Effects of cavitation bubble dynamics near a free surface on gas layer stability and impact loading of biomimetic microstructured surfaces

The dynamics of cavitation bubbles critically affect the stability of gas layers and induce intense impact forces on adjacent surfaces. This study numerically investigates the complex interaction mechanisms among a cavitation bubble, a free surface, and three representative biomimetic gas–entrapping microstructured surfaces. A compressible volume of fluid multiphase model with equations of state is developed and validated against experimental observations of bubble morphology, gas layer evolution, and free surface deformation. The effects of bubble–surface (γf = 0.25–1.0) and bubble–wall (γw = 0.8–1.5) stand–off distances are systematically examined, focusing on liquid jet characteristics, shock wave propagation, wall shear stress, and the resulting force and impulse on the microstructured surface. The results reveal that the hierarchical microstructure provides superior gas layer retention, sustaining a higher gas volume fraction (αg = 0.87) and attenuating impact loading (p/p* = 45) compared to micropillar and re-entrant microstructures. The evolution of wall shear stress shows alternating outward and inward patterns driven by bubble-induced radial flows, with peak values of 282 kPa (outward) and 89 kPa (inward) for the hierarchical microstructure. Furthermore, variations in γf and γw significantly influence the jet dynamics, modify the spatial distribution of wall pressure and shear stress, and determine the resulting force and impulse on the microstructured surface. These findings offer theoretical insight into mitigating cavitation-induced erosion and enhancing gas layer stability in marine hydrodynamics and fluid machinery.