Study of Drag Reduction Devices on a Flatback Airfoil

Abstract

Various trailing edge drag reduction devices, including a new Flap device, were examined experimentally on a flatback airfoil in a wind tunnel. The tests concerned a 30% thick airfoil with 10.6% thick trailing edge. Pressure, Hot Wire and Stereo PIV measurements were performed at a chord Reynolds number of Re=1.5e6. Results show that the best performing devices decrease drag, increase the vortex shedding frequency and reduce flow variation downstream of the wing trailing edge. When a characteristic height for each device is defined the corresponding Strouhal number indicates bluff body shedding at 0.20 < St < 0.25. The best performing device was a combination of the Flap with an Offset Cavity plate. It increased the lift to drag ratio of the plane airfoil by 138%, increased the shedding frequency from 217Hz to 281Hz and reduced the amplitude of the main frequency by 84%. RANS simulations predict St = 0.20 for the plane airfoil, but do not predict vortex shedding for the other cases. Further investigation is required for the optimization of the new device and in order to examine its effects on noise reduction, load mitigation and control.