高马赫数球状气泡动力学理论研究

The compressibility of fluids has a profound influence on oscillating bubble dynamics,as characterized by the Mach number.However,current theoretical frameworks for bubbles,whether at the first or second order of the Mach number,are primarily confined to scenarios characterized by weak compressibility.Thus,a critical need to elucidate the precise range of applicability for both first-and second-order bubble theories arises.Herein,we investigate the suitability and constraints of bubble theories with different orders through a comparative analysis involving experimental data and numerical simulations.The focal point of our investigation encompasses theories such as the Rayleigh–Plesset,Keller,Herring,and second-order bubble equations.Furthermore,the impact of parameters inherent in the second-order equations is examined.For spherical oscillating bubble dynamics in a free field,our findings reveal that the first-and second-order bubble theories are applicable when Ma≤0.3 and 0.4,respectively.For a single sonoluminescence bubble,we define an instantaneous Mach number,Mai.The second-order theory shows abnormal sensibility when Mai is high,which is negligible when Mai≤0.4.The results of this study can serve as a valuable reference for studying compressible bubble dynamics.

Numerical study of the kinematic and acoustic characteristics of bubble clusters

Direct numerical simulations are performed to study single gas/vapor bubble and spherical bubble clusters containing 13–352 vapor bubbles in compressible flow fields.The numerical results show that the single cavitation bubble keeps spherical during the collapse process,and the far-field acoustic pressure calculated by the Ffowcs William-Hawkings(FW-H)formulation is basically consistent with the analytical solution obtained based on the volume acceleration calculation.However,the spherical bubble cluster collapses layer by layer due to the strong coupling between bubbles.The closer to the center of the bubble cluster,the shorter the collapse time and the stronger the non-spherical deformation.The collapse of a bubble cluster would generate multiple acoustic pressure peaks,which cannot be accurately predicted by the volume fluctuation sound source theory.The size and volume fraction of the bubble cluster have a significant influence on the collapse time and the distribution of sound pressure.We found that when the volume fraction of a bubble cluster is large,the total collapse time is basically the same as that of its corresponding single bubble with the equal volume.The frequency distribution of sound pressure of a dense bubble cluster is also close to that of its corresponding single bubble.In addition,we found that a bubble cluster with randomly distributed bubble diameters collapses asymmetrically and rebounds in the late stage of the collapse process.The above study reveals part of the mechanism of bubble cluster collapse and sound generation,and provides a theoretical basis for the establishment of cavitation noise model.