A computational fluid dynamics (CFD) method is developed to investigate the radical motion of single cavitating bubble in the oscillating pressure field of a cavitating water jet. Regarding water as a compressible flu...A computational fluid dynamics (CFD) method is developed to investigate the radical motion of single cavitating bubble in the oscillating pressure field of a cavitating water jet. Regarding water as a compressible fluid, the simulation is performed at different oscillating frequencies. It is found that the bubble motion presents obvious nonlinear feature, and bifurcation and chaos appear on some conditions. The results manifest the indetermination of the cavitating bubble motion in the oscillating pressure field of the cavitating water jet.展开更多
Sonodynamic therapy(SDT)has emerged as a novel and highly researched advancement in the medical field.Traditional ultrasound contrast agents and novel bubble-shaped agents are used to stimulate cavitation and enhance ...Sonodynamic therapy(SDT)has emerged as a novel and highly researched advancement in the medical field.Traditional ultrasound contrast agents and novel bubble-shaped agents are used to stimulate cavitation and enhance SDT efficiency.However,the impact of artificially modified shell structures on the acoustic properties of microbubbles remains to be explored.Alternatively,in the absence of bubble-shaped agents,some clinically available organic sonosensitizers and advanced inorganic materials are also used to enhance the efficacy of SDT.Diagnostic and therapeutic ultrasound can also activate cavitation bubbles,which supply energy to sonosensitive agents,leading to the production of cytotoxic free radicals to achieve therapeutic effects.While inorganic materials often spark controversy in clinical applications,their relatively simple structure enables researchers to gain insight into the mechanism by which SDT produces various free radicals.Some organic-inorganic hybrid sonosensitive systems have also been reported,combining the benefits of inorganic and organic sonosensitive agents.Alternatively,by employing cell surface modification engineering to enable cells to perform functions such as immune escape,drug loading,gas loading,and sonosensitivity,cellular sonosensitizers have also been developed.However,further exploration is needed on the acoustic properties,ability to generate reactive oxygen species(ROS),and potential clinical application of this cellular sonosensitizer.This review offers a comprehensive analysis of vesical microbubbles and nanoscale sonocatalysts,including organic,inorganic,combined organic-inorganic sonosensitizers,and cellular sonosensitizers.This analysis will enhance our understanding of SDT and demonstrate its important potential in transforming medical applications.展开更多
A level set method of non-uniform grids is used to simulate the whole evolution of a cavitation bubble, including its growth, collapse and rebound near a rigid wall. Single-phase Navier-Stokes equation in the liquid r...A level set method of non-uniform grids is used to simulate the whole evolution of a cavitation bubble, including its growth, collapse and rebound near a rigid wall. Single-phase Navier-Stokes equation in the liquid region is solved by MAC projection algorithm combined with second-order ENO scheme for the advection terms. The moving inter-face is captured by the level set function, and the interface velocity is resolved by ＂one-side＂ velocity extension from the liquid region to the bubble region, complementing the second-order weighted least squares method across the interface and projection inside bubble. The use of non-uniform grid overcomes the difficulty caused by the large computational domain and very small bubble size. The computation is very stable without suffering from large flow-field gradients, and the results are in good agreements with other studies. The bubble interface kinematics, dynamics and its effect on the wall are highlighted, which shows that the code can effectively capture the ＂shock wave＂-like pressure and velocity at jet impact, toroidal bubble, and complicated pressure structure with peak, plateau and valley in the later stage of bubble oscillating.展开更多
Supercavitation in the diesel nozzle increases the instability of droplets in part due to the two-phase mixture, while the effect of cavitation bubbles on the instability of drops is still unclear. In order to investi...Supercavitation in the diesel nozzle increases the instability of droplets in part due to the two-phase mixture, while the effect of cavitation bubbles on the instability of drops is still unclear. In order to investigate the breakup of cavitation bubbles within the diesel droplet, a new mathematical model describing the disturbance growth rate of the diesel bubble instability is developed. The new mathematical model is applied to predict the effects of fluids viscosity on the stability of cavitation bubbles. The predicted values reveal that the comprehensive effect of fluids viscosity makes cavitation bubbles more stable. Compared with the viscosities of air and cavitation bubble, the diesel droplet＇s viscosity plays a dominant role on the stability of cavitation bubbles. Furthermore, based on the modified bubble breakup criterion, the effects of bubble growth speed, sound speed, droplet viscosity, droplet density, and bubble-droplet radius ratio on the breakup time and the breakup radius of cavitation bubbles are studied respectively. It is found that a bubble with large bubble-droplet radius ratio has the initial condition for breaking easily. For a given bubble-droplet radius ratio （0.2）, as the bubble growth speed increases （from 2 m/s to 60 m/s）, the bubble breakup time decreases（from 3.59 gs to 0.17 ps） rapidly. Both the greater diesel droplet viscosity and the greater diesel droplet density result in the increase of the breakup time. With increasing initial bubble-droplet radius ratio （from 0.2 to 0.8）, the bubble breakup radius decreases （from 8.86 trn to 6.23 tm）. There is a limited breakup radius for a bubble with a certain initial bubble-droplet radius ratio. The mathematical model and the modified bubble breakup criterion are helpful to improve the study on the breakup mechanism of the secondary diesel droplet under the condition of supercavitation.展开更多
Comprehensive numerical and experimental analyses of the effect of viscosity on cavitation oscillations are performed. This numerical approach is based on the Rayleigh-Plesset equation. The model predictions are compa...Comprehensive numerical and experimental analyses of the effect of viscosity on cavitation oscillations are performed. This numerical approach is based on the Rayleigh-Plesset equation. The model predictions are compared with experimental results obtained by using a fibre-optic diagnostic technique based on optical beam deflection （OBD）. The maximum and minimum bubble radii as well as the oscillation times for each oscillation cycle are determined according to the characteristic signals. It is observed that the increasing of viscosity decreases the maximum bubble radii but increases the minimum bubble radii and the oscillation time. These experimental results are consistent with numerical results.展开更多
