Optimisation of the AH-64A Blade Planform Based on High-Fidelity CFD Methods

This paper presents the demonstration of a high-fidelity optimisation framework applied to the AH-64A rotor blade planform. The framework implementation includes an adjoint-harmonic balance method, which allows for efficient performance predictions and evaluation of the design sensitivities for unsteady rotor flows, whilst maintaining the f idelity of the Navier-Stokes equations. A re-design of the AH-64A blade is performed, leading to significant performance benefits, and showing the great potential of high-fidelity CFD coupled with optimisation methods. The key design features that lead to performance improvements in hover and forward flight are discussed, including the advantages and disadvantages of blades with an offloaded blade tip. The influence of the optimisation setup, including the impact of the blade surface parameterisation, treatment of trim and number of harmonic balance modes within the CFDsolution on the final optimised shape is analysed throughout the paper.