Viscous Flow Simulation of Rotor Blades with Tip Slots in Hover

Abstract

The effect of tip slots oil the tip-vortex formation of a rotor blade in hover has been numerically investigated using unstructured meshes. The slots embedded inside the blade surface were physically modeled, and the How through file slots was simulated as a part of the numerical solution. The mass-flow rates through the slots were estimated at the slot exits, and the effects of slot position and the number of slots on the tip-vortex initial roll-tip mechanism and the core structure were examined. Comparison of the vorticity contours inside the tip-vortex core showed that the tip vortex generated from the slotted blade was less well organized and was more scattered than that of the baseline rotor blade. It was found that for the slotted blade, the maximum vorticity of the tip-vortex core was much lower than the baseline blade from the initial roll-tip stage. Also, the vorticity diffusion rate of the slotted blade was much higher than that of the baseline blade. These effects were further magnified as the number of slots was increased and also as the Reynolds number and the blade tip Mach number were increased. It was demonstrated that tip slots can be used effectively to diffuse the tip vortex and potentially to alleviate the blade-vortex interaction noise of helicopter rotor blades.