Flow Field Measurements to Characterize Flap Side-Edge Noise Generation

Abstract

n this paper, the relation between noise generated at flap side-edges (FSE) and mean flow characteristics in the vicinity of the FSE solid surface is investigated. Of interest is (1) the identification of mean flow features near the flap tip which are important to FSE noise generation, (2) the extraction of quantitative parameters relating flap settings to the emitted noise levels and, finally, (3) the formulation of a prediction scheme based on these observations. The results of the investigation demonstrate that FSE noise can be properly represented by the summed contributions of two independent source mechanisms. Moreover, this new formulation necessitates only a limited knowledge of the mean flow parameters in the vicinity of the FSE to model the noise emission. It is assumed that unsteady vorticity fluctuations, originating from the unstable pressure side shear layer, sweeping over the forward half of the upper tip edge, lead to midto- high frequency noise production. Flow unsteadiness in the proximity of the suction side surface near the FSE aft half, are assumed to be the main contributor in the low-to-mid frequency range. A prediction scheme is formulated and validated for a wide range of experimental measurements at small scale wing configurations. This new formulation only necessitates knowledge of the flap chord length and lift coefficient to provide accurate estimates of the far field noise radiation.