test. However it can be applied to the pump impeller performance test in the future with little modification

  8. Numerical investigation on cavitation flow of hydrofoil and its flow noise with emphasis on turbulence models

    Directory of Open Access Journals (Sweden)

    Sanghyeon Kim

    2017-06-01

    Full Text Available In this study, cavitation flow of hydrofoils is numerically investigated to characterize the effects of turbulence models on cavitation-flow patterns and the corresponding radiated sound waves. The two distinct flow conditions are considered by varying the mean flow velocity and angle of attack, which are categorized under the experimentally observed unstable or stable cavitation flows. To consider the phase interchanges between the vapor and the liquid, the flow fields around the hydrofoil are analyzed by solving the unsteady compressible Reynolds-averaged Navier–Stokes equations coupled with a mass-transfer model, also referred to as the cavitation model. In the numerical solver, a preconditioning algorithm with dual-time stepping techniques is employed in generalized curvilinear coordinates. The following three types of turbulence models are employed: the laminar-flow model, standard k − ε turbulent model, and filter-based model. Hydro-acoustic field formed by the cavitation flow of the hydrofoil is predicted by applying the Ffowcs Williams and Hawkings equation to the predicted flow field. From the predicted results, the effects of the turbulences on the cavitation flow pattern and radiated flow noise are quantitatively assessed in terms of the void fraction, sound-pressure-propagation directivities, and spectrum.

  9. Cavitation erosion resistance of diamond-like carbon coating on stainless steel

    Energy Technology Data Exchange (ETDEWEB)

    Cheng, Feng; Jiang, Shuyun, E-mail: jiangshy@seu.edu.cn

    2014-02-15

    Two diamond-like carbon (DLC) coatings are prepared on stainless steel 304 by cathodic arc plasma deposition technology at different substrate bias voltages and arc currents (−200 V/80 A, labeled DLC-1, and −100 V/60 A, labeled DLC-2). Cavitation tests are performed by using a rotating-disk test rig to explore the cavitation erosion resistance of the DLC coating. The mass losses, surface morphologies, chemical compositions and the phase constituents of the specimens after cavitation tests are examined by using digital balance, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD), respectively. The results indicate that the DLC-2 coatings can elongate the incubation period of stainless steel, leading to an excellent cavitation erosion resistance as compared to the untreated stainless steel specimens. After duration of 100 h cavitation test, serious damaged surfaces and plenty of scratches can be observed on the surfaces of the stainless steel specimens, while only a few grooves and tiny pits are observed on the DLC-2 coatings. It is concluded that, decreasing micro defects and increasing adhesion can reduce the delamination of DLC coating, and the erosion continues in the stainless steel substrate after DLC coating failure, and the eroded surface of the substrate is subjected to the combined action from cavitation erosion and slurry erosion.

  10. Review of numerical models of cavitating flows with the use of the homogeneous approach

    Directory of Open Access Journals (Sweden)

    Niedźwiedzka Agnieszka

    2016-06-01

    Full Text Available The focus of research works on cavitation has changed since the 1960s; the behaviour of a single bubble is no more the area of interest for most scientists. Its place was taken by the cavitating flow considered as a whole. Many numerical models of cavitating flows came into being within the space of the last fifty years. They can be divided into two groups: multi-fluid and homogeneous (i.e., single-fluid models. The group of homogenous models contains two subgroups: models based on transport equation and pressure based models. Several works tried to order particular approaches and presented short reviews of selected studies. However, these classifications are too rough to be treated as sufficiently accurate. The aim of this paper is to present the development paths of numerical investigations of cavitating flows with the use of homogeneous approach in order of publication year and with relatively detailed description. Each of the presented model is accompanied by examples of the application area. This review focuses not only on the list of the most significant existing models to predict sheet and cloud cavitation, but also on presenting their advantages and disadvantages. Moreover, it shows the reasons which inspired present authors to look for new ways of more accurate numerical predictions and dimensions of cavitation. The article includes also the division of source terms of presented models based on the transport equation with the use of standardized symbols.

  11. Swirling cavitation improves the emulsifying properties of commercial soy protein isolate.

    Science.gov (United States)

    Yang, Feng; Liu, Xue; Ren, Xian'e; Huang, Yongchun; Huang, Chengdu; Zhang, Kunming

    2018-04-01

    Since emulsifying properties are important functional properties of soy protein, many physical, chemical, and enzymatic methods have been applied to treat soy protein to improve emulsifying properties. In this study, we investigated the effects of swirling cavitation at different pressures and for different times on emulsifying and physicochemical properties of soy protein isolate (SPI). The SPI treated with swirling cavitation showed a significant decrease in particle size and increase in solubility. Emulsions formed from treated SPI had higher emulsifying activity and emulsifying stability indexes, smaller oil droplet sizes, lower flocculation indexes, higher adsorbed proteins, lower interfacial protein concentrations, and lower creaming indexes than those formed from untreated SPI, indicating that swirling cavitation improved the emulsifying properties of the SPI. Furthermore, swirling cavitation treatment significantly enhanced the surface hydrophobicity, altered the disulfide bond and exposed sulfhydryl group contents of the SPI. The secondary structure of the SPI was also influenced by swirling cavitation, with an increase in β-sheet content and a decrease in α-helix, β-turn, and random coil contents. In addition, several significant correlations between physicochemical and emulsifying properties were revealed by Pearson correlation analysis, suggesting that the physicochemical changes observed in treated SPI, including the decreased particle size, increased solubility and surface hydrophobicity, and enhanced β-sheet formation, may explain the improved emulsifying properties of the isolate. Thus, our findings implied that swirling cavitation treatment may be an effective technique to improve the emulsifying properties of SPI. Copyright © 2017 Elsevier B.V. All rights reserved.

  12. 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.

  13. 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.

  14. A detector for monitoring the onset of cavitation during therapy-level measurements of ultrasonic power

    International Nuclear Information System (INIS)

    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 (≤ 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

  15. Visualization of the cavitation bubbles produced by a clinical shock wave field using a micropulse LED light

    Science.gov (United States)

    Kang, Gwansuk; Huh, Jung Sik; Choi, Min Joo

    2017-07-01

    Extracorporeal shock wave therapy employs intense shock waves that produce cavitation bubbles understood to play an important role in therapeutic effects. This study considers shock-wave-induced cavitation bubbles, expected to be closely associated with treated therapeutic regions. A simple optical method was devised to visualize the cavitation bubbles under micropulse LED light illumination and to capture an afterimage of the bubbles for their entire lifetime from formation to collapse. The optical images of the cavitation bubbles produced by a clinical shock wave therapeutic device were shown to preserve the characteristics of the focusing shock wave field. The similarity of the characteristics may enable the cavitation cloud image to provide the intensity and location of shock wave irradiation for the clinical quality assurance of therapeutic devices. Further research that includes the dynamic effects in the static images of cavitation bubbles is suggested.

  16. Integrated ultrasound and magnetic resonance imaging for simultaneous temperature and cavitation monitoring during focused ultrasound therapies.

    Science.gov (United States)

    Arvanitis, Costas D; McDannold, Nathan

    2013-11-01

    Ultrasound can be used to noninvasively produce different bioeffects via viscous heating, acoustic cavitation, or their combination, and these effects can be exploited to develop a wide range of therapies for cancer and other disorders. In order to accurately localize and control these different effects, imaging methods are desired that can map both temperature changes and cavitation activity. To address these needs, the authors integrated an ultrasound imaging array into an MRI-guided focused ultrasound (MRgFUS) system to simultaneously visualize thermal and mechanical effects via passive acoustic mapping (PAM) and MR temperature imaging (MRTI), respectively. The system was tested with an MRgFUS system developed for transcranial sonication for brain tumor ablation in experiments with a tissue mimicking phantom and a phantom-filled ex vivo macaque skull. In experiments on cavitation-enhanced heating, 10 s continuous wave sonications were applied at increasing power levels (30-110 W) until broadband acoustic emissions (a signature for inertial cavitation) were evident. The presence or lack of signal in the PAM, as well as its magnitude and location, were compared to the focal heating in the MRTI. Additional experiments compared PAM with standard B-mode ultrasound imaging and tested the feasibility of the system to map cavitation activity produced during low-power (5 W) burst sonications in a channel filled with a microbubble ultrasound contrast agent. When inertial cavitation was evident, localized activity was present in PAM and a marked increase in heating was observed in MRTI. The location of the cavitation activity and heating agreed on average after registration of the two imaging modalities; the distance between the maximum cavitation activity and focal heating was -3.4 ± 2.1 mm and -0.1 ± 3.3 mm in the axial and transverse ultrasound array directions, respectively. Distortions and other MRI issues introduced small uncertainties in the PAM

  17. A Study on Cavitation Erosion Behaviors of Corrosion-resistance Thermal Spray Coating Materials

    International Nuclear Information System (INIS)

    Jin, Hee Seok

    2003-02-01

    The hydraulic machinery of screw propeller and pump impellers is damaged by cavitation erosion in sea water. The cavitation erosion is a phenomenon leading a functional disorder of various fluid machinery and dropping off in efficiency by cavity fluid fluctuation. This study is investigated the cavitation erosion of various metallic coatings made by thermal spraying methods. The coating materials are AMDRY625, Cr 2 O 3 , SUS316, Zn, Al. These metals are coated on substrate of high strength brass ( Cu - Zn ). Test specimens are immersed in 3.5% NaCl solution for 500 and 1000 hours, respectively. After pre-corrosion, the cavitation erosion test was conducted on coating specimens in 3.5% NaCl solution along 210 minutes. The results are summarized as follows : 1. Both substrate and test specimens coated by thermal spray underwent weight loss in proportion to the time length of the cavitation erosion test, and the weight loss happened more to 1,000 hour-immersed test specimens and 500 hour-immersed ones in the time order rather than the ones in non-corrosion condition. 2. Substrate and Amdry625 and SUS316 test specimens were all influenced very little by weight loss regardless of the time length and the conditions of the test. 3. The amount of weight loss of aluminum and zinc test specimens and Cr 2 O 3 test specimens heavily increased at the early stage regardless of the conditions but later decreased after the coated layers were fretted by cavitation erosion. 4. The comparison of weight loss after the test showed that Amdry625, SUS316 and substrate underwent very little weight loss, proving to be the very likely materials to bear cavitation erosion but aluminum and zinc and Cr 2 O 3 underwent very great weight loss, proving to be the very unlikely materials to bear cavitation erosion. 5. After the test, the surfaces of Amdry625, SUS316 and substrate showed that they had been less damaged by cavitation erosion but the rest showed that they had been very much damaged by

  18. 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

  19. Numerical prediction of cavitating flow around a hydrofoil using pans and improved shear stress transport k-omega model

    Directory of Open Access Journals (Sweden)

    Zhang De-Sheng

    2015-01-01

    Full Text Available The prediction accuracies of partially-averaged Navier-Stokes model and improved shear stress transport k-ω turbulence model for simulating the unsteady cavitating flow around the hydrofoil were discussed in this paper. Numerical results show that the two turbulence models can effectively reproduce the cavitation evolution process. The numerical prediction for the cycle time of cavitation inception, development, detachment, and collapse agrees well with the experimental data. It is found that the vortex pair induced by the interaction between the re-entrant jet and mainstream is responsible for the instability of the cavitation shedding flow.

  20. Extracting a Whisper from the DIN: A Bayesian-Inductive Approach to Learning an Anticipatory Model of Cavitation

    Energy Technology Data Exchange (ETDEWEB)

    Kercel, S.W.

    1999-11-07

    For several reasons, Bayesian parameter estimation is superior to other methods for inductively learning a model for an anticipatory system. Since it exploits prior knowledge, the analysis begins from a more advantageous starting point than other methods. Also, since "nuisance parameters" can be removed from the Bayesian analysis, the description of the model need not be as complete as is necessary for such methods as matched filtering. In the limit of perfectly random noise and a perfect description of the model, the signal-to-noise ratio improves as the square root of the number of samples in the data. Even with the imperfections of real-world data, Bayesian methods approach this ideal limit of performance more closely than other methods. These capabilities provide a strategy for addressing a major unsolved problem in pump operation: the identification of precursors of cavitation. Cavitation causes immediate degradation of pump performance and ultimate destruction of the pump. However, the most efficient point to operate a pump is just below the threshold of cavitation. It might be hoped that a straightforward method to minimize pump cavitation damage would be to simply adjust the operating point until the inception of cavitation is detected and then to slightly readjust the operating point to let the cavitation vanish. However, due to the continuously evolving state of the fluid moving through the pump, the threshold of cavitation tends to wander. What is needed is to anticipate cavitation, and this requires the detection and identification of precursor features that occur just before cavitation starts.

  1. Relations between acoustic cavitation and skin resistance during intermediate- and high-frequency sonophoresis.

    Science.gov (United States)

    Rich, Kyle T; Hoerig, Cameron L; Rao, Marepalli B; Mast, T Douglas

    2014-11-28

    Enhanced skin permeability is known to be achieved during sonophoresis due to ultrasound-induced cavitation. However, the mechanistic role of cavitation during sonophoresis has been extensively investigated only for low-frequency (LFS, sonophoresis (HFS, >1 MHz). The electrical resistance of skin, a surrogate measure of the permeability of skin to a variety of compounds, was measured to quantify the reduction and subsequent recovery of the skin barrier during and after exposure to pulsed (1 second pulse, 20% duty cycle) 0.41 and 2.0 MHz ultrasound over a range of acoustic powers (0-21.7 W) for 30 min. During IFS, significant skin resistance reductions and acoustic emissions from cavitation were measured exclusively when cavitation was isolated outside of the skin. Time-dependent skin resistance reductions measured during IFS correlated significantly with subharmonic and broadband emission levels. During HFS, significant skin resistance reductions were accompanied by significant acoustic emissions from cavitation measured during trials that isolated cavitation activity either outside of skin or within skin. Time-dependent skin resistance reductions measured during HFS correlated significantly greater with subharmonic than with broadband emission levels. The reduction of the skin barrier due to sonophoresis was reversible in all trials; however, effects incurred during IFS recovered more slowly and persisted over a longer period of time than HFS. These results quantitatively demonstrate the significance of cavitation during sonophoresis and suggest that the mechanisms and post-treatment longevity of permeability enhancement due to IFS and HFS treatments are different. Copyright © 2014 Elsevier B.V. All rights reserved.

  2. Cavitation experiments at butterfly valves in water and in sodium at 850K

    International Nuclear Information System (INIS)

    Mendte, K.; Klemm, J.

    1976-01-01

    Throttling valves fabricated by Gebrueder Adams, Bochum will be installed in the SNR-300 plant, serving as flow control devices during postscram operation. Valves of the same type were used in the pump test facility at INTERATOM (APB) to throttle down the sodium pump head. This test loop was to demonstrate at the same time that the prototype SNR valves could withstand the design conditions (flow and temperature) during endurance tests. To optimize the pump test facility design, a 350mm diameter valve was tested in water under cavitational conditions. With the aid of calculational method described herein, the hydraulic kinetic relationships of the throttled flow could predict the influences leading to cavitation. The results of the calculational model showed close agreement with that, actually incurred during visual observations. Valves of the same type and in 350mm as well as in 600mm diameter sizes were again cavitation tested in sodium. During this test, in addition to the hydraulic data, noise measurements were taken using accelerometers. Concerning such tests, the following inherent difficulties are to be noted: a) The noise measurements would register influences of general entrained bubbles (gas and vapor bubbles) causing increased attenuation of the noise in the medium of transmission. Therefore, it is mandatory that the loop be carefully degassed to enable measurement of the cavitational bubbles. b) The primary function of these valves in the test loop APB is to dissipate the pressure head of the pump being tested. Through energy dissipation across the valves, they become strong sources of noise generation, in broad-band frequency levels at these locations up to a factor 50 larger than those at the pump. The cavitation dependent vaporizing noise, developed by incipient cavitation, was, inspite of background noise, measurable. Similar to that for the water test runs, incipient cavitation was detected at the valves when the corresponding sigma worths were

  3. Sonoluminescence and acoustic emission spectra at different stages of cavitation zone development.

    Science.gov (United States)

    Dezhkunov, N V; Francescutto, A; Serpe, L; Canaparo, R; Cravotto, G

    2018-01-01

    The way in which a cavitation zone develops in a focused pulsed ultrasound field is studied in this work. Sonoluminescence (SL), total hydrophone output and cavitation noise spectra have been recorded across a gradual, smooth increase in applied voltage. It is shown that the cavitation zone passes through a number of stages of evolution, according to increasing ultrasound intensity, decreasing pulse period and increasing ultrasound pulse duration. Sonoluminescence is absent in the first phase and the hydrophone output spectra consists of a main line with two or three harmonics whose intensity is much lower than that of the main (fundamental) line. The second stage sees the onset of SL whose intensity increases smoothly and is accompanied by the appearance of higher harmonics and subharmonics in the cavitation noise spectra. In some cases, the wide-band (WBN) component can be seen in noise spectra during the final part of the second stage. In the third stage, SL intensity increases significantly and often quite sharply, while WBN intensity increases in the same manner. This is accompanied by a synchronous increase in the absorption of ultrasound by the cavitation zone, which is manifested in a sharp decrease in the hydrophone output. In the fourth stage, both SL and WBN intensities tend to decrease despite the increased voltage applied to the transducer. Furthermore, the fundamental line tends to decrease in strength as well, despite the increasing ultrasound intensity. The obtained results clearly identify the different stages of cavitation zone development using cavitation noise spectra analyses. We then hypothesize that three of the above stages may be responsible for three known types of ultrasound action on biological cells: damping viability, reversible cell damage (sonoporation) and irreversible damage/cytotoxicity. Copyright © 2017 Elsevier B.V. All rights reserved.

  4. Grain-boundary cavitation and migration during high temperature fatigue

    International Nuclear Information System (INIS)

    Snowden, K.U.; Stathers, P.A.; Hughes, D.S.

    1980-01-01

    Studies have been made of the grain-boundary phenomena (cavitation, grain-boundary migration, fractional density change) that occurred during high temperature fatigue tests on commercial purity copper and crystal bar zirconium. The tests were performed on sheet specimens in reverse plane bending at 16 Hz at constant strain amplitudes and under vacuum. The temperature ranges were 360 to 550 0 C for copper and 600 to 775 0 C for zirconium. The numbers of cavities per unit area were estimated at various stages of the fatigue life for copper and zirconium tested at a strain amplitude of +- 0.21%. Most cavities were nucleated during the first 10 to 20% of the fatigue life, when an orthogonal or 'square' grain structure was formed by grain-boundary migration. The rate of migration was highest during this period and the average migration distance was proportional to Nsup(α), where N is the number of strain cycles and α = 2/3. The fractional density change was proportional to N throughout the fatigue life. For zirconium, the temperature dependence of the rates of boundary migration and fractional density change exhibited two distinct regions, which were characterised by differences in apparent activation energy. However, in the case of copper, there was no evidence for a transition temperature. The variations of the fractional density change with N and with temperature were compared with those predicted by theories of high temperature fatigue. (author)

  5. Corner-transport-upwind lattice Boltzmann model for bubble cavitation

    Science.gov (United States)

    Sofonea, V.; Biciuşcǎ, T.; Busuioc, S.; Ambruş, Victor E.; Gonnella, G.; Lamura, A.

    2018-02-01

    Aiming to study the bubble cavitation problem in quiescent and sheared liquids, a third-order isothermal lattice Boltzmann model that describes a two-dimensional (2D) fluid obeying the van der Waals equation of state, is introduced. The evolution equations for the distribution functions in this off-lattice model with 16 velocities are solved using the corner-transport-upwind (CTU) numerical scheme on large square lattices (up to 6144 ×6144 nodes). The numerical viscosity and the regularization of the model are discussed for first- and second-order CTU schemes finding that the latter choice allows to obtain a very accurate phase diagram of a nonideal fluid. In a quiescent liquid, the present model allows us to recover the solution of the 2D Rayleigh-Plesset equation for a growing vapor bubble. In a sheared liquid, we investigated the evolution of the total bubble area, the bubble deformation, and the bubble tilt angle, for various values of the shear rate. A linear relation between the dimensionless deformation coefficient D and the capillary number Ca is found at small Ca but with a different factor than in equilibrium liquids. A nonlinear regime is observed for Ca≳0.2 .

