Rayleigh wave induced cavitation bubble structures

A localized energy deposition in a thin layer of liquid between two solid glass plates excites waves in the liquid, solids, and their interfaces. Of particular interest is an elastic surface wave (Rayleigh wave) on the liquid-solid interface that travels faster than the shock wave in the liquid. The surface deformation caused by the Rayleigh wave expands the layer of liquid, thereby locally reducing the pressure below the cavitation threshold. The created tension nucleates many cavitation bubbles, which later collapse due to the passage of the trailing shock wave in the liquid. Interestingly, the bubbles are not arranged homogeneously but on concentric rings centered on the location of the energy deposition. We explain the formation of the concentric rings with the interaction between neighboring bubbles. The fluid-structure interaction is modeled with a coupled finite volume solver that couples a multi-phase compressible fluid region (water and bubble gas) with an elastic solid (glass). We find that the nucleation of bubbles in such a geometry relaxes the tension in their immediate vicinity and thereby suppresses the growth of neighboring bubble nuclei. This idea is confirmed by a Rayleigh-Plesset model of a bubble driven by a far-field pressure obtained from the finite volume simulation. The observed ring patterns are thus the result of the successive activation of statistically distributed nucleation sites into explosively expanding cavitation bubbles in an axisymmetric geometry, whose strong interaction on short distances leads to a hindrance of bubble growth in radially distinct regions.