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 simulations of the flow field and aerodynamic forces are possible, but often leads to long simulation time. For a given solver, the two most significant aspects of the simulation time is the spatial temporal resolution. In this study, these two aspects were investigated using the realistic vehicle model DrivAer with notchback geometry as the test case. To ensure an accurate comparison with wind tunnel measurements, performed at TU Berlin, a large section of the wind tunnel was also modeled. All simulations were performed for a Reynolds number of 3.0 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 showed small differences to the finest investigated mesh, as well excellent agreement with wind tunnel measurements. An investigation of the temporal resolution was made, in order to see its effect on the simulation speed and accuracy of the results. The finest temporal resolution resulted in a Courant-Friedrichs-Lewy (CFL) number less than unity, while the coarsest reached CFL number of around 100. From the results, it can be seen that it is possible to reduce the simulation time with more than 90 % (CFL 20) and still keep sufficient accuracy.