Scale-Resolved and Time-Averaged Simulations of the Flow over a NASCAR Cup Series Racecar 2023-01-0735

In spite of growing popularity of scale resolved transient simulations, like the Detached Eddy Simulation (DES), among the mainstream automotive OEMs for the aerodynamic optimization of the production vehicles, Reynolds Averaged Navier-Stokes (RANS) simulations is still the most widely used Computational Fluid Dynamics (CFD) approach in motorsports. This is partially due to the usage-limitations imposed by the sanctioning bodies like, the FIA and NASCAR, restricting not only the hours of wind tunnel operation but also limiting the amount of CFD compute resource. This, coupled with speed requirements for aerodynamic development prevent the widespread use of scale-resolved modeling, such as Large Eddy Simulation (LES) or Detached Eddy Simulation (DES) methodologies that require an order of magnitude more computational resources. However, a number of investigations on the efficacy of turbulence modeling approaches using the Ahmed body and DrivAer showed that the hybrid turbulence modeling increases the accuracy of the numerical predictions of force coefficients and general flow field. However, such studies involving a NASCAR Cup racecar geometry is yet to be seen. This paper, thus, presents an investigation of the effectiveness of the Shear Stress Transport (SST) k-ω based Improved Delayed Detached Eddy Simulation (IDDES) model for the prediction of the flow-fields around a Gen-6 NASCAR racecar. The IDDES simulations were validated against moving-ground, open-jet wind tunnel (Windshear) data using two ride-heights and two crosswind angles. The primary objectives of this study are, firstly to develop a framework for SST k-ω based IDDES simulation, and secondly, compare and contrast flow field predictions by the RANS and IDDES approaches. Additionally, a spectral analysis of all force and moment coefficients is presented to aid in the analyses presented in this study.