scholarly journals Dynamics and acoustics of cavitation bubble in adverse external pressure gradient

2020 ◽  
Author(s):  
К.В. Рождественский
Keyword(s):  
Pressure Gradient ◽  
Cavitation Bubble ◽  
Acoustic Pressure ◽  
Bubble Radius ◽  
Pressure Rise ◽  
Leading Edge ◽  
External Pressure ◽  
Gas Content ◽  
Bubble Collapse ◽  
Spectral Parameters

В статье приводятся аналитические и численные результаты по динамике и акустике кавитационного пузырька при повышении внешнего давления. В начале рассматривается модельная задача о сжатии пузырька вплоть до коллапса при мгновенном повышении давления. При этом уравнение Рэлея-Плессета рассматривается с учетом газосодержания, поверхностного натяжения и вязкости. Акустическое давление, вызванное сжатием пузырька, записанное в безразмерном виде, определяется как с привлечением формул, так и численным путем. Показано, что если наряду с паром, внутри пузырька имеется некоторое количество газа, скорость его сжатия и акустическое давление оказываются конечными вплоть до полного схлопывания. Кроме того, возможно многократное повторение цикла расширения-сжатия с затуханием амплитуды колебаний. На каждом периоде колебаний вблизи момента времени коллапса (достижения минимального радиуса) наблюдается импульсное возрастание давления. Во второй части аналогичное исследование проводится для случая, когда кавитационный пузырек возникает в закругленной носовой части подводного крылового профиля. При этом демонстрируется зависимость динамического поведения пузырька и вызываемого им в заданной точке контура профиля акустического давления от типа профиля, его толщины и угла атаки. По периоду первого цикла схлопывания спектральные параметры акустического импульса определяются как у эквивалентного треугольного импульса. Presented in this paper are analytical and numerical results on dynamics and acoustics of a cavitation bubble in adverse external pressure gradient. First considered is a model problem of bubble collapse due to instantaneous increase of pressure. Therewith, the Rayleigh-Plesset equation is treated with account of gas content, surface tension and viscosity. Non-dimensional acoustic pressure caused by the compression of the bubble, is determined both with use of relevant formulae and numerically. It is shown that if together with vapor the bubble contains some quantity of gas, than its collapse rate and acoustic pressure during compression turn out to be finite. In addition, multiple expansion compression cycles are possible. For each period of bubble radius variation there occurs near the moment of collapse (moment of reaching a minimum radius) an impulse acoustic pressure rise. In the second part of the paper a similar investigation is carried out for the case when the bubble occurs near the rounded leading edge of a hydrofoil. Demonstrated therewith is the dependence of the bubble dynamic behavior and accompanying acoustic pressure pulses upon the foil type, thickness and angle of attack. Based on the period of the first bubble collapse cycle the spectral parameters of the induced acoustic pressure impulse are determined as for an equivalent triangular impulse.

Numerical Investigation of Liquid Parameters Effect on the Oscillation of Cavitation Bubble

2014 ◽  
Vol 568-570 ◽  
pp. 1794-1800
Author(s):  
Xiu Mei Liu ◽  
Bei Bei Li ◽  
Wen Hua Li ◽  
Jie He ◽  
Jian Lu ◽  
...  
Keyword(s):  
Surface Tension ◽  
Cavitation Bubble ◽  
Bubble Dynamics ◽  
Dynamic Performance ◽  
Bubble Radius ◽  
Gas Content ◽  
Viscous Force ◽  
Bubble Collapse ◽  
Hydraulic Systems ◽  
Increasing Temperature

Cavitation is a common harmful phenomenon in hydraulic transmission systems. It not only damages flow continuity and reduces medium physical performance, but also induces vibration and noise. At the same time, the efficiency of a system is reduced due to cavitation, especially dynamic performance are deteriorated. Applying commercial CFD software FLUENT, the cavitation issuing from the orifice was numerically investigated, reducing the harm. The effect of liquid parameters (such as surface tension, gas content, and the temperature) on the oscillation of bubble is studied numerically. The modified Rayleigh-Plesset equations are presented to describe the oscillation of bubble in different liquids. Employing the finite difference calculus, the behavior of a cavitation bubble in liquids with different physics parameters are obtained. Meanwhile, the numerical results are compared with experiment results. It is observed that the viscous force decreases the growth and collapse of a bubble, making it expand or collapse less violently. And the surface-tension forces stave bubble growth progress and speed up bubble collapse process. On the other hand, both the maximum bubble radius and bubble lifetime increase with increasing temperature. These results can provide theory basis for understanding cavitation bubble dynamics in the hydraulic systems.

