Measurements of Flow Around a Flap Side Edge with Porous Edge Treatment

Abstract

Wind-tunnel experiments were performed to investigate a flap side-edge vortex, which is a contributor to airframe noise. The flowfield investigation showed that the peak turbulent stresses were contained in the shear layer that rolled up to form the flap side-edge vortex. The wake from the main element was also entrained by the side-edge vortex. The near-field pressure fluctuations where the turbulent shear layer impinged on the flap side edge were broadband in nature from a Strouhal number of 10 to 50. Hot-wire measurements on the downstream vortex identified a broadband instability centered around a Strouhal number of 13.2. A porous side-edge treatment was applied to the half-span flap to modify the flap side-edge flowfield. The effect of applying a porous side edge was to reduce the Reynolds stresses contained within the vortex and the shear layer that formed it. The porous material also had the effect of displacing the vortex further away from the flap surface. This led to a reduction in the broadband pressure perturbations measured at the flap side edge. Compared with the accuracy of the measurements of the aerodynamic forces, the aerodynamic impact of the porous flap side edge was almost negligible.