Investigation of Side-View Mirror Flow-Induced Vibration Phenomena

Abstract

The primary objective of this research is to develop an understanding of the flow mechanisms which induce side-view mirror vibrations. The unsteady nature of the flow over side-view mirrors causes unsteady aerodynamic load distributions and flow-induced vibrations on the mirror assembly. These vibrations generate blurred rear-view images and higher noise levels, affecting the safety and comfort of the passengers. Geometrical design features of side-view mirrors exacerbate the flow-induced vibration levels of the mirror assembly significantly. This work quantifies the impact of these design features on the vibration amplitude; develops a methodology for testing mirror vibrations in a small, low-speed wind tunnel using only the mirror of interest; and delves into the interactions between the bluff body mirror geometry and its wake. Two similar side-view mirror designs, a baseline design and a turn-signal design, were investigated. The baseline mirror has a sharp-edged corner near the trailing edge, while the turn-signal design has an edge with an increased radius of curvature for the tip profile. A laser-based vibration measurement technique was developed and used to quantify vibration levels. Flow visualization, Particle Image Velocimetry (PIV), Constant Temperature Anemometry (CTA), and Surface Stress Sensitive Film (S3F) techniques were used to understand the separation characteristics over the mirrors since the time-dependent changes in separation location directly affect the unsteady loading on the mirror. The flow over the turn signal mirror with larger tip radius has larger excursions in the separation location, a wider wake, increased unsteadiness, and higher vibration levels. Results at the high Reynolds numbers for these test conditions indicate the absence of a discrete vortex shedding frequency. However, vortical structures in the wake are correlated with unsteady movement of the separation location.

Numerical investigation and experimental test on aerodynamic noises of the bionic rear view mirror in vehicles

“…Experimental results showed that aerodynamic noise caused by the rear view mirror was increased obviously with the increased vehicle speed. Tomac [13] quantitatively studied the impact of those design features of rear view mirrors on the vibration amplitude; developed a methodology for testing mirror vibrations in a small, low-speed wind tunnel using only the mirror of interest; and delved into the interactions between the bluff body mirror geometry and its wake. Onur [14] has tested the flow fields over a rearview side mirror in a wind tunnel and the results showed that the static pressures are presented different distribution over the rear view mirror and took smaller values at the separation points of the boundary layer from the mirror surface.…”