Automotive Mirror Wind Noise Simulations and Wind Tunnel Measurements

Numerical simulations using Fluent were conducted to study the wind noise generated by GMT 360 mirror, one of the two mirrors mounted on the top of a specially designed table in the GM aerodynamics Lab (GMAL) wind tunnel. This study is part of an on-going project to develop a transient CFD procedure to accurately predict wind noises generated by the exterior surfaces of a moving vehicle. This paper focuses mainly on the numerical aspects of using large eddy simulation (LES) to predict both the flow and noise for the GMT 360 mirror with inlet speeds of 70 and 90 mph at 0 yaw angle. The design and scope of the wind tunnel test are also described. The mirror-on-the-table test was done with four flow speeds, 30, 50, 70 and 90 mph and three yaw angles, 0, -10 and +10 degrees for each mirror. The data collected during the test are: (1). time averaged static pressure along the centerline of the table, (2). nine surface microphones for noise sources, and (3). six far field microphones, 18 inches above the top surface of the table. The Fluent’s LES approach for wind noise predictions were conducted with reasonably fine mesh, up to 18 millions. Both dynamic and constant coefficients in the Smagorinsky sub-grid scale (SGS) model were used. It reveals that the LES simulations with the dynamic coefficient show improved accuracy than the model with the constant coefficient despite the fact that both models, in general, compare very favorable for the static pressure distribution and the noise spectra for both flow speeds. The transient LES result right above the table surface shows a very complex flow structure which is responsible for the noise generation.