Flap Vortex Management Using Active Gurney Flaps

Abstract

An experimental study was conducted to assess the applicability of limited-span Gurney flaps for altering the flap-edge vortex characteristics of a swept constant-chord half-model with a commercial aircraft airfoil and high-lift system (slat and flap). The strategy employed was based on the well-known vortex roll-up relations between the span loading and the wake that were extended and modified to include configurations with flapped wings. Phase I of the study involved the testing of static Gurney flaps mounted at the trailing edge and flap edge, in which different flap heights and fractions of flap span were evaluated. Data acquisition included particle image velocimetry measurements downstream of the flap edge, six-component load measurements, and surface pressure measurement on the main element and in the flap-edge region. The Gurney flaps produced significant variation of the vortex centroids, up to 5.3% of the semispan (13.1% of chord), with corresponding small changes to lift and drag coefficients. Phase II of the study involved the evaluation of dynamically deployed Gurney flaps, in which phase-averaged particle image velocimetry measurements were made of the vortex trailing the flap. This was motivated by the desire to periodically perturb the vortex centroids, with a view to exciting wake instabilities and thus triggering a faster decay. When driving the Gurney flap and hence perturbing the vortices at wavelengths shorter or longer than the wingspan, the authority over the vortex centroids did not materially change.