Coupled effects of backstep structure and jet intensity on the dynamics of ventilated cavity

Abstract

Supercavitation reduces underwater vehicle drag by forming a supercavity, yet its stability is highly sensitive to projectile configuration and engine exhaust jets. Therefore, it is essential to investigate supercavity behavior under coupled effects of these two factors. A numerical method based on the OpenFOAM platform is developed for compressible gas-liquid two-phase flow and experiments are conducted for further validation. This study reveals the influence of jets with various intensities on cavity morphology and stability. Then the coupled effects of backstep structures and jet intensities on cavity closure characteristics, the stability, and pressure fluctuations are systematically analyzed. The results demonstrate that increased jet intensity transitions the cavity from a supercavity to a partial cavity, accompanied by high-frequency pressure oscillations and rapid velocity reduction along the jet axis. A larger backstep diameter suppresses the upstream propagation of the re-entrant jet, stabilizing pressure within the cavity and maintaining a consistent thrust-to-drag ratio under different jet intensities. However, an excessively large backstep diameter disturbs the cavity interface and increases drag. An initial supercavity-to-projectile diameter ratio of approximately 2.1 helps maintain favorable cavity morphology and dynamic characteristics. These findings offer a novel perspective for the matching design of the backstep structure of the projectile and the engine exhaust jet.