  6. Sonoluminescence and dynamics of cavitation bubble populations in sulfuric acid.

    Science.gov (United States)

    Thiemann, Andrea; Holsteyns, Frank; Cairós, Carlos; Mettin, Robert

    2017-01-01

    The detailed link of liquid phase sonochemical reactions and bubble dynamics is still not sufficiently known. To further clarify this issue, we image sonoluminescence and bubble oscillations, translations, and shapes in an acoustic cavitation setup at 23kHz in sulfuric acid with dissolved sodium sulfate and xenon gas saturation. The colour of sonoluminescence varies in a way that emissions from excited non-volatile sodium atoms are prominently observed far from the acoustic horn emitter ("red region"), while such emissions are nearly absent close to the horn tip ("blue region"). High-speed images reveal the dynamics of distinct bubble populations that can partly be linked to the different emission regions. In particular, we see smaller strongly collapsing spherical bubbles within the blue region, while larger bubbles with a liquid jet during collapse dominate the red region. The jetting is induced by the fast bubble translation, which is a consequence of acoustic (Bjerknes) forces in the ultrasonic field. Numerical simulations with a spherical single bubble model reproduce quantitatively the volume oscillations and fast translation of the sodium emitting bubbles. Additionally, their intermittent stopping is explained by multistability in a hysteretic parameter range. The findings confirm the assumption that bubble deformations are responsible for pronounced sodium sonoluminescence. Notably the observed translation induced jetting appears to serve as efficient mixing mechanism of liquid into the heated gas phase of collapsing bubbles, thus potentially promoting liquid phase sonochemistry in general. Copyright © 2016 Elsevier B.V. All rights reserved.

  7. Restorative treatment for initial, cavitated and gross coronal carious lesions.

    Science.gov (United States)

    Brennan, D S; Balasubramanian, M; Spencer, A J

    2016-09-01

    Treatment patterns for caries have been shown to reflect high rates of restorative services. The objective of this study was to investigate types of restorative treatment provided to patients with a main diagnosis of coronal caries in relation to the severity of the caries lesion. A random sample of Australian dentists was surveyed by mailed questionnaires in 2009-2010 (response rate 67%). Data on types of restorative treatment, patient characteristics and main diagnosis were collected from a service log. Models of service rates adjusted for age, gender, insurance status and reason for visit showed that compared to the reference category of initial caries lesions, there were lower rates [Rate Ratio, 95% CI] of adhesive anterior restorative services [0.57, 0.34-0.95] and lower rates of adhesive posterior restorations [0.56, 0.40-0.79] for gross lesions. Treatment of coronal caries was characterized by high rates of adhesive posterior restorative services, but gross lesions had lower rates of both anterior and posterior adhesive restorations. Types of restorative treatment for coronal caries were similar between initial and cavitated lesions. This could indicate scope for the adoption of more minimum intervention approaches to the management of initial carious lesions. © 2015 Australian Dental Association.

  8. MACULAR DETACHMENT ASSOCIATED WITH INTRACHOROIDAL CAVITATION IN NONPATHOLOGICAL MYOPIC EYES.

    Science.gov (United States)

    Ando, Yoshimasa; Inoue, Makoto; Ohno-Matsui, Kyoko; Kusumi, Yumi; Iida, Tomohiro; Hirakata, Akito

    2015-10-01

    To report the characteristics of a macular detachment associated with peripapillary intrachoroidal cavitation (ICC) and the outcomes of vitrectomy. The medical records of 69 eyes of 61 patients who underwent vitrectomy for macular detachment or macular retinoschisis but without vitreomacular traction or optic disc pit were reviewed. Optical coherence tomography was used to determine the morphology of the ICC. The outcomes of vitrectomy including the creation of a posterior vitreous detachment and internal limiting membrane peeling were evaluated. An ICC was detected in 3 of 3 eyes without pathologic myopia but none in 66 eyes with pathologic myopia (P detachment in all eyes. Optical coherence tomography detected a connection between the vitreous cavity and the ICC in two eyes with pit-like splitting and between the subretinal space and the ICC in two eyes. The macular detachment was resolved 5 months to 6 months postoperatively with improvement of vision. A macular detachment with ICC can be present in nonpathological myopic eyes. Vitreous surgery to create a posterior vitreous detachment with internal limiting membrane peeling may help resolve the macular detachment.

  9. Water hammer and cavitational hammer in process plant pipe systems

    International Nuclear Information System (INIS)

    Dudlik, A.; Schoenfeld, S.B.H.; Hagemann, O.; Fahlenkamp, H.

    2003-01-01

    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.)

  10. Shock waves from non-spherically collapsing cavitation bubbles

    Science.gov (United States)

    Supponen, Outi; Obreschkow, Danail; Farhat, Mohamed

    2017-11-01

    Combining simultaneous high-speed imaging and hydrophone measurements, we uncover details of the multiple shock wave emission from laser-induced cavitation bubbles collapsing in a non-spherical way. For strongly deformed bubbles collapsing near a free surface, we identify the distinct shock waves caused by the jet impact onto the opposite bubble wall and by the individual collapses of the remaining bubble segments. The energy carried by each of these shocks depends on the level of bubble deformation, quantified by the anisotropy parameter ζ, the dimensionless equivalent of the Kelvin impulse. For jetting bubbles, at ζ hammer pressure is found to be the most energetic shock. Through statistical analysis of the experimental data and theoretical derivations, and by comparing bubbles deformed by different sources (variable gravity achieved on parabolic flights, and neighboring free and rigid surfaces), we find that the shock peak pressure may be approximated as the jet impact-induced water hammer as ph = 0.45 (ρc2 Δp) 1 / 2ζ-1 .

  11. [Polyphenolic antioxidants efficiently protect urease from inactivation by ultrasonic cavitation].

    Science.gov (United States)

    Metelitsa, D I; Tarun, E I; Losev, Iu P

    2002-01-01

    Inactivation of urease (25 nM) in aqueous solutions (pH 5.0-6.0) treated with low-frequency ultrasound (LFUS; 27 kHz, 60 Wt/cm2, 36-56 degrees C) or high-frequency ultrasound (HFUS; 2.64 MHz, 1 Wt/cm2, 36 or 56 degrees C) has been characterized quantitatively, using first-order rate constants: kin, aggregate inactivation; kin*, thermal inactivation; and kin* (US), ultrasonic inactivation. Within the range from 1 nM to 10 microM, propyl gallate (PG) decreases approximately threefold the rate of LFUS-induced inactivation of urease (56 degrees C), whereas resorcinol poly-2-disulfide prevents this process at 1 nM or higher concentrations. PG completely inhibits HFUS-induced inactivation of urease at 1 nM (36 degrees C) or 10 nM (56 degrees C). At 0.2-10 microM, human serum albumin (HSA) increases the resistance of urease (at 56 degrees C) treated with HFUS to temperature- and cavitation-induced inactivation. Complexes of gallic acid polydisulfide (GAPDS) with HSA (GAPDS-HSA), formed by conjugation of 1.0 nM PGDS with 0.33 nM HSA, prevent HFUS-induced urease inactivation (56 degrees C).

  12. Application of hydrodynamic cavitation in ballast water treatment.

    Science.gov (United States)

    Cvetković, Martina; Kompare, Boris; Klemenčič, Aleksandra Krivograd

    2015-05-01

    Ballast water is, together with hull fouling and aquaculture, considered the most important factor of the worldwide transfer of invasive non-indigenous organisms in aquatic ecosystems and the most important factor in European Union. With the aim of preventing and halting the spread of the transfer of invasive organisms in aquatic ecosystems and also in accordance with IMO's International Convention for the Control and Management of Ships Ballast Water and Sediments, the systems for ballast water treatment, whose work includes, e.g. chemical treatment, ozonation and filtration, are used. Although hydrodynamic cavitation (HC) is used in many different areas, such as science and engineering, implied acoustics, biomedicine, botany, chemistry and hydraulics, the application of HC in ballast water treatment area remains insufficiently researched. This paper presents the first literature review that studies lab- and large-scale setups for ballast water treatment together with the type-approved systems currently available on the market that use HC as a step in their operation. This paper deals with the possible advantages and disadvantages of such systems, as well as their influence on the crew and marine environment. It also analyses perspectives on the further development and application of HC in ballast water treatment.

  13. High strain-rate soft material characterization via inertial cavitation

    Science.gov (United States)

    Estrada, Jonathan B.; Barajas, Carlos; Henann, David L.; Johnsen, Eric; Franck, Christian

    2018-03-01

    Mechanical characterization of soft materials at high strain-rates is challenging due to their high compliance, slow wave speeds, and non-linear viscoelasticity. Yet, knowledge of their material behavior is paramount across a spectrum of biological and engineering applications from minimizing tissue damage in ultrasound and laser surgeries to diagnosing and mitigating impact injuries. To address this significant experimental hurdle and the need to accurately measure the viscoelastic properties of soft materials at high strain-rates (103-108 s-1), we present a minimally invasive, local 3D microrheology technique based on inertial microcavitation. By combining high-speed time-lapse imaging with an appropriate theoretical cavitation framework, we demonstrate that this technique has the capability to accurately determine the general viscoelastic material properties of soft matter as compliant as a few kilopascals. Similar to commercial characterization algorithms, we provide the user with significant flexibility in evaluating several constitutive laws to determine the most appropriate physical model for the material under investigation. Given its straightforward implementation into most current microscopy setups, we anticipate that this technique can be easily adopted by anyone interested in characterizing soft material properties at high loading rates including hydrogels, tissues and various polymeric specimens.

  14. Cavitation microstreaming and stress fields created by microbubbles.

    Science.gov (United States)

    Collis, James; Manasseh, Richard; Liovic, Petar; Tho, Paul; Ooi, Andrew; Petkovic-Duran, Karolina; Zhu, Yonggang

    2010-02-01

    Cavitation microstreaming plays a role in the therapeutic action of microbubbles driven by ultrasound, such as the sonoporative and sonothrombolytic phenomena. Microscopic particle-image velocimetry experiments are presented. Results show that many different microstreaming patterns are possible around a microbubble when it is on a surface, albeit for microbubbles much larger than used in clinical practice. Each pattern is associated with a particular oscillation mode of the bubble, and changing between patterns is achieved by changing the sound frequency. Each microstreaming pattern also generates different shear stress and stretch/compression distributions in the vicinity of a bubble on a wall. Analysis of the micro-PIV results also shows that ultrasound-driven microstreaming flows around bubbles are feasible mechanisms for mixing therapeutic agents into the surrounding blood, as well as assisting sonoporative delivery of molecules across cell membranes. Patterns show significant variations around the bubble, suggesting sonoporation may be either enhanced or inhibited in different zones across a cellular surface. Thus, alternating the patterns may result in improved sonoporation and sonothrombolysis. The clear and reproducible delineation of microstreaming patterns based on driving frequency makes frequency-based pattern alternation a feasible alternative to the clinically less desirable practice of increasing sound pressure for equivalent sonoporative or sonothrombolytic effect. Surface divergence is proposed as a measure relevant to sonoporation.

  15. Characterization of Cavitation Effects in Therapeutic Ultrasound: Sonophoresis Experiments and Quantitative Emission Measurements

    Science.gov (United States)

    Rich, Kyle Thomas

    Fundamental to the use of ultrasound for therapeutic benefit is a comprehensive understanding and identification of the underlying mechanisms. Specifically, consequential bioeffects during therapeutic ultrasound commonly coincide with the onset of microbubble cavitation, especially for drug-delivery applications. Hence, there is a need for monitoring and characterization techniques that provide quantitative metrics for assessing cavitation activity during ultrasound exposure in order to monitor treatment progress, identify interactions of cavitation with tissue, and provide dosimetry metrics for avoiding potentially harmful exposures both for therapeutic and diagnostic purposes. The primary goal of the work presented in this dissertation was to characterize the role of cavitation during sonophoresis using quantitative and system-independent approaches. First, this goal was accomplished using traditional passive cavitation detection techniques to monitor cavitation emissions during in vitro intermediate- (IFS, insonation frequency f 0 = 0.1-1 MHz) and high-frequency sonophoresis (HFS, f0 >1 MHz) treatments of in vitro porcine skin samples in Chapter 2. The relative intensity of subharmonic acoustic emissions from stable cavitation occurring near the skin surface was measured using a single-element PCD and was shown to correspond with reductions in skin resistivity, a surrogate measure of permeability, for all sonophoresis treatments. However, the acoustic emissions measured during sonophoresis provided incommensurable quantities between the different treatment regimes due to unaccounted frequency-dependent variations in the sensitivity of the PCD and diffraction effects in the cavitation-radiated pressure field received by the PCD. Second, methods were developed and employed to characterize the wideband absolute receive sensitivity of single-element focused and unfocused receivers in Chapter 3. By employing these characterization techniques and by accounting for the

  16. Cavitation Estimates by Orbit Prediction of a Journal Bearing - Finite Element Modelling and Experimental Studies Cavitation Estimates by Orbit Prediction of a Journal Bearing - Finite Element Modelling and Experimental Studies

    DEFF Research Database (Denmark)

    Christiansen, Christian Kim; Klit, Peder; Walther, Jens Honore

    2015-01-01

    . Validation of the results is done against the Ruston and Hornsby 6VEB-X Mk III engine. Besides the numerical investigations a cavitation test rig has been developed. With this rig it is possible to generate cavitation under controlled conditions in terms ofload/eccentricity and rotational speed...

  17. Comparison of Nannochloropsis sp. cells disruption between hydrodynamic cavitation and conventional extraction

    Directory of Open Access Journals (Sweden)

    Setyawan Martomo

    2018-01-01

    Full Text Available Biodiesel production from microalgae is one of the solution of the future energy problem, but its production cost is still high. One of the costly stages of this process is the lipid extraction process. It can be reduced by microalgae cell disruption. One of the mechanical method to cell disruption with the lowest energy requirement is hydrodynamic cavitation. This aim of this study is to evaluate the distribution coefficient and the mass transfer coefficient value of lipid extraction of Nannochloropsis sp. assisted by hydrodynamic cavitation and compare with conventional extraction. The hydrodynamic cavitation extraction was done at 34 °C, 1 atm. The conventional extraction was done at 34 °C, 1 atm with stirring speed 260 and 1000 rpm. The experimental result shows that the distribution coefficient dependent on the temperature with the values for 50, 44, 38 and 34 °C were 0.502, 0.394, 0.349, and 0.314 respectively. And it was according to Van’ Hoff equation with the values of ΔH° was 20.718 kJ/mol and ΔS° was 58.05 J/mol/K. The hydrodynamic cavitation extraction was faster than conventional. The mass transfer coefficient values for hydrodynamic cavitation, conventional 260 rpm and 1000 rpm were 7.373, 0.534 and 0.121 1/s respectively.

  18. Shear-induced hydrodynamic cavitation as a tool for pharmaceutical micropollutants removal from urban wastewater.

    Science.gov (United States)

    Zupanc, Mojca; Kosjek, Tina; Petkovšek, Martin; Dular, Matevž; Kompare, Boris; Širok, Brane; Stražar, Marjeta; Heath, Ester

    2014-05-01

    In this study, the removal of clofibric acid, ibuprofen, naproxen, ketoprofen, carbamazepine and diclofenac residues from wastewater, using a novel shear-induced cavitation generator has been systematically studied. The effects of temperature, cavitation time and H2O2 dose on removal efficiency were investigated. Optimisation (50°C; 15 min; 340 mg L(-1) of added H2O2) resulted in removal efficiencies of 47-86% in spiked deionised water samples. Treatment of actual wastewater effluents revealed that although matrix composition reduces removal efficiency, this effect can be compensated for by increasing H2O2 dose (3.4 g L(-1)) and prolonging cavitation time (30 min). Hydrodynamic cavitation has also been investigated as either a pre- or a post-treatment step to biological treatment. The results revealed a higher overall removal efficiency of recalcitrant diclofenac and carbamazepine, when hydrodynamic cavitation was used prior to as compared to post biological treatment i.e., 54% and 67% as compared to 39% and 56%, respectively. This is an important finding since diclofenac is considered as a priority substance to be included in the EU Water Framework Directive. Copyright © 2013 Elsevier B.V. All rights reserved.

  19. Bacterial leakage in roots filled with different medicaments and sealed with Cavit.

    Science.gov (United States)

    Barthel, Claudia R; Zaritzki, Felix F; Raab, Wolfgang H-M; Zimmer, Stefan

    2006-02-01

    The aim of this study was to evaluate the time required by four different root canal medications coupled with the temporary filling material Cavit (ESPE, Seefeld, Germany) to prevent penetration of bacteria into the root canal. There were 145 roots prepared in a standardized manner. Four groups with 15 samples each were dressed with calcium hydroxide (Ca(OH)(2)), a 5% chlorhexidine gel (CHX), a chloromono-campherphenolic compound (ChKM), and Ledermix (LM), respectively, and sealed with Cavit. Four control groups contained identical medications but the roots were left unsealed. The 25 remaining roots served as additional controls. A standard setup for bacterial leakage studies was chosen with Staphylococcus epidermidis as test strain. Cavit application resulted in a significantly better seal compared with the unsealed groups. In the Cavit-sealed groups, all groups differed significantly from one another except for the CHX and the ChKM groups. The Ca(OH)(2) medicated roots provided the longest protection (median of 36 days), followed by the Ledermix-group (27 days) and the CHX (18 days) or ChKM groups (19 days). It may be concluded that Cavit-sealed and medicated root canals do not provide adequate protection against bacterial leakage for more than 1 month.

  20. Continuous Cavitation Designed for Enhancing Radiofrequency Ablation via a Special Radiofrequency Solidoid Vaporization Process.

    Science.gov (United States)

    Zhang, Kun; Li, Pei; Chen, Hangrong; Bo, Xiaowan; Li, Xiaolong; Xu, Huixiong

    2016-02-23

    Lowering power output and radiation time during radiofrequency (RF) ablation is still a challenge. Although it is documented that metal-based magnetothermal conversion and microbubbles-based inertial cavitation have been tried to overcome above issues, disputed toxicity and poor magnetothermal conversion efficiency for metal-based nanoparticles and violent but transient cavitation for microbubbles are inappropriate for enhancing RF ablation. In this report, a strategy, i.e., continuous cavitation, has been proposed, and solid menthol-encapsulated poly lactide-glycolide acid (PLGA) nanocapsules have been constructed, as a proof of concept, to validate the role of such a continuous cavitation principle in continuously enhancing RF ablation. The synthesized PLGA-based nanocapsules can respond to RF to generate menthol bubbles via distinctive radiofrequency solidoid vaporization (RSV) process, meanwhile significantly enhance ultrasound imaging for HeLa solid tumor, and further facilitate RF ablation via the continuous cavitation, as systematically demonstrated both in vitro and in vivo. Importantly, this RSV strategy can overcome drawbacks and limitations of acoustic droplet vaporization (ADV) and optical droplet vaporization (ODV), and will probably find broad applications in further cancer theranostics.

  1. Cavitation Effect of Shock Pressure about Nuclear Power Plant Component Cleaning or Crud Removal

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Seong Man; Lee, Seung Won; Park, Sung Dae; Kang, Sarah; Bang, In Cheol [Ulsan National Institute of Science and Technology, Ulsan (Korea, Republic of)

    2011-05-15

    In nuclear power plant, the problems are caused by corrosion phenomena on the pipe or fuel elements. It can cause the additional cost for plant component recycling or disassembly. Those solutions of problem are chemical method and physical method. Recently ultrasonic and laser methods for cleaning are developing. If fluid flow is attached to the high speed surface of a blade, a large number of bubbles are developed. As it reaches vapor pressure, the fluid vaporizes and forms small bubbles of gas. This is cavitation. Previous study of cavitation shows that predict the onset of cavitation within the pump blade and the degradation in the pressure rise due to the generation and transport of vapor. But cavitation erosion effect can be used for optimized corrosion cleaning. Cavitation can be created in restrict region such as static mixer and orifice. When the bubbles collapse later, they typically cause very strong local shock waves in the fluid, which may be audible and may even damage the blades. Purpose of this study is using shock pressure by micro bubble collapse for second time cleaning in the fluid region of the on product surface

  2. Numerical predictions of the turbulent cavitating flow around a marine propeller and an axial turbine

    Science.gov (United States)

    Morgut, M.; Jošt, D.; Nobile, E.; Škerlavaj, A.

