Necessity of Ventilation Compressibility in Numerical Simulation for Predicting Ventilated Supercavity Geometry and Supercavitation Flow Characteristics

Abstract In the numerical simulation of ventilated supercavitation, ventilation gas is typically treated as an incompressible fluid to enhance numerical convergence. However, the validity of this assumption has not been fully substantiated. This study aims to identify the influence of ignoring gas compressibility on ventilated supercavitation flow and to evaluate the significance of considering ventilation compressibility. A comparative analysis was conducted to investigate the geometry and closure modes of supercavities, focusing on the differences between compressible and incompressible supercavities with two representative closure modes: twin-vortex and reentrant jet. The consequences of neglecting the compressibility of ventilation gas are discussed in detail, with a focus on supercavity geometry, flow structure, and closure mode. Ignoring gas compressibility leads to discrepancies in the predicted supercavitation flow and gas leakage behavior when compared to actual physical processes. As a result, the supercavity shape and dimensions become unreasonable, exhibiting significant deviations in geometry, particularly because ambient pressure does not influence the dimensions of an incompressible supercavity. Therefore, the results cannot quantitatively predict the geometry of a ventilated supercavity with accuracy. Our study highlights the importance of considering the compressibility of ventilation gas in computational fluid dynamics (CFD).