Numerical Study of the Dynamics of a Gas Bubble Near a Wall Under Ultrasound Excitation

A numerical study of the dynamics of a gas bubble in water near a plane rigid wall under ultrasound excitation has been performed. The bubble dynamics is excited at the natural frequency of the radial oscillations of the bubble in the absence of the wall. The dynamics of the bubble with the formation on its surface of a cumulative liquid jet directed to the wall is considered. A regime of the ultrasound excitation is investigated, at which the cumulative jet impact against the bubble surface part closer to the wall is realized at the moment of the beginning of the second expansion of the bubble. At this moment two known mechanisms of emitting pressure pulses into liquid by a bubble start working simultaneously. The first one is due to the bubble expansion. The second one results from the impact of the cumulative jet. The boundary element method is used. The study has revealed the dependencies of the ultrasound excitation amplitude, at which the indicated regime is realized, on the distance between the bubble and the wall, as well as the influence of the bubble-to-wall distance on the jet impact velocity and the pressure inside the bubble corresponding to that regime.