On the Influence of the Near Wall Formulation of Turbulence Models for Prediction of Aerodynamic Coefficients for Ground Vehicles

Numerical and modeling errors in computational aerodynamics consist of multiple components. Previous investigations at Volvo have shown that low Reynolds k-ε models generally give better levels in pressure over the rear base area of the car than the corresponding wall function based model. However, these computations were carried out on car shapes without wheels. This paper presents numerical simulations of the flow field around three versions of the Volvo validation car series (VRAK). The geometry is a typical car with flat floor and simplified tires. The three car models differ by their rear shape. The configurations are: one with a nearly flat base, a fastback with a sloping rear window, and a car with a roof wing.

The influence of the near wall formulation of the standard k-ε model on drag and lift is investigated. The performance of the low Reynolds number version of the cubic k-ε model by Suga [7] is also investigated. The results from the simulations are compared with each other and with experimental data in terms of aerodynamic drag, lift and surface pressure. Sensitivity to boundary conditions and grid resolution is reported. The low Reynolds number linear k-ε model investigated here is numerically robust, and nearly grid independent solutions are obtained. This model gives a higher contribution to drag from the front of the car than the other models tested. The study indicates that the low Reynolds number version of the cubic k-ε model by Suga [7] is well suited for drag predictions on basic car shapes.