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.

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This work is funded by the Defence Science and Technology Laboratory’s project no. 74260. A part of the technical work has been completed under the collaboration project The Technical Cooperation Program AERospace Systems Group (TTCP AER) CP13.A1, titled “Next Generation Rotor Blade Design.” This work used the Cirrus U.K. National Tier-2 High Performance Computing (HPC) Service at EPCC. This work used the Advanced Research Computing High End Resource (ARCHER) U.K. National Supercomputing Service.

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Received13 October 2020
Accepted29 May 2021
Published online28 July 2021

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

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