    2015-12-01

    The numerical predictions of cavitating flow around a marine propeller working in non-uniform inflow and an axial turbine are presented. The cavitating flow is modelled using the homogeneous (mixture) model. Time-dependent simulations are performed for the marine propeller case using OpenFOAM. Three calibrated mass transfer models are alternatively used to model the mass transfer rate due to cavitation and the two-equation SST (Shear Stress Transport) turbulence model is employed to close the system of the governing equations. The predictions of the cavitating flow in an axial turbine are carried out with ANSYS-CFX, where only the native mass transfer model with tuned parameters is used. Steady-state simulations are performed in combination with the SST turbulence model, while time-dependent results are obtained with the more advanced SAS (Scale Adaptive Simulation) SST model. The numerical results agree well with the available experimental measurements, and the simulations performed with the three different calibrated mass transfer models are close to each other for the propeller flow. Regarding the axial turbine the effect of the cavitation on the machine efficiency is well reproduced only by the time dependent simulations.

  3. Vulnerability to drought-induced cavitation in poplars: synthesis and future opportunities.

    Science.gov (United States)

    Fichot, Régis; Brignolas, Franck; Cochard, Hervé; Ceulemans, Reinhart

    2015-07-01

    Vulnerability to drought-induced cavitation is a key trait of plant water relations. Here, we summarize the available literature on vulnerability to drought-induced cavitation in poplars (Populus spp.), a genus of agronomic, ecological and scientific importance. Vulnerability curves and vulnerability parameters (including the water potential inducing 50% loss in hydraulic conductivity, P50) were collected from 37 studies published between 1991 and 2014, covering a range of 10 species and 12 interspecific hybrid crosses. Results of our meta-analysis confirm that poplars are among the most vulnerable woody species to drought-induced cavitation (mean P50  = -1.44 and -1.55 MPa across pure species and hybrids, respectively). Yet, significant variation occurs among species (P50 range: 1.43 MPa) and among hybrid crosses (P50 range: 1.12 MPa), within species and hybrid crosses (max. P50 range reported: 0.8 MPa) as well as in response to environmental factors including nitrogen fertilization, irradiance, temperature and drought (max. P50 range reported: 0.75 MPa). Potential implications and gaps in knowledge are discussed in the context of poplar cultivation, species adaptation and climate modifications. We suggest that poplars represent a valuable model for studies on drought-induced cavitation, especially to elucidate the genetic and molecular basis of cavitation resistance in Angiosperms. © 2014 John Wiley & Sons Ltd.

  4. Effects of non-condensable gas on the dynamic oscillations of cavitation bubbles

    Science.gov (United States)

    Zhang, Yuning

    2016-11-01

    Cavitation is an essential topic of multiphase flow with a broad range of applications. Generally, there exists non-condensable gas in the liquid and a complex vapor/gas mixture bubble will be formed. A rigorous prediction of the dynamic behavior of the aforementioned mixture bubble is essential for the development of a complete cavitation model. In the present paper, effects of non-condensable gas on the dynamic oscillations of the vapor/gas mixture bubble are numerically investigated in great detail. For the completeness, a large parameter zone (e.g. bubble radius, frequency and ratio between gas and vapor) is investigated with many demonstrating examples. The mechanisms of mass diffusion are categorized into different groups with their characteristics and dominated regions given. Influences of non-condensable gas on the wave propagation (e.g. wave speed and attenuation) in the bubbly liquids are also briefly discussed. Specifically, the minimum wave speed is quantitatively predicted in order to close the pressure-density coupling relationship usually employed for the cavitation modelling. Finally, the application of the present finding on the development of cavitation model is demonstrated with a brief discussion of its influence on the cavitation dynamics. This work was financially supported by the National Natural Science Foundation of China (Project No.: 51506051).

  5. Pseudopotential multi-relaxation-time lattice Boltzmann model for cavitation bubble collapse with high density ratio

    International Nuclear Information System (INIS)

    Shan Ming-Lei; Zhu Chang-Ping; 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 the present work, the modified forcing scheme for the pseudopotential multi-relaxation-time lattice Boltzmann model developed by Li Q et al. [Li Q, Luo K H and Li X J 2013 Phys. Rev. E 87 053301] 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. It is found that the thermodynamic consistency and surface tension are independent of kinematic viscosity. By homogeneous and heterogeneous cavitation simulation, the ability 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 a collapsing bubble is consistent with the results from experiments and simulations by other numerical methods. It is demonstrated that the present pseudopotential multi-relaxation-time lattice Boltzmann model is applicable and efficient, and the lattice Boltzmann method is an alternative tool for collapsing bubble modeling. (paper)

  6. Predicting the Onset of Cavitation in Automotive Torque Converters—Part I: Designs with Geometric Similitude

    Directory of Open Access Journals (Sweden)

    D. L. Robinette

    2008-01-01

    Full Text Available Dimensional analysis has been applied to automotive torque converters to understand the response of performance to changes in torque, size, working fluid, or operating temperature. The objective of this investigation was to develop a suitable dimensional analysis for estimating the effect of exact geometric scaling of a particular torque converter design on the onset of cavitation. Torque converter operating thresholds for cavitation were determined experimentally with a dynamometer test cell at the stall operating condition using nearfield acoustical measurements. Dimensionless quantities based upon either speed or torque at the onset of cavitation and flow properties (e.g., pressures and temperature dependent fluid properties were developed and compared. The proposed dimensionless stator torque quantity was found to be the most appropriate scaling law for extrapolating cavitation thresholds to multiple diameters. A power product model was fit on dimensionless stator torque data to create a model capable of predicting cavitation thresholds. Comparison of the model to test data taken over a range of operating points showed an error of 3.7%. This is the first paper of a two-part paper. In Part II, application of dimensional analysis will be expanded from torque converters with exact geometric similitude to those of more general design.

  7. Cavitation at the air/water interface induced by CO2 laser: formation, dynamics and mechanism

    Science.gov (United States)

    Hu, Man; Wang, Feng; Deng, Daosheng

    2017-11-01

    We report CO2-laser-induced cavitation at the interface between air and water, since strong photo-thermal effect of water occurs at the infrared wavelength. Using high-speed camera, we record explosive evaporation and the evolution of cavitation at the interface. By analyzing the growth dynamics of cavitation at various experimental conditions, we identify two stages of its growth associated with different mechanisms correspondingly. One stage is an initial faster expanding process driven by the influx of dissolved gas expelled from the surrounding water due to laser heating; and the other stage is a subsequent slower isobaric expanding process related with liquid properties. More quantitatively, we find that the evolution of cavitation at first stage is characterized by scaling law with an exponent of 1/3 for its diameter as a function of time, while its evolution at the second stage can be well described by Rayleigh-Plesset theory. This study of interfacial cavitation due to photo-thermal effect might have implications for solar-steam technology and infrared-laser surgery as well.

  8. A study of wakes trailing a cavitating and ventilated NACA 0015 hydrofoil

    Science.gov (United States)

    Time, Rune W.; Kjeldsen, Morten; Arndt, Roger E.

    2007-11-01

    In certain types of pumping applications oscillations are induced by operation with liquids containing immiscible gas in solution. To understand the physics of this process, a series of tests with a ventilated 2D NACA 0015 hydrofoil were performed in the water tunnel at the St. Anthony Falls Laboratory of the University of Minnesota. A relation between the cavitation index for both ventilated and naturally cavitating flows has been established. This allows direct comparison between the two types of two-phase flows. A good correspondence is found when comparing drag, lift break-down and lift/drag oscillation amplitudes for a properly defined cavitation index. A careful analysis is required to compare the spectral content of oscillatory flow. This study concentrates on analyzing wake structure for selected ventilation rates and cavitation numbers. The wake structure is mapped by conventional PIV techniques. Results for high cavitation/ventilation number flows are presented. Since conventional PIV represents snap shots of a time evolving phenomenon special care needs to be taken for the analysis.

  9. Effect of polymer surface activity on cavitation nuclei stability against dissolution

    Science.gov (United States)

    Porter, Tyrone M.; Crum, Lawrence A.; Stayton, Patrick S.; Hoffman, Allan S.

    2004-08-01

    The persistence of acoustic cavitation in a pulsed wave ultrasound regime depends upon the ability of cavitation nuclei, i.e., bubbles, to survive the off time between pulses. Due to the dependence of bubble dissolution on surface tension, surface-active agents may affect the stability of bubbles against dissolution. In this study, measurements of bubble dissolution rates in solutions of the surface-active polymer poly(propyl acrylic acid) (PPAA) were conducted to test this premise. The surface activity of PPAA varies with solution pH and concentration of dissolved polymer molecules. The surface tension of PPAA solutions (55-72 dynes/cm) that associated with the polymer surface activity was measured using the Wilhelmy plate technique. Samples of these polymer solutions then were exposed to 1.1 MHz high intensity focused ultrasound, and the dissolution of bubbles created by inertial cavitation was monitored using an active cavitation detection scheme. Analysis of the pulse echo data demonstrated that bubble dissolution time was inversely proportional to the surface tension of the solution. Finally, comparison of the experimental results with dissolution times computed from the Epstein-Plesset equation suggests that the radii of residual bubbles from inertial cavitation increase as the surface tension decreases.

  10. Cavitation erosion tests of high tensile stainless steels for the Techno-Superliner (TSL-F) hulls; Techno superliner (TSL-F) sentai kozoyo kokyodo stainless ko no cavitation erosion

    Energy Technology Data Exchange (ETDEWEB)

    Matsuo, M.; Ito, H.; Shibasaki, K. [NKK Corp., Tokyo (Japan); Mizuta, A.; Sugimoto, H. [Kawasaki Heavy Industries, Ltd., Kobe (Japan); Tomono, Y. [Hitachi Zosen Corp., Osaka (Japan)

    1996-12-31

    Investigations were given by using the magnetostrictive vibration method and the high-speed fluid testing method on cavitation erosion resistance of high-tensile stainless steels thought to have high applicability to submerged hull structures of Techno-Supeliner (TSL-L). The investigations revealed that these steels have nearly equivalent resistance to even SUS 304 or 15-5PH steel which is thought to have the highest cavitation erosion resistance among the conventional materials used customarily. An experiment using both materials provided a result different quantitatively but similar qualitatively in relative merits between the materials. Correlation between both materials was presented. A cavitation erosion experiment using a 1/6 scale model of the actual TSL-F was carried out to measure the amount of cavitation erosion generated on wing surfaces. Results from the experiment were used to attempt estimation of cavitation erosion amount at the level of the actual TSL-F. 21 refs., 12 figs., 3 tabs.

  11. Transient cavitating vortical flows around a hydrofoil using k-ω partially averaged Navier-Stokes model

    Science.gov (United States)

    Luo, Xianwu; Huang, Renfang; Ji, Bin

    2016-01-01

    For accurate simulations of wall-bounded turbulent cavitating flows, the present paper proposed a partially averaged Navier-Stokes (PANS) method derived from the k-ω turbulence model. Transient cavitating vortical flows around a NACA66 hydrofoil were simulated by using the k-ω PANS model with various filter parameters (fk = 0.2, 0.5 and 1, while fω = 1/fk) and a mass transfer cavitation model based on the Rayleigh-Plesset equation. Compared with the available experimental data, the k-ω PANS model with fk = 0.2 can accurately reproduce the cavitation evolution with more complicated structures due to the reduction in the predicted eddy viscosity. Further analyses, using the vorticity transport equation, indicate that the transition of cavitation structure from two dimension to three dimension is associated with strong vortex-cavitation interaction, where vortex stretching and dilation may play a major role. Therefore, the k-ω PANS model with the filter parameter of fk = 0.2 is an effective method to numerically predict the transient cavitating vortical flows around hydrofoils. The results obtained in this paper are helpful to provide a physical insight into the mechanisms of cavitation shedding dynamics.

  12. Effects of size and concentration of silt particles on flow and performance of a centrifugal pump under cavitating conditions

    Science.gov (United States)

    Zhao, Weiguo; Han, Xiangdong; Li, Rennian; Zheng, Yingjie; Wang, Yanyan

    2017-12-01

    To research effects of silt particles on the performance and cavitation flow fields, silt-laden cavitation flow was simulated in the centrifugal pump. Silt mean diameters are 0.005 mm and 0.010 mm and silt concentrations are 0.5% and 1.0%. Results show that silt particles with silt mean diameter 0.005 mm and silt concentration 1.0% and silt particles with silt mean diameter 0.010 mm and silt concentration 0.5% promote the development of cavitation and distribution range of vapor is larger than pure water. Effects of silt particles and cavitation make distribution range of turbulent kinetic energy larger than pure water and streamlines are more disorderedly. Silt particles with silt mean diameter 0.010 mm and silt concentration 1.0% have little effect on cavitation and distribution range of vapor is similar with pure water. Effects of silt particles make distribution range of turbulent kinetic energy larger than pure water and streamlines are more disorderedly than pure water. With the increase of silt mean diameter and silt concentration, head and efficiency decrease gradually. For silt particles promoting the evolution of cavitation, distribution range of turbulent kinetic energy is larger and streamlines are more disorderly than silt-laden cavitation flow with silt particles inhibiting the development of cavitation.

  13. Improvement of corrosion resistance of low-alloy steels by resurfacing using multifunction cavitation in water

    Science.gov (United States)

    Ijiri, Masataka; Yoshimura, Toshihiko

    2018-02-01

    Low-alloy steels are based on carbon steel in combination with several percent or less (in many cases, 1 mass%) alloying elements, and they offer improved resistance to corrosion at a cost slightly higher than that of carbon steel. However, these materials do not exhibit the same corrosion resistance as stainless steel. The authors have previously developed a novel multifunction cavitation (MFC) technique, which combines ultrasonic cavitation with water jet cavitation. In this study, MFC was used to modify the surface of Cr-Mo steel (SCM435) and Ni-Cr-Mo steel (SNCM630). MFC was found to improve the residual stress value of the material as the result of surface modification while also imparting high strength and superior corrosion resistance.

  14. Review of parameters influencing the structural response of a submerged body under cavitation conditions

    International Nuclear Information System (INIS)

    Escaler, X; De La Torre, O; Farhat, M

    2015-01-01

    Submerged structures that operate under extreme flows are prone to suffer large scale cavitation attached to their surfaces. Under such conditions the added mass effects differ from the expected ones in pure liquids. Moreover, the existence of small gaps between the structure and surrounding bodies filled with fluid also influence the dynamic response. A series of experiments and numerical simulations have been carried out with a truncated NACA0009 hydrofoil mounted as a cantilever beam at the LMH-EPFL cavitation tunnel. The three first modes of vibration have been determined and analysed under various hydrodynamic conditions ranging from air and still water to partial cavitation and supercavitation. A remote nonintrusive excitation system with piezoelectric patches has been used for the experiments. The effects of the cavity properties and the lateral gap size on the natural frequencies and mode shapes have been determined. As a result, the significance of several parameters in the design of such structures is discussed. (paper)

  15. Lowering of the cavitation threshold in aqueous suspensions of porous silicon nanoparticles for sonodynamic therapy applications

    Energy Technology Data Exchange (ETDEWEB)

    Sviridov, A. P., E-mail: asagittarius89@gmail.com; Osminkina, L. A. [Faculty of Physics, Lomonosov Moscow State University, 119991 Moscow (Russian Federation); Nikolaev, A. L. [Faculty of Chemistry, Lomonosov Moscow State University, 119991 Moscow (Russian Federation); Kudryavtsev, A. A. [Institute of Theoretical and Experimental Biophysics, Russian Academy of Science, 142290 Pushino, Moscow Region (Russian Federation); Vasiliev, A. N. [Faculty of Physics, Lomonosov Moscow State University, 119991 Moscow (Russian Federation); Theoretical Physics and Applied Mathematics Department, Ural Federal University, 620002 Ekaterinburg (Russian Federation); Timoshenko, V. Yu. [Faculty of Physics, Lomonosov Moscow State University, 119991 Moscow (Russian Federation); Tomsk State University, 634050 Tomsk (Russian Federation)

    2015-09-21

    A significant decrease of the cavitation threshold in aqueous suspensions of porous silicon nanoparticles (PSi NPs) with sizes about 100 nm as compared with pure water was observed for ultrasound irradiation (USI) with therapeutic frequency (0.88 MHz) and intensities (about 1 W/cm{sup 2}). This effect is explained by porous morphology of PSi NPs, which promotes the nucleation of cavitation bubbles. In vitro experiments revealed a suppression of the proliferation of cancer cells with the introduced PSi NPs after exposure to USI related to the enhanced cavitation processes, which led to the cell destruction. The obtained results demonstrate that PSi NPs are prospective for applications as sonosensitizers in mild cancer therapy.

  16. Influence of Prewhirl Regulation by Inlet Guide Vanes on Cavitation Performance of a Centrifugal Pump

    Directory of Open Access Journals (Sweden)

    Lei Tan

    2014-02-01

    Full Text Available 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 and impeller are analyzed in order to reveal the mechanism how the IGVs realize the prewhirl regulation. The calculated results show that the influence of IGVs on the cavitation performance of centrifugal pump is limited by a maximum total pressure drop of 1777 Pa, about 7.6% of the total pressure at the suction pipe inlet for a prewhirl angle of 24°.

  17. Influence of Splitter Blades on the Cavitation Performance of a Double Suction Centrifugal Pump

    Directory of Open Access Journals (Sweden)

    Wei Yang

    2014-04-01

    Full Text Available In order to study the influence of splitter blades on double suction centrifugal pumps two impellers with and without splitter blades were investigated numerically and experimentally. Three-dimensional turbulence simulations with and without full cavitation model were applied to simulate the flow in the two pumps with different impellers. The simulation results agreed with the experiment results and the internal flows were analyzed. Both the numerical and experimental results show that by adding splitter blades the hydraulic performance and the cavitation performance of the pump are improved. The pump efficiency is increased especially at high flow rate condition. The pump high efficiency area is extended dramatically. At the same time since the splitter blades share some part of the blade loading, the pump critical NPSH value is decreased. Obvious pressure increase and velocity decrease at blade suction surface near leading edge were observed in the pump impeller with splitter blades. And the pump cavitation performance was improved consequently.

  18. Experimental investigation of cavitational bubble dynamics under multi-frequency system.

    Science.gov (United States)

    Avvaru, Balasubrahmanyam; Pandit, Aniruddha B

    2008-04-01

    Acoustic emission spectra measurements have been carried out under mono and multi-frequency acoustic sources to understand the fundamental difference in bubble/cavity dynamics. The effect of introducing the dual and triple frequency acoustic waves of different frequency on the sono-chemical yield has also been investigated experimentally. The introduction of a second wave has increased the number of cavitating bubbles and as well as the collapsing intensity of cavities resulting into higher sono-chemical yield, and better effective utilization of reactor volume with a large number of resonating cavitating bubbles. To get the information about the intensity of each of the cavity oscillating events, decomposition of the pressure signal measured by the hydrophone in the frequency domain of the FFT power spectrum has been carried out. Inverse fourier reconstruction technique, has been used to elaborate the dynamics of the cavitating bubbles in the multi-frequency system.

  19. EURISOL-DS Multi-MW Target: Cavitations detection by the a Laser Doppler Vibrometer

    CERN Document Server

    Cyril Kharoua, Yacine Kadi, Jacques Lettry, Laure Blumenfeld, Karel Samec (CERN)Knud Thomsen, Sergej Dementevjs, Rade Milenkovich (PSI)Anatoli Zik, Erik Platacis (IPUL)

    This technical note summarises the innovative measurement devices used within Task #2 of the European Isotope Separation On-Line Radioactive Ion Beam Facility Design Study (EURISOL-DS) to detect the occurrence of cavitation in liquid metal flowing inside the CGS target mock-up.During the METEX hydraulic experiment carried out at IPUL (Institute of Physics of the University of Latvia), a Laser Doppler Vibrometer was used to characterize the wall vibrations of the beam window at different flow regimes. A series of tests proved the high sensitivity of the LDV to detect the occurrence of cavitation in the liquid metal flowing inside the target. In this context, a dedicated test procedure was developed to establish the validity of using LDV for detecting the onset of cavitation.

