Characterization of Separated Turbulent Flow Regions in CFD Results for a Pontiac NASCAR Race Car 2004-01-3556

Computational fluid dynamics (CFD), is used in the GM Racing NASCAR program to support race team operations and aerodynamic research projects. To function as a practical tool, the setup process for industrial CFD tools must use real engineering models of race vehicles and must realistically simulate on-track aerodynamic conditions. Then, these tools must provide realistic simulation for high-Reynolds number flow over the complex geometry of a real race car. The biggest challenge to CFD tools is accurate prediction in regions of separated turbulent flow, such as flow in the wake and underbody regions. These regions have a significant effect on race vehicle performance. Because of the critical nature of separated turbulent regions both for better understanding of vehicle aerodynamics and for evaluating accuracy of the CFD results, these regions warrant detailed study. This paper applies methods of characterizing turbulent features to analysis of flow over a 2003 Pontiac NASCAR vehicle at several Reynolds numbers and with simulation configurations representing both track testing and wind tunnel testing. Time-averaged turbulence quantities are used to compare the contributions of resolved turbulence scales to scales represented by the turbulence model. Time-series and frequency-domain analyses are performed on data obtained from six different separated flow regions around the vehicle, in order to describe the characteristics of turbulence in each region. Finally, the connections between the time-dependence of aerodynamic forces with pressure and velocity fluctuations in the turbulent flow regions are explored.