Body Force Model for the Aerodynamics of Inclined Perforated Surfaces

This is a joint experimental and computational research effort on the aerodynamics of perforated surfaces inclined to a freestream. The goal is to characterize the key parameters affecting the flowfield in order to construct a macroscopic computational model that obviates resolution of the detailed perforations. The model simulates the effects of the perforated surfaces by locally applying a body force term in the momentum equation. The study considers wedge-shaped deflectors used for jet noise reduction in turbofan engine nozzles in the form of flaps with varying angles and perforation shapes. The experiments measured the mean velocity field inside and in the wake of theflapswhile the numerical analysis comprised direct computations of simplifiedperforatedflaps and computations using the body force model. It is found that the effective porosity of the surface is affected by flow separation within the perforations. Theflowblockage of the separation regions is primarily a function of the angle to the freestreamand the ratio of the thickness to hole diameter. Accordingly, 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.