Experimental and Numerical Investigations on Steady and Unsteady Behaviour of a Rotor Airfoil with a Piezoelectric Trailing Edge Flap

Active control technology is subject of investigations in recent years, after two decades of research in Higher Harmonic Control (HHC) and Individual Blade Control (IBC). Within the collaborative program named RACT (Rotor Active Control Technology), DLR, Eurocopter Deutschland (ECD), and Daimler-Benz Research and Technology (DB) investigate various IBC systems. One of these use an actively controlled trailing edge flap for creation of additional moments on a rotor blade. In order to obtain reliable data of an existing modern rotor airfoil equipped with a trailing edge flap at real Mach and Reynolds numbers, both numerical studies and a wind tunnel test using a piezoelectric actuator were performed. In this paper, steady and unsteady 2D Navier-Stokes (NS) results will be presented and compared to the wind tunnel test data. Effects of wind tunnel corrections and three-dimensionality of the flow are discussed. A semi-empirical mathematical model for computation of the steady and unsteady airfoil coefficients is presented and validated against the NS data. This model is faster by about three orders of magnitude compared to the NS code in computing the airfoil’s lift, drag and moment. Therefore it is an efficient tool for industry and research organizations to include unsteady flap aerodynamics into rotor simulation codes.