A modified mathematical model is used to study the effects of various forces on the stability of cavitation bubbles within a diesel droplet. The principal finding of the work is that viscous forces of fluids stabilize...A modified mathematical model is used to study the effects of various forces on the stability of cavitation bubbles within a diesel droplet. The principal finding of the work is that viscous forces of fluids stabilize the cavitation bubble, while inertial force destabilizes the cavitation bubble. The droplet viscosity plays a dominant role on the stability of cavitation bubbles compared with that of air and bubble. Bubble–droplet radius ratio is a key factor to control the bubble stability, especially in the high radius ratio range. Internal hydrodynamic and surface tension forces are found to stabilize the cavitation bubble, while bubble stability has little relationship with the external hydrodynamic force. Inertia makes bubble breakup easily, however, the breakup time is only slightly changed when bubble growth speed reaches a certain value(50 m·s-1). In contrast, viscous force makes bubble hard to break. With the increasing initial bubble–droplet radius ratio, the bubble growth rate increases, the bubble breakup radius decreases, and the bubble breakup time becomes shorter.展开更多
The dynamics of cavitation bubble is analyzed in the compressible fluid by use of the boundary integral equation considering the compressibility. After the vertical incidence of plane wave to the rigid wall, the motio...The dynamics of cavitation bubble is analyzed in the compressible fluid by use of the boundary integral equation considering the compressibility. After the vertical incidence of plane wave to the rigid wall, the motion characteristics of single cavitation bubble near the rigid wall with initial equilibrium state are researched with different parameters. The results show that after the driving of acoustic wave, the cavitation bubble near the rigid wall will expand or contract, and generate the jet pointing to the wall. Also, the existence of the wall will elongate time for one oscillation. With the compressible model, the oscillation amplitude is reduced, as well as the peak value of inner pressure and jet tip velocity. The effect of the wall on oscillation amplitude is limited. However with the increment of initial vertical distance, the effect of wall on the jet velocity is from acceleration to limitation, and finally to acceleration again.展开更多
The flotation process is a particle-hydrophobic surface-based separation technique. To improve the essential flotation steps of collision and attachment probabilities, and reduce the step of detachment probabilities b...The flotation process is a particle-hydrophobic surface-based separation technique. To improve the essential flotation steps of collision and attachment probabilities, and reduce the step of detachment probabilities between air bubbles and hydrophobic particles, a selectively designed cavitation venturi tube combined with a static mixer can be used to generate very high numbers of pico and nano bubbles in a flotation column. Fully embraced by those high numbers of tiny bubbles, hydrophobic particles readily attract the tiny bubbles to their surfaces. The results of column flotation of Pittsburgh No. 8 seam coal are obtained in a 5.08 cm ID and 162 cm height flotation column equipped with a static mixer and cavitation venturi tube, using kerosene as collector and MIBC as frother. Design of the experimental procedure is combined with a statistical two-stepwise analysis to determine the optimal operating conditions for maximum recovery at a specified grade. The effect of independent variables on the responses has been explained. Combustible material recovery of 85–90% at clean coal product of 10–11% ash is obtained from feed of 29.6% ash, with a much-reduced amount of frother and collector than that used in conventional column flotation. The column flotation process utilizing pico and nano bubbles can also be extended to the lower limit and upper limit of particle size ranges, minus 75 lm and 300–600 lm, respectively, for better recovery.展开更多
The interaction between cavitation bubble and solid surface is a fundamental topic which is deeply concerned for the utilization or avoidance of cavitation effect.The complexity of this topic is that the cavitation bu...The interaction between cavitation bubble and solid surface is a fundamental topic which is deeply concerned for the utilization or avoidance of cavitation effect.The complexity of this topic is that the cavitation bubble collapse includes many extreme physical phenomena and variability of different solid surface properties.In the present work,the cavitation bubble collapse in hydrophobic concave is studied using the pseudopotential multi-relaxation-time lattice Boltzmann model(MRT-LB).The model is modified by involving the piecewise linear equation of state and improved forcing scheme.The fluid-solid interaction in the model is employed to adjust the wettability of solid surface.Moreover,the validity of the model is verified by comparison with experimental results and grid-independence verification.Finally,the cavitation bubble collapse in a hydrophobic concave is studied by investigating density field,pressure field,collapse time,and jet velocity.The superimposed effect of the surface hydrophobicity and concave geometry is analyzed and explained in the framework of the pseudopotential LBM.The study shows that the hydrophobic concave can enhance cavitation effect by decreasing cavitation threshold,accelerating collapse and increasing jet velocity.展开更多
A multicomponent thermal multi-relaxation-time(MRT)lattice Boltzmann method(LBM)is presented to study collapsing cavitation bubble.The simulation results satisfy Laplace law and the adiabatic law,and are consistent wi...A multicomponent thermal multi-relaxation-time(MRT)lattice Boltzmann method(LBM)is presented to study collapsing cavitation bubble.The simulation results satisfy Laplace law and the adiabatic law,and are consistent with the numerical solution of the Rayleigh-Plesset equation.To study the effects of the non-condensable gas inside bubble on collapsing cavitation bubble,a numerical model of single spherical bubble near a solid wall is established.The temperature and pressure evolution of the two-component two-phase flow are well captured.In addition,the collapse process of the cavitation bubble is discussed elaborately by setting the volume fractions of the gas and vapor to be the only variables.The results show that the non-condensable gas in the bubble significantly affects the pressure field,temperature field evolution,collapse velocity,and profile of the bubble.The distinction of the pressure and temperature on the wall after the second collapse becomes more obvious as the non-condensable gas concentration increases.展开更多
