The Mechanism for the Quasi-Back-Attack Phenomenon of Gas Jets Submerged in Water

Over-expanded and under-expanded gas jets submerged in water have been studied through numerical simulation and experiments. Comparisons between numerical and experimental results are made to validate the conclusion that the ‘quasi-back-attack’ phenomenon in high-unexpanded conditions is caused by the obstruction of the shock waves acted on back-attacked gas. As a consequence, back-attacked gas cannot reach the wall of the motor. A detailed analysis of the results reveals the underlying mechanism of the structure of the gas jet under different operating conditions. Meanwhile, the characterization of the motor’s thrust indicates that the oscillation amplitude of thrust drops sharply after the occurrence of quasi-back-attack phenomenon, which is beneficial to the stability of the motor.