Cavitation bubble induced wall shear stress on an elastic boundary

Abstract

A cavitation bubble imposes shear stresses onto a nearby structure during its expansion and collapse. Experimentally, we probe the tangential stresses on an elastic surface by measuring the displacement of embedded particles and the deformation of an elastic structure. Corresponding numerical simulations are done using a fluid–structure interaction Volume-of-Fluid solver in OpenFOAM, where a linear elastic solid is coupled to two viscous, immiscible, and compressible fluids. We find good agreement in terms of bubble dynamics and displacement motions. During the initial bubble expansion and its first collapse, the experiment agrees with the simulation that the strain of the elastic sheet at a distance of 1.25 Rmax from the stagnation point center is larger than at 0.51 Rmax. The maximum lateral strain occurs at a non-dimensionalized bubble stand-off distance of γ≈1.1. The highest calculated wall shear stress is 250 kPa (for position y = 0). However, the largest overall shear stress of 1.9 MPa is found within the elastic sheet at y=24 μm that corresponds to a maximum displacement of Dx=44.5μm. Thus, fracture may start from within the elastic material rather than from the surface. To further examine the fluid–structure interaction, we construct a simple axisymmetrical elastic ring and analyze its deformation. In this case, we find strong deformations not only during the bubble collapse but also during the bubble's initial expansion.