Modeling of External Pressure Gradient Influence on the Stability of Disturbances in the Boundary Layers of Compressed Gas

2013 ◽  
Vol 8 (4) ◽  
pp. 64-75
Author(s):  
Sergey Gaponov ◽  
Natalya Terekhova
Keyword(s):  
Mach Number ◽  
Pressure Gradient ◽  
Boundary Layers ◽  
Leading Edge ◽  
External Pressure ◽  
Transition To Turbulence ◽  
Compressed Gas ◽  
High Mach ◽  
The Stability ◽  
Very High

This work continues the research on modeling of passive methods of management of flow regimes in the boundary layers of compressed gas. Authors consider the influence of pressure gradient on the evolution of perturbations of different nature. For low Mach number M = 2 increase in pressure contributes to an earlier transition of laminar to turbulent flow, and, on the contrary, drop in the pressure leads to a prolongation of the transition to turbulence. For high Mach number M = 5.35 found that the acoustic disturbances exhibit a very high dependence on the sign and magnitude of the external gradient, with a favorable gradient of the critical Reynolds number becomes smaller than the vortex disturbances, and at worst – boundary layer is destabilized directly on the leading edge

scholarly journals Numerical Simulation and Investigation of System Parameters of Sonochemical Process

2013 ◽  
Vol 2013 ◽  
pp. 1-14 ◽  
Author(s):  
Sankar Chakma ◽  
Vijayanand S. Moholkar
Keyword(s):  
Cavitation Bubble ◽  
Bubble Dynamics ◽  
Bubble Radius ◽  
Gas Content ◽  
Small Radius ◽  
Dissolved Gas ◽  
High Vapor ◽  
Higher Temperature ◽  
Simulation Results ◽  
Main Effects

This paper presents the effects of various parameters that significantly affect the cavitation. In this study, three types of liquid mediums with different physicochemical properties were considered as the cavitation medium. The effects of various operating parameters such as temperature, pressure, initial bubble radius, dissolved gas content and so forth, were investigated in detail. The simulation results of cavitation bubble dynamics model showed a very interesting link among these parameters for production of oxidizing species. The formation of •OH radical and H2O2 is considered as the results of main effects of sonochemical process. Simulation results of radial motion of cavitation bubble dynamics revealed that bubble with small initial radius gives higher sonochemical effects. This is due to the bubble with small radius can undergo many acoustic cycles before reaching its critical radius when it collapses and produces higher temperature and pressure inside the bubble. On the other hand, due to the low surface tension and high vapor pressure, organic solvents are not suitable for sonochemical reactions.

Cavitation Bubble Collapse Near a Heated Wall and Its Effect on the Heat Transfer

2013 ◽  
Vol 136 (2) ◽  
Author(s):  
Bin Liu ◽  
Jun Cai ◽  
Xiulan Huai ◽  
Fengchao Li
Keyword(s):  
Heat Transfer ◽  
Cavitation Bubble ◽  
Stokes Equations ◽  
Saturated Vapor ◽  
Bubble Diameter ◽  
Bubble Radius ◽  
Heated Wall ◽  
Bubble Collapse ◽  
Flow State ◽  
Vof Model

In the present work, a numerical investigation on the mechanism of heat transfer enhancement by a cavitation bubble collapsing near a heated wall has been presented. The Navier–Stokes equations and volume of fluid (VOF) model are employed to predict the flow state and capture the liquid-gas interface. The model was validated by comparing with the experimental data. The results show that the microjet violently impinges on the heated wall after the bubble collapses completely. In the meantime, the thickness of the thermal boundary layer and the wall temperature decrease significantly within the active scope of the microjet. The fresh low-temperature liquid and the impingement brought by the microjet should be responsible for the heat transfer reinforcement between the heated wall and the liquid. In addition, it is found that the impingement width of the microjet on the heated wall always keeps 20% of the bubble diameter. And, the enhancement degree of heat transfer significantly depends on such factors as stand-off distance, saturated vapor pressure, and initial bubble radius.

