Investigation of cavitation bubble dynamics near a solid wall by high-resolution numerical simulation

We investigate dynamics of a single cavitation bubble in the vicinity of a horizontal wall throughout expansion and collapse using a sharp-interface level-set method. The numerical scheme is based on a finite-volume formulation with low-dissipation high-order reconstruction schemes. Viscosity and surface tension are taken into account. The simulations are conducted in three-dimensional axi-symmetric space. A wide range of initial bubble wall standoff distances is covered. We focus, however, on the near-wall region where the distance between the bubble and the wall is small. We reproduce three jetting regimes: needle, mixed, and regular jets. The needle jets impose a significant load on the solid wall, exceeding the force induced by the collapse of the pierced torus bubble. For intermediate standoff distances, the large delay time between jet impact and torus bubble collapse leads to a significant decrease in the imposed maximum wall pressure. A liquid film between bubble and wall is observed whenever the bubble is initially detached from the wall. Its thickness increases linearly for very small standoff distances and growths exponentially for intermediate distances leading to a significant increase in wall-normal bubble expansion and bubble asymmetry. For configurations where the torus bubble after jet impact reaches maximum size, the collapse time of the cavitation bubble also is maximal, leading to a plateau in the overall prolongation of the cycle time of the bubble. Once the initial bubble is attached to the solid wall, a significant drop of all macroscopic time and length scales toward a hemispherical evolution is observed.