Water entry of axisymmetric body with flow diversion orifice: Impact load reduction and inner flow visualization

Water entry with consideration of impact load reduction is one of the most important issues in the area of marine vehicle. In the present work, the water entry experiments of a series of specially designed transparent resin models of axisymmetric body with flow diversion orifice were performed, to investigate the impact load feature, specific cavity structures, and flow details inside the orifices. The water entry of solid, hollow, and through-hole models were studied in comparison at different Froude numbers. The results demonstrate that the models with diversion orifice can significantly reduce water entry impact, and generate air-entraining cavities and jet column carrying bubbles. The jet will impact the two parts of the cavity which split after the cavity pinch-off, effectively dissipating the kinetic energy of the cavity and preventing the instability of the model attitude caused by tail impact. The flow inside the orifice can develops into a unique toroidal tip jet. The water entry impact of the model with orifice shows a weaker acoustic signal spreading in water in contrast to the solid models. The through-hole structure significantly alters the flow field structure of the impact zone, reduces the impact energy, and effectively mitigates the hydrodynamic impact load.