Air-Cushioning Effect in High-Speed Liquid Impact

The surrounding gas influence, which is manifested at a small distance to the target, on the high-speed liquid impact is studied. The impact on the surface of an unbounded liquid mass and on the surface of a liquid layer on a solid wall is considered. The mathematical model is based on the Navier–Stokes equations for compressible flow with implicit treatment of the interface. The impact of a millimeter-sized water droplet with velocities of 100 and 500 m/s surrounded by air and initiated at a distance of 0.1 droplet radius from the target was investigated. It was found that at the pre-impact stage, gas compression in the gap between the impacting liquid and the target leads to perturbation and deceleration (with the appearance of horizontal momentum) of the frontal part of the impacting liquid and the corresponding perturbation of the target. This results in a rather gradual (not abrupt) increase of the impact pressure and a decrease of its maximum value compared to the case without gas-cushioning. It was found that the effect of gas-cushioning is more pronounced at subsonic (for gas) impact velocities and is enhanced with increasing ambient pressure.