Numerical study on the Blade-Vortex interaction of helicopter rotor with lateral blowing

As a method to reduce Blade-Vortex Interaction (BVI) noise of helicopter rotor, the effects of lateral wing-tip blowing were analyzed for the generation and behavior of tip vortical flow. Three-dimensional compressible Euler/Navier-Stokes solver was used to calculate the effect of blowing air from blade tip on the tip vortex of fixed single blade at the various flow and jet conditions. The numerical results include the position of the vortex center along the vortical flow, the size and strength of the rolled tip vortex, and circulation and maximum tangential velocity of the tip vortex. Jet blowing from the wing-tip can diffuse the tip vortex in the way to make larger core sizes and less velocity gradients, which can be effective way to reduce BVI noise of rotary wing. The predictions of BVI noise were performed using a combined method of an unsteady Euler code with an aeroacounstic code based on Ffowcs-Williams and Hawkings formulation. A moving overlapped grid system with three types of grids (blade grid, inner and outer background grid) was used to simulate BVI of helicopter with two OLS-airfoil blades in forward/descending flight condition. The calculated waveform of BVI noise clearly shows the distinct peaks caused by the interaction between blade and tip vortex and the effect of lateral blowing at tip to reduce BVI noise.
Special Publication of National Aerospace Laboratory
航空宇宙技術研究所特別資料