Measurements of Flow around a Split Flap Configuration

Experiments were performed on a two-element wing model with a split flap configuration to investigate the flowfield and to determine likely noise sources. Particle image velocimetry and oil flow were used to visualise and quantify the flowfield. On-surface microphones provided nearfield acoustic measurements. Qualitative spatial noise source maps were obtained using a phased microphone array. The flowfield around the split flap configuration was characterised by a high speed flow through the gap between the trailing-edge of the main element and the deflected flap. This flow was a significant source of noise. The noise levels measured depended on the size of the gap. At lower flap deflection angles when the gap was effectively reduced, lower levels of mid frequency noise were measured. For noise control, an open cell aluminium foam material was applied to the flap side-edge region. The effect of the porous material was to reduce the strength of the flap side-edge vortex. This slowed the flow through the gap resulting in a weaker shear layer, leading to a drop in the mid frequency noise.