Cavitation bubble induced wall shear stress*

The shear flow generated by the collapse of a cavitation bubble near a rigid boundary is relevant in surface cleaning and cell membrane poration among other applications. However, neither the spatio-temporal distribution nor the magnitude of the shear stress are well known. Here, we report on recent numerical simulations of the wall shear stress induced by a single cavitation bubble. The simulation is done based on a compressible two-phase Volume of Fluid (VOF) solver from the OpenFOAM framework. The numerical results show good agreement with the experimental results. The flow region with constant shear rate in the boundary layer is reproduced with a locally refined mesh spacing Δx=0.05 μm. Very high stresses of 100 kPa are found during the early spreading of the high-speed transient jet from the collapsing bubble. Later, the main spreading flow and  the re-expansion of the toroidal bubble together produce a vortex ring, which stabilizes the flow and thereby slows down the decay of the shear stress. In particular, a spatio-temporal map on the wall shear stress is provided, which summarizes the complex distribution of the shear stress on the solid boundary.