Air cushioning during disc impact on a water surface*

We study the influence of air in the early phase of a slamming solid-liquid impact, in the geometry of a horizontal disc approaching a free liquid surface. To determine the role played by the intermediate air layer, we measure the free-surface deformation by means of an in-house developed profilometric technique based on total internal reflection, using an experimental setup in which a linear motor impacts a disc with a well-controlled velocity onto a water surface. Simultaneously, the force on the disc and the pressure in the air-water phase below it are measured, using strain gauge and pressure sensors. The experiments reveal the entrapment of an air pocket. They are compared to simulations using a two-phase boundary integral method in order to understand the cushioning effect of the entrapped air layer on the load that is experienced by the disc.