Measurements of pressure during the forced water entry of a cone into pure and aerated water

The present paper aims at analyzing the pressure distribution arising during water entry of a rigid cone on the free surface of pure water and aerated water initially at rest. For this purpose, impact tests were carried out using a hydraulic machine for a cone with a deadrise angle of 7° and for several impact velocities (5, 7 and 9 m/s) and air volume fractions (0, 0.35 and 1.1%). The impact pressure was measured at four different locations on the cone surface. The evolution of the pressure and the pressure impulse, the pressure maxima and the wetted surface expansion velocity are analyzed. For pure water, the results are in good agreement with the predictions of existing model analytical models of water impact based on Wagner's theory, with a relative difference smaller than 2% percent for the wetted surface expansion velocity and 8% for the pressure impulse. For aerated water, the measured pressure evolutions are much less repeatable than for pure water and the pressure distribution is no longer axisymmetric and self-similar, likely due to inhomogeneous distributions of the bubbles in the water. Aeration is shown to induce a significant reduction of the impact pressure. A decrease of about 25% (in comparison to pure water) for both the peak pressures and the rate of increase of the pressure impulse was observed for a void volume fraction of 1.1%.