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High subsonic and low reynolds number airfoil optimization of high-altitude propeller

This paper presents an airfoil optimization at high subsonic and low Reynolds number condition, to improve the efficiency of an E387-based HALE UAV propeller at cruising condition. The optimization design method is based on surrogate model coupled with validated RANS simulation. The optimal airfoil shape is flat and sharp leading-edged, which remarkably differs from the original and resembles a very thin airfoil in reversed configuration. Significant increment of lift-to-drag ratio and aerodynamical independency of Mach and Reynolds number were observed due to expanded supersonic flow region, weakened shock wave, and considerably reduced flow separation. By applying the optimized airfoil to propeller outboard, the new propeller’s efficiency increased more than 2%, while maintained required thrust, as proved by both Blade Element Theory and CFD simulation.