Study on the Capability of an Open Source CFD Software for Unsteady Vehicle Aerodynamics 2012-01-0585

A wind-tunnel experiment investigating unsteady flow phenomena around a generic notchback during single crosswind gusts is modeled with the open source CFD package OpenFOAM®. The overall objective is to assess the capability and accuracy achieved by the simulation tool with respect to its potential for industrial usage. Transient yaw simulations apply a sliding interface between two computational grids, which are generated using the commercial software Spider®. It is shown that a stable simulation process is feasible but requires long computation times. The physical accuracy of the investigated phenomena depends on the computational grid and on the turbulence model used. Although the obtained aerodynamic loads qualitatively correspond with the experimental results, the absolute values are not satisfactory when working with a coarse grid with 6.2 million cells. Then, characteristic surface pressure distributions and their transient development differ from the experimental data. Consequently, the phase shifts of the computed load transients against the model motion are incorrect. In contrast, steady calculations for constant yaw on a refined mesh with 10.9 million cells using alternative turbulence models deliver better results. A realizable k-ε model proves to predict the wake flow most accurately, since solely this model captures the dominating leeward inflow at the rear lights observed in the experiment. As a consequence, the estimation of aerodynamic loads being relevant for the driving stability of vehicles in gusty crosswind is largely improved by using this setup. Considering the additional computational resources needed for performing transient yaw simulations with the improved setup, this was not accomplished in this study.