Accuracy and Speed for Scale-Resolving Simulations of the DrivAer Reference Model 2019-01-0639

In aerodynamic development of ground vehicles, the use of Computational Fluid Dynamics (CFD) is crucial for improving the aerodynamic performance, stability and comfort of the vehicle. Simulation time and accuracy are two key factors of a well working CFD procedure. Using scale-resolving simulations, accurate predictions of the flow field and aerodynamic forces are possible, but often leads to long simulation time. For a given solver, one of the most significant aspects of the simulation time/cost is the temporal resolution. In this study, this aspect is investigated using the realistic vehicle model DrivAer with the notchback geometry as the test case. To ensure a direct and accurate comparison with wind tunnel measurements, performed at TU Berlin, a large section of the wind tunnel is included in the simulation domain. All simulations are performed at a Reynolds number of 3.12 million, based on the vehicle length. Three spatial resolutions were compared, where it could be seen that a hybrid element mesh consisting of 102 million cells only revealed small differences to the finest mesh investigated, well as showing excellent agreement with wind tunnel measurements. An investigation of the temporal resolution is performed, in order to see its effect on the simulation time/cost and accuracy of the results. The finest temporal resolution resulted in a Courant-Friedrichs-Lewy number less than unity, while the coarsest reached a CFL number of around 100. From these results, it is seen that it is possible to reduce the simulation time with more than 90 % (CFL 20) and still keep sufficient accuracy of the forces and important features of the flow field.