This paper presents analytical and numerical results of vapor bubble dynamics and acoustics in a variable pressure field.First,a classical model problem of bubble collapse due to sudden pressure increase is introduced...This paper presents analytical and numerical results of vapor bubble dynamics and acoustics in a variable pressure field.First,a classical model problem of bubble collapse due to sudden pressure increase is introduced.In this problem,the Rayleigh–Plesset equation is treated considering gas content,surface tension,and viscosity,displaying possible multiple expansion–compression cycles.Second,a similar investigation is conducted for the case when the bubble originates near the rounded leading edge of a thin and slightly curved foil at a small angle of attack.Mathematically the flow field around the foil is constructed using the method of matched asymptotic expansions.The outer flow past the hydrofoil is described by linear(small perturbations)theory,which furnishes closed-form solutions for any analytical foil.By stretching local coordinates inversely proportionally to the radius of curvature of the rounded leading edge,the inner flow problem is derived as that past a semi-infinite osculating parabola for any analytical foil with a rounded leading edge.Assuming that the pressure outside the bubble at any moment of time is equal to that at the corresponding point of the streamline,the dynamics problem of a vapor bubble is reduced to solving the Rayleigh-Plesset equation for the spherical bubble evolution in a time-dependent pressure field.For the case of bubble collapse in an adverse pressure field,the spectral parameters of the induced acoustic pressure impulses are determined similarly to equivalent triangular ones.The present analysis can be extended to 3D flows around wings and screw propellers.In this case,the outer expansion of the solution corresponds to a linear lifting surface theory,and the local inner flow remains quasi-2D in the planes normal to the planform contour of the leading edge of the wing(or screw propeller blade).Note that a typical bubble contraction time,ending up with its collapse,is very small compared to typical time of any variation in the flow.Therefore,the approach can also be applied to unsteady flow problems.展开更多
The cavitation bubble collapse near a cell can cause damage to the cell wall. This effect has received increasing attention in biomedical supersonics. Based on the lattice Boltzmann method, a multiple-relaxation-time ...The cavitation bubble collapse near a cell can cause damage to the cell wall. This effect has received increasing attention in biomedical supersonics. Based on the lattice Boltzmann method, a multiple-relaxation-time Shan–Chen model is built to study the cavitation bubble collapse. Using this model, the cavitation phenomena induced by density perturbation are simulated to obtain the coexistence densities at certain temperature and to demonstrate the Young–Laplace equation. Then, the cavitation bubble collapse near a curved rigid wall and the consequent high-speed jet towards the wall are simulated. Moreover, the influences of initial pressure difference and bubble-wall distance on the cavitation bubble collapse are investigated.展开更多
The cavitation cloud of different internal structures results in different collapse pressures owing to the interaction among bubbles. The internal structure of cloud cavitation is required to accurately predict collap...The cavitation cloud of different internal structures results in different collapse pressures owing to the interaction among bubbles. The internal structure of cloud cavitation is required to accurately predict collapse pressure. A cavitation model was developed through dimensional analysis and direct numerical simulation of collapse of bubble cluster. Bubble number density was included in proposed model to characterize the internal structure of bubble cloud. Implemented on flows over a projectile, the proposed model predicts a higher collapse pressure compared with Singhal model. Results indicate that the collapse pressure of detached cavitation cloud is affected by bubble number density.展开更多
A gas-liquid coupling excitation mode is proposed and the gas-liquid excitation experimental system is developed. Air from pulse generator is mixed with liquid,through which the generated cavitation bubbles can strip ...A gas-liquid coupling excitation mode is proposed and the gas-liquid excitation experimental system is developed. Air from pulse generator is mixed with liquid,through which the generated cavitation bubbles can strip contaminants adhered to the pipe inner wall rapidly. The kinematics equation of the bubble inside the hydraulic oil is established and the numerical simulations are carried out. The influential factors such as gas pressure, excitation frequency,initial bubble radius and fluid viscosity are analyzed.The results show that the cavitation will evolve from steady state to transient state with the increasing gas pressure and initial bubble radius. The pulse generator frequency has a slightly effect on the growth of the bubble radius,and the breakup time of the bubble is shortened with the rising frequency. Similarly, the increasing viscosity of liquid has minimal impact on cavitation effect,which can weaken the growth and the collapse of the bubble. Moreover,the temperature inside the cavitation bubble is investigated,indicating that the instantaneous temperature inside the bubble increases with the rising gas pressure. Once the gas pressure is raised to a certain value greater than the fluid static pressure, the instantaneous temperature inside the bubble will rise sharply. So, it can be concluded that the gas-liquid coupling excitation-induced cavitation process is controllable, and some theoretical basis of the new excitation mode is presented,which is expected to be applied in the online cleaning of the complex hydraulic system.展开更多
Dynamics of a single cavitation bubble in sodium dodecyl sulfate（SDS） aqueous solutions is investigated experimentally and theoretically. The bubble pulsation is measured by a phase-locked integrated imaging techniq...Dynamics of a single cavitation bubble in sodium dodecyl sulfate（SDS） aqueous solutions is investigated experimentally and theoretically. The bubble pulsation is measured by a phase-locked integrated imaging technique,and the ambient radius is obtained by fitting the numerical calculation based on the Rayleigh–Plesset bubble dynamics model to the experimental data. The results show that, under the same driving condition, the ambient radius of the cavitation bubble decreases correspondingly with the increase of SDS concentration within the critical micelle concentration, while the compression ratio of the radius increases, which indicates that the addition of SDS decreases the internal molecular number of the cavitation bubble and increases the power capability of the cavitation bubble. In addition, bubble oscillation increases the concentration of the surfactant molecules on the bubble wall, so that the effect of SDS on a single cavitation bubble is reduced when the SDS concentration is greater than 0.8 m M.展开更多
