Multiphase fluid-solid coupled analysis of shock-bubble-stone interaction in shock wave lithotripsy

Abstract

A novel multiphase CFD-CSD coupled computational framework is applied to investigate the interaction of a kidney stone immersed in liquid with a lithotripsy shock wave (LSW) and a gas bubble near the stone. The main objective is to elucidate the effects of a bubble in the shock path to the elastic and fracture behaviors of the stone. The computational framework couples a finite volume two-phase computational fluid dynamics (CFD) solver with a finite element (FE) computational solid dynamics (CSD) solver. The stone surface is represented as a dynamic embedded boundary in the CFD solver. The evolution of the bubble surface is captured by solving the level set equation. The interface conditions are enforced through the construction and solution of local fluid-solid and two-fluid Riemann problems. The results of shock-bubble-stone simulations suggest that the dynamic response of a bubble to LSW varies dramatically depending on its initial size. Bubbles with an initial radius smaller than a threshold collapse within 1 μs after the passage of LSW; whereas larger bubbles do not. Moreover, this study suggests that a non-collapsing bubble imposes a negative effect on stone fracture while a collapsing bubble may promote fracture on the proximal surface of the stone.