In the present study, the formation of the wing-tip vortex from a rectangular NACA0015 wing with a square tip at the Reynolds number of 1.8×105 and the angles of attack(AOA) α= 8o and 10o were simulated with an incompressible detached eddy simulation(DES) method and the Reynolds averaged Navier-Stokes(RANS) equations with the SA model respectively. Numerical results were compared with experimental results to validate the capability of the employed methods in resolving tip vortex flows. The results show that DES model could capture the complicated three-dimensional structures in the vortex, and the streamwise vorticity and the cross-flow velocity agree with the experiment results quite well, but RANS-SA model with the same grid as that of DES failed to capture the correct structures and under-predicted the streamwise vorticity in the vortex by 40%. The present study suggests that under the same calculation cost, DES but not RANS-SA could be used to effectively predict the flow characteristics in tip vortex.
When a high-speed cavitated weapon moves under water, the flow properties are important issues for the sake of the trajectory predication and control. In this paper, a single-fluid multiphase flow method coupled with a natural cavitation model is proposed to numerically simulate the free moving phase of an underwater supercavitated vehicle under the action of the external thrust. The influence of the cavitator's deflection angle ranging from -o3 to o3 on the cavity pattern, the hydrodynamics and the underwater trajectory is investigated. Based on computational results, several conclusions are qualitatively drawn by an analysis. The deflection angle has very little effect on the cavity pattern. When the deflection angle increases, the variation curves of the vertical linear velocity, the lift coefficient and the pitching moment coefficient become flatter. In the phase of the second natural cavitation, at a same time, the greater the deflection angle is, the lower the drag and the lift coefficients will be and the higher the pitching moment coefficient becomes. At the finishing time of the free moving phase, when the deflection angle lies in the small range of -1o-1o, the position of the center of mass and the pitching angle of the vehicle are more close to each other. However, when the deflection angle is less than -1o or greater than o1, the position of the center of mass and the pitching angle change greatly. If a proper deflection angle of the cavitator is adopted, the underwater vehicle can navigate in a pseudo-fixed depth.