This study investigated dissolution processes of cavitation bubbles generated during in vivo shock wave（SW）-induced treatments. Both active cavitation detection（ACD） and the B-mode imaging technique were applied t...This study investigated dissolution processes of cavitation bubbles generated during in vivo shock wave（SW）-induced treatments. Both active cavitation detection（ACD） and the B-mode imaging technique were applied to measure the dissolution procedure of bi Spheres contrast agent bubbles by in vitro experiments. Besides, the simulation of SW-induced cavitation bubbles dissolution behaviors detected by the B-mode imaging system during in vivo SW treatments, including extracorporeal shock wave lithotripsy（ESWL） and extracorporeal shock wave therapy（ESWT）, were carried out based on calculating the integrated scattering cross-section of dissolving gas bubbles with employing gas bubble dissolution equations and Gaussian bubble size distribution. The results showed that（i） B-mode imaging technology is an effective tool to monitor the temporal evolution of cavitation bubbles dissolution procedures after the SW pulses ceased, which is important for evaluation and controlling the cavitation activity generated during subsequent SW treatments within a treatment period;（ii） the characteristics of the bubbles, such as the bubble size distribution and gas diffusion, can be estimated by simulating the experimental data properly.展开更多
A fractal geometric boundary with natural wall features is introduced into a hybrid lattice-Boltzmann-method(LBM)multiphase model. The physical model of cavitation bubble collapse near the irregular geometric wall is ...A fractal geometric boundary with natural wall features is introduced into a hybrid lattice-Boltzmann-method(LBM)multiphase model. The physical model of cavitation bubble collapse near the irregular geometric wall is established to study the thermodynamic characteristics of the bubble collapse. Due to the lack of periodicity, symmetry, spatial uniformity and obvious correlation in the LBM simulation of the bubble collapse near the fractal wall, the morphological analysis based on Minkowski functional is introduced into the thermodynamic investigation of cavitation bubble so as to analyze and obtain the effective information. The results show that the Minkowski functional method can employed to study the temperature information in complex physical fields hierarchically and quantitatively. The high/low temperature region of the cavitation flow is explored, and thermal effect between irregular and fractal geometric wall and cavitation bubble can be revealed. It illustrates that LBM and morphological analysis complement each other, and morphological analysis can also be used as an optional and potential tool in research field of complex multiphase flows.展开更多
The dynamic behavior of a cavitation bubble near an asymmetric hydrofoil is investigated experimentally through high-speed photography and theoretically using a Kelvin impulse model.The typical deformations arising du...The dynamic behavior of a cavitation bubble near an asymmetric hydrofoil is investigated experimentally through high-speed photography and theoretically using a Kelvin impulse model.The typical deformations arising during bubble collapse near the hydrofoil are analyzed qualitatively.The effects of the bubble position and the hydrofoil’s eccentricity angle are analyzed quantitatively.The spatial distribution of the Kelvin impulse near the hydrofoil are explored.Different morphological evolutions of a bubble near an asymmetric hydrofoil are revealed,with B-shaped,heart-shaped,and arc-shaped collapses.The velocity of the bubble interface close to the hydrofoil is significantly affected by the bubble-hydrofoil distance and the hydrofoil’s eccentricity angle,increasing as both the distance and the eccentricity angle grow.It is found that the Kelvin impulse sensitivity varies at different positions with respect to the asymmetric hydrofoil,being higher at the head and tail,and lower in the middle.展开更多
Capturing and studying the process of cavitation bubble collapse can help elucidate the mechanism of cavitation erosion.In this paper,a high-spatiotemporal-resolution double-exposure photographic method is used to inv...Capturing and studying the process of cavitation bubble collapse can help elucidate the mechanism of cavitation erosion.In this paper,a high-spatiotemporal-resolution double-exposure photographic method is used to investigate the collapse of laser-induced cavitation bubbles at two values of the dimensionless distance from the bubble to the wall,γ=d/R_(max)=0.9 and 1.25(where d is the vertical distance between the bubble center and the wall and R_(max)is the maximum radius of the bubble).Complete high-resolution evolution sequences of bubbles near a rigid wall are captured from optical breakdown to second collapse.The generation and development of microjets and shock waves during cavitation bubble collapse are described in detail.The oscillations of the bubble near the rigid wall and the microjets and shock waves generated by the collapse are analyzed.It is shown that the presence of the rigid wall affects the development of the bubble and microjets.The microjet velocity can reach up to 64 m/s.Multiple shock waves are found to be generated by bubble collapse.展开更多
Vortex dynamics and wall shear stress induced by cavitation bubble oscillations under the influence of particles are numerically investigated with the aid of a compressible two-phase flow solver in OpenFOAM.The genera...Vortex dynamics and wall shear stress induced by cavitation bubble oscillations under the influence of particles are numerically investigated with the aid of a compressible two-phase flow solver in OpenFOAM.The generation,evolution,and disappearance of vortexes for three jet behaviors are discussed in detail.The variations of wall shear stress induced by the jets and the vortexes during the bubble oscillations are analyzed.Numerical results reveal that vortex dynamics is related to bubble evolution and jet behavior.After the jet pierces the bubble,an annular vortex with the bubble as the vortex core is generated by the bubble collapse.For the bubble that collapses near the wall,it generates multiple small vortexes near the wall and causes discontinuities in the wall shear stress.For the bubble that collapses away from the wall,it does not generate vortexes near the wall,and its oscillations cause the wall shear stress to vary periodically with different periods.In addition,the wall shear stress at the axis of symmetry increases abruptly when the jet hits the wall.展开更多
基金the National Natural Science Foundation of China (No.50074035).
