Numerical simulations of cavitation bubble growth near a soft gel object

Biomedical therapies use focused ultrasound to treat pathogenic tissues and stones. These ultrasound waves generate cavitation bubbles that inertially grow and collapse in and near the target tissue or stone. Earlier numerical simulations have treated the bubble contents as a mixture of water vapor and non-condensable gas, but it is known that phase change affects the bubble dynamics. During bubble oscillations, the liquid evaporates into the gas bubble, water vapor condenses, and non-condensable gases dissolve into the liquid. Additionally, the nearby stone or soft gel object can affect the growth dynamics and vice versa. We conduct 3D simulations of a cavitating bubble rapidly growing near a soft (agarose) gel object using the open-source Multi-component Flow Code [Bryngelson et al. Comp. Phys. Comm. (2021)]. MFC solves the 3D, compressible Navier--Stokes equations using a six-equation multiphase numerical model, including a phase change model. Simulations show wall-attached cavitation from the wall-reflected rarefaction of a nearby exploding water vapor-gas bubble. Maximum pressures and stresses in the soft gel object for varying driving bubble expansion pressure and bubble stand-off distances from the water-gel material interface are presented.