Computational Method to Determine the Cooling Airflow Utilization Ratio of Passenger Cars Considering Component Deformation

Abstract

In order to improve the efficiency of passenger cars, developments focus on decreasing their aerodynamic drag, part of which is caused by cooling air. Thus, car manufacturers try to seal the cooling air path to prevent leakage flows. Nevertheless, gaps between the single components of the cooling air path widen due to the deformation of components under aerodynamic load. For simulating the cooling airflow utilization ratio (CAUR), computational fluid dynamics (CFD) simulations are used, which neglect component deformation. In this paper, a computational method aiming at sufficient gap resolution and determining the CAUR of passenger cars under the consideration of component deformation is developed. Therefore, a partitioned approach of fluid structure interaction (FSI) simulations is used. The fluid field is simulated in OpenFOAM, whereas the structural simulations are conducted using Pam-Crash. In order to validate the simulation results, the CAUR of a battery electric and an internal combustion engine powered vehicle is determined at a specifically developed cooling air test rig. Additionally, wind tunnel measurements determining wall pressures and component deformations are conducted. Furthermore, an experimental method was developed to measure three-dimensional deformations applying the “Structure from Motion” method to phosphorescent marker points. It could be shown, that areas of deformation can be detected by the developed simulation method and that the deformations negatively influence the CAUR. Comparing the results of the FSI simulations to single CFD simulations, this work was able to reduce the maximum estimation error of the CAUR from +12 %P to +3 %P. Finally, remaining error sources are outlined.