A Porous-Wall Acoustic Shield for Accurate Inlet Noise Tests

Abstract

A CFD study was conducted using the WIND NavierStokes code to investigate the effect of placement of an acoustic shield on flow distortion in the Engine Fan Simulator (EFS) inlet. The EFS inlet flow field was analyzed with and without the acoustic shield present at the flow conditions tested at the Boeing Large Subsonic Aeroacoustics Facility (LSAF). The spinner geometry and the effect of rotating fan were also accounted for. The Chimera overset-mesh scheme was used with the WIND code to generate effective boundary layer meshes for both the inlet and the acoustic shield surfaces. The turbulent flow properties were calculated using the k-ω SST turbulence model. Analyses were conducted using the parallel processing mode of the WIND code on an SGI ORIGIN 2000 computer system. The predicted results indicated that the solid-wall acoustic shield could cause inlet flow distortion (contamination of inlet noise) when it is placed at the forward position close to the inlet. A porous-wall acoustic shield design was developed to minimize the inlet flow distortion and was evaluated using CFD. The predicted results demonstrated the effectiveness of the porous-wall acoustic shield in avoiding inlet flow distortion. This paper describes the CFD analyses conducted for the EFS inlet under different test flow and acoustic shield conditions. A calibration procedure for inlet noise testing using the porous-wall acoustic shield is also described.