  20. Numerical simulation of cavitation erosion on a NACA0015 hydrofoil based on bubble collapse strength

    Science.gov (United States)

    Hidalgo, V.; Luo, X.; Escaler, X.; Huang, R.; Valencia, E.

    2015-12-01

    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 flow, implicit LES and Zwart cavitation model. The 3D unsteady flow simulation has been solved using OpenFOAM. Python language and OpenFOAM calculator (foamCalcEx) have been used to obtain and represent Sb. The obtained results clearly show the instants of erosive bubble collapse and the affected surface areas.

  1. Numerical investigation of time-dependent cloud cavitating flow around a hydrofoil

    Directory of Open Access Journals (Sweden)

    Zhang De-Sheng

    2016-01-01

    Full Text Available Time-dependent cloud cavitation around the 2-D Clark-Y hydrofoil was investigated in this paper based on an improved filter based model and a density correction method. The filter-scale in filter based model simulation was discussed and validated according to the grid size. Numerical results show that in the transition from sheet cavitation to cloud cavitation, the sheet cavity grows slowly to the maximum length during the re-entrant jet develops. The mild shedding bubble cluster convects downwards the hydrofoil and continues to grow up after detaching from the suction surface of hydrofoil, and a bubble cluster introduced at the rear part of hydrofoil. While the sheet cavity generates, the bubble cluster breakups.

  2. Review of parameters influencing the structural response of a submerged body under cavitation conditions

    Science.gov (United States)

    Escaler, X.; De La Torre, O.; Farhat, M.

    2015-12-01

    Submerged structures that operate under extreme flows are prone to suffer large scale cavitation attached to their surfaces. Under such conditions the added mass effects differ from the expected ones in pure liquids. Moreover, the existence of small gaps between the structure and surrounding bodies filled with fluid also influence the dynamic response. A series of experiments and numerical simulations have been carried out with a truncated NACA0009 hydrofoil mounted as a cantilever beam at the LMH-EPFL cavitation tunnel. The three first modes of vibration have been determined and analysed under various hydrodynamic conditions ranging from air and still water to partial cavitation and supercavitation. A remote nonintrusive excitation system with piezoelectric patches has been used for the experiments. The effects of the cavity properties and the lateral gap size on the natural frequencies and mode shapes have been determined. As a result, the significance of several parameters in the design of such structures is discussed.

  3. Effect of shaft frequency on cavitation in a journal bearing for noncentered circular whirl

    Science.gov (United States)

    Brewe, David E.; Khonsari, M. M.

    The effect of shaft frequency on the performance of a submerged journal undergoing noncentered circular whirl is examined. The main emphasis of the paper is on the behavior of the vapor cavitation bubble and its effect on the bearing performance as a function of frequency. A cavitation algorithm due to Elrod was implemented in a computer program which solves a time-dependent Reynolds equation. This algorithm automatically handles the boundary conditions by using a switch function and a control volume approach which conserves mass throughout the entire flow. The shaft frequencies in this investigation ranged from 0 rad/s (squeeze-film damper) to -104 rad/s (a case in which oil-whip condition was produced momentarily). For the particular vibration amplitude chosen in this investigation it was observed that vapor cavitation had an effect on the load components for the full range of shaft frequencies investigated.

  4. Cavitation erosion of chromium-manganese and chromium-cobalt coatings processed by laser beam

    International Nuclear Information System (INIS)

    Giren, B.G.; Szkodo, M.

    2002-01-01

    In this work the cavitation erosion of chromium-manganese and chromium-cobalt clads were tested, each of them for three cases: (1) without additional processing; (2) after laser heating of the solid state and (3) after laser remelting of the material. Armco iron, carbon steel 45 and chromium-nickel steel 0H18N9T were used as substrates. C.W. CO 2 laser with a beam power of 1000 W was used as a source of radiation. The investigated samples were subjected to cavitation impingement in a rotating disk facility. The results indicate that laser processing of the thick, electrode deposited coatings by laser beam leads in some cases to an increase of their cavitation resistance. Strong dependence of the coatings performance on the substrate, both for the laser processed or unprocessed parts of the materials was also discovered. (author)

  5. Effect of shaft frequency on cavitation in a journal bearing for noncentered circular whirl

    Science.gov (United States)

    Brewe, David E.; Khonsari, M. M.

    1987-01-01

    The effect of shaft frequency on the performance of a submerged journal undergoing noncentered circular whirl is examined. The main emphasis of the paper is on the behavior of the vapor cavitation bubble and its effect on the bearing performance as a function of frequency. A cavitation algorithm due to Elrod was implemented in a computer program which solves a time-dependent Reynolds equation. This algorithm automatically handles the boundary conditions by using a switch function and a control volume approach which conserves mass throughout the entire flow. The shaft frequencies in this investigation ranged from 0 rad/s (squeeze-film damper) to -104 rad/s (a case in which oil-whip condition was produced momentarily). For the particular vibration amplitude chosen in this investigation it was observed that vapor cavitation had an effect on the load components for the full range of shaft frequencies investigated.

  6. Acoustic detection of a cavitation noise in the French breeder reactor Phenix

    International Nuclear Information System (INIS)

    Brunet, M.; Desprets, A.

    1981-06-01

    The French Phenix reactor is provided with an in-core multi-sensor acoustic surveillance system. But its efficiency with regard to early boiling detection is still to be proven. For lack of boiling events within the core, a cavitating dummy steel subassembly has been loaded into the reactor, as a simulation of boiling signal. Cavitation is controlled through a slow rise of the primary flow in various core conditions: isothermal situation and during a rise of power. Assuming that the signal to noise ratio is of the same order of magnitude for cavitation signals as for boiling ones, the response of several signal processing techniques is evaluated. Pulse connecting seems to be the most efficient conventional method while pattern recognition appears as a promising alternative solution

  7. A Ffowcs Williams and Hawkings formulation for hydroacoustic analysis of propeller sheet cavitation

    Science.gov (United States)

    Testa, C.; Ianniello, S.; Salvatore, F.

    2018-01-01

    A novel hydroacoustic formulation for the prediction of tonal noise emitted by marine propellers in presence of unsteady sheet cavitation, is presented. The approach is based on the standard Ffowcs Williams and Hawkings equation and the use of transpiration (velocity and acceleration) terms, accounting for the time evolution of the vapour cavity attached on the blade surface. Drawbacks and potentialities of the method are tested on a marine propeller operating in a nonhomogeneous onset flow, by exploiting the hydrodynamic data from a potential-based panel method equipped with a sheet cavitation model and comparing the noise predictions with those carried out by an alternative numerical approach, documented in literature. It is shown that the proposed formulation yields a one-to-one correlation between emitted noise and sheet cavitation dynamics, carrying out accurate predictions in terms of noise magnitude and directivity.

  8. Passive control of cavitating flow around an axisymmetric projectile by using a trip bar

    Directory of Open Access Journals (Sweden)

    Jian Huang

    2017-07-01

    Full Text Available Quasi-periodical evolutions such as shedding and collapsing of unsteady cloud cavitating flow, induce strong pressure fluctuations, what may deteriorate maneuvering stability and corrode surfaces of underwater vehicles. This paper analyzed effects on cavitation stability of a trip bar arranged on high-speed underwater projectile. Small scale water tank experiment and large eddy simulation using the open source software OpenFOAM were used, and the results agree well with each other. Results also indicate that trip bar can obstruct downstream re-entrant jet and pressure wave propagation caused by collapse, resulting in a relatively stable sheet cavity between trip bar and shoulder of projectiles. Keywords: Unsteady cavitating flow, Trip bar, Re-entrant jet, Passive flow control

  9. Application of Ultra High Pressure Cavitation Peening to Prevent PWSCC on Primary Plant Components

    Energy Technology Data Exchange (ETDEWEB)

    Poling, G.R.

    2015-07-01

    Primary Water Stress Corrosion Cracking (PWSCC) on Alloy 600/82/182 susceptible materials can lead to increased costs for maintenance and repair/replacement activities on nuclear power plant primary components. A process called Ultra High Pressure (UHP) cavitation peening can be safely and cost effectively applied to the susceptible materials to generate compressive stresses on the surface and prevent PWSCC initiation. AREVA has developed the tooling systems to apply the UHP cavitation peening process on reactor vessel head penetration nozzles, bottom mounted nozzles and primary nozzles. Applying the UHP cavitation peening process before PWSCC initiation will prevent future repairs/replacements, reduce maintenance costs, and provide more effective on-time for the reactor. (Author)

  10. Improvement of the cavitation erosion resistance for Cr3Si film on stainless steel by double cathode glow discharge

    Science.gov (United States)

    Ding, Hongqin; Qiu, Yujiang

    2017-04-01

    In this study, sputter-deposited Cr3Si film was prepared by double cathode glow discharge (DCGD) technique onto 304 stainless steel. The phase constituents, surface microstructure and chemical compositions of the film were examined by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). After the DCGD process, the hardness of Cr3Si film was 26 GPa, about 10 times of the stainless steel, 2.5 GPa. The cavitation erosion resistance of Cr3Si film and stainless steel were investigated by using an ultrasonic vibration cavitation erosion system. After 30 hours of cavitation tests, the cumulative mass loss of Cr3Si film was only 60% of the stainless steel. Compared with the untreated stainless steel, the cavitation erosion resistance of Cr3Si film was improved. The cavitation mechanism of Cr3Si film is due to the delamination and spalling of local surface layer derived from its inherent brittleness.

  11. A mesoscale quantification method of cavitation in semicrystalline polymers using X-ray microtomography

    Energy Technology Data Exchange (ETDEWEB)

    Rosenberg, E. [IFP Energies nouvelles, 1 et 4 avenue de Bois Preau, 92852 Rueil-Malmaison Cedex (France); Brusselle-Dupend, N., E-mail: nadege.brusselle@ifpen.fr [IFP Energies nouvelles, 1 et 4 avenue de Bois Preau, 92852 Rueil-Malmaison Cedex (France); Epsztein, T. [TECHNIP, rue Jean Hure, 76580 Le Trait (France)

    2011-08-15

    Highlights: {yields} X-ray microtomography to quantify cavitation in strained semicrystalline polymers. {yields} Method based on correlation of the linear attenuation coefficient with 3-D porosity. {yields} Validation of the mesoscale quantification method. {yields} Application: cavitation process investigation in PVF2 from unloaded specimens. {yields} Effect of the triaxiality ratio and of the stretching degree on cavitation process. - Abstract: The ability of X-ray microtomography to quantify the cavitation in highly strained semicrystalline polymers is investigated on polyvinylidene fluoride. The cavitation phenomenon is studied on Circumferentially Notched Round Bars tested in tension. The tensile deformation induces void formation as attested by the whitening of the notch and SEM observations. The aim of this paper is to highlight the interest of a non destructive method based on X-ray microtomography in order to quantify the developed porosity in the cavited area and to follow step by step after relaxation, or continuously the evolution of the porosity during a tensile test. As voids may have a submicrometric size, as attested by SEM images in PVF2, the X-ray microtomography does not intend to image all the voids but to quantify them as a whole, including the non resolved voids. The method is designed to be used either with a laboratory microtomograph or with a synchrotron microtomography device. The quantification uses the correlation between the attenuation coefficient of the material and the porosity developed in the material. The measure is first validated on synchrotron images. Then the method is adapted to the laboratory microtomography prone to beam hardening artefacts. The results obtained with both devices are compared to each other and compared to the results obtained from local SEM analysis. Finally, the analysis of notched tensile specimens with varying notch root radius is investigated after interrupted tests. The analyses of the in situ tensile

  12. Cavitation inception by the backscattering of pressure waves from a bubble interface

    Energy Technology Data Exchange (ETDEWEB)

    Takahira, Hiroyuki, E-mail: takahira@me.osakafu-u.ac.jp; Ogasawara, Toshiyuki, E-mail: oga@me.osakafu-u.ac.jp; Mori, Naoto, E-mail: su101064@edu.osakafu-u.ac.jp; Tanaka, Moe [Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai-shi, Osaka 599-8531 (Japan)

    2015-10-28

    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 t{sub 0} to a characteristic time of wave propagation t{sub S}, η = t{sub 0}/t{sub s}, 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.

  13. Cavitation-enhanced delivery of insulin in agar and porcine models of human skin

    Science.gov (United States)

    Feiszthuber, Helga; Bhatnagar, Sunali; Gyöngy, Miklós; Coussios, Constantin-C.

    2015-03-01

    Ultrasound-assisted transdermal insulin delivery offers a less painful and less invasive alternative to subcutaneous insulin injections. However, ultrasound-based drug delivery, otherwise known as sonophoresis, is a highly variable phenomenon, in part dependent on cavitation. The aim of the current work is to investigate the role of cavitation in transdermal insulin delivery. Fluorescently stained, soluble Actrapid insulin was placed on the surface of human skin-mimicking materials subjected to 265 kHz, 10% duty cycle focused ultrasound. A confocally and coaxially aligned 5 MHz broadband ultrasound transducer was used to detect cavitation. Two different skin models were used. The first model, 3% agar hydrogel, was insonated with a range of pressures (0.25-1.40 MPa peak rarefactional focal pressure—PRFP), with and without cavitation nuclei embedded within the agar at a concentration of 0.05% w/v. The second, porcine skin was insonated at 1.00 and 1.40 MPa PRFP. In both models, fluorescence measurements were used to determine penetration depth and concentration of delivered insulin. Results show that in agar gel, both insulin penetration depth and concentration only increased significantly in the presence of inertial cavitation, with up to a 40% enhancement. In porcine skin the amount of fluorescent insulin was higher in the epidermis of those samples that were exposed to ultrasound compared to the control samples, but there was no significant increase in penetration distance. The results underline the importance of instigating and monitoring inertial cavitation during transdermal insulin delivery.

  14. Novel cavitation fluid jet polishing process based on negative pressure effects.

    Science.gov (United States)

    Chen, Fengjun; Wang, Hui; Tang, Yu; Yin, Shaohui; Huang, Shuai; Zhang, Guanghua

    2018-04-01

    Traditional abrasive fluid jet polishing (FJP) is limited by its high-pressure equipment, unstable material removal rate, and applicability to ultra-smooth surfaces because of the evident air turbulence, fluid expansion, and a large polishing spot in high-pressure FJP. This paper presents a novel cavitation fluid jet polishing (CFJP) method and process based on FJP technology. It can implement high-efficiency polishing on small-scale surfaces in a low-pressure environment. CFJP uses the purposely designed polishing equipment with a sealed chamber, which can generate a cavitation effect in negative pressure environment. Moreover, the collapse of cavitation bubbles can spray out a high-energy microjet and shock wave to enhance the material removal. Its feasibility is verified through researching the flow behavior and the cavitation results of the negative pressure cavitation machining of pure water in reversing suction flow. The mechanism is analyzed through a computational fluid dynamics simulation. Thus, its cavitation and surface removal mechanisms in the vertical CFJP and inclined CFJP are studied. A series of polishing experiments on different materials and polishing parameters are conducted to validate its polishing performance compared with FJP. The maximum removal depth increases, and surface roughness gradually decreases with increasing negative outlet pressures. The surface becomes smooth with the increase of polishing time. The experimental results confirm that the CFJP process can realize a high material removal rate and smooth surface with low energy consumption in the low-pressure environment, together with compatible surface roughness to FJP. Copyright © 2017 Elsevier B.V. All rights reserved.

  15. Comprehensive Numerical Investigations of Unsteady Internal Flows and Cavitation Characteristics in Double-Suction Centrifugal Pump

    Directory of Open Access Journals (Sweden)

    Xuelin Tang

    2017-01-01

    Full Text Available The RNG k-ε turbulence model combined with cavitation model was used to simulate unsteady cavitating flows inside a double-suction centrifugal pump under different flow rate conditions based on hexahedral structured grid. The numerical external characteristic performances agree well with the experimental performances. The predicted results show that the turbulence kinetic energy and the turbulence dissipation rate inside the impeller at design flow rate are lower than those at other off-design flow rates, which are caused by various vortexes. Based on frequency-domain analyses in the volute casing, the blade passing frequency is the dominant one of the pressure fluctuations except the vicinity of volute tongue for all operating cases, and the dominant frequency near the volute tongue ranges from 0 to 0.5 times the blade passing frequency for other off-design points, while the blade passing one near the volute tongue is the dominant one of the pressure fluctuations at design point. The increase of flow rate reduces the pressure fluctuations amplitude. For cavitation cases, the blade loading of the middle streamline increases a bit during the initial stage, but, for serious cavitation, the blade loading near the blade inlet reduces to 0 and even negative values, and the serious cavitation bubbles block the blade channels, which results in a sharp drop in pump head. Under noncavitation condition, the predicted power related to the pressure in the impeller channels increases from the inlet to the exit, while, under different cavitation conditions at the design flow rate, these power-transformation distributions in the impeller channels show that these power conversions are affected by the available NPSHa and the corresponding work in leading regions of the blades increases increases gradually a bit, and then it increases sharply in the middle regions, but it decreases in the blade trailing regions and is greatly influenced by secondary flows.

  16. Removal of residual cavitation nuclei to enhance histotripsy fractionation of soft tissue.

    Science.gov (United States)

    Duryea, Alexander P; Cain, Charles A; Roberts, William W; Hall, Timothy L

    2015-12-01

    Remanent bubble nuclei generated by primary cavitation collapse can limit the efficiency of histotripsy softtissue fractionation. When these residual bubbles persist from one histotripsy pulse to the next, they can seed the repetitive nucleation of cavitation bubbles at a discrete set of sites within the focal volume. This effect-referred to as cavitation memory- manifests in inefficient lesion formation, because certain sites within the focal volume are overtreated whereas others remain undertreated. Although the cavitation memory effect can be passively mitigated by using a low pulse repetition frequency (PRF) that affords remanent nuclei sufficient time for dissolution between successive pulses, this low PRF also results in slow lesion production. As such, it would be highly desirable to maintain the high per-pulse efficiency associated with low pulse rates when much higher PRFs are utilized. In this vein, we have developed a strategy for the active removal of the remanent bubble nuclei following primary cavitation collapse, using low-amplitude ultrasound sequences (termed bubble-removal sequences) to stimulate the aggregation and subsequent coalescence of these bubbles. In this study, bubbleremoval sequences were incorporated in high-PRF histotripsy treatment (100 Hz) of a red blood cell tissue-mimicking phantom that allows for the visualization of lesion development in real time. A series of reference treatments were also conducted at the low PRF of 1 Hz to provide a point of comparison for which cavitation memory effects are minimal. It was found that bubble-removal sequences as short as 1 ms are capable of maintaining the efficacious lesion development characteristics associated with the low PRF of 1 Hz when the much higher pulse rate of 100 Hz is used. These results were then extended to the treatment of a large volume within the tissue phantom, and optimal bubble-removal sequences identified for the singlefocal- spot case were utilized to homogenize a 10

  17. The role of stress waves and cavitation in stone comminution in shock wave lithotripsy.

    Science.gov (United States)

    Zhu, Songlin; Cocks, Franklin H; Preminger, Glenn M; Zhong, Pei

    2002-05-01

    Using an experimental system that mimics stone fragmentation in the renal pelvis, we have investigated the role of stress waves and cavitation in stone comminution in shock-wave lithotripsy (SWL). Spherical plaster-of-Paris stone phantoms (D = 10 mm) were exposed to 25, 50, 100, 200, 300 and 500 shocks at the beam focus of a Dornier HM-3 lithotripter operated at 20 kV and a pulse repetition rate of 1 Hz. The stone phantoms were immersed either in degassed water or in castor oil to delineate the contribution of stress waves and cavitation to stone comminution. It was found that, while in degassed water there is a progressive disintegration of the stone phantoms into small pieces, the fragments produced in castor oil are fairly sizable. From 25 to 500 shocks, clinically passable fragments (stones with a primary composition of calcium oxalate monohydrate. After 200 shocks, 89% of the fragments of the kidney stones treated in degassed water became passable, but only 22% of the fragments of the kidney stones treated in castor oil were less than 2 mm in size. This apparent size limitation of the stone fragments produced primarily by stress waves (in castor oil) is likely caused by the destructive superposition of the stress waves reverberating inside the fragments, when their sizes are less than half of the compressive wavelength in the stone material. On the other hand, if a stone is only exposed to cavitation bubbles induced in SWL, the resultant fragmentation is much less effective than that produced by the combination of stress waves and cavitation. It is concluded that, although stress wave-induced fracture is important for the initial disintegration of kidney stones, cavitation is necessary to produce fine passable fragments, which are most critical for the success of clinical SWL. Stress waves and cavitation work synergistically, rather than independently, to produce effective and successful disintegration of renal calculi in SWL

  18. Effect of acoustic parameters on the cavitation behavior of SonoVue microbubbles induced by pulsed ultrasound.

    Science.gov (United States)

    Lin, Yutong; Lin, Lizhou; Cheng, Mouwen; Jin, Lifang; Du, Lianfang; Han, Tao; Xu, Lin; Yu, Alfred C H; Qin, Peng

    2017-03-01

    SonoVue microbubbles could serve as artificial nuclei for ultrasound-triggered stable and inertial cavitation, resulting in beneficial biological effects for future therapeutic applications. To optimize and control the use of the cavitation of SonoVue bubbles in therapy while ensuring safety, it is important to comprehensively understand the relationship between the acoustic parameters and the cavitation behavior of the SonoVue bubbles. An agarose-gel tissue phantom was fabricated to hold the SonoVue bubble suspension. 1-MHz transmitting transducer calibrated by a hydrophone was used to trigger the cavitation of SonoVue bubbles under different ultrasonic parameters (i.e., peak rarefactional pressure (PRP), pulse repetition frequency (PRF), and pulse duration (PD)). Another 7.5-MHz focused transducer was employed to passively receive acoustic signals from the exposed bubbles. The ultraharmonics and broadband intensities in the acoustic emission spectra were measured to quantify the extent of stable and inertial cavitation of SonoVue bubbles, respectively. We found that the onset of both stable and inertial cavitation exhibited a strong dependence on the PRP and PD and a relatively weak dependence on the PRF. Approximate 0.25MPa PRP with more than 20μs PD was considered to be necessary for ultraharmonics emission of SonoVue bubbles, and obvious broadband signals started to appear when the PRP exceeded 0.40MPa. Moreover, the doses of stable and inertial cavitation varied with the PRP. The stable cavitation dose initially increased with increasing PRP, and then decreased rapidly after 0.5MPa. By contrast, the inertial cavitation dose continuously increased with increasing PRP. Finally, the doses of both stable and inertial cavitation were positively correlated with PRF and PD. These results could provide instructive information for optimizing future therapeutic applications of SonoVue bubbles. Copyright © 2016 Elsevier B.V. All rights reserved.

