Cavitation bubble induced wall shear stress at an elastic structure*

Cavitation bubbles created near a rigid boundary are known to violently collapse and create jet flows onto the boundary. The thereby produced strong flows, water hammer pressure and shock waves are associated with erosion of even tough surfaces like ship propellers. In the application of ultrasound baths the created shear stress is used for surface cleaning. Despite great academic interest in bubble dynamics near a surface, the hereby created wall shear stress is difficult to measure and the erosion and cleaning mechanisms are still not fully understood. We present a study of the fluid-structure interaction between a single submillimeter sized bubble in water near an elastic structure, with focus on the stresses produced during the first oscillation cycle of the bubble. For this we developed a novel numerical solver in OpenFOAM by combining an existing fluid-structure interaction solver, which couples a linear elastic solid with an incompressible viscous fluid, with a compressible, viscous multi-component solver with phase fraction interface modeling. Numerical simulations are directly compared to experimental high-speed recordings of a laser-induced bubble near a photopolymer resin structure with particles to track the deformation. Multiple geometries are studied, including a plane elastic sheet, a cylindrical pillar and a cylindrical ring. The influence of the material elasticity on the bubble dynamics is examined. The dependence of the bubble dynamics and produced stresses on the stand-off distance is studied.