PIV Analysis Comparing Flow Past NASCAR COT Rear Wing and Spoiler Traveling Forward and Backwards

There have been claims that the rear wing on the NASCAR Car of Tomorrow (COT) race car causes lift in the condition where the car spins during a crash and is traveling backwards down the track at high speed [1,2]. When enough lift is generated, the race car can lose control and even become airborne. At least in part, to address this concern, a new rear spoiler was designed by NASCAR to replace the wing and prevent this dangerous condition. This paper looks at the flow characteristics of both the rear wing and the new spoiler using particle image velocimetry (PIV) to provide qualitative analysis as well as flow visualization. In particular, the interaction of these downforce devices with "roof flaps" (which are designed to prevent lift) is explored. These experiments are done in a continuous flow water tunnel having a cross section of 1.0 m² using a simplified 10% scale model COT body with either a wing or spoiler attached. Flow structures are identified and compared for both the wing and spoiler under Reynolds number conditions between 1x10⁵ and 3x10⁵. We also review the same conditions when the car is traveling backwards as it might during a crash. This paper highlights the differences and similarities between the two devices, providing insights into the advantages and disadvantages of the new design. The data suggest that the ineffectiveness of the wing in preventing lift when traveling in reverse is due to the fluid stream traveling underneath the wing. This flow may cause a decrease in downforce on the wing and allow the mean stream fluid to reattach to the roof earlier than on the car fitted with a spoiler.