Interference effects of cooling airflows on a generic car body

Abstract

A significant contribution to the aerodynamics of road vehicles is caused by the cooling airflow. The cooling air flows through the engine compartment. Internal losses occur through the radiator and through the engine compartment. Additionally interference effects occur between the flow through the engine compartment and the flow field around the car. For most cars, all these effects result in additional aerodynamic drag, which is caused by the cooling airflow.In this study, numerical and experimental investigations were performed to understand the effects of cooling-air flow on the vehicle's aerodynamics. A generic car-model was equipped with a simplified underhood section. The cooling air mass flow could be varied to understand the cooling air mass flow on the cooling drag. A variety of measurements and numerical simulations were performed to explain the phenomenona of cooling air flows. Total pressure and hot-wire measurements in the wake of the car visualise the flow field, which is altered by the cooling air. Force measurements, surface pressure measurements and oil-streak patterns were performed to understand the influence of the cooling air on the bluff body. With the measurements and with the CFD-simulations, this study will explain where the cooling drag originates from and how the cooling air interferes with the external aerodynamics.