An objective function for estimating cooling efficiency of battery electric vehicles

Maintaining optimal temperatures across the various components and the cabin of a passenger vehicle requires exchange of heat with the surroundings, typically accomplished by allowing air to flow through the underhood. This, however, adversely affects the aerodynamic drag. The magnitude of this penalty depends on several factors, including the location of the air inlet and outlets, and the required cooling airflow rate which may vary even at a constant driving speed. In this study, the cooling efficiency of the AeroSUV, was assessed across a range of airflow conditions, for six outlet configurations placed in three key areas: the front wheelhouse, the underbody, and the hood. High-fidelity numerical simulations were performed on a modified version of the vehicle equipped with active grille shutters and a fan to provide a large range of airflow rates. With fully opened shutters, the wheelhouse outlet delivered the highest airflow rates, while the hood outlet provided the greatest efficiency, exhibiting the lowest aerodynamic drag for a given flow rate. Powering the fan introduced high energy losses, equivalent to 0.015 C D , which must be included in the drag calculation for a fair evaluation of performance among the different exits. The wheelhouse outlet presented a near-linear efficiency trend, whereas the hood outlet showed improved efficiency at higher flow rates. To evaluate overall performance, an objective function was defined by averaging aerodynamic drag and fan power across the desired flow-rate spectrum. Results indicated that the optimal configuration depends on the operating condition: the wheelhouse outlet was most effective at higher flow rates, while the hood outlet was more suitable for lower flow rates.