On wedge-slamming pressures

Abstract

The water entry of a wedge has become a model test in marine and naval engineering research. Wagner theory, originating in 1932, predicts impact pressures, and accounts for contributions to the total pressure arising from various flow domains in the vicinity of the wetting region on the wedge. Here we study the slamming pressures on a wedge and a cone, impacting on water keeping a constant, well-controlled velocity, throughout the process, using high-fidelity sensors. Pressures at two locations on the impactor are measured during and after impact. Pressure time series from the two impactors are discussed using inertial pressure and time scales. The non-dimensionalised pressure time series are compared with sensor-integrated averaged composite Wagner solutions, Logvinovich solution (Hydrodynamics of Flows with Free Boundaries. Naukova Dumka, 1969, 4.7), modified Logvinovich solution, and generalised Wagner models. In addition, we provide an independent experimental justification of approximations made in the literature in extending the Wagner model to three dimensions. The second part of the paper deals with pre-impact air cushioning - an important concern since it is responsible for determining the thickness of the air layer trapped upon impact. Using a custom-made technique we measure the air-water interface dynamics as it responds to the build up of pressure in the air layer intervening in between the impactor and the free surface. We show both experimentally and using two-fluid boundary integral simulations, that the pre-impact deflection of the interface due to air-cushioning is fully described by potential flow.