AgustaWestland's application of HMB to simulate the active Gurney flap

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Baverstock, K.
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This paper describes the way in which the CFD solver HMB 2.0 has been used by AgustaWestland to calculate unsteady aerofoil characteristics in support of rotor performance calculations using blade element methods, and to provide local loads in support of structural design. Initial steady simulations and comparison between the predicted effects of Gurney flaps and those from wind tunnel testing are shown. The limitations of steady analysis, some of the key observations regarding the performance of Gurney flaps, and the effect of unsteady vortex shedding from them are noted. The method by which aerofoil external profiles have been modified to accommodate an active Gurney flap while maintaining the characteristics of the original section is described and the results presented. The significant computational effort required simulating each point as a time accurate simulation at fixed incidence over the range of incidence and Mach number possible in flight is noted and a novel method of look-up table generation via low ramp-rate CFD simulations is described. Beyond simple pseudo steady data table generation, comparisons are made between dynamic stall predictions for the original clean aerofoil and the modified aerofoil with Gurney flap. These justify the use of simple first generation dynamic stall prediction tools for Gurney flap configurations. Finally, simulations of the dynamic deployment of a Gurney flap on an aerofoil with varying incidence and Mach number, representative of operating conditions on a main rotor and the provision of local aerodynamic loads in support of detailed design are presented.