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TRAILING VORTICES IN THE WAKE OF A CAR
Japan Society of Mechanical Engineers

The photo was taken in a wind tunnel, looking upstream toward the rear of the car. A grid with small cotton tufts attached to it is placed in the wake of the car, and the tufts align themselves with the local flow direction and indicate the streamline direction. Large counter-rotating vortices are revealed. Next time you see a car on a cold day, notice how the exhaust fumes (mostly condensed water) are entrained in the wake of the car to show the presence of the vortical flows. A car travelling along a dirt road on a dry day will also reveal these flow patterns.

From Visualized Flow, Japan Society of Mechanical Engineers, Pergamon Press, 1988.

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