Analysis on coupling characteristics of ventilated cavitation and supersonic exhaust jet of a supercavitating vehicle

For the supercavitating vehicle, the complex interaction between the external cavitating flow and the supersonic exhaust makes it difficult to maintain stable cavity morphology. This paper establishes an internal-external flow coupling model for supercavitating vehicles in complex multiphase environments, analyzing the effects of ventilation rate and combustion chamber pressure on jet-cavity coupling evolution, engine performance, and hydrodynamic characteristics. The accuracy of the numerical model is validated using a gravity-driven water tunnel experimental system. The results indicate that that cavity evolution exhibits a periodic cycle consisting of three stages: shrinkage-collapse, regrowth, and supercavitation. After engine ignition, the cavity truncation and collapse cause severe oscillations in the gas-liquid interface and back pressure, with the back pressure exhibiting periodic oscillations during subsequent cavity evolution. Increasing the combustion chamber pressure enhances the stability of the core jet region and suppresses tail backpressure fluctuations, while raising the ventilation rate helps enlarge the cavity size but amplifies pressure oscillations during tail cavity pinch-off. Engine thrust varies synchronously with the nozzle mass flow rate; however, liquid backflow induced by cavity collapse can cause thrust peaks with amplitudes tens of times greater than the designed value. Furthermore, the cavitation number and vehicle drag exhibit significant time-varying characteristics across different evolution stages. Optimizing the vehicle configuration to establish a dual-cavity flow pattern can effectively improve the overall stability of the force system.