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To-days low-noise high-bypass-ratio engines have made airframe noise for large commercial aircraft in the approach configuration to be compatible to that of the engines. As a consequence, flow noise from landing gears and from high lift devices (HLD) on wings -and its control -will become ever more important. In a study, dedicated to HLD flow noise, parametric wind tunnel experiments were performed on scaled wing sections in the Aeroacoustic Wind Tunnel Braunschweig, on a complete scale model aircraft and a full scale wingsection in the German-Dutch Wind Tunnel to identify relevant airframe noise mechanisms and develop noise prediction schemes. As one essential result of these tests deployed slats were identified as prominent noise contributors. Based on an extensive set of farfield noise data and on first results from measurements of the unsteady local flow properties in the slat area the effects of flow velocity and aircraft angle-of-attack on slat noise radiation characteristics were determined. The test results support the assumption that slat noise originates from the upper slat trailing-edge and scales with the slat cove vortex dimension. As a consequence the transposition of slat noise data from scale model tests towards a full scale situation can approximately be based on the geometric scale factor. Based on the findings of this experimental study a simplified source model is considered for slat noise prediction.

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