Numerical simulation of traveling bubble cavitation

2006 ◽  
Vol 16 (4) ◽  
pp. 393-416 ◽  
Author(s):  
Sunil Mathew ◽  
Theo G. Keith Theo G. Keith ◽  
Efstratios Nikolaidis
Keyword(s):  
Cavitation Bubble ◽  
Bubble Radius ◽  
Random Variable ◽  
Bubble Collapse ◽  
Maximum Pressure ◽  
Local Pressure ◽  
New Approach ◽  
Content Type ◽  
Collapse Pressure ◽  
Bubble Cavitation

PurposeThe purpose is to present a new approach for studying the phenomenon of traveling bubble cavitation.Design/methodology/approachA flow around a rigid, 2D hydrofoil (NACA‐0012) with a smooth surface is analyzed computationally. The Rayleigh‐Plesset equation is numerically integrated to simulate the growth and collapse of a cavitation bubble moving in a varying pressure field. The analysis is performed for both incompressible and compressible fluid cases. Considering the initial bubble radius as a uniformly distributed random variable, the probability density function of the maximum collapse pressure is determined.FindingsThe significance of the liquid compressibility during bubble collapse is illustrated. Furthermore, it is shown that the initial size of the bubble has a significant effect on the maximum pressure generated during the bubble collapse. The maximum local pressure developed during cavitation bubble collapse is of the order of 104 atm.Research limitations/implicationsA single bubble model that does not account for the effect of neighboring bubbles is used in this analysis. A spherical bubble is assumed.Originality/valueA new approach has been developed to simulate traveling bubble cavitation by interfacing a CFD solver for simulating a flow with a program simulating the growth and collapse of the bubble. Probabilistic analysis of the local pressure due to bubble collapse has been performed.

scholarly journals Pressure Field Generated by Nonspherical Bubble Collapse

1983 ◽  
Vol 105 (3) ◽  
pp. 356-362 ◽  
Author(s):  
G. L. Chahine ◽  
A. G. Bovis
Keyword(s):  
Velocity Potential ◽  
Pressure Field ◽  
Solid Wall ◽  
Bubble Radius ◽  
Computer Time ◽  
Gas Content ◽  
Bubble Collapse ◽  
System Of Differential Equations ◽  
Spherical Bubble ◽  
Complex Cases

The method of matched asymptotic expansions is used to investigate the behavior of a collapsing bubble near a solid wall. Cases are studied in which the ratio ε between the initial spherical bubble radius and its distance from the wall is small. Expansions in powers of ε lead to a simple system of differential equations which is solved numerically. The bubble shape, the velocity potential and the pressure field are determined as functions of time. The deformation of the bubble is a singular perturbation of the pressure field around it. An increase in the value of ε augments the pressure on the solid wall by orders of magnitude. The influence of surface tension and the proximity of the wall, gas content and its law of compression, are investigated. The results are compared to previous investigations. One advantage of the method employed is the fact that it leads to a numerical solution which costs very little computer time. In addition, it can be extended very easily to more complex cases such as multibubble configurations or to walls coated with elastomeric coatings.

Cavitation Bubble Collapse Observations in a Venturi

1966 ◽  
Vol 88 (3) ◽  
pp. 649-657 ◽  
Author(s):  
R. D. Ivany ◽  
F. G. Hammitt ◽  
T. M. Mitchell
Keyword(s):  
Pressure Gradient ◽  
Cavitation Bubble ◽  
Small Bubble ◽  
Bubble Collapse ◽  
Cavitating Flows ◽  
Spherical Bubble ◽  
Slowing Down ◽  
Large Pressure ◽  
Large Pressure Gradient ◽  
The Asymmetry

Bubbles collapsing in water in a cavitating venturi are photographically observed. The large pressure gradient in the venturi causes the bubbles to collapse by flattening in the direction of flow. In many cases a torus is formed, implying the existence of a central jet which, as has been suggested by other investigators, may well be the primary damaging mechanism in cavitating flows. The effect of adjacent bubbles upon each other is visually observed. Numerous bubble rebounds, even in relatively degassed water, are noted. A comparison of observed collapse rates with incompressible theory for a spherical bubble indicates that the slowing down of collapse herein observed at small bubble radii probably results primarily from the asymmetry of the collapse and perhaps also from metastable compression of vapor within the bubble.

