Flow over a realistic car model: Wall modeled large eddy simulations assessment and unsteady effects

Numerical simulations are carried out on the flow over a realistic generic car geometry, the DrivAer-fastback car model. Pure large eddy simulations (LES) and wall-modeled large eddy simulations (WMLES) are used and compared to numerical and experimental results to assess the validity of these approaches when solving the flow field around complex automotive geometries. Results show a 70% CPU time reduction when using the wall model. Drag coefficient results show the influence of the wall model on coarser meshes is positive, reducing the difference on those obtained using finer meshes. Pressure profiles exhibit mixed results. The wall model used works well in adverse pressure gradients and smooth geometry changes. Results worsen in sections where the flow detaches and experiences large pressure drops. Flow structures and unsteady effects around the car are also analyzed, obtaining several characteristic frequencies for the different flow structures encountered. It should be noted that the present investigation shows how WMLES helps to reduce the computing cost and response vs pure LES, while providing high-quality unsteady data, although computational cost remains high. Results show potential in the introduction of this tool as a competitive simulation strategy for complex geometries.