Experimental investigation of wake structure around an external rear view mirror of a passenger car

In order to investigate the wake structure around the external rear view mirror of a passenger car, velocity vector fields and spectra of velocity fluctuations in the mirror wake were measured by hot wire anemometry and laser Doppler velocimetry in a blow down wind tunnel at Re=200,000. Time-averaged velocity fields were measured on one streamwise vertical plane and three cross-sectional planes. In early wake, an alternating vortex was found along the upper and the lower edge line of the mirror housing, and in the downstream, a vortex wrap like a tip vortex was also found. A reverse flow region was observed at up to 1.2 times the mirror vertical width. In the moment measurements on the cross-sectional planes, peak values of the root-mean-square fluctuation velocity appeared near the tip edge of the mirror due to significant vortex shedding. Corresponding skewness and kurtosis factors clearly deviated from the Gaussian distribution, which shows mirror wake boundaries. Spectral characteristics of the mirror wake obtained on the cross-sectional planes showed that the frequencies of most of the vortex shedding in the mirror wake was less than 50 Hz, and that the peaks of the vortex shedding energy were near the outside edge of the mirror housing.

► Reverse flow region was observed at up to 1.2 times the mirror vertical width.
► Alternating vortices developed counter-rotating separation bubbles in a mirror wake.
► Vortex wrap like a tip vortex of the fixed wing was formed in a mirror wake.
► Most dominant frequencies of vortex shedding were found to be below 50 Hz.