Wake deceleration of a racecar multielement airfoil in ground effect

The importance of aerodynamic downforce in competitive motorsports has been well established. Much of this aerodynamic downforce is produced from the inverted multielement wings at the front and the rear of the car. While such a high-lift system is capable of producing high downforce as a result of the interaction between flows around adjacent elements, there may exist off-the-surface flow reversal, commonly known as wake bursting, causing an adverse effect on the downforce generated. Since the phenomenon of off-the-surface flow reversal occurs as a result of retardation of a wake under adverse pressure gradients, wake bursting is also referred to as wake deceleration in this study. A steady-state two-dimensional CFD analysis of a racecar multielement airfoil was carried out to study wake deceleration characteristics in ground effect. Simulations were performed using ANSYS® Fluent™, which is a finite-volume method (FVM) based commercial hybridgrid Reynolds-averaged Navier-Stokes (RANS) equations solver. Computational results were obtained using a two equation shear stress transport (SST) k-ω model coupled with a one equation intermittency transition model to predict the laminar-to-turbulent boundary layer transition. Effects of ground clearance height on the main element decelerated wake were analyzed. Effects of varying flap ratio, flap deflection, angle of attack, and gap sizes on the wake deceleration patterns have been investigated. It was found that decreasing the ground clearance led to a significant increase in the amount of the main element wake bursting. Increased wake bursting at higher angles of attack was found to have caused a drop in downforce without any surface-flow separation. Although the main element wake was strongly affected while varying each of these parameters, the size of the flap wake was not affected significantly.