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An experimental investigation of the underhood cooling airflow of a production passenger car has been carried out with a 3/8-scale model in a water filled tow tank at Texas Tech University and with a production vehicle in the Maritime Dynamics Laboratory tow basin of SSPA Maritime Consulting AB in Gothenburg, Sweden. The primary objectives for both the 3/8 and production vehicle investigations were to obtain a better understanding of the cooling airflow behavior within the engine compartment of an automobile and to identify the major factors influencing the flow field. The tests consisted of running a fan on a stationary and moving vehicle with pressure measurements and extensive flow visualizations within the engine bay.

Over the past decades substantial advances have been made in reducing the drag of automobiles. As might have been expected, the early performance gains were relatively easy but future gains are becoming increasingly difficult to achieve. A diagnostic method which is both quantitative and independent of the model is sorely needed. This paper discusses experimental measurements of wakes behind. 154-scale model production cars and comparisons to balance measurements. Models, test equipment, and data analysis are discussed. Explanations of the wake flow results in relation to the car modifications are included. Correlation of the wake drag integral to the balance drag measurement is good; however, some questions remain relative to the influence of fixed-ground skin friction.