Numerical Study on Supercavitation Turbulence

Supercavitation uses a bubble of gas inside a liquid large enough to encompass an object travelling through the liquid so that the skin friction on the object can be greatly reduced and high speed can be obtained. In this study, direct numerical simulation is used to investigate the turbulence in supercavitation. The study builds on an in-house simulation code that uses the coupled level set and volume of fluid method to accurately capture the interface between the water and gas phases. A ventilated disk cavitator is used for the bubble generation, and it is modeled by a sharp interface immersed boundary method. Based on the simulation data, we have discovered two structures near the closure of the cavity, the shear layer (SL) and the jet layer (JL), which have distinct flow patterns. Through the analyses of turbulent kinetic energy (TKE) and its budget, different roles played by SL and JL in the TKE transportation and generation processes are revealed. Using a kinematic criterion, conditional statistics are obtained in these two layers. Based on conditional temporal spectra, we have identified the dominant frequencies in SL and JL, with the highest one belonging to the transverse motion of JL and determined by the frequency of the vortex shedding at the closure of cavity.