Investigation of Vibration Phenomena Induced by Air Flow Over Side View Mirror

Abstract

This work develops an understanding of the flow mechanisms that induce vibrations on automotive side view mirrors. 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 mirror functionality and passenger comfort. Certain geometrical design features of side view mirrors can 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 were investigated in this work by using laser-based vibrometry, flow visualization, particle image velocimetry, hot film anemometry, and surface stress sensitive film techniques. The magnitude of the vibrations was found to depend on the level of excursion in the dynamic location of flow separation, particularly when characteristic flow frequencies couple with the mirror housing natural frequency.