Curved surface effect on high-speed droplet impingement

In the present study, high-speed droplet impingement on typical curved surfaces is numerically investigated to analyse the inherent complex wave structures and cavitation. A three-component compressible multi-phase flow model is utilised considering fluid phase transitions, but the calculation of coupling with the solid structure is neglected. A detailed comparative analysis is presented of the dynamic processes, including the evolution of confined water-hammer shock waves, occurrence and collapse of cavities and spatiotemporal pressure distribution on concave, convex and flat surfaces. The synclastic curvature of a concave surface can increase a shock wave's strength, but an incongruous curvature can decrease its strength and a flat surface has moderate intensity. Both homogenous and near-surface heterogeneous cavitation can occur in three cases; the cavitation is the strongest in the concave case and, hence, the collapse waves are strongest running toward the surface. The pressure wave distributions and their evolutions are more complex in curved surface impacts than in flat surfaces. Both the confined shock wave inside the impacted droplet and near-surface lateral jet are weakest, and the near-surface cavitation level is also lowest in the convex case. Therefore, it can be inferred that a convex surface can reduce the possible surface damage during high-speed impingement. The two-dimensional axisymmetric numerical results show that both the converging and diverging motions of waves intensify, which further increases the curvature influence on concave surface damage.