文摘A computational fluid dynamics (CFD) method is developed to investigate the radical motion of single cavitating bubble in the oscillating pressure field of a cavitating water jet. Regarding water as a compressible fluid, the simulation is performed at different oscillating frequencies. It is found that the bubble motion presents obvious nonlinear feature, and bifurcation and chaos appear on some conditions. The results manifest the indetermination of the cavitating bubble motion in the oscillating pressure field of the cavitating water jet.
基金supported by the National Natural Science Foundation of China(NSFC)(52100014 and 12274220)。
文摘Sonodynamic therapy(SDT)has emerged as a novel and highly researched advancement in the medical field.Traditional ultrasound contrast agents and novel bubble-shaped agents are used to stimulate cavitation and enhance SDT efficiency.However,the impact of artificially modified shell structures on the acoustic properties of microbubbles remains to be explored.Alternatively,in the absence of bubble-shaped agents,some clinically available organic sonosensitizers and advanced inorganic materials are also used to enhance the efficacy of SDT.Diagnostic and therapeutic ultrasound can also activate cavitation bubbles,which supply energy to sonosensitive agents,leading to the production of cytotoxic free radicals to achieve therapeutic effects.While inorganic materials often spark controversy in clinical applications,their relatively simple structure enables researchers to gain insight into the mechanism by which SDT produces various free radicals.Some organic-inorganic hybrid sonosensitive systems have also been reported,combining the benefits of inorganic and organic sonosensitive agents.Alternatively,by employing cell surface modification engineering to enable cells to perform functions such as immune escape,drug loading,gas loading,and sonosensitivity,cellular sonosensitizers have also been developed.However,further exploration is needed on the acoustic properties,ability to generate reactive oxygen species(ROS),and potential clinical application of this cellular sonosensitizer.This review offers a comprehensive analysis of vesical microbubbles and nanoscale sonocatalysts,including organic,inorganic,combined organic-inorganic sonosensitizers,and cellular sonosensitizers.This analysis will enhance our understanding of SDT and demonstrate its important potential in transforming medical applications.
基金the National Natural Science Foundation of China(10272032 and 10672043).
文摘A level set method of non-uniform grids is used to simulate the whole evolution of a cavitation bubble, including its growth, collapse and rebound near a rigid wall. Single-phase Navier-Stokes equation in the liquid region is solved by MAC projection algorithm combined with second-order ENO scheme for the advection terms. The moving inter-face is captured by the level set function, and the interface velocity is resolved by ＂one-side＂ velocity extension from the liquid region to the bubble region, complementing the second-order weighted least squares method across the interface and projection inside bubble. The use of non-uniform grid overcomes the difficulty caused by the large computational domain and very small bubble size. The computation is very stable without suffering from large flow-field gradients, and the results are in good agreements with other studies. The bubble interface kinematics, dynamics and its effect on the wall are highlighted, which shows that the code can effectively capture the ＂shock wave＂-like pressure and velocity at jet impact, toroidal bubble, and complicated pressure structure with peak, plateau and valley in the later stage of bubble oscillating.
基金supported by National Natural Science Foundation of China(Grant No.51276011)Beijing Municipal Natural Science Foundation of China(Grant No.3132016)+1 种基金National Hi-tech Research and Development Program of China(863 Program,Grant No.2013AA065303)Opening Foundation of State Key Laboratory of Engines of China(Grant No.K2013-3)
文摘Supercavitation in the diesel nozzle increases the instability of droplets in part due to the two-phase mixture, while the effect of cavitation bubbles on the instability of drops is still unclear. In order to investigate the breakup of cavitation bubbles within the diesel droplet, a new mathematical model describing the disturbance growth rate of the diesel bubble instability is developed. The new mathematical model is applied to predict the effects of fluids viscosity on the stability of cavitation bubbles. The predicted values reveal that the comprehensive effect of fluids viscosity makes cavitation bubbles more stable. Compared with the viscosities of air and cavitation bubble, the diesel droplet＇s viscosity plays a dominant role on the stability of cavitation bubbles. Furthermore, based on the modified bubble breakup criterion, the effects of bubble growth speed, sound speed, droplet viscosity, droplet density, and bubble-droplet radius ratio on the breakup time and the breakup radius of cavitation bubbles are studied respectively. It is found that a bubble with large bubble-droplet radius ratio has the initial condition for breaking easily. For a given bubble-droplet radius ratio （0.2）, as the bubble growth speed increases （from 2 m/s to 60 m/s）, the bubble breakup time decreases（from 3.59 gs to 0.17 ps） rapidly. Both the greater diesel droplet viscosity and the greater diesel droplet density result in the increase of the breakup time. With increasing initial bubble-droplet radius ratio （from 0.2 to 0.8）, the bubble breakup radius decreases （from 8.86 trn to 6.23 tm）. There is a limited breakup radius for a bubble with a certain initial bubble-droplet radius ratio. The mathematical model and the modified bubble breakup criterion are helpful to improve the study on the breakup mechanism of the secondary diesel droplet under the condition of supercavitation.
基金supported by the National Natural Science Foundation of China (Grant No 60578015)the Teaching and Research Award Program for Outstanding Young Teachers in Higher Education Institute of China (2003-2008)the National Key Opening Experiment Foundation of Laser Technology of China (Grant No 2005)
文摘Comprehensive numerical and experimental analyses of the effect of viscosity on cavitation oscillations are performed. This numerical approach is based on the Rayleigh-Plesset equation. The model predictions are compared with experimental results obtained by using a fibre-optic diagnostic technique based on optical beam deflection （OBD）. The maximum and minimum bubble radii as well as the oscillation times for each oscillation cycle are determined according to the characteristic signals. It is observed that the increasing of viscosity decreases the maximum bubble radii but increases the minimum bubble radii and the oscillation time. These experimental results are consistent with numerical results.
