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Wake flow modification of vehicle external door mirror with slots

A passive flow control method is applied to a vehicle external door mirror by introducing flow from a slot drilling from the front surface to four slots around the rear surface. The wake flow fields behind the door mirror and slotted door mirror are experimentally investigated via particle image velocimetry measurements at a Reynolds number of 12,736. The time-averaged flow fields suggest that the reverse-flow region of the slotted door mirror is reduced and pushed downstream; correspondingly, the turbulent kinetic energy of the slotted door mirror is reduced, implying the suppression of unsteadiness and a reduction in the drag force acting on the door mirror. As a result of the jet flow, the wake flow of the slotted door mirror exhibits a weaker spatial correlation and a smaller length scale, indicating the suppression of large-scale vortex shedding and the enhancement of small-scale flow motion by the slots. The jet flows from the left and right slots of the slotted door mirror prevent the upper and lower shear layers from interacting with each other, which promotes symmetric vortex shedding in the near-wake region. The power spectral density and modal energy distributions suggest that the strength of the primary vortex shedding is reduced by the slotted door mirror. The spatial patterns of the first two proper orthogonal decomposition modes suggest that the jet flow distorts the dominant large-scale structure, reducing the strength of the flow oscillation behind the slotted door mirror. The spatial distributions of modes 3 and 4 suggest that the symmetric vortex shedding is enhanced by the jet flow from the slotted door mirror.