Effects of wall wettability on vortex flows induced by collapses of cavitation bubbles: A numerical study

The collapse of a cavitation bubble near a rigid wall induces a vortex flow that spreads along the wall with a high shear rate, and an important factor affecting the behavior of the bubble dictated by its contact lines is the wettability of the wall. However, the mechanism for the dynamics of the vortex flow and wall shear stress remains to be settled. A numerical study conducted using the multiphase compressible InterFoam solver in the OpenFOAM framework is reported here. The wall wettability is modeled by the contact angle b and slip velocity uslip, and the results show that compared with a neutral surface, superhydrophobic and hydrophilic surfaces broaden the wall-vortex regimes. The main area of shear stress is enlarged both spatially and temporally in the case of a superhydrophobic surface, while it is extended spatially and shortened temporally for a hydrophilic surface. The wall-vortex flow produces a long-term wall shear stress with high magnitude, the maximum value of which is 174.41 kPa for the superhydrophobic surface, 131.82 kPa for the hydrophilic surface, and 103.12 kPa for the neutral surface. Integrating the shear stress over time and space shows that the slip velocity uslip is mainly responsible for affecting the distribution of the shear stress in the vortex flow induced by the collapse of a cavitation bubble. The present findings provide a good guide for ultrasonic cleaning in engineering applications.