基金Supported by the National Natural Science Foundation of China(51276011)the National High Technology Research and Development Program of China(2013AA065303)+1 种基金Beijing Municipal Natural Science Foundation of China(3132016)the Opening Foundation of State Key Laboratory of Engines(K2013-3)
文摘A modified mathematical model is used to study the effects of various forces on the stability of cavitation bubbles within a diesel droplet. The principal finding of the work is that viscous forces of fluids stabilize the cavitation bubble, while inertial force destabilizes the cavitation bubble. The droplet viscosity plays a dominant role on the stability of cavitation bubbles compared with that of air and bubble. Bubble–droplet radius ratio is a key factor to control the bubble stability, especially in the high radius ratio range. Internal hydrodynamic and surface tension forces are found to stabilize the cavitation bubble, while bubble stability has little relationship with the external hydrodynamic force. Inertia makes bubble breakup easily, however, the breakup time is only slightly changed when bubble growth speed reaches a certain value(50 m·s-1). In contrast, viscous force makes bubble hard to break. With the increasing initial bubble–droplet radius ratio, the bubble growth rate increases, the bubble breakup radius decreases, and the bubble breakup time becomes shorter.
基金financially supported by the National Natural Science Foundation of China(Grant No.51279038)the Excellent Young Science Foundation of the National Natural Science Foundation of China(Grant No.51222904)
文摘The dynamics of cavitation bubble is analyzed in the compressible fluid by use of the boundary integral equation considering the compressibility. After the vertical incidence of plane wave to the rigid wall, the motion characteristics of single cavitation bubble near the rigid wall with initial equilibrium state are researched with different parameters. The results show that after the driving of acoustic wave, the cavitation bubble near the rigid wall will expand or contract, and generate the jet pointing to the wall. Also, the existence of the wall will elongate time for one oscillation. With the compressible model, the oscillation amplitude is reduced, as well as the peak value of inner pressure and jet tip velocity. The effect of the wall on oscillation amplitude is limited. However with the increment of initial vertical distance, the effect of wall on the jet velocity is from acceleration to limitation, and finally to acceleration again.
基金provided by West Virginia State Coal and Energy Research Bureau (CERB)the Department of Mining Engineering,West Virginia University
文摘The flotation process is a particle-hydrophobic surface-based separation technique. To improve the essential flotation steps of collision and attachment probabilities, and reduce the step of detachment probabilities between air bubbles and hydrophobic particles, a selectively designed cavitation venturi tube combined with a static mixer can be used to generate very high numbers of pico and nano bubbles in a flotation column. Fully embraced by those high numbers of tiny bubbles, hydrophobic particles readily attract the tiny bubbles to their surfaces. The results of column flotation of Pittsburgh No. 8 seam coal are obtained in a 5.08 cm ID and 162 cm height flotation column equipped with a static mixer and cavitation venturi tube, using kerosene as collector and MIBC as frother. Design of the experimental procedure is combined with a statistical two-stepwise analysis to determine the optimal operating conditions for maximum recovery at a specified grade. The effect of independent variables on the responses has been explained. Combustible material recovery of 85–90% at clean coal product of 10–11% ash is obtained from feed of 29.6% ash, with a much-reduced amount of frother and collector than that used in conventional column flotation. The column flotation process utilizing pico and nano bubbles can also be extended to the lower limit and upper limit of particle size ranges, minus 75 lm and 300–600 lm, respectively, for better recovery.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11874140 and 11574072)the Fund from the State Key Laboratory of Acoustics,Chinese Academy of Sciences(Grant No.SKLA201913)+1 种基金the National Key Research and Development Program of China(Grant No.2016YFC0401600)the Postgraduate Research&Practice Innovation Program of Jiangsu Province,China(Grant Nos.2018B741X14 and KYCX180552)。
文摘The interaction between cavitation bubble and solid surface is a fundamental topic which is deeply concerned for the utilization or avoidance of cavitation effect.The complexity of this topic is that the cavitation bubble collapse includes many extreme physical phenomena and variability of different solid surface properties.In the present work,the cavitation bubble collapse in hydrophobic concave is studied using the pseudopotential multi-relaxation-time lattice Boltzmann model(MRT-LB).The model is modified by involving the piecewise linear equation of state and improved forcing scheme.The fluid-solid interaction in the model is employed to adjust the wettability of solid surface.Moreover,the validity of the model is verified by comparison with experimental results and grid-independence verification.Finally,the cavitation bubble collapse in a hydrophobic concave is studied by investigating density field,pressure field,collapse time,and jet velocity.The superimposed effect of the surface hydrophobicity and concave geometry is analyzed and explained in the framework of the pseudopotential LBM.The study shows that the hydrophobic concave can enhance cavitation effect by decreasing cavitation threshold,accelerating collapse and increasing jet velocity.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11874140 and 11574072)the State Key Laboratory of Acoustics,Chinese Academy of Sciences(Grant No.SKLA201913)+3 种基金the National Key Research and Development Program of China(Grant No.2016YFC0401600)the Primary Research and Development Plan of Jiangsu Province,China(Grant No.BE2016056)the Postgraduate Research&Practice Innovation Program of Jiangsu Province,China(Grant Nos.2018B741X14 and KYCX180552)the Postgraduate Research&Practice Innovation Program of Changzhou Campus,Hohai University,China(Grant No.17B01110)。
文摘A multicomponent thermal multi-relaxation-time(MRT)lattice Boltzmann method(LBM)is presented to study collapsing cavitation bubble.The simulation results satisfy Laplace law and the adiabatic law,and are consistent with the numerical solution of the Rayleigh-Plesset equation.To study the effects of the non-condensable gas inside bubble on collapsing cavitation bubble,a numerical model of single spherical bubble near a solid wall is established.The temperature and pressure evolution of the two-component two-phase flow are well captured.In addition,the collapse process of the cavitation bubble is discussed elaborately by setting the volume fractions of the gas and vapor to be the only variables.The results show that the non-condensable gas in the bubble significantly affects the pressure field,temperature field evolution,collapse velocity,and profile of the bubble.The distinction of the pressure and temperature on the wall after the second collapse becomes more obvious as the non-condensable gas concentration increases.
