Abstract: For the vertical launch of underwater vehicles, igniting the solid rocket engine in the tail cavity to control movements is an essential approach to stabilize the trajectory under the interference of complex factors. Based on the fluid volume model, standard k-ε turbulence model and dynamic mesh method, and by solving Reynolds-averaged Navier-Stokes equations, the flow field characteristics and evolution law of the coupling effect between supersonic jet and tail cavity in the early stage are studied. The results show that the semi-ellipsoidal appendage tail cavity formed after an underwater vehicle leaves the launch tube gradually evolves into a gourd-shaped cavity due to the supersonic jet effect. The internal flow is reconstructed after damage without forming a reentrant jet flow. The supersonic jet flow is completely limited in the tail cavity, and the radial size of the jet flow is basically equal to the diameter of the nozzle outlet. Primary and secondary vortex rings appear successively in the tail cavity due to jet cogging and the effect of the cavity surface, while pressures at the tail of the underwater vehicle and the center of the launch tube exit show wide-amplitude oscillations. The maximum amplitude is about 1.2 times of the water pressure at the launching spot, causing significant variance in the jet structure and engine thrust.

Key words: underwatervehicle, supersonicjet, tailcavity, flowfieldcharacteristics, momentumjet