Expansion and collapse of single cavitation bubbles right at a solid boundary

Abstract

We present results from numerical simulations modeling the dynamics of single (laser-generated) cavitation bubbles expanding and collapsing right at a plane solid boundary. The model consists of a bubble filled with a small amount of non-condensable gas in a compressible liquid. The Navier-Stokes equations are discretized with the finite volume method. The volume of fluid method is used to capture the interface between liquid and gas. The model is implemented in the open source software package OpenFOAM.

A millimeter sized bubble in water serves as reference to discuss bubble dynamics. The most intriguing phenomenon that occurs in this configuration is the formation of a fast jet that is directed towards the solid with a speed of the order of 1000 m/s. The jet formation mechanism is explained. Paradoxically, in this setting, jet formation causally is related to the viscosity of the liquid.

Bubble size and liquid viscosity are varied. It is shown that fast jet formation persists for a wide range of liquid viscosities, including e.g.~50 cSt silicone oil. Bubble dynamics and the jet formation mechanism are discussed for values of a bubble Reynolds number, $\Reyb$, ranging from 15 to 50 000, with fast jet formation occurring for $\Reyb \gtrsim 300$.