Dynamics of an Acoustically Excited Gas Cavity Attached to a Rigid Surface

Abstract

Expansion, collapse and impact of a gas bubble onto a rigid wall are numerically studied. The bubble is adjacent to the wall, it is initially spherical, at the equilibrium state. Its dynamics results from harmonic variation of the surrounding liquid pressure. The impulse action of the bubble on the wall is realized by means of impact of a cumulative jet arising on the surface of the bubble during its collapse. The expansion of the bubble and its collapse prior to the jet collision with the wall is calculated using the boundary element method under the assumption that the liquid is ideal incompressible and its movement is potential. The jet impact on the wall, during which the liquid compressibility is significant, is calculated using the equations of gas dynamics and the CIP-CUP method. It is found that in the considered frequency range of the liquid pressure oscillations, the shape of the jet at the beginning of its impact remains nearly the same. For the frequency corresponding to the wall pressure maximum, estimates of the pulse loading on the wall are obtained. It is shown that the pressure distribution on the wall during impact is violently nonuniform with a pronounced peak at the periphery of the loaded area. The maximum pressure on the wall averaged over the loaded area is equal to the water hammer pressure, whereas the maximum peripheral pressure is about 2.5 times as much.