Control calculation of helicopter rotor tip vortex in forward flight using steady air mass injection

A high-accuracy numerical method was established to simulate the rotor flowfield of rotor tip vortex with tip air mass injection (TAMI) control in forward flight. In the existing method, the finite volume method was used for spatial discretization. The upwind Roe scheme with a fifth-order WENO (weighted essentially non-oscillatory) scheme was employed to calculate convective fluxes on control faces. A dual-time method was utilized in time marching and the high-efficiency implicit LU-SGS (lower upper symmetric Gauss-Seidal) scheme was applied to every pseudo time step. A surface boundary condition which may effectively simulate the effect of TAMI was introduced into this method. The moving overset grid method of refining the blade grid and background grid pertinently was adopted to simulate the blade flapping and rotating motions. Based on the presented method, rotor tip vortex with TAMI control in forward flight was calculated. It demonstrated that there existed obvious difference between the tip vortex induced at the front side of rotor disk and that induced at the rear side. The core strength of tip vortex induced at the front side was smaller than that at the rear side. Tip vortex induced at the front side of the rotor disk cannot be weakened. However, tip vortex induced at the rear side can be effectively weakened by the steady TAMI.