Experimental study of the effect of the ventilation mode on the water-exit of the vehicle

The water-exit problem of active ventilation vehicles has complex cavity dynamics and hydrodynamic characteristics. This study explores the influence of the ventilation parameters on the dynamic evolution of the cavity and the hydrodynamic forces by experimentation. The full development of cavities is beneficial for hydrodynamic stability. The ventilation parameters focus on two influencing factors: the ventilation opening type and the ventilation angle between the direction of gas flow and the axis of the vehicle. The former includes porous structure, ventilation hole, and ventilation seam, while the latter includes 30° and 90°. Compared to the cases of holes and seams, the cavities formed under the porous structure opening condition have larger diameters and shorter lengths. This is not conducive to the hydrodynamic performance, which includes frictional resistance, pressure drag, and impact pressure at the closure point. When the cavity transits from a partial state to a supercavity state, the frictional resistance no longer changes significantly, and the axial drag coefficient tends to be stable. The increase in the cavity diameter leads to an increase in the pressure drag and the impact pressure at the cavity closure. The ventilation angle mainly affects the stability of the internal pressure and the morphology of the cavity. This work can provide reference for the design of artificial cavity of underwater vehicles.