Investigation of Three-Dimensional Shock Control Bumps for Transonic Buffet Alleviation

This experimental study investigates the use of shock control bumps (SCBs) for controlling transonic buffet. Threedimensional SCBs have been applied on the suction side of an OAT15A supercritical airfoil with the experiments conducted in the transonic-supersonic wind tunnel of Delft University of Technology at fully developed buffet conditions (M alpha = 0.7, alpha = 3.5 deg and Re = 2.6 x 10(6)). The effectiveness of the SCBs for different spanwise array spacings (ranging from 20 to 30%c) was verified using two optical techniques: schlieren visualization and particle image velocimetry. Both techniques confirmed the potential of controlling buffet using such devices, resulting in a reduction of the flow unsteadiness in terms of both shock oscillation and pulsation of the separated area. A dedicated particle image velocimetry investigation in a spanwise-chordwise measurement plane was conducted in order to characterize the effect of the spatial distribution of the bumps, focusing on the interaction of the shock-wave structures along the span. The configuration with a spacing of Delta(ySCB) = 25%c was demonstrated to be the most efficient in reducing the transonic buffet oscillations and was able to reduce the reverse flow region size as compared to the clean configuration.