Aerodynamic Geometry Optimization of Coaxial Rigid Rotors in Forward Flight

Coaxial rigid rotor configuration provides helicopter higher forward flight speed than single-rotor configuration. Aiming at obtaining a coaxial-rotor blade shape with better aerodynamics in forward flight, a compressible RANS solver for aerodynamics simulations and an optimization method for blade design are established. The optimization method combining a surrogate-based approach and genetic algorithms is suitable for solving the complicated multiobjective blade geometry optimization problem. On the basis of previous research, the blade geometry is optimized towards a shape with nonlinear chord distribution and a tapered swept-back tip. The optimized rotor blade reaches a higher value of lift-drag ratio over a large advance ratio range compared with rectangular blade of the same size. And the new shape suppresses the flow separation and weakens the shock over the blade surface to a certain degree in high-speed forward flight. Meanwhile, the optimized blade also contributes to reducing high-speed impulsive noise generated in forward flight.