Flow in the engine compartment: analysis and optimisation

Abstract

In the current sustainable development context, car manufacturers have to keep doing efforts to reduce the aerodynamic drag of automotive vehicle, and consequently their CO2 and greenhouse gas emissions. The cooling airflow through the engine compartment of vehicles contributes from 5% to 10% to the total aerodynamic drag. By means of a simplified car geometry, equipped with an engine compartment, flow in the engine compartment is analysed by three complementary approaches: an experimental approach, a numerical approach and an analytical approach. The experimental approach is mainly used to measure drag values and to explain the drag variations induced by modifications of the outlet location. The purpose of the numerical simulations is to evaluate the flow rates through the engine compartment and particularly through the heat exchangers. Finally, the analytical approach establishes a model to connect the aerodynamic drag with the cooling flow rate. Configurations favourable to low cooling drag values and high cooling flow rates are identified. They correspond to vehicles with an engine compartment outlet located at the rear end.