Air cushioning and impact pressures during a wedge slamming on water*

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 of a wedge and a cone with a deadrise angle of 10 degrees. Using a linear motor, a constant, well-controlled velocity is maintained throughout the impact event. Using an in-house visualisation technique, we reveal that air-cushioning under the cone causes a significant deflection of the water surface prior to impact. Pressures at two locations on the impactor are measured during and after impact. Pressure time-series from the two impactors are discussed using appropriate hydrodynamic pressure, and inertial time scales. The non-dimensionalised pressure time series are compared to composite Wagner solutions (Zhao & Faltinsen 1993). It is shown that, without a single free parameter, the space-averaged composite solutions reproduce the measurements near perfectly well, and a finite size of the sensor is why the peak pressure has a non-singular rise. Approximations made in the inner-domain for extending the Wagner model to three-dimensions are experimentally justified.