  19. Cleaning lateral morphological features of the root canal: the role of streaming and cavitation.

    Science.gov (United States)

    Robinson, J P; Macedo, R G; Verhaagen, B; Versluis, M; Cooper, P R; van der Sluis, L W M; Walmsley, A D

    2018-01-01

    To investigate the effects of ultrasonic activation file type, lateral canal location and irrigant on the removal of a biofilm-mimicking hydrogel from a fabricated lateral canal. Additionally, the amount of cavitation and streaming was quantified for these parameters. An intracanal sonochemical dosimetry method was used to quantify the cavitation generated by an IrriSafe 25 mm length, size 25 file inside a root canal model filled with filtered degassed/saturated water or three different concentrations of NaOCl. Removal of a hydrogel, demonstrated previously to be an appropriate biofilm mimic, was recorded to measure the lateral canal cleaning rate from two different instruments (IrriSafe 25 mm length, size 25 and K 21 mm length, size 15) activated with a P5 Suprasson (Satelec) at power P8.5 in degassed/saturated water or NaOCl. Removal rates were compared for significant differences using nonparametric Kruskal-Wallis and/or Mann-Whitney U-tests. Streaming was measured using high-speed particle imaging velocimetry at 250 kfps, analysing both the oscillatory and steady flow inside the lateral canals. There was no significant difference in amount of cavitation between tap water and oversaturated water (P = 0.538), although more cavitation was observed than in degassed water. The highest cavitation signal was generated with NaOCl solutions (1.0%, 4.5%, 9.0%) (P streaming. The oscillatory velocities were higher inside the lateral canal 3 mm compared to 6 mm from WL and were higher for NaOCl than for saturated water, which in turn was higher than for degassed water. Measurements of cavitation and acoustic streaming have provided insight into their contribution to cleaning. Significant differences in cleaning, cavitation and streaming were found depending on the file type and size, lateral canal location and irrigant used. In general, the IrriSafe file outperformed the K-file, and NaOCl performed better than the other irrigants tested. The cavitation and

  20. Numerical evaluation of cavitation void ratio significance on hydrofoil dynamic response

    Science.gov (United States)

    Liu, Xin; Wang, Zhengwei; Escaler, Xavier; Zhou, Lingjiu

    2015-12-01

    The added mass effects on a NACA0009 hydrofoil under cavitation conditions determined in a cavitation tunnel have been numerically simulated using finite element method (FEM). Based on the validated model, the effects of averaged properties of the cavity considered as a two-phase mixture have been evaluated. The results indicate that the void ratio of the cavity plays an increasing role on the frequency reduction ratio and on the mode shape as the mode number increases. Moreover, the sound speed shows a more important role than the average cavity density.

  1. Cavitation phenomena in a fuel injection nozzle of a diesel engine by neutron radiography

    International Nuclear Information System (INIS)

    Takenaka, N.; Kawabata, Y.; Miyata, D.; Kawabata, Y.; Sim, C. M.; Lim, I. C.

    2005-01-01

    Visualization of cavitation phenomena in a Diesel engine fuel injection nozzle was carried out by using neutron radiography system in Research Reactor Institute in Kyoto University and HANARO in Korea Atomic Energy Research Institute. A neutron chopper was synchronized to the engine rotation for high shutter speed exposures. A multi exposure method was applied to obtain a clear image as an ensemble average of the synchronized images. Some images were successfully obtained and suggested new understanding of the cavitation phenomena in a Diesel engine fuel injection nozzle

  2. Mesure de champs de vitesse en PIV Diphasique. Application aux écoulements cavitants.

    OpenAIRE

    Prothin, Sebastien; Djeridi, Henda; Billard, Jean-Yves

    2008-01-01

    Ce travail s’insère dans le cadre d’une étude du comportement hydrodynamique et cavitant de profils épais de type NACA bidimensionnel. Ces profils sont largement utilisés en hydrodynamique navale pour les systèmes de propulsion électrique en nacelle, pour les gouvernails et sont sujet à des décollements à faible incidence ainsi qu’à des cavitations instationnaires voisines de poches se développant sur l’extrados. Le but de ce travail expérimental est de caractériser la topologie de l’écouleme...

  3. Boundary lubrication of heterogeneous surfaces and the onset of cavitation in frictional contacts.

    Science.gov (United States)

    Savio, Daniele; Pastewka, Lars; Gumbsch, Peter

    2016-03-01

    Surfaces can be slippery or sticky depending on surface chemistry and roughness. We demonstrate in atomistic simulations that regular and random slip patterns on a surface lead to pressure excursions within a lubricated contact that increase quadratically with decreasing contact separation. This is captured well by a simple hydrodynamic model including wall slip. We predict with this model that pressure changes for larger length scales and realistic frictional conditions can easily reach cavitation thresholds and significantly change the load-bearing capacity of a contact. Cavitation may therefore be the norm, not the exception, under boundary lubrication conditions.

  4. The research and test of the cavitation performance of first stage impeller of centrifugal charging pump in nuclear power stations

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, Rongsheng; Fu, Qiang [National Research Center of Pumps, Jiangsu University, Zhenjiang 212013, Jiangsu (China); Liu, Yong, E-mail: beijitadeyouxiang@163.com [National Research Center of Pumps, Jiangsu University, Zhenjiang 212013, Jiangsu (China); He, Bo [Power China SPEM Limited Company, Shanghai 201316 (China); Wang, Xiuli [National Research Center of Pumps, Jiangsu University, Zhenjiang 212013, Jiangsu (China)

    2016-04-15

    The safety production is the most important index for nuclear power development, and the CVCS (chemical and volume control system) occupies an important place in safety control system. The CCP (centrifugal charging pump) is an important component of CVCS system and its particularity decides the high requirements on the cavitation performance, so the research on CCP cavitation has great significance. Using the 3D Pro/E software, the paper makes models of the flow passage components of first stage prototype of CCP in nuclear power stations, and completes the cavitation steady-state computation in the case that the high flow rate of first stage prototype reaches Q = 160 m{sup 3}/h using the numerical computation software ANSYS CFX. The cavitation is divided into the following five stages according to its development process: inception operating condition, development operating condition, critical operating condition, serious operating condition and fracture operating condition. The research analyze the flow field, static pressure fields and bubble distribution conditions in the impeller in different cavitation states, and selects the middle flow line, the front shroud flow line and the back shroud flow line from the same blade for the comparative analysis; to verify the reliability of computation, the researcher made a first stage cavitation prototype to verify its hydraulic performance and cavitation performance. After the comparative analysis on the flow field, pressure and bubble distribution conditions of CCP first stage impeller in different cavitation states, the research draws the following conclusions: (1) as the inlet pressure decreases, the cavitation degree increases, the bubble distribution area extends from impeller inlet to impeller outlet and shows different laws in different cavitation states; (2) the generation of cavitation is affected by the pressure changes in impeller passages, and when the inlet pressure decreases, the static pressure in impeller

  5. Analysis of the cavitating flow induced by an ultrasonic horn – Experimental investigation on the influence of actuation phase, amplitude and geometrical boundary conditions

    Directory of Open Access Journals (Sweden)

    Müller Saskia

    2014-03-01

    Full Text Available Till today, factors influencing the formation and collapse of densely distributed, interacting cavitation bubbles are only qualitatively understood. The aim of the present study is to investigate experimentally the influence of selected boundary conditions on the number and size distribution of cavitation bubbles created by an ultrasonic horn (sonotrode. Cavitation bubble clouds below the sonotrode were recorded by means of phase-locked shadowgraphy imaging. The time integrated number of cavitation bubbles was found to decrease exponentially with growing bubble radius. The number of bubbles was increased with growing actuation amplitude and gap width between the sonotrode tip and an opposing solid wall. Furthermore, it could be shown that the number of cavitation bubbles depends on the actuation phase. Future investigations will focus on establishing a statistical relation between the number and size distribution of cavitation bubbles in the near wall region and the resulting cavitation erosion on solid surfaces.

  6. Identification of Large Scale Structures in the Wake of Cavitating Hydrofoils Using LES and TR-PIV

    Science.gov (United States)

    Wosnik, Martin

    2005-11-01

    Large-scale three-dimensional cavitating structures exist in the wake of two-dimensional hydrofoils, as a result of sheet/cloud cavitation. This type of cavitation produces unsteady lift on most hydrofoils -- including the NACA 0015 studied here -- but is sufficiently periodic to have potential for control. A Large Eddy Simulation (LES) based on a virtual single-phase, fully compressible cavitation model captures the complex dynamical features of this highly unsteady cavitating flow well. The LES results are compared to Time-Resolved Particle Image Velocimetry (TR-PIV, recorded at 2000Hz) in the region immediately downstream of the hydrofoil, with particular attention to the predicted vortex shedding mechanisms. With a careful choice of photometric parameters and adaptive masking, the large, vortical, cavitating structures are identified quantitatively. The existence of the primary vortex pair predicted by the LES is confirmed by TR-PIV. This vortex pair produces large cross-stream velocities, with a general ejection direction of 3/4 π to the free stream. However, the shedding pattern as recorded with TR-PIV is not nearly as regular as in the LES, due to the limited number of spanwise grid points in the simulation and the highly three- dimensional nature of cloud cavitation shedding in the experiment.

  7. [Kinetics of catalase inactivation induced by ultrasonic cavitation].

    Science.gov (United States)

    Potapovich, M V; Eremin, A N; Metelitsa, D I

    2003-01-01

    Kinetic patterns of sonication-induced inactivation of bovine liver catalase (CAT) were studied in buffer solutions (pH 4-11) within the temperature range from 36 to 55 degrees C. Solutions of CAT were exposed to low-frequency (20.8 kHz) ultrasound (specific power, 48-62 W/cm2). The kinetics of CAT inactivation was characterized by effective first-order rate constants (s-1) of total inactivation (kin), thermal inactivation (*kin), and ultrasonic inactivation (kin(us)). In all cases, the following inequality was valid: kin > *kin. The value of kin(us) increased with the ultrasound power (range, 48-62 W/cm2) and exhibited a strong dependence on pH of the medium. On increasing the initial concentration of CAT (0.4-4.0 nM), kin(us) decreased. The three rate constants were minimum within the range of pH 6.5-8; their values increased considerably at pH 9. At 36-55 degrees C, temperature dependence of kin(us) was characterized by an activation energy (Eact) of 19.7 kcal/mol, whereas the value of Eact for CAT thermoinactivation was equal to 44.2 kcal/mol. Bovine serum and human serum albumins (BSA and HSA, respectively) inhibited sonication-induced CAT inactivation; complete prevention was observed at concentrations above 2.5 micrograms/ml. Dimethyl formamide (DMFA), a scavenger of hydroxyl radicals (HO.), prevented sonication-induced CAT inactivation at 10% (kin and *kin increased with the content of DMFA at concentrations in excess of 3%). The results obtained indicate that free radicals generated in the field of ultrasonic cavitation play a decisive role in the inactivation of CAT, which takes place when its solutions are exposed to low-frequency ultrasound. However, the efficiency of CAT inactivation by the radicals is determined by (1) the degree of association between the enzyme molecules in the reaction medium and (2) the composition thereof.

  8. Development of a confocal ultrasound device using an inertial cavitation control for transfection in-vitro

    Science.gov (United States)

    Mestas, J. L.; Chettab, K.; Roux, S.; Prieur, F.; Lafond, M.; Dumontet, C.; Lafon, C.

    2015-12-01

    Sonoporation using low-frequency high-pressure ultrasound (US) is a non-viral approach for in vitro and in vivo gene delivery. We developed a new sonoporation device designed for spatial and temporal control of ultrasound cavitation. This device was evaluated for the in vitro transfection efficiency of a plasmid coding for Green Fluorescent Protein (peGFP- C1) in adherent and non-adherent cell lines. The frequency spectrum of the signal receive by a hydrophone is used to compute a cavitation index (CI) representative of the inertial cavitation activity. The influence of the CI on transfection efficiency, as well as reproducibility were determined. A real-time feedback loop control on CI was integrated in the process to regulate the cavitation level during sonoporation. In both adherent and non-adherent cell lines, the sonoporation device produced a highly efficient transfection of peGFP-C1 (40-80%), as determined by flow cytometry analysis of GFP expression, along with a low rate of mortality assessed by propidium iodide staining. Moreover, the sonoporation of non-adherent cell lines Jurkat and K562 was found to be equivalent to nucleofection in terms of efficiency and toxicity while these two cell lines were resistant to transfection with lipofection.

  9. Acoustic cavitation in 1-butyl-3-methylimidazolium bis(triflluoromethyl-sulfonyl)imide based ionic liquid.

    Science.gov (United States)

    Merouani, Slimane; Hamdaoui, Oualid; Haddad, Boumediene

    2018-03-01

    In this work, a comparison between the temperatures/pressures within acoustic cavitation bubble in an imidazolium-based room-temperature ionic liquid (RTIL), 1-butyl-3-methylimidazolium bis(triflluoromethyl-sulfonyl)imide ([BMIM][NTf 2 ]), and in water has been made for a wide range of cavitation parameters including frequency (140-1000kHz), acoustic intensity (0.5-1Wcm -2 ), liquid temperature (20-50°C) and external static pressure (0.7-1.5atm). The used cavitation model takes into account the liquid compressibility as well as the surface tension and the viscosity of the medium. It was found that the bubble temperatures and pressures were always much higher in the ionic liquid compared to those predicted in water. The valuable effect of [BMIM][NTf 2 ] on the bubble temperature was more pronounced at higher acoustic intensity and liquid temperature and lower frequency and external static pressure. However, confrontation between the predicted and the experimental estimated temperatures in ionic liquids showed an opposite trend as the temperatures measured in some pure ionic liquids are of the same order as those observed in water. The injection of liquid droplets into cavitation bubbles, the pyrolysis of ionic liquids at the bubble-solution interface as well as the lower number of collapsing bubbles in the ionic liquid may be the responsible for the lower measured bubble temperatures in ionic liquids, as compared with water. Copyright © 2017 Elsevier B.V. All rights reserved.

  10. VULNERABILITY TO CAVITATION IN GRAPEVINES HAS BEEN OVERESTIMATED BY THE CENTRIFUGE TECHNIQUE

    Science.gov (United States)

    Grapevines are considered among the most vulnerable woody plant species to water stress-induced cavitation with embolism forming at slight tensions. However, we found that native embolism in stems of field grown Vitis vinifera cv. Chardonnay never exceeded 30% despite xylem water potentials ('x) rea...

  11. Microleakage of Cavit temporary filling material in endodontic access cavities in monkey teeth.

    Science.gov (United States)

    Lamers, A C; Simon, M; van Mullem, P J

    1980-06-01

    Sealing properties of Cavit-W temporary filling material were tested in vivo in the control group of a usage experiment in which root canal disinfectants were studied. Histologic examination (Brown and Brenn staining) of the root canals showed a statistical significance in the occurrence of microorganisms with increase in time. Microleakage past the filling material was considered to be responsible.

  12. Cavitation tunnel analysis of radiated sound from the resonance of a propeller tip vortex cavity

    NARCIS (Netherlands)

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

    2016-01-01

    The goal of this study is to test the hypothesis that the resonance of a tip vortex cavity is responsible for high-amplitude broadband pressure-fluctuations, typically between 40 and 70 Hz,Hz, for a full scale propeller. This is achieved with a model propeller in a cavitation tunnel. Simultaneous

  13. Optimization of biodiesel production in a hydrodynamic cavitation reactor using used frying oil.

    Science.gov (United States)

    Ghayal, Dyneshwar; Pandit, Aniruddha B; Rathod, Virendra K

    2013-01-01

    The present work demonstrates the application of a hydrodynamic cavitation reactor for the synthesis of biodiesel with used frying oil as a feedstock. The synthesis involved the transesterification of used frying oil (UFO) with methanol in the presence of potassium hydroxide as a catalyst. The effect of geometry and upstream pressure of a cavitating orifice plate on the rate of transesterification reaction has been studied. It is observed that the micro level turbulence created by hydrodynamic cavitation somewhat overcomes the mass transfer limitations for triphasic transesterification reaction. The significant effects of upstream pressure on the rate of formation of methyl esters have been seen. It has been observed that flow geometry of orifice plate plays a crucial role in process intensification. With an optimized plate geometry of 2mm hole diameter and 25 holes, more than 95% of triglycerides have been converted to methyl esters in 10 min of reaction time with cavitational yield of 1.28 × 10(-3) (Grams of methyl esters produced per Joule of energy supplied). The potential of UFO to produce good quality methyl esters has been demonstrated. Copyright © 2012 Elsevier B.V. All rights reserved.

  14. Characterization of HIFU transducers designed for sonochemistry application: Cavitation distribution and quantification

    Czech Academy of Sciences Publication Activity Database

    Hallez, L.; Touyeraz, F.; Hihn, J. Y.; Klíma, Jiří; Guey, J.-L.; Spajer, M.; Bailly, Y.

    2010-01-01

    Roč. 50, č. 2 (2010), s. 310-317 ISSN 0041-624X Institutional research plan: CEZ:AV0Z40400503 Keywords : HIFU * acoustic cavitation * MBSCL threshold * sonoreactors Subject RIV: CG - Electrochemistry Impact factor: 1.599, year: 2010

  15. Testing hypotheses that link wood anatomy to cavitation resistance and hydraulic conductivity in the genus Acer

    NARCIS (Netherlands)

    Lens, F.; Sperry, J.S.; Christmas, M.A.; Rabaey, D.; Jansen, S.

