Investigations in a Cooling Air Flow System under the Influence of Road Simulation 2008-01-0796

This paper presents some recent results concerning the generation and minimization of cooling air drag, achieved in an integrated approach of numerical and experimental investigations. The baseline configuration of a production cars' cooling air flow system is analyzed. The analysis of the created drag shows, that most of the force changes due to the cooling air flow appear in the front region of the vehicle. However, the forces generated by heat exchangers are only a small share of the total changes. Additional drag is generated for example by the front wheels and by the components of the underhood compartment.

The investigation of the influence of the vehicle rear end shape on the aerodynamics of the cooling air flow system shows, that two similar cars with different rear end shapes (notchback and squareback) can feature different cooling air drag values. This difference is independent of the cooling air flow rate since these values were found to remain constant for the different rear end shapes by experiment. The cooling air drag value, on the other hand is largely affected by the ground simulation technique used in the wind tunnel. The influence of the vehicle rear end shape on the cooling air drag is especially significant for the investigated production vehicles in cases without any ground simulation. It disappears with the use of Road Simulation in the wind tunnel. The region around the front wheels and therefore the wheel arch flow due to the cooling air can be identified as the main cause for these differences, leading in combination with the vehicle shape to differences in the cooling air drag.