Accuracy of Drag Predictions on Cars Using CFD - Effect of Grid Refinement and Turbulence Models

Computations of the flow around a basic car shape, the Volvo ECC, have been done using different turbulence models: two lowRe k-ε model, the standard k-ε model and the IP and Gibson-Launder version of the Reynolds Stress Model (RSM). Results from the different computations are compared to windtunnel measurements of drag, pressure and velocity. The effect of the turbulence model on the accuracy of predicted pressure and drag is studied. To provide a basis for this work grid refinement studies have been performed to study the effect of mesh resolution and mesh quality on the error in pressure and drag. It is shown that mesh quality is important to preserve the order of the difference schemes but that the grid related error may be virtually eliminated. Further the computations show that a lowRe k-e model yields the best prediction of experimental data.