    2011-01-01

    • Vulnerability to cavitation and conductive efficiency depend on xylem anatomy. We tested a large range of structure–function hypotheses, some for the first time, within a single genus to minimize phylogenetic ‘noise’ and maximize detection of functionally relevant variation. • This integrative

  16. Preparation of experimental and numerical research on unsteady cavitating flow around hydrofoil

    Science.gov (United States)

    Komárek, Martin; Sedlář, Milan; Vyroubal, Michal; Zima, Patrik; Müller, Miloš; Pálka, Tomáš

    2015-05-01

    This paper describes the preparation of the experimental setup and the results of the CFD analysis for the investigation of the unsteady cavitating flow around a prismatic NACA 2412 hydrofoil at different flow conditions. The experimental research is carried out in the cavitation water tunnel located in the Centre of Hydraulic Research in Lutín. The tunnel is integrated into the closed horizontal loop of the hydraulic test rig. The transparent test section provides a full view of the flow around the hydrofoil. The hydrofoil incidence angle is fully adjustable. Two variants of hydrofoil of the same geometry have been designed. One variant is equipped with pressure tap holes for the measurement of the static pressure, and the other variant is covered with a grid of five PVDF films, fully integrated in the hydrofoil. The PVDF films enable to measure the impact forces exerted on the hydrofoil surface by the collapsing cavitation structures. The high-frequency pressure oscillations downstream of the hydrofoil trailing edge are measured using the PVDF hydrophone. The cavitating flow is visualized using two simultaneously operating high-speed cameras providing the top and side views of the flow. A preliminary CFD analysis using the ANSYS CFX package helped to determine the flow regimes for the experimental study. The obtained CFD results agree well with the preliminary measurements.

  17. Preparation of experimental and numerical research on unsteady cavitating flow around hydrofoil

    Directory of Open Access Journals (Sweden)

    Komárek Martin

    2015-01-01

    Full Text Available This paper describes the preparation of the experimental setup and the results of the CFD analysis for the investigation of the unsteady cavitating flow around a prismatic NACA 2412 hydrofoil at different flow conditions. The experimental research is carried out in the cavitation water tunnel located in the Centre of Hydraulic Research in Lutín. The tunnel is integrated into the closed horizontal loop of the hydraulic test rig. The transparent test section provides a full view of the flow around the hydrofoil. The hydrofoil incidence angle is fully adjustable. Two variants of hydrofoil of the same geometry have been designed. One variant is equipped with pressure tap holes for the measurement of the static pressure, and the other variant is covered with a grid of five PVDF films, fully integrated in the hydrofoil. The PVDF films enable to measure the impact forces exerted on the hydrofoil surface by the collapsing cavitation structures. The high-frequency pressure oscillations downstream of the hydrofoil trailing edge are measured using the PVDF hydrophone. The cavitating flow is visualized using two simultaneously operating high-speed cameras providing the top and side views of the flow. A preliminary CFD analysis using the ANSYS CFX package helped to determine the flow regimes for the experimental study. The obtained CFD results agree well with the preliminary measurements.

  18. 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 th...

  19. A homozygous mutation in the NDUFS1 gene presents with a mild cavitating leukoencephalopathy

    NARCIS (Netherlands)

    Kashani, A.; Thiffault, I.; Dilenge, M.E.; Saint-Martin, C.; Guerrero, K.; Tran, L.T.; Shoubridge, E.; van der Knaap, M.S.; Braverman, N.; Bernard, G.

    2014-01-01

    We report a case of mild cavitating leukoencephalopathy associated with a homozygous c.755A > G (p.Asp252Gly) NDUFS1 mutation in a 7-year old boy. Biochemical analysis confirmed an isolated reduction in complex I activity. Magnetic resonance imaging of the brain showed a diffuse cystic

  20. Numerical simulation and analysis of cavitation flows in a double suction centrifugal pump

    International Nuclear Information System (INIS)

    Meng, G; Tan, L; Cao, S L; Jian, W; Liu, W W; Jiang, D J

    2015-01-01

    Cavitation is an unsteady phenomenon, which is nearly inevitable in pumps. It would degrade the pump performance, generate vibrations and noises, and even erode pump flow passage components. The double suction centrifugal pump at design flow rate and large flow rate is numerically simulated using the k-ω turbulence model and the mass transport cavitation model. As a result, the calculated variation of pump head with pump inlet pressure agreed well with the experimental data. The results demonstrate that the numerical model and method can accurately predict the cavitation flows in a double suction centrifugal pump. The cavitation characteristics are analysed in great details. In addition, based on the calculation results, the reason that the plunge of pump head curve is revealed. It is found that the steep fall of pump head happens when the cavity reaches the blade to blade throat and the micro-vortex group appears at the back of the blade suction side. At the same time, this practice can provide guidance for the optimal design of double suction pumps

  1. Ecological differentiation in xylem cavitation resistance is associated with stem and leaf structural traits

    NARCIS (Netherlands)

    Markesteijn, L.; Poorter, L.; Paz, H.; Sack, L.; Bongers, F.

    2011-01-01

    Cavitation resistance is a critical determinant of drought tolerance in tropical tree species, but little is known of its association with life history strategies, particularly for seasonal dry forests, a system critically driven by variation in water availability. We analysed vulnerability curves

  2. Mesenteric lymph node cavitation in celiac disease: Ultrasound and CT findings

    International Nuclear Information System (INIS)

    Gonzalez, P.; Quiros, J.F.B. de; Nukiz, J.R.; Vicente, M.; Montes, A.

    1996-01-01

    We present a 42 years old female patient with celiac disease and mesenteric lymph node cavitation syndrome. This is a rare complication in patients with mal absorption syndrome, and in has been poorly studied. We describe the sonographic and CT changes in the earlier stage as well as later on, and we review the literature. (Author) 12 refs

  3. Cavitation behaviors in a tetragonal zirconia polycrystal subjected to superplastic deformations measured by SANS method

    Czech Academy of Sciences Publication Activity Database

    Harjo, S.; Motohashi, Y.; Šaroun, Jan; Ryukhtin, Vasyl; Strunz, Pavel; Baron, M.; Loidl, R.

    Roč. 447, č. 4 ( 2004 ), s. 67-72 ISSN 0255-5476 Institutional research plan: CEZ:AV0Z1048901 Keywords : cavitation * small-angle neutron scattering Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.498, year: 2004

  4. Cavitation inception on micro-particles: a self propelled particle accelerator

    NARCIS (Netherlands)

    Arora, M.; Ohl, C.D.; Morch, Knud Aage; Gutkowski, Witold; Kowalewski, Tomasz A.

    2004-01-01

    Corrugated, hydrophilic particles with diameters between 30 �m and 150 �m are found to cause cavitation inception at their surfaces when they are exposed to a short, intensive tensile stress wave. The growth of cavity and its interaction with the original nucleating particle is recorded by means of

  5. Influence of porosity on cavitation instability predictions for elastic-plastic solids

    DEFF Research Database (Denmark)

    Tvergaard, Viggo; Vadillo, G.

    2007-01-01

    Cavitation instabilities have been found for a single void in a ductile metal stressed under high triaxiality conditions. Here, the possibility of unstable cavity growth is studied for a metal containing many voids. The central cavity is discretely represented, while the surrounding voids...... the deformation process. It is found that interaction with the neighbouring voids reduces the critical stress for unstable cavity growth....

  6. Marginal Sealing Quality of IRM and Cavit as Assessed by Microbial Penetration.

    Science.gov (United States)

    1980-06-01

    phosphate cement. In contrast, Bramante and others8 using 1311 found IRM making a better seal than Cavit. Many variables such as molecular size, pH ...trypticase soy broth (TSB) culture medium could be placed in contact with the exposed cut pulpal surface of the crown. The external tooth enamel-acrylic

  7. Dynamics and acoustics of a cavitating Venturi flow using a homogeneous air-propylene glycol mixture

    Science.gov (United States)

    Navarrete, M.; Naude, J.; Mendez, F.; Godínez, F. A.

    2015-12-01

    Dynamics and acoustics generated in a cavitating Venturi tube are followed up as a function of the input power of a centrifugal pump. The pump of 5 hp with a modified impeller to produce uniform bubbly flow, pumps 70 liters of propylene glycol in a closed loop (with a water cooling system), in which the Venturi is arranged. The goal was to obtain correlations among acoustical emission, dynamics of the shock waves and the light emission from cavitation bubbles. The instrumentation includes: two piezoelectric transducers, a digital camera, a high-speed video camera, and photomultipliers. As results, we show the cavitation patterns as function of the pump power, and a graphical template of the distribution of the Venturi conditions as a function of the cavitation parameter. Our observations show for the first time the sudden formation of bubble clouds in the straight portion of the pipe after the diverging section of the Venturi. We assume that this is due to pre-existing of nuclei-cloud structures which suddenly grow up by the tensile tails of propagating shock waves (producing a sudden drop in pressure).

  8. A numerical study of unsteady cavitation on a hydrofoil by les and URANS method

    NARCIS (Netherlands)

    Li, Zi Ru; Zhang, Guang Ming; He, Wei Dong; van Terwisga, T.J.C.; Farhat, M.; Müller, A.

    2015-01-01

    In this paper, the unsteady cavitation phenomena on a NACA0015 hydrofoil is numerically simulated by unsteady Reynolds-Averaged Navier-Stokes (URANS) method and Large Eddy Simulation (LES) in single-fluid approaches to multiphase modelling, respectively. It is observed that the large-scale

  9. The effect of casting porosities on cavitational erosion of intermetallic alloy FeAl36

    Directory of Open Access Journals (Sweden)

    R. Jasionowski

    2010-07-01

    Full Text Available The machinery and equipment elements operating in a turbulent fluid flow, are exposed to destruction as a result of the impact of thecavitation, corrosion and abrasion processes, among which are hardest to minimize the imploding cavitation bubbles. Repeated cavitationimplosions of bubbles give rise to cracks, material loss, resulting in increased flow resistance and reduction of the efficiency of the device, or even its destruction. In order to prevent or mitigate the cavitation phenomenon and its harmful effects, two basic methods are applied. The first of these is the selection of geometrical parameters and hydraulic machinery and the relevant elements of the streamlined shape and flow channels. The second solution is the selection of engineering plastics with greater resistance to cavitation. In case of materials manufactured with the casting method, a very important role is being played by the quality of manufactured casting having the smallest number of casting defects. The aim of the present study was to examine the effect of casting porosities of an intermetallic alloy FeAl36 on cavitational erosion.

  10. Preparation of graphene by using an intense cavitation field in a pressurized ultrasonic reactor

    Czech Academy of Sciences Publication Activity Database

    Štengl, Václav

    2012-01-01

    Roč. 18, č. 44 (2012), s. 14047-14054 ISSN 0947-6539 Institutional support: RVO:61388980 Keywords : cavitation field * graphene * nanostructures * ultrasound * X-ray diffraction Subject RIV: CA - Inorganic Chemistry Impact factor: 5.831, year: 2012

  11. Numerical simulation of flow in centrifugal pump under cavitation and sediment condition

    Science.gov (United States)

    Guo, P. C.; Lu, J. L.; Zheng, X. B.; Zhao, Q.; Luo, X. Q.

    2012-11-01

    The sediment concentration is very high in many rivers in the world, especially in China. The pumps that designed for the clear water are usually seriously abraded. The probability of pump cavitation is greatly enhanced due to the existence of sand. Under the joint action and mutual promotion of sand erosion and cavitation, serious abrasion could occurred, and the hydraulic performance of the pump may be greatly descended, meanwhile the safety and stability of the whole pump are greatly threatened. Therefore, it is significant to investigate the cavitation characteristic of pump under sediment flow condition. In this paper, the flow in a single stage centrifugal pump under cleat water and sediment flow conditions was numerically simulated. The cavitation performance under clear water was firstly analyzed. Then, The pressure, velocity and solid particle distribution in centrifugal pump under different particle diameter and different particle concentration was investigated by using the two-fluid model; The area and extent of erosion was illustrated by using the particle track model. Finally, the influence of mixed sand on centrifugal pump performance was investigated.

  12. Theoretical investigation of boundary slip on the hydrodynamic lubrication performance in pocketed bearings including cavitation

    NARCIS (Netherlands)

    Muchammad, M.; Tauviqirrahman, Mohammad; Pratomo, Ariawan Wahyu; Jamari, J.; Schipper, Dirk Jan

    2017-01-01

    Boundary slip in bearings is becoming more and more popular to improve the hydrodynamic performance (pressure and shear stress). However, most of previously published works regarding textured bearings neglected the cavitation effect and make their results questionable. The main aim of this paper is

  13. Supplementary Methods for "Comment on 'Nuclear Emissions During Self-Nucleated Acoustic Cavitation'"

    OpenAIRE

    Naranjo, B.

    2006-01-01

    Neutron simulation methods and statistical fitting methods for "Comment on 'Nuclear Emissions During Self-Nucleated Acoustic Cavitation'" are presented. The fit that underlies the Comment's background-subtracted "Cf-252" curve is shown. Also included are numerically sampled distributions of the goodness-of-fit variable for the four candidate neutron sources and a sketch of the assumed geometry.

  14. Cavitation bubble oscillation period as a process diagnostic during the laser shock peening process

    CSIR Research Space (South Africa)

    Glaser, Daniel

    2017-09-01

    Full Text Available : Materials Science & Processing, vol. 123(9): DOI 10.1007/s00339-017-1209-6 Cavitation bubble oscillation period as a process diagnostic during the laser shock peening process Glaser, D Polese, C ABSTRACT: Laser shock peening (LSP) technology...

  15. Cavitation erosion resistance of 13/4 and 21-4-N steels

    Indian Academy of Sciences (India)

    ASTM G32-06 2007 Standard test method for cavitation erosion using vibratory apparatus, West. Conshohocken, PA. Liu W, Zheng Y G, Liu C S, Yao Z M and Ke W 2003 Wear 254: 713. Okada T, Iwai Y and Yamamoto A 1983 Wear 84: 297. Garzon C M, Thomas H, Santos J F and Tschiptschin A P 2005 Wear 259: 145.

  16. CAVITATION OF THE GHON FOCUS IN AN HIV-INFECTED INFANT ...

    African Journals Online (AJOL)

    2009-03-16

    Mar 16, 2009 ... Primary pulmonary tuberculosis (TB) in children typically forms a Ghon complex visible on the chest radiograph as perihilar or paratracheal lymphadenopathy with or without an area of parenchymal infiltrate (Ghon fo- cus). Cavitation or breakdown of lung parenchyma is significantly more common in ...

  17. Disinfection of Escherichia coli bacteria using hybrid method of ozonation and hydrodynamic cavitation with orifice plate

    Science.gov (United States)

    Karamah, Eva F.; Ghaudenson, Rioneli; Amalia, Fitri; Bismo, Setijo

    2017-11-01

    This research aims to evaluate the performance of hybrid method of ozonation and hydrodynamic cavitation with orifice plate on E.coli bacteria disinfection. In this research, ozone dose, circulation flowrate, and disinfection method were varied. Ozone was produced by commercial ozonator with ozone dose of 64.83 mg/hour, 108.18 mg/hour, and 135.04 mg/hour. Meanwhile, hydrodynamic cavitation was generated by an orifice plate. The disinfection method compared in this research were: hydrodynamic cavitation, ozonation, and the combination of both. The best result on each method was achieved on the 60th minutes and with a circulation flowrate of 7 L/min. The hybrid method attained final concentration of 0 CFU/mL from the initial concentration of 2.10 × 105 CFU/mL. The ozonation method attained final concentration of 0 CFU/mL from the initial concentration of 1.32 × 105 CFU/mL. Cavitation method gives the least disinfection with final concentration of 5.20 × 104 CFU/mL from the initial concentration of 2.17 × 105 CFU/mL. In conclusion, hybrid method gives a faster and better disinfection of E.coli than each method on its own.

  18. The detection of cavitation in hydraulic machines by use of ultrasonic signal analysis

    International Nuclear Information System (INIS)

    Gruber, P; Odermatt, P; Etterlin, M; Lerch, T; Frei, M; Farhat, M

    2014-01-01

    This presentation describes an experimental approach for the detection of cavitation in hydraulic machines by use of ultrasonic signal analysis. Instead of using the high frequency pulses (typically 1MHz) only for transit time measurement different other signal characteristics are extracted from the individual signals and its correlation function with reference signals in order to gain knowledge of the water conditions. As the pulse repetition rate is high (typically 100Hz), statistical parameters can be extracted of the signals. The idea is to find patterns in the parameters by a classifier that can distinguish between the different water states. This classification scheme has been applied to different cavitation sections: a sphere in a water flow in circular tube at the HSLU in Lucerne, a NACA profile in a cavitation tunnel and a Francis model test turbine both at LMH in Lausanne. From the signal raw data several statistical parameters in the time and frequency domain as well as from the correlation function with reference signals have been determined. As classifiers two methods were used: neural feed forward networks and decision trees. For both classification methods realizations with lowest complexity as possible are of special interest. It is shown that three signal characteristics, two from the signal itself and one from the correlation function are in many cases sufficient for the detection capability. The final goal is to combine these results with operating point, vibration, acoustic emission and dynamic pressure information such that a distinction between dangerous and not dangerous cavitation is possible

  19. Dynamics of cavitation clouds within a high-intensity focused ultrasonic beam

    NARCIS (Netherlands)

    Lu, Yuan; Katz, Joseph; Prosperetti, Andrea

    2013-01-01

    In this experimental study, we generate a 500 kHz high-intensity focused ultrasonic beam, with pressure amplitude in the focal zone of up to 1.9 MPa, in initially quiescent water. The resulting pressure field and behavior of the cavitation bubbles are measured using high-speed digital in-line

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

    DEFF Research Database (Denmark)

    Kessel, Line; Nymand, Jose; Harbst, Michael

    , which did not change the total exposure time needed to form a cavitation. This suggests that local heating did not play a significant role in producing the observed phenomenon, suggesting that photochemical reactions may be involved. These results demonstrate that there are several types of ultrafast...

  1. Interspecific variation in xylem vulnerability to cavitation among tropical tree and shrub species.

    Science.gov (United States)

    Lopez, Omar R; Kursar, Thomas A; Cochard, Hervé; Tyree, Melvin T

    2005-12-01

    In tropical moist forests, seasonal drought limits plant survival, productivity and diversity. Drought-tolerance mechanisms of tropical species should reflect the maximum seasonal water deficits experienced in a particular habitat. We investigated stem xylem vulnerability to cavitation in nine tropical species with different life histories and habitat associations. Stem xylem vulnerability was scored as the xylem water potential causing 50 and 75% loss of hydraulic conductivity (P50 and P75, respectively). Four shade-tolerant shrubs ranged from moderately resistant (P50=-1.9 MPa for Ouratea lucens Kunth. Engl.) to highly resistant to cavitation (P50=-4.1 MPa for Psychotria horizontalis Sw.), with shallow-rooted species being the most resistant. Among the tree species, those characteristic of waterlogged soils, Carapa guianensis Aubl., Prioria copaifera Griseb. and Ficus citrifolia Mill., were the most vulnerable to cavitation (P50=-0.8 to -1.6 MPa). The wet-season, deciduous tree, Cordia alliodora (Ruiz and Pav.) Oken., had resistant xylem (P50=-3.2 MPa), whereas the dry-season, deciduous tree, Bursera simaruba (L.) Sarg. was among the most vulnerable to cavitation (P50=-0.8 MPa) of the species studied. For eight out of the nine study species, previously reported minimum seasonal leaf water potentials measured in the field during periods of drought correlated with our P50 and P75 values. Rooting depth, deciduousness, soil type and growth habit might also contribute to desiccation tolerance. Our results support the functional dependence of drought tolerance on xylem resistance to cavitation.

