Experimental Characterization of Upper Trailing Edge Flaps for Transonic Buffet Control

Abstract

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, α = 3.5°. 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 α = 2.5°).

Connecting transonic buffet with incompressible low-frequency oscillations on aerofoils

“…2017; Caruana et al. 2005; D'Aguanno, Schrijer & van Oudheusden 2023) on affecting buffet could be possibly reinterpreted as due to their effect on the global flow field and especially boundary layer characteristics. Similarly, the results of Paladini et al.…”

Towards extending the aircraft flight envelope by mitigating transonic airfoil buffet

“…By counteracting the shock movement with trailing edge pressure changes induced by the flap movement, these devices can successfully control transonic buffet 42 – 46 . Their passive counterpart, i.e., a flap with a fixed deflection angle, is at least able to reduce the amplitude of the shock wave oscillations 47 , 48 . Such trailing-edge flaps are usually used as high-lift devices to improve the aerodynamic performance during take-off and landing.…”