The Effect of Inlet Turbulence Specifications on the RANS CFD Predictions of a NASCAR Gen-6 Racecar 2018-01-0736

Turbulence modeling and the specific boundary conditions are among the two major simulation physics setup variables that affect the prediction veracity of a CFD simulation. The existing literature is rich with studies investigating the effect of the inlet boundary conditions on the predictability of a CFD simulation, and it is recognized that the turbulence characteristics of the freestream flow, viz. the turbulence intensity and length scale, can impact the simulation results significantly, even with the same turbulence model. However, none of these studies encompasses the significance of these two boundary specifications on the CFD analysis of a realistic racecar model. Against this backdrop, the purpose of this study is to systematically investigate the effect of different freestream turbulence specifications on the CFD predictions of the aerodynamic characteristics of a latest generation NASCAR Cup racecar model. Finite volume CFD simulations are carried out with: (a) five turbulence intensities of 0.1%, 0.5%, 1%, 5%, and 10% with a fixed turbulence length scale of 1 mm to examine the effect of the inlet turbulence intensity variability, and (b) five turbulence length scales, ranging from 0.1 mm to 10 mm, with a fixed turbulence intensity of 0.5% to evaluate the effect of turbulence length scales. This study reveals that the effects resulting from the choice of these two parameters are confined to their smaller values, as the Cup racecar aero characteristics tend to be independent of the freestream specifications at larger values of these two variables. Although one could expect very large values of either of these two parameters on a racetrack, these large values are too high and unrealistic in a wind-tunnel environment.