Modeling of Wedge-Shaped Porous Flaps for Jet Noise Reduction

This article presents experimental and computational analyses of the flow field associated with porous wedge-shaped deflectors used for jet noise reduction in turbofan engines. The goal is to characterize the key parameters affecting the flow field in order to construct a macroscopic computational model of the deflector that obviates resolution of its detailed perforations. The model simulates the effects of the inclined porous surfaces by applying locally a body force term in the conservation equations. The investigation encompassed wedge deflectors, in the form of flaps, with varying angles and different perforation shapes. The experiments measured the mean velocity field inside and in the wake of the flaps. The numerical effort comprised direct computations of simplified perforations and approximate computations using the body force model. It is found that the flow field is affected not only by the porosity of the deflectors but also by the illumination angle defined by the shape and thickness of the perforation. A formulation for the body force model is proposed that incorporates this finding. The resulting velocity field is in good agreement with the experiments and with the direct computations.