基金Supported by the Ministry of Science and Higher Education of the Russian Federation as part of the World-class Research Center Program:Advanced Digital Technologies(contract No.075-15-2020-903 dated 16.11.2020).
文摘This paper presents analytical and numerical results of vapor bubble dynamics and acoustics in a variable pressure field.First,a classical model problem of bubble collapse due to sudden pressure increase is introduced.In this problem,the Rayleigh–Plesset equation is treated considering gas content,surface tension,and viscosity,displaying possible multiple expansion–compression cycles.Second,a similar investigation is conducted for the case when the bubble originates near the rounded leading edge of a thin and slightly curved foil at a small angle of attack.Mathematically the flow field around the foil is constructed using the method of matched asymptotic expansions.The outer flow past the hydrofoil is described by linear(small perturbations)theory,which furnishes closed-form solutions for any analytical foil.By stretching local coordinates inversely proportionally to the radius of curvature of the rounded leading edge,the inner flow problem is derived as that past a semi-infinite osculating parabola for any analytical foil with a rounded leading edge.Assuming that the pressure outside the bubble at any moment of time is equal to that at the corresponding point of the streamline,the dynamics problem of a vapor bubble is reduced to solving the Rayleigh-Plesset equation for the spherical bubble evolution in a time-dependent pressure field.For the case of bubble collapse in an adverse pressure field,the spectral parameters of the induced acoustic pressure impulses are determined similarly to equivalent triangular ones.The present analysis can be extended to 3D flows around wings and screw propellers.In this case,the outer expansion of the solution corresponds to a linear lifting surface theory,and the local inner flow remains quasi-2D in the planes normal to the planform contour of the leading edge of the wing(or screw propeller blade).Note that a typical bubble contraction time,ending up with its collapse,is very small compared to typical time of any variation in the flow.Therefore,the approach can also be applied to unsteady flow problems.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11674173,81627802,11474161,11374155 and 11474001the Qing Lan Project
文摘The cavitation bubble collapse near a cell can cause damage to the cell wall. This effect has received increasing attention in biomedical supersonics. Based on the lattice Boltzmann method, a multiple-relaxation-time Shan–Chen model is built to study the cavitation bubble collapse. Using this model, the cavitation phenomena induced by density perturbation are simulated to obtain the coexistence densities at certain temperature and to demonstrate the Young–Laplace equation. Then, the cavitation bubble collapse near a curved rigid wall and the consequent high-speed jet towards the wall are simulated. Moreover, the influences of initial pressure difference and bubble-wall distance on the cavitation bubble collapse are investigated.
基金support from the National Natural Science Foundation of China (11402276)
文摘The cavitation cloud of different internal structures results in different collapse pressures owing to the interaction among bubbles. The internal structure of cloud cavitation is required to accurately predict collapse pressure. A cavitation model was developed through dimensional analysis and direct numerical simulation of collapse of bubble cluster. Bubble number density was included in proposed model to characterize the internal structure of bubble cloud. Implemented on flows over a projectile, the proposed model predicts a higher collapse pressure compared with Singhal model. Results indicate that the collapse pressure of detached cavitation cloud is affected by bubble number density.
基金National Natural Science Foundation of China(No.U1404513)
文摘A gas-liquid coupling excitation mode is proposed and the gas-liquid excitation experimental system is developed. Air from pulse generator is mixed with liquid,through which the generated cavitation bubbles can strip contaminants adhered to the pipe inner wall rapidly. The kinematics equation of the bubble inside the hydraulic oil is established and the numerical simulations are carried out. The influential factors such as gas pressure, excitation frequency,initial bubble radius and fluid viscosity are analyzed.The results show that the cavitation will evolve from steady state to transient state with the increasing gas pressure and initial bubble radius. The pulse generator frequency has a slightly effect on the growth of the bubble radius,and the breakup time of the bubble is shortened with the rising frequency. Similarly, the increasing viscosity of liquid has minimal impact on cavitation effect,which can weaken the growth and the collapse of the bubble. Moreover,the temperature inside the cavitation bubble is investigated,indicating that the instantaneous temperature inside the bubble increases with the rising gas pressure. Once the gas pressure is raised to a certain value greater than the fluid static pressure, the instantaneous temperature inside the bubble will rise sharply. So, it can be concluded that the gas-liquid coupling excitation-induced cavitation process is controllable, and some theoretical basis of the new excitation mode is presented,which is expected to be applied in the online cleaning of the complex hydraulic system.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11334005 and 11574150
文摘Dynamics of a single cavitation bubble in sodium dodecyl sulfate（SDS） aqueous solutions is investigated experimentally and theoretically. The bubble pulsation is measured by a phase-locked integrated imaging technique,and the ambient radius is obtained by fitting the numerical calculation based on the Rayleigh–Plesset bubble dynamics model to the experimental data. The results show that, under the same driving condition, the ambient radius of the cavitation bubble decreases correspondingly with the increase of SDS concentration within the critical micelle concentration, while the compression ratio of the radius increases, which indicates that the addition of SDS decreases the internal molecular number of the cavitation bubble and increases the power capability of the cavitation bubble. In addition, bubble oscillation increases the concentration of the surfactant molecules on the bubble wall, so that the effect of SDS on a single cavitation bubble is reduced when the SDS concentration is greater than 0.8 m M.