PIV Measurements of Cavitation Bubble Collapse Flow Induced by Pressure Wave

2010 ◽  
Author(s):  
Sheng-Hsueh Yang ◽  
Shenq-Yuh Jaw ◽  
Keh-Chia Yeh
Keyword(s):  
Cavitation Bubble ◽  
High Speed ◽  
Bubble Radius ◽  
Ccd Camera ◽  
Bubble Surface ◽  
Bubble Collapse ◽  
Solid Boundary ◽  
Liquid Jet ◽  
Pressure Waves ◽  
Critical Position

In this study, a single cavitation bubble is generated by rotating a U-tube filled with water. A series of bubble collapse flows induced by pressure waves of different strengths are investigated by positioning the cavitation bubble at different stand-off distances to a solid boundary. Particle images of bubble collapse flow recorded by high speed CCD camera are analyzed by multi-grid, iterative particle image distortion method. Detail velocity variations of the transient bubble collapse flow are obtained. It is found that a Kelvin–Helmholtz vortex is formed when a liquid jet penetrates the bubble surface. If the bubble center to the solid boundary is within one to three times of the bubble radius, the liquid jet is able to impinge the solid boundary to form a stagnation ring. The fluid inside the stagnation ring will be squeezed toward the center of the ring to form a counter jet. At certain critical position, the bubble collapse flow will produce a Kelvin–Helmholtz vortex, the Richtmyer-Meshkov instability, or the generation of a counter jet flow, depending on the strengths of the pressure waves. If the bubble surface is in contact with the solid boundary, the liquid jet can only splash inside-out without producing the stagnation ring and the counter jet. The complex phenomenon of cavitation bubble collapse flows is clearly manifested in this study.

Numerical Study on Mass Transfer Effects on Spherical Cavitation Bubble Collapse in an Acoustic Field

2010 ◽  
Author(s):  
Ehsan Samiei ◽  
Mehrzad Shams ◽  
Reza Ebrahimi
Keyword(s):  
Mass Transfer ◽  
Cavitation Bubble ◽  
Bubble Dynamics ◽  
Numerical Study ◽  
Bubble Radius ◽  
Numerical Code ◽  
Bubble Collapse ◽  
Growth Time ◽  
Transfer Effects ◽  
Low Amplitude

A numerical code to simulate mass transfer effects on spherical cavitation bubble collapse in an acoustic pressure domain in quiescent water has been developed. Gilmore equation is used to simulate bubble dynamics, with considering mass diffusion and heat transfer. Bubbles with different initial radii were considered in quiescent infinite water in interaction with sinusoidal shock waves with different magnitudes of amplitude and frequency. Simulations were done in two cases; with and without considering mass transfer. Good agreement with reference data was achieved. For bubbles with small radii in high frequency pressure field with low amplitude, mass transfer causes larger maximum radii and growth time, and more violent resultant collapse. Decreasing pressure frequency or increasing its amplitude causes larger maximum radii, longer collapse time, and more violent collapse. But, in cases with mass transfer because at the last moments of collapse stage a large amount of water vapor is trapped inside the bubble, the collapse will become less violent. For larger bubbles collapse becomes more violent for the cases without mass transfer in all pressure amplitudes and higher frequencies. But decreasing pressure frequency makes the collapse of the bubbles with mass transfer more violent. However, mass transfer effects decreases with increasing initial bubble radius.

Two Aspects of Cavitation Damage in the Incubation Zone: Scaling by Energy Considerations and Leading Edge Damage

1980 ◽  
Vol 102 (4) ◽  
pp. 481-485 ◽  
Author(s):  
D. R. Stinebring ◽  
J. William Holl ◽  
Roger E. A. Arndt
Keyword(s):  
Damage Zone ◽  
Pressure Rise ◽  
Leading Edge ◽  
Bubble Collapse ◽  
Test Model ◽  
Cavitation Damage ◽  
Pit Formation ◽  
Rate Versus ◽  
Wide Range ◽  
Edge Damage

This study focused on two aspects of the cavitation damage problem, namely an energy approach to the scaling of cavitation damage in the incubation zone and damage near the leading edge of a test model. The damage to the surface of the models was in the form of small indentations in which no material was removed. For a wide range of velocities namely 14.9 to 59.3 m/s the rate of pit formation per unit area in the maximum damage zone increased by the sixth power of velocity. Furthermore it is shown that the damage rate versus velocity data are in good agreement with three other investigations. The volumes of the pits were found to increase by the fifth power of velocity. A relationship between the volume of a pit and the cavitation bubble collapse energy absorbed was developed. The damage to the leading edge was felt to be due to the reentrant jet striking the leading edge of the cavity creating a short term pressure rise causing the collapse of any cavitation bubbles in this area.

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