The flow field of automobile add-ons - with particular reference to the vibration of external mirrors

The flowfield of externally mounted car mirrors is discussed and a wind-tunnel study of the local flowfield is presented. Mean velocities, pitch and yaw angles and turbulence intensities and spectra were measured using hot-wire anemometers. The flow is complex and turbulent due to a Vortex that is associated with the car A pillar and local turbulence intensities were found to reach 40%. The vehicle yaw angle was varied from -12 degrees to +12 degrees and was shown to have a strong influence on the flow characteristics. Translational and rotational vibrations of the mirror glass were also measured in the wind tunnel and on-road. At frequencies above about 20 Hz there was very close agreement between the on-road and wind-tunnel vibration spectra indicating that the main forcing functions were aerodynamic rather than arising from mechanical sources such as road-induced vibrations or rotational imbalances. (C) 1999 Elsevier Science Ltd, All rights reserved.