Numerical investigations of shear flow generated by collapsing bubbles near a rigid wall

Collapse of cavitation bubbles near solid objects leads to the formation of a high-velocity re-entrant jet toward the surface which plays an important role in ultrasonic cleaning. The jet impact accompanies radially spreading wall shear flow capable of removing particles from the surface. Due to the experimental challenge to resolve the bubble dynamics and the resulting fluid flow, the particle removal mechanism is not well understood. Here, we simulate the so-called Rayleigh bubble collapse near a no-slip, rigid wall to quantify the wall shear flow, which paints a more clear picture of the complex dynamics of the cleaning process. We solve 3-D compressible Navier-Stokes equations for a multiphase system using a solution-adaptive, high-order accurate discontinuity capturing/central differencing method. We simulate the collapse of an air bubble (100 µm in radius) driven by a sudden increase in the water pressure (57 times higher than the bubble pressure). Our simulations show that generation of wall shear flow falls into three stages: bubble shrinkage, shock emission, and jet impact. We will also consider the collapse of multiple bubbles and its suppression effects on the wall shear stress.