Effect of exhaust angle on evolutionary and flow characteristics of pressure-equalizing film on surface of underwater vehicle

Pressure-equalizing exhaust is an effective flow control technique to improve the hydrody-namic characteristics of underwater vehicles and to inhibit their pitching moment. In this paper, numerical simulation is conducted to study the underwater vertical movement process of an underwater vehicle with pressure-equalizing exhaust. The variation of the flow rate and velocity of the exhaust as well as the film length under different exhaust angles are given. The influence of the exhaust angle on the unsteady development of the pressure-equalizing film and the hydrodynamic characteristics of the flow field around the vehicle is analyzed. The topological structure is established for the flow field near and downstream the exhaust hole as well as the re-entrant jet field at the film tail. Besides, the shape feature and evolution of the pressure-equalizing film and its mechanism to reduce the pressure on the surface of underwater vehicles are discussed. The results are helpful for looking further into the physical nature of the improvement in the hydrodynamic characteristics of underwater vehicles by means of the pressure-equalizing exhaust technique.