  2. Shape Optimization of Three-Way Reversing Valve for Cavitation Reduction

    International Nuclear Information System (INIS)

    Lee, Myeong Gon; Han, Seung Ho; Lim, Cha Suk

    2015-01-01

    A pair of two-way valves typically is used in automotive washing machines, where the water flow direction is frequently reversed and highly pressurized clean water is sprayed to remove the oil and dirt remaining on machined engine and transmission blocks. Although this valve system has been widely used because of its competitive price, its application is sometimes restricted by surging effects, such as pressure ripples occurring in rapid changes in water flow caused by inaccurate valve control. As an alternative, one three-way reversing valve can replace the valve system because it provides rapid and accurate changes to the water flow direction without any precise control device. However, a cavitation effect occurs because of the complicated bottom plug shape of the valve. In this study, the cavitation index and percent of cavitation (POC) were introduced to numerically evaluate fluid flows via computational fluid dynamics (CFD) analysis. To reduce the cavitation effect generated by the bottom plug, the optimal shape design was carried out through a parametric study, in which a simple computer-aided engineering (CAE) model was applied to avoid time consuming CFD analysis and difficulties in achieving convergence. The optimal shape design process using full factorial design of experiments (DOEs) and an artificial neural network meta-model yielded the optimal waist and tail length of the bottom plug with a POC value of less than 30%, which meets the requirement of no cavitation occurrence. The optimal waist length, tail length and POC value were found to 6.42 mm, 6.96 mm and 27%, respectively

  3. Shape optimization of three-way reversing valve for cavitation reduction

    International Nuclear Information System (INIS)

    Lee, Myeong Gon; Han, Seung Ho; Lim, Cha Suk

    2015-01-01

    A pair of two-way valves typically is used in automotive washing machines, where the water flow direction is frequently reversed and highly pressurized clean water is sprayed to remove the oil and dirt remaining on machined engine and transmission blocks. Although this valve system has been widely used because of its competitive price, its application is sometimes restricted by surging effects, such as pressure ripples occurring in rapid changes in water flow caused by inaccurate valve control. As an alternative, one three-way reversing valve can replace the valve system because it provides rapid and accurate changes to the water flow direction without any precise control device. However, a cavitation effect occurs because of the complicated bottom plug shape of the valve. In this study, the cavitation index and percent of cavitation (POC) were introduced to numerically evaluate fluid flows via computational fluid dynamics (CFD) analysis. To reduce the cavitation effect generated by the bottom plug, the optimal shape design was carried out through a parametric study, in which a simple computer-aided engineering (CAE) model was applied to avoid time-consuming CFD analysis and difficulties in achieving convergence. The optimal shape design process using full factorial design of experiments (DOEs) and an artificial neural network meta-model yielded the optimal waist and tail length of the bottom plug with a POC value of less than 30%, which meets the requirement of no cavitation occurrence. The optimal waist length, tail length and POC value were found to 6.42 mm, 6.96 mm and 27%, respectively

  4. PTEN induces apoptosis and cavitation via HIF-2-dependent Bnip3 upregulation during epithelial lumen formation

    Science.gov (United States)

    Qi, Y; Liu, J; Saadat, S; Tian, X; Han, Y; Fong, G-H; Pandolfi, P P; Lee, L Y; Li, S

    2015-01-01

    The tumor suppressor phosphatase and tensin homolog (PTEN) dephosphorylates PIP3 and antagonizes the prosurvival PI3K-Akt pathway. Targeted deletion of PTEN in mice led to early embryonic lethality. To elucidate its role in embryonic epithelial morphogenesis and the underlying mechanisms, we used embryonic stem cell-derived embryoid body (EB), an epithelial cyst structurally similar to the periimplantation embryo. PTEN is upregulated during EB morphogenesis in parallel with apoptosis of core cells, which mediates EB cavitation. Genetic ablation of PTEN causes Akt overactivation, apoptosis resistance and cavitation blockade. However, rescue experiments using mutant PTEN and pharmacological inhibition of Akt suggest that the phosphatase activity of PTEN and Akt are not involved in apoptosis-mediated cavitation. Instead, hypoxia-induced upregulation of Bnip3, a proapoptotic BH3-only protein, mediates PTEN-dependent apoptosis and cavitation. PTEN inactivation inhibits hypoxia- and reactive oxygen species-induced Bnip3 elevation. Overexpression of Bnip3 in PTEN-null EBs rescues apoptosis of the core cells. Mechanistically, suppression of Bnip3 following PTEN loss is likely due to reduction of hypoxia-inducible factor-2α (HIF-2α) because forced expression of an oxygen-stable HIF-2α mutant rescues Bnip3 expression and apoptosis. Lastly, we show that HIF-2α is upregulated by PTEN at both transcriptional and posttranscriptional levels. Ablation of prolyl hydroxylase domain-containing protein 2 (PHD2) in normal EBs or inhibition of PHD activities in PTEN-null EBs stabilizes HIF-2α and induces Bnip3 and caspase-3 activation. Altogether, these results suggest that PTEN is required for apoptosis-mediated cavitation during epithelial morphogenesis by regulating the expression of HIF-2α and Bnip3. PMID:25394489

  5. Wastewater treatment using hybrid treatment schemes based on cavitation and Fenton chemistry: a review.

    Science.gov (United States)

    Bagal, Manisha V; Gogate, Parag R

    2014-01-01

    Advanced oxidation processes such as cavitation and Fenton chemistry have shown considerable promise for wastewater treatment applications due to the ease of operation and simple reactor design. In this review, hybrid methods based on cavitation coupled with Fenton process for the treatment of wastewater have been discussed. The basics of individual processes (Acoustic cavitation, Hydrodynamic cavitation, Fenton chemistry) have been discussed initially highlighting the need for combined processes. The different types of reactors used for the combined processes have been discussed with some recommendations for large scale operation. The effects of important operating parameters such as solution temperature, initial pH, initial pollutant concentration and Fenton's reagent dosage have been discussed with guidelines for selection of optimum parameters. The optimization of power density is necessary for ultrasonic processes (US) and combined processes (US/Fenton) whereas the inlet pressure needs to be optimized in the case of Hydrodynamic cavitation (HC) based processes. An overview of different pollutants degraded under optimized conditions using HC/Fenton and US/Fenton process with comparison with individual processes have been presented. It has been observed that the main mechanism for the synergy of the combined process depends on the generation of additional hydroxyl radicals and its proper utilization for the degradation of the pollutant, which is strongly dependent on the loading of hydrogen peroxide. Overall, efficient wastewater treatment with high degree of energy efficiency can be achieved using combined process operating under optimized conditions, as compared to the individual process. Copyright © 2013 Elsevier B.V. All rights reserved.

  6. Diagnosing non-cavitated lesions in epidemiological studies: practical and scientific considerations.

    Science.gov (United States)

    Carvalho, Joana Christina; Mestrinho, Heliana Dantas

    2014-01-01

    Over the last decade, there has been growing interest in diagnosing non-cavitated lesions in epidemiological studies involving large numbers of preschool children, schoolchildren and young adults. In this context, assessment of lesions characteristics indicating whether or not there is ongoing mineral loss is also considered relevant. The reasoning sustained by these studies is that diagnosis of the caries process limited to the cavitated level is no longer in accordance with current state-of-the-art knowledge in cariology. This paper highlights one topic of the lecture entitled "Caries Process: Evolving Evidence and Understanding," presented at the 18th Congress of the Brazilian Association for Oral Health Promotion (Associação Brasileira de Odontologia de Promoção de Saúde - ABOPREV) in April 2013. In the framework of epidemiological studies, the interest in diagnosing active and inactive non-cavitated lesions was elucidated. However, relevant questions associated with the diagnosis of non-cavitated lesions that might raise concerns among researchers and health administrators were not addressed. The present paper aims to bring these questions into discussion. The contribution of this discussion in terms of developing the understanding of caries decline is analyzed by using data from a caries trends study of Brazilian preschool children residing in the Federal District of Brazil as an example. The inclusion of active and inactive non-cavitated lesions in the diagnosis of the caries process allowed us to demonstrate that, in Brazilian 1- to 5-year-old children, caries prevalence decreased significantly from 1996 to 2006, simultaneously with a reduction in the rate of caries progression.

  7. Acoustic cavitation-based monitoring of the reversibility and permeability of ultrasound-induced blood-brain barrier opening

    International Nuclear Information System (INIS)

    Sun, Tao; Samiotaki, Gesthimani; Wang, Shutao; Acosta, Camilo; Chen, Cherry C; Konofagou, Elisa E

    2015-01-01

    Cavitation events seeded by microbubbles have been previously reported to be associated with MR- or fluorescent-contrast enhancement after focused ultrasound (FUS)-induced blood-brain barrier (BBB) opening. However, it is still unknown whether bubble activity can be correlated with the reversibility (the duration of opening and the likelihood of safe reinstatement) and the permeability of opened BBB, which is critical for the clinical translation of using passive cavitation detection to monitor, predict and control the opening. In this study, the dependence of acoustic cavitation on the BBB opening duration, permeability coefficient and histological damage occurrence were thus investigated. Transcranial pulsed FUS at 1.5 MHz in the presence of systemically circulating microbubbles was applied in the mouse hippocampi (n  =  60). The stable and inertial cavitation activities were monitored during sonication. Contrast-enhanced MRI was performed immediately after sonication and every 24 h up to 6 d thereafter, to assess BBB opening, brain tissue permeability and potential edema. Histological evaluations were used to assess the occurrence of neurovascular damages. It was found that stable cavitation was well correlated with: (1) the duration of the BBB opening (r 2   =  0.77); (2) the permeability of the opened BBB (r 2   =  0.82); (3) the likelihood of safe opening (P  <  0.05, safe opening compared to cases of damage; P  <  0.0001, no opening compared to safe opening). The inertial cavitation dose was correlated with the resulting BBB permeability (r 2   =  0.72). Stable cavitation was found to be more reliable than inertial cavitation at assessing the BBB opening within the pressure range used in this study. This study demonstrates that the stable cavitation response during BBB opening holds promise for predicting and controlling the restoration and pharmacokinetics of FUS-opened BBB. The stable cavitation response

  8. Evaluation of the sealing ability of amalgam, Cavit, and glass ionomer cement in the repair of furcation perforations.

    Science.gov (United States)

    Alhadainy, H A; Himel, V T

    1993-03-01

    Perforations created in the pulpal floors of 30 extracted molars were repaired with amalgam, Cavit, and light cured glass ionomer cement. After the pulp chambers and access openings were filled with composite resin, the teeth were then immersed in 2% Erythrocin B solution for 1 week. After longitudinal sectioning of the teeth, dye penetration was measured. The results indicated significant differences between the three materials. Light cured glass ionomer exhibited the least dye penetration followed by Cavit and amalgam.

  9. Visual scoring of non-cavitated caries lesions and clinical trial efficiency, testing xylitol in caries active adults

    Science.gov (United States)

    Brown, JP; Amaechi, BT; Bader, JD; Gilbert, GH; Makhija, SK; Lozano-Pineda, J; Leo, MC; Chuhe, C; Vollmer, WM

    2013-01-01

    Objectives To better understand the effectiveness of xylitol in caries prevention in adults, and to attempt improved clinical trial efficiency. Methods As part of the Xylitol for Adult Caries Trial (X-ACT), non-cavitated and cavitated caries lesions were assessed in subjects who were experiencing the disease. The trial was a test of the effectiveness of 5 grams/day of xylitol, consumed by dissolving in the mouth five 1 gram lozenges spaced across each day, compared with a sucralose placebo. For this analysis, seeking trial efficiency, 538 subjects aged 21–80, with complete data for four dental examinations were selected from the 691 randomized into the three year trial, conducted at three sites. Acceptable inter and intra examiner reliability before and during the trial was quantified using the kappa statistic. Results The mean annualized non-cavitated plus cavitated lesion transition scores in coronal and root surfaces, from sound to carious favoured xylitol over placebo, during the three cumulative periods of 12, 24, and 33 months, but these clinically and statistically non-significant differences declined in magnitude over time. Restricting the present assessment to those subjects with a higher baseline lifetime caries experience showed possible but inconsistent benefit. Conclusions There was no clear and clinically relevant preventive effect of xylitol on caries in adults with adequate fluoride exposure when non-cavitated plus cavitated lesions were assessed. This conformed to the X-ACT trial result assessing cavitated lesions. Including non-cavitated lesion assessment in this full scale, placebo controlled, multi site, randomized, double blinded clinical trial in adults experiencing dental caries, did not achieve added trial efficiency or demonstrate practical benefit of xylitol. Trial Registration ClinicalTrials.Gov NCT00393055 PMID:24205951

  10. Numerical study of a confocal ultrasonic setup for creation of cavitation

    Energy Technology Data Exchange (ETDEWEB)

    Lafond, Maxime, E-mail: maxime.lafond@inserm.fr; Chavrier, Françoise; Prieur, Fabrice [Inserm, U1032, LabTau, Lyon, F-69003 (France); Université de Lyon, Lyon, F-69003 (France); Université Lyon 1, Lyon, F-69003 (France); Mestas, Jean-Louis; Lafon, Cyril [Inserm, U1032, LabTau, Lyon, F-69003 (France); Université de Lyon, Lyon, F-69003 (France); Université Lyon 1, Lyon, F-69003 (France); Caviskills SAS, Vaulx-En-Velin, F-69120 (France)

    2015-10-28

    Acoustic cavitation is used for various therapeutic applications such as local enhancement of drug delivery, histotripsy or hyperthermia. One of the utmost important parameter for cavitation creation is the rarefaction pressure. The typical magnitude of the rarefaction pressure required to initiate cavitation from gas dissolved in tissue is beyond the range of the megapascal. Because nonlinear effects need to be taken into account, a numerical simulator based on the Westervelt equation was used to study the pressure waveform and the acoustic field generated by a setup for creation of cavitation consisting of two high intensity focused ultrasound transducers mounted confocally. At constant acoustic power, simulations with only one and both transducers from the confocal setup showed that the distortion of the pressure waveform due to the combined effects of nonlinearity and diffraction is less pronounced when both confocal transducers are used. Consequently, the confocal setup generates a greater peak negative pressure at focus which is more favorable for cavitation initiation. Comparison between the confocal setup and a single transducer with the same total emitting surface puts in evidence the role of the spatial separation of the two beams. Furthermore, it has been previously shown that the location of the peak negative pressure created by a single transducer shifts from focus towards the transducers in the presence of nonlinear effects. The simulator was used to study a configuration where the acoustical axes of transducers intersect on the peak negative pressure instead of the geometrical focus. For a representative confocal setup, namely moderate nonlinear effects, a 2% increase of the peak negative pressure and 8% decrease of the peak positive pressure resulted from this configuration. These differences tend to increase by increasing nonlinear effects. Although the optimal position of the transducers varies with the nonlinear regimen, the intersection point

  11. Tip-leakage cavitation in the clearance of a 2D hydrofoil with fillets: high-speed visualization and PIV/PTV measurements

    Science.gov (United States)

    Zapryagaev, Ivan I.; Timoshevskiy, Mikhail V.; Pervunin, Konstantin S.

    2017-09-01

    Tip-clearance cavitation is one of the most aggressive forms of cavitation as it can cause surface erosion of hydraulic machinery elements and, as a result, their fatigue damage and disturb designed operating conditions. At present, the literature lacks for detailed experimental data on the inception and development of this type of cavitation at various flow conditions. In the paper, a tip-leakage cavitation occurring in the clearance between an end face of a 2D hydrofoil (a scaled-down model of guide vanes (GV) of a Francis turbine) and a transparent wall of the test section was studied. The experiments were carried out for different cavitating regimes on the cavitation number and two attack angles of 3° and 9°, with the gap size (tip clearance width) varied in the range from 0.4 to 0.8 mm. In order to determine the cavitation inception conditions and investigate the dynamics of the tip-leakage cavitation, a high-speed visualization was applied. A modified PIV/PTV technique with a diverging laser beam instead of a laser light sheet was used to measure the mean velocity distributions within the gap. It was shown that the cavitation pattern on the suction side of the GV model impacts the dynamics of the leakage flow in the gap but does not affect the sheet cavity formed close to the foil leading edge in the clearance as well as its size and dynamics. When the gap size is increased, the tip-leakage cavitation initiates at higher cavitation numbers or, in other words, conditions for the cavitation occurrence become more favorable.

  12. Influence of Heat Treatment on Mercury Cavitation Resistance of Surface Hardened 316LN Stainless Steel

    Energy Technology Data Exchange (ETDEWEB)

    Pawel, Steven J [ORNL; Hsu, Julia [Massachusetts Institute of Technology (MIT)

    2010-11-01

    The cavitation-erosion resistance of carburized 316LN stainless steel was significantly degraded but not destroyed by heat treatment in the temperature range 500-800 C. The heat treatments caused rejection of some carbon from the carburized layer into an amorphous film that formed on each specimen surface. Further, the heat treatments encouraged carbide precipitation and reduced hardness within the carburized layer, but the overall change did not reduce surface hardness fully to the level of untreated material. Heat treatments as short as 10 min at 650 C substantially reduced cavitation-erosion resistance in mercury, while heat treatments at 500 and 800 C were found to be somewhat less detrimental. Overall, the results suggest that modest thermal excursions perhaps the result of a weld made at some distance to the carburized material or a brief stress relief treatment will not render the hardened layer completely ineffective but should be avoided to the greatest extent possible.

  13. Increased fragmentation efficiency by enhancement of cavitation for extracorporal shock wave lithotripsy

    International Nuclear Information System (INIS)

    Loske, A.M.; Fernandez, F.; Gutierrez, J.

    2005-01-01

    The non-invasive disintegration of kidney stones using shock waves, referred to as extracorporal shock wave lithotripsy, has been successful for more than twenty years in treating patients having renal and ureteral stones. Two modified shock wave generators are described in this article. The novel systems produce two similar shock waves (tandem shock waves) generated with a short time delay. The second shock wave arrives during collapse of the bubbles generated in the neighborhood of the stone due to the first shock wave. This may increase cavitation bubble collapse and could enhance cavitation-induced damage to kidney stones during shock wave lithotripsy. In vitro comparison of standard systems with the new designs showed that fragmentation efficiency of artificial kidney stones was significantly enhanced using tandem shock waves. (orig.)

  14. Effect of state of stress on the cavitation behavior of Al 5083 superplastic material

    Energy Technology Data Exchange (ETDEWEB)

    Chandra, Namas; Kalu, Peter [Dept. of Mech. Eng., Florida State Univ., Tallahassee, FL (United States); Khraisheh, Marwan K. [Dept. of MEch. Eng., Univ. of Kentucky, Lexington, KY (United States)

    2005-07-01

    In this paper we address the controversial issue of nucleation of cavities in Al 5083 alloys and their subsequent growth to coalescence and failure. We focus on the origin and growth of cavities not only during the primary processing of Al 5083 in sheet forms, but also during the manufacture of these sheets into SPF (superplastic forming) components. Experimental observations of pre-existing cavities in this alloy are made using optical and electron microscopy. The role of sheet rolling direction, and the state of stress during superplastic deformation on the cavity formation and coalescence are also discussed. The effect of the state of stress (uniaxial, plane strain, balanced biaxial, and tri-axial) on the growth characteristics of cavitation is also examined. It is found that the uniaxial model based cavitation cannot directly be extended to predict the behavior of more complex stress states, unless great care is taken to identify the right strain measure for the mapping process. (orig.)

  15. Intramembrane Cavitation as a Predictive Bio-Piezoelectric Mechanism for Ultrasonic Brain Stimulation

    Science.gov (United States)

    Plaksin, Michael; Shoham, Shy; Kimmel, Eitan

    2014-01-01

    Low-intensity ultrasonic waves can remotely and nondestructively excite central nervous system (CNS) neurons. While diverse applications for this effect are already emerging, the biophysical transduction mechanism underlying this excitation remains unclear. Recently, we suggested that ultrasound-induced intramembrane cavitation within the bilayer membrane could underlie the biomechanics of a range of observed acoustic bioeffects. In this paper, we show that, in CNS neurons, ultrasound-induced cavitation of these nanometric bilayer sonophores can induce a complex mechanoelectrical interplay leading to excitation, primarily through the effect of currents induced by membrane capacitance changes. Our model explains the basic features of CNS acoustostimulation and predicts how the experimentally observed efficacy of mouse motor cortical ultrasonic stimulation depends on stimulation parameters. These results support the hypothesis that neuronal intramembrane piezoelectricity underlies ultrasound-induced neurostimulation, and suggest that other interactions between the nervous system and pressure waves or perturbations could be explained by this new mode of biological piezoelectric transduction.

  16. Background nuclei measurements and implications for cavitation inception in hydrodynamic test facilities

    Science.gov (United States)

    Venning, J. A.; Khoo, M. T.; Pearce, B. W.; Brandner, P. A.

