Wind Noise Measurements for Automotive Mirrors

In order to understand the flow and wind noise characteristics generated by the outside rearview (OSRV) mirror, a series of wind noise measurements for two production mirrors was conducted at the GM Aerodynamics Lab (GMAL) wind tunnel. These measurements included the time-averaged static pressures, surface noise sources, and far field propagation noise. The data obtained in this investigation will be used for future CFD numerical validations. The two mirrors chosen for the test are the GMT360 (a truck mirror) and the GMX320 (a sedan mirror). The test mirror was mounted on an elevated table which was specially designed for the current project to avoid any significant flow boundary layer buildup on the wind tunnel floor. The test conditions reported in this paper include four inlet speeds of 30, 50, 70 and 90 mph at 0 yaw angle. To record the wind noise sources, nine surface flush-mount microphones were used. The microphones were arranged in such a pattern that the sound directivity could be identified in the wake region downstream of the mirror. The far field noises were monitored at six locations by microphone probes located 18 inches above the table top surface. In addition to the microphones, 13 pressure taps were installed along the centerline of the table to record time-averaged surface pressures. Furthermore, noise data were also collected for the wind tunnel and the table without the mirror(s) for further comparison.