基金Project partially supported by the National Natural Science Foundation of China(Grant Nos.81627802,81473692,81673995,11374155,11574156,11474001,11474161,11474166,and 11674173)Natural Science Foundation of Jiangsu Province,China(Grant No.BK20151007)the Qing Lan Project of Jiangsu Province,China
文摘This study investigated dissolution processes of cavitation bubbles generated during in vivo shock wave（SW）-induced treatments. Both active cavitation detection（ACD） and the B-mode imaging technique were applied to measure the dissolution procedure of bi Spheres contrast agent bubbles by in vitro experiments. Besides, the simulation of SW-induced cavitation bubbles dissolution behaviors detected by the B-mode imaging system during in vivo SW treatments, including extracorporeal shock wave lithotripsy（ESWL） and extracorporeal shock wave therapy（ESWT）, were carried out based on calculating the integrated scattering cross-section of dissolving gas bubbles with employing gas bubble dissolution equations and Gaussian bubble size distribution. The results showed that（i） B-mode imaging technology is an effective tool to monitor the temporal evolution of cavitation bubbles dissolution procedures after the SW pulses ceased, which is important for evaluation and controlling the cavitation activity generated during subsequent SW treatments within a treatment period;（ii） the characteristics of the bubbles, such as the bubble size distribution and gas diffusion, can be estimated by simulating the experimental data properly.
基金supported by the National Natural Science Foundation of China (Grant Nos. 11874140 and 12174085)Basic Science (Natural Science) Research Project for the Universities of Jiangsu Province (Grant No. 23KJD140002)the Natural Science Foundation of Nantong (Grant No. JC2023081)。
文摘A fractal geometric boundary with natural wall features is introduced into a hybrid lattice-Boltzmann-method(LBM)multiphase model. The physical model of cavitation bubble collapse near the irregular geometric wall is established to study the thermodynamic characteristics of the bubble collapse. Due to the lack of periodicity, symmetry, spatial uniformity and obvious correlation in the LBM simulation of the bubble collapse near the fractal wall, the morphological analysis based on Minkowski functional is introduced into the thermodynamic investigation of cavitation bubble so as to analyze and obtain the effective information. The results show that the Minkowski functional method can employed to study the temperature information in complex physical fields hierarchically and quantitatively. The high/low temperature region of the cavitation flow is explored, and thermal effect between irregular and fractal geometric wall and cavitation bubble can be revealed. It illustrates that LBM and morphological analysis complement each other, and morphological analysis can also be used as an optional and potential tool in research field of complex multiphase flows.
基金supported by the National Natural Science Foundation of China(Project No.51976056).
文摘The dynamic behavior of a cavitation bubble near an asymmetric hydrofoil is investigated experimentally through high-speed photography and theoretically using a Kelvin impulse model.The typical deformations arising during bubble collapse near the hydrofoil are analyzed qualitatively.The effects of the bubble position and the hydrofoil’s eccentricity angle are analyzed quantitatively.The spatial distribution of the Kelvin impulse near the hydrofoil are explored.Different morphological evolutions of a bubble near an asymmetric hydrofoil are revealed,with B-shaped,heart-shaped,and arc-shaped collapses.The velocity of the bubble interface close to the hydrofoil is significantly affected by the bubble-hydrofoil distance and the hydrofoil’s eccentricity angle,increasing as both the distance and the eccentricity angle grow.It is found that the Kelvin impulse sensitivity varies at different positions with respect to the asymmetric hydrofoil,being higher at the head and tail,and lower in the middle.
基金support given by the National Natural Science Foundation of China(Grant Nos.52179092 and 52222904).
文摘Capturing and studying the process of cavitation bubble collapse can help elucidate the mechanism of cavitation erosion.In this paper,a high-spatiotemporal-resolution double-exposure photographic method is used to investigate the collapse of laser-induced cavitation bubbles at two values of the dimensionless distance from the bubble to the wall,γ=d/R_(max)=0.9 and 1.25(where d is the vertical distance between the bubble center and the wall and R_(max)is the maximum radius of the bubble).Complete high-resolution evolution sequences of bubbles near a rigid wall are captured from optical breakdown to second collapse.The generation and development of microjets and shock waves during cavitation bubble collapse are described in detail.The oscillations of the bubble near the rigid wall and the microjets and shock waves generated by the collapse are analyzed.It is shown that the presence of the rigid wall affects the development of the bubble and microjets.The microjet velocity can reach up to 64 m/s.Multiple shock waves are found to be generated by bubble collapse.
基金Project supported by the National Natural Science Foundation of China(Grant No.51976056)。
文摘Vortex dynamics and wall shear stress induced by cavitation bubble oscillations under the influence of particles are numerically investigated with the aid of a compressible two-phase flow solver in OpenFOAM.The generation,evolution,and disappearance of vortexes for three jet behaviors are discussed in detail.The variations of wall shear stress induced by the jets and the vortexes during the bubble oscillations are analyzed.Numerical results reveal that vortex dynamics is related to bubble evolution and jet behavior.After the jet pierces the bubble,an annular vortex with the bubble as the vortex core is generated by the bubble collapse.For the bubble that collapses near the wall,it generates multiple small vortexes near the wall and causes discontinuities in the wall shear stress.For the bubble that collapses away from the wall,it does not generate vortexes near the wall,and its oscillations cause the wall shear stress to vary periodically with different periods.In addition,the wall shear stress at the axis of symmetry increases abruptly when the jet hits the wall.