    2018-04-01

    Water susceptibility and background nuclei content in a water tunnel are investigated using a cavitation susceptibility meter. The measured cumulative histogram of nuclei concentration against critical pressure shows a power law dependence over a large range of concentrations and pressures. These results show that the water strength is not characterised by a single tension but is susceptible to `all' tensions depending on the relevant timescale. This background nuclei population is invariant to tunnel conditions showing that it is stabilised against dissolution. Consideration of a practical cavitating flow about a sphere shows that although background nuclei may be activated, their numbers are so few compared with other sources that they are insignificant for this case.

  17. Examination of observed and predicted measures of creep cavitation damage accumulation

    Energy Technology Data Exchange (ETDEWEB)

    Brear, J.M.; Church, J.M. [ERA Technology Ltd., Leatherhead (United Kingdom); Eggeler, G. [University of Bochum-Ruhr (Germany)

    1998-12-31

    Brittle intergranular cavitation represents a primary degradation mechanism for high temperature plant operating within the creep range. Fundamental to formulating estimates of remanent life, or consumed life fraction for such components are: the observation and quantification of the level of actual creep cavitation, typically using an A-parameter type approach, and the correlation of observed creep damage accumulation with some phenomenological model which characterizes the rate of damage evolution and, thereby, rupture lifetime. The work described here treats inhomogeneous damage accumulation - in otherwise uniform material and loading situations. Extensions to the A-parameter are considered as a practical measure of damage localization and an extension of the Kachanov-Rabotnov continuum damage mechanics model is proposed to allow theoretical treatment. (orig.) 4 refs.

  18. Numerical Investigation of Viscous Flow Velocity Field around a Marine Cavitating Propeller

    Directory of Open Access Journals (Sweden)

    Zhifeng Zhu

    2014-11-01

    Full Text Available Velocity field around a ship cavitating propeller is investigated based on the viscous multiphase flow theory. Using a hybrid grid, the unsteady Navier-stokes (N-S and the bubble dynamics equations are solved in this paper to predict the velocity in a propeller wake and the vapor volume fraction on the back side of propeller blade for a uniform inflow. Compared with experimental results, the numerical predictions of cavitation and axial velocity coincide with the measured data. The evolution of tip vortex is shown, and the interaction between the tip vortex of the current blade and the wake of the next one occurs in the far propeller wake. The frequency of velocity signals changes from shaft rate to blade rate. The phenomena reflect the instability of propeller wake.

  19. Experimental Facility for Checking the Possibility to Obtain Super-High Temperature Due to Acoustic Cavitation

    CERN Document Server

    Miller, M B; Sobolev, Yu G; Kostenko, B F

    2004-01-01

    An experimental facility developed for checking the possibility to obtain super-high temperature sufficient for thermonuclear reaction D($d, n$)$^{3}$He in an acoustic cavitation is described. The acoustic part of the instrumentation consists of a resonator and a system exciting high amplitude of the acoustic field within the resonator. The cavitation process is controlled with the use of fast neutron pulses. The instrument includes a system of pumping out solute gases from the liquid (acetone enriched with deuterium up to 99{\\%}) without losses of matter. Measuring of the field is based on the calibration procedure including observation of sonoluminescence. The system of detection and identification of D($d, n$)$^{3}$He reaction is based on a scintillation detector of fast neutrons and a system of measuring multiparameter events by the correlation technique with separation of the neutrons from the $\\gamma $-radiation background (pulse shape discrimination).

  20. Study of unsteady cavitation on NACA66 hydrofoil using dynamic cubic nonlinear subgrid-scale model

    Directory of Open Access Journals (Sweden)

    Xianbei Huang

    2015-11-01

    Full Text Available In this article, we describe the use of a new dynamic cubic nonlinear model, a new nonlinear subgrid-scale model, for simulating the cavitating flow around an NACA66 series hydrofoil. For comparison, the dynamic Smagorinsky model is also used. It is found that the dynamic cubic nonlinear model can capture the turbulence spectrum, while the dynamic Smagorinsky model fails. Both models reproduce the cavity growth/destabilization cycle, but the results of the dynamic cubic nonlinear model are much smoother. The re-entrant jet is clearly captured by the models, and it is shown that the re-entrant jet cuts the cavity into two parts. In general, the dynamic cubic nonlinear model provides improvement over the dynamic Smagorinsky model for the calculation of cavitating flow.

  1. Computational Treatments of Cavitation Effects in Near-Free-Surface Underwater Shock Analysis

    Directory of Open Access Journals (Sweden)

    Michael A. Sprague

    2001-01-01

    Full Text Available Fluid cavitation constitutes an expensive computational nuisance in underwater-shock response calculations for structures at or just below the free surface. In order to avoid the use of a large array of cavitating acoustic finite elements (CAFE, various wet-surface approximations have been proposed. This paper examines the performance of two such approximations by comparing results produced by them for 1-D canonical problems with corresponding results produced by more rigorous CAFE computations. It is found that the fundamental limitation of wet-surface approximations is their inability to capture fluid-accretion effects. As an alternative, truncated CAFE fluid meshes with plane-wave radiation boundaries are shown to give good results. In fact, a single layer of CAFE is found to be comparable in accuracy to the better of the wet-surface approximations. The paper concludes with an examination of variations in CAFE modeling.

  2. Blade Section Design of Marine Propellers with Minimum Cavitation Induced Pressure Fluctuations

    Science.gov (United States)

    Zeng, Zhibo; Kuiper, Gert

    2015-12-01

    To minimize cavitation induced pressure fluctuations by marine propellers with minimum efficiency loss, the paper presents a new design and optimization method using a blade section design method. The sheet cavity volume variation on a two-dimensional blade section in quasi-steady condition has been simplified to a relation with only a limited number of non-dimensional parameters. This results in a fast prediction method of the cavity volume of a blade section passing a wake peak, using a pre-calculated database. This makes optimization feasible. The optimization method was applied to the propeller of a container ship. Extensive tests in a towing tank and a cavitation channel validated the reduction of pressure fluctuations: 33% reduction in the first blade frequency amplitude and 18% reduction in the second blade frequency amplitude, with the same open water efficiency.

  3. Cavitation pitting and erosion of aluminum 6061-T6 in mineral oil water

    Science.gov (United States)

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

    1983-01-01

    Cavitation erosion studies of aluminum 6061-T6 in mineral oil and in ordinary tap water are presented. The maximum erosion rate (MDPR, or mean depth of penetration rate) in mineral oil was about four times that in water. The MDPR in mineral oil decreased continuously with time, but the MDPR in water remained approximately constant. The cavitation pits in mineral oil were of smaller diameter and depth than the pits in water. Treating the pits as spherical segments, we computed the radius r of the sphere. The logarithm of h/a, where h is the pit depth and 2a is the top width of the pit, was linear when plotted against the logarithm of 2r/h - 1.

  4. Characterisation of creep cavitation damage in a stainless steel pressure vessel using small angle neutron scattering

    CERN Document Server

    Bouchard, P J; Treimer, W

    2002-01-01

    Grain-boundary cavitation is the dominant failure mode associated with initiation of reheat cracking, which has been widely observed in austenitic stainless steel pressure vessels operating at temperatures within the creep range (>450 C). Small angle neutron scattering (SANS) experiments at the LLB PAXE instrument (Saclay) and the V12 double-crystal diffractometer of the HMI-BENSC facility (Berlin) are used to characterise cavitation damage (in the size range R=10-2000 nm) in a variety of creep specimens extracted from ex-service plant. Factors that affect the evolution of cavities and the cavity-size distribution are discussed. The results demonstrate that SANS techniques have the potential to quantify the development of creep damage in type-316H stainless steel, and thereby link microstructural damage with ductility-exhaustion models of reheat cracking. (orig.)

  5. Intramembrane Cavitation as a Predictive Bio-Piezoelectric Mechanism for Ultrasonic Brain Stimulation

    Directory of Open Access Journals (Sweden)

    Michael Plaksin

    2014-01-01

    Full Text Available Low-intensity ultrasonic waves can remotely and nondestructively excite central nervous system (CNS neurons. While diverse applications for this effect are already emerging, the biophysical transduction mechanism underlying this excitation remains unclear. Recently, we suggested that ultrasound-induced intramembrane cavitation within the bilayer membrane could underlie the biomechanics of a range of observed acoustic bioeffects. In this paper, we show that, in CNS neurons, ultrasound-induced cavitation of these nanometric bilayer sonophores can induce a complex mechanoelectrical interplay leading to excitation, primarily through the effect of currents induced by membrane capacitance changes. Our model explains the basic features of CNS acoustostimulation and predicts how the experimentally observed efficacy of mouse motor cortical ultrasonic stimulation depends on stimulation parameters. These results support the hypothesis that neuronal intramembrane piezoelectricity underlies ultrasound-induced neurostimulation, and suggest that other interactions between the nervous system and pressure waves or perturbations could be explained by this new mode of biological piezoelectric transduction.

  6. Properties of sound attenuation around a two-dimensional underwater vehicle with a large cavitation number

    International Nuclear Information System (INIS)

    Ye Peng-Cheng; Pan Guang

    2015-01-01

    Due to the high speed of underwater vehicles, cavitation is generated inevitably along with the sound attenuation when the sound signal traverses through the cavity region around the underwater vehicle. The linear wave propagation is studied to obtain the influence of bubbly liquid on the acoustic wave propagation in the cavity region. The sound attenuation coefficient and the sound speed formula of the bubbly liquid are presented. Based on the sound attenuation coefficients with various vapor volume fractions, the attenuation of sound intensity is calculated under large cavitation number conditions. The result shows that the sound intensity attenuation is fairly small in a certain condition. Consequently, the intensity attenuation can be neglected in engineering. (paper)

  7. Current knowledge and potential applications of cavitation technologies for the petroleum industry.

    Science.gov (United States)

    Avvaru, Balasubrahmanyam; Venkateswaran, Natarajan; Uppara, Parasuveera; Iyengar, Suresh B; Katti, Sanjeev S

    2018-04-01

    Technologies based on cavitation, produced by either ultrasound or hydrodynamic means, are part of growing literature for individual refinery unit processes. In this review, we have explained the mechanism through which these cavitation technologies intensify individual unit processes such as enhanced oil recovery, demulsification of water in oil emulsions during desalting stage, crude oil viscosity reduction, oxidative desulphurisation/demetallization, and crude oil upgrading. Apart from these refinery processes, applications of this technology are also mentioned for other potential crude oil sources such as oil shale and oil sand extraction. The relative advantages and current situation of each application/process at commercial scale is explained. Copyright © 2017 Elsevier B.V. All rights reserved.

  8. Water Treatment using Discharge Generated in Cavitation Field with Micro Bubble Cloud

    Science.gov (United States)

    Ihara, Satoshi; Hirohata, Taiki; Kominato, Yuichi; Yamabe, Chobei; Ike, Hideaki; Hakiai, Kazunori; Hirabayashi, Kazuya; Tamagawa, Masaaki

    New method of water treatment for wastewater using discharge in water cavitation field, in which numerous micro bubbles were generated by high-speed water flow, was proposed in this paper. Indigo carmine solution, which is a type of dye, with a concentration of 9mg/Liter was used as a specimen for demonstration of water treatment. The total volume of solution and average speed of solution in the cavitation field was 20 Liter and about 7.4 m/s, respectively. A reduction ratio of absorbance of 96% was obtained in 50 min of treatment time at an electrode distance of 2 mm and a discharge power of 16 W. Also it was found that the efficiency of decolorization was improved by changing the electrode location.

  9. A histologic evaluation of periodontal tissues adjacent to root perforations filled with Cavit.

    Science.gov (United States)

    Jew, R C; Weine, F S; Keene, J J; Smulson, M H

    1982-07-01

    Root perforations were created in dog premolars; thirty-one were filled with Cavit, whereas seventeen were left unfilled. The animals were killed after 1, 15, 30, 60, 120, and 180 days, and hematoxylin and eosin sections were prepared. Perforations near the gingival sulcus usually led to severe destruction, whereas those surrounded by ample bone tended to gain a favorable response, even when left unfilled.

  10. Use of the ultrasonic cavitation in wool dyeing process: Effect of the dye-bath temperature.

    Science.gov (United States)

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

    2017-03-01

    The present work aims to study the effect of the liquid temperature on the performance of ultrasounds (US) in a dyeing process. The approach was both theoretical and experimental. In the theoretical part the simplified model of a single bubble implosion is used to demonstrate that the "maximum implosion pressure" calculated with the well known Rayleigh-Plesset equation for a single bubble can be correlated with the cavitation intensity experimentally measured with an Ultrasonic Energy Meter (by PPB Megasonics). In particular the model was used to study the influence of the fluid temperature on the cavitation intensity. The "relative" theoretical data calculated from the implosion pressure were satisfactorily correlated with the experimental ones and evidence a zone, between 50 and 60°C, were the cavitation intensity is almost constant and still sufficiently high. Hence an experimental part of wool dyeing was carried out both to validate the previous results and to verify the dyeing quality at low temperatures (40-70°C) in presence of US. A prototype dyeing equipment able to treat textile samples with US system of 600W power, was used. The dyeing performances in the presence and absence of US were verified by measuring ΔE (colour variation), R e,% (reflectance percentage), K/S (colour strength) and colour fastness. The US tests performed in the temperature range of 40-70°C were compared with the conventional wool dyeing at 98°C. The obtained results show that a temperature close to 60°C should be chosen as the recommended US dyeing condition, being a compromise between the cavitation intensity and the kinetics which rules the dyestuff diffusion within the fibres. Copyright © 2016 Elsevier B.V. All rights reserved.

  11. On cavitation in liquid helium in a flow due to a vibrating quartz fork

    Czech Academy of Sciences Publication Activity Database

    Blažková, Michaela; Schmoranzer, D.; Skrbek, Ladislav

    2008-01-01

    Roč. 34, 4/5 (2008), s. 298-307 ISSN 1063-777X R&D Projects: GA ČR GA202/05/0218 Grant - others:GAUK(CZ) 7953/2007 Institutional research plan: CEZ:AV0Z10100520 Keywords : cavitation * He I * He II * quartz tuning fork Subject RIV: BK - Fluid Dynamics Impact factor: 0.780, year: 2008

  12. Cavitation in liquid helium observed in a flow due to a vibrating quartz fork

    Czech Academy of Sciences Publication Activity Database

    Blažková, Michaela; Chagovets, Tymofiy; Rotter, M.; Schmoranzer, D.; Skrbek, L.

    2008-01-01

    Roč. 150, 3-4 (2008), s. 194-199 ISSN 0022-2291 R&D Projects: GA ČR GA202/05/0218 Grant - others:GAUK(CZ) 7953/2007 Institutional research plan: CEZ:AV0Z10100520 Keywords : cavitation * He I * He II * quartz tuning fork Subject RIV: BK - Fluid Dynamics Impact factor: 1.034, year: 2008

  13. Molecular dynamics study of cavitation in carbon nanotube reinforced polyethylene nanocomposite

    Science.gov (United States)

    Logunov, M. A.; Orekhov, N. D.

    2018-01-01

    Carbon nanotubes (CNTs) have proved to be very promising fillers for polymer nanocomposites. However, because of the lack of a detailed understanding of the principles of the nanoinclusion interaction with polymer matrixes, the properties of such materials are poorly understood. In the present study, within the coarse-grained molecular-dynamics methods, aspects of the interaction of amorphous polyethylene matrix with carbon nanotubes and the influence of CNTs on the cavitation during the nanocomposite deformation are studied.

  14. Review of parameters influencing the structural response of a submerged body under cavitation conditions

    OpenAIRE

    Escaler, X; De La Torre, O; Farhat, M

    2015-01-01

    Submerged structures that operate under extreme flows are prone to suffer large scale cavitation attached to thei r surfaces. Under such conditions the added mass effects differ from the expected ones in pure liquids. Moreover, the existence of small gaps between the structure and surrounding bodies filled with fluid also influence the dynamic response. A series of experiments and numerical simulations have been carried out with a truncated NACA0009 hydrofoil mounted as a cantilever beam at t...

  15. Cavitation effects on the pressure distribution of a squeeze film damper bearing

    Science.gov (United States)

    Zeidan, Fouad Y.; Vance, John M.

    1989-01-01

    High speed motion pictures have revealed several operating regimes in a squeeze film damper. Pressure measurements corresponding to these distinct regimes were made to examine their effect on the performance of such dampers. Visual observation also revealed the means by which the pressure in the feed groove showed higher amplitudes than the theory predicts. Comparison between vapor and gaseous cavitation are made based on their characteristic pressure wave, and the effect this has on the total force and its phase.

  16. Unsteady Lift and Drag Characteristics of Cavitating Clark Y-11.7% Hydrofoil

    International Nuclear Information System (INIS)

    Watanabe, S; Yamaoka, W; Furukawa, A

    2014-01-01

    Unsteady cavitating flow and lift/drag characteristics of a two-dimensional Clark Y- 11.7% hydrofoil are experimentally investigated in order to clarify the relation between the lift drop mechanism and the unsteady cavity behavior. Unsteady lift and drag forces are measured by strain gauges attached on the cantilever supporting the hydrofoil, assuming the negligible bending moment. In combination with the above force measurements, the cavitating flow is filmed from both top and side simultaneously using two high speed video cameras. It is clearly observed that, in larger attack angle conditions (4-10 degrees), the time-averaged lift coefficient slightly increases from that in the non-cavitating condition. After the slight increase, the lift gradually decreases then its steep decrease starts to occur. On the other hand, in a small attack angle case (2 degrees), little increase of the lift is observed, and just after that the sudden lift drop occurs. From the instantaneous frequency spectra of the lift, the followings are found; during the slight increase of the lift, the cavity is being a partial cavity in almost steady state, but during the subsequent gradual lift decrease, the partial cavity oscillates with cloud cavity shedding, in other word, the partial cavity oscillation occurs, whose frequency decreases with the growth of the cavity. During the sudden lift drop, the low frequency transitional cavity oscillation occurs, in which the cavity dramatically changes between partial and super cavities. The typical events of cavity behavior during the cavitation instabilities are found to be able to be related with the behavior of instantaneous lift force and pressure

  17. A high speed photography study of cavitation in a dynamically loaded journal bearing

    Science.gov (United States)

    Sun, D. C.; Brewe, D. E.

    1991-01-01

    The earlier study made by Jacobson and Hamrock on the cavitation of liquid lubricant films in a dynamically loaded journal bearing was repeated with a quartz sleeve, which was more rigid than the Polymethylmethacrylate (PMMA) sleeve used previously. Various improvements of the test rig were made concomitantly so that the experimental errors could be better controlled and assessed. The updated speed photography experiment and its results are described.

  18. A high-speed photography study of cavitation in a dynamically loaded journal bearing

    Science.gov (United States)

    Sun, D. C.; Brewe, D. E.

    1990-01-01

    The earlier study made by Jacobson and Hamrock on the cavitation of liquid lubricant films in a dynamically loaded journal bearing was repeated with a quartz sleeve, which was more rigid than the Polymethylmethacrylate (PMMA) sleeve used previously. Various improvements of the test rig were made concomitantly so that the experimental errors could be better controlled and assessed. The updated speed photography experiment and its results are described.

  19. LENR BEC Clusters on and below Wires through Cavitation and Related Techniques

    Science.gov (United States)

    Stringham, Roger; Stringham, Julie

    2011-03-01

    During the last two years I have been working on BEC cluster densities deposited just under the surface of wires, using cavitation, and other techniques. If I get the concentration high enough before the clusters dissipate, in addition to cold fusion related excess heat (and other effects, including helium-4 formation) I anticipate that it may be possible to initiate transient forms of superconductivity at room temperature.

  20. Feasibility study into a computational approach for marine propeller noise and cavitation modelling

    OpenAIRE

    Lidtke, Artur Konrad; Humphrey, Victor; Turnock, Stephen

    2015-01-01

    There is increased interest in the ability to predict the noise associated with commercial ship propellers. Key components of the computational analysis process are considered for two test cases and the future direction in resolving the associated challenges is presented. Firstly, the Potsdam Propeller Test Case is used to compute tonal blade passage noise using the Ffowcs Williams–Hawkings acoustic analogy. Cavitation extents predicted using the Sauer and Schnerr mass transfer model agree we...