Rotor-Blade Planform Design Based on an Overset Harmonic-Balance-Adjoint Optimization Framework

Abstract

Optimization methods in conjunction with computational fluid dynamics are a key tool in advancing current rotor design. High-fidelity optimization of unsteady rotor flows in forward flight, however, is a challenging problem due to the high computational resources required. To minimize the computational costs, a fully turbulent, overset, adjoint harmonic-balance optimization framework has been developed, which maintains the fidelity of the Navier–Stokes equations. The framework is demonstrated in the aerodynamic redesign of the AH-64A rotor blade. An analysis of the optimized rotor blade is presented, including the key design features that contribute to the performance benefits in each of the examined design conditions. In particular, the benefits and drawbacks of rotor designs with an offloaded blade tip have been discussed. The formulation of the optimization objective function, blade surface parameterization, and treatment of trim were seen to have an impact on the final planform shape; and they have been deemed to be key in obtaining a practical rotor design suitable for use on real-life helicopters.