Experimental Characterization of Upper Trailing Edge Flaps for Transonic Buffet Control

This experimental study investigates the possibility of controlling transonic buffet by means of a trailing edge flap with an upward deflection (referred to as upper trailing edge flap, or: UTEF). Different geometries (straight and serrated) and dimensions of UTEFs (with heights ranging between 1 and 2% of the chord) have been studied with respect to their impact on the buffet behavior. The effectiveness of the UTEFs has been investigated with schlieren and particle image velocimetry (PIV) in the transonic-supersonic wind tunnel of TU Delft at Ma = 0.70, alpha = 3.5 degrees. The schlieren results demonstrated the efficacy of the use of UTEFs for reducing the range of the buffet oscillations when the height of the UTEF was equal to at least 1.5%c. This result was corroborated by a flow characterization with PIV data and which highlighted that, in presence of a control system, not only the shock oscillation range is reduced but also the intensity of the separated area pulsation. The use of serrated UTEFs, despite having an effect on the local flow field, was found to be ineffective in alleviating buffet oscillations. The adoption of the best behaving UTEF configuration (straight 2%c UTEF) proved to only slightly alter the circulation value compared to the clean configuration, while it also proved to be effective in an off-buffet condition (Ma = 0.74 and alpha = 2.5 degrees).

Automated summary

This experimental study investigates the potential of using an upward deflection trailing edge flap (UTEF) to control transonic buffet. Different geometries and dimensions of UTEFs were studied and the results showed that the straight 2% chord UTEF configuration was the most effective in reducing buffet oscillations, while serrated UTEF configuration was found to be ineffective.