A Numerical Study on the Water Entry of Cylindrical Trans-Media Vehicles

In recent years, more attention has been paid to vehicles that can travel between air and water, known as trans-media vehicles. They are often designed as cylindrical bodies in order to reduce the impact load during water entry. In this paper, the water-entry processes of small-sized cylindrical trans-media vehicles, with a characteristic length of 1 m, were investigated numerically by solving the unsteady Reynolds-averaged Navier–Stokes equations using the volume-of-fluid method, the dynamic grid method and the six degrees of freedom solver. The numerical methods were first validated by comparing the numerical results with the existing experimental data. Then, the effects of the body mass, the diameter-to-length ratio, the water-entry angle and the head shape on the water-entry process were investigated. The results show that the peak impact load, measured by the peak force exerted by water on the body, can be significantly reduced by decreasing the body mass, decreasing the diameter, entering the water at an optimum water-entry angle or installing an ellipsoidal head. In particular, the peak impact load was found to be approximately proportional to the square of the body mass or the cube of the cylinder diameter. Furthermore, installing an ellipsoidal head can reduce about 94% of the peak impact load experienced by a cylindrical body.