Structures of flow around a full scale side mirror of a car with relevance to aerodynamic noise

Abstract

Noise radiated from a side mirror has been studied using spatial and temporal characteristics of surface-pressure fluctuations. The relevant structures of turbulent flow were examined by visualization and by local measurements of dynamic pressure behind a full-scale side mirror, which was placed in a wind tunnel and exposed to an approach velocity of 42 m/s. The results showed that sudden changes of surface curvature and flow separations behind the mirror support led to the generation of significant pressure fluctuations. The wake vortices were strongly influenced by the curvature effects at the corners of the mirror casing, which resulted in selective amplification of naturally occurring modes. As a result, turbulent energy was transferred from large-scale vortices to smaller scales and this process was promoted by the interactions with the vortices shed from the mirror support.