Dynamics of an acoustically driven cavitation bubble cluster in the vicinity of a solid surface

Abstract

The dynamics of a cavitation bubble cluster under the influence of an acoustic field is a complex multiphase system that can be observed in acoustic cavitation. In the present study, a three-dimensional computational technique based on the multiphase lattice Boltzmann method (LBM) with multiple relaxation time (MRT) is adopted to investigate the acoustically driven cavitation bubble cluster dynamics near a solid wall at different wetting conditions. Herein, the Peng-Robinson-Stryjek-Vera equation of state with an acentric factor is incorporated in the LBM to accurately impose the physical properties of actual fluids. The validity and capability of the adopted MRT-LBM are confirmed by the excellent agreement of the present results compared to the computed data based on the Rayleigh-Plesset equation for a heterogeneous cavitation phenomenon. The obtained results for the acoustically driven cavitation bubble cluster dynamics demonstrate that the shielding effect of top bubbles prevents the pressure pulse from reaching the lower bubbles. Therefore, the cluster core and the bubbles near the solid surface are more affected by the destruction of the upper layer bubbles than the acoustic field. Also, it is found that the wettability of the solid wall significantly affects the irradiated impulsive pressure waves around the cluster. To justify this result from the physical point of view, the magnitude of the primary and secondary Bjerknes forces is measured and, accordingly, the growth and collapse of bubbles in the cluster under the influence of the acoustic field are discussed in detail.