Effect of Aero Covers on Underfloor Wind Noise; Conclusions from a Wind Tunnel Validated Aero-Vibro-Acoustic Model

Low frequency interior wind noise is typically dominated by underfloor flow noise. The source mechanisms are fluctuating surface pressure loading from both flow turbulence and acoustic field levels developed in the semi-reverberant cavity between floor and road. Previous studies have used computation fluid dynamics (CFD) to estimate the aero-acoustic loading applied to a vibro-acoustic model, which is then used to predict the transmitted interior wind noise. This paper reports a new perspective in two respects. First it uses novel surface pressure microphone arrays to directly measure the underfloor aero-acoustic loading in the wind tunnel. Second, it considers two different underfloor aerodynamic configurations - with and without lightweight aero cover panels, which are installed primarily to reduce aerodynamic drag. Results are presented showing the relative contributions of turbulence versus acoustic sources and demonstrating validation of the aero-vibro-acoustic model for predicting floor vibration response and interior wind noise. The model explains the measured effectiveness of lightweight aero cover panels in reducing underfloor wind noise. The model is then used to identify design changes capable of improving the noise reduction performance of aero covers.