The A-Pillar is defined as the region where the windshield joins the side window and is a source of large vortex shedding which consequently produces sizeable levels of induced drag. This flow behaviour can be attributed to the accelerated flow over the A-Pillar meeting the lower velocity flow travelling along the side of the car. This difference in flow velocity - and thus static pressure - results in vortex shedding similar to that found on the wing tips of aeroplanes. The presence of wing mirrors mounted on the A-Pillar encourages this vortex shedding due to the wing mirror decelerating the flow in this region and thus increasing the difference in velocity, and consequently pressure (as shown in Figure 3).
Intelligent design and placement of the wing mirror can help reduce this vortex shedding and therefore can have a significant influence on the overall drag characteristics of a vehicle.
