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The design of more efficient automotive cooling systems requires better understanding of the losses in fluid mechanical energy through conversion to thermal energy for the air flow through the front end cooling openings. A wind tunnel study with simplified models has been conducted to investigate the factors affecting the cooling opening mechanical energy losses. The data from this study have been sucessfully correlated using newly defined dimensionless parameters. The influence of the controlled geometrical factors are clearly identifiable with the data presented in dimensionless form. An algorithm has been devised which accurately correlates the behavior of a combination of cooling openings given the behavior of each of the openings operating individually.

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.

Wind tunnel force-balance and wake-traverse tests were made on .154-scale car models with various degrees of streamlining to determine the significance of ground treatment for increasing levels of aerodynamic cleanness. The wake-traverse analysis included investigations of spanwise distributions of vortex and viscous drag, which gave insight into the flow mechanisms involved. It was found from these tests that thick, uncontrolled tunnel-floor boundary layers yielded wakes with viscous “side-lobes” at floor level, which were absent with a moving ground representation. For “bluff car designs, this was the only effect. For “slippery” designs, more typical of modern design practice, other more significant changes were noted. Measured changes in trailing-vortex strength and the associated vortex drag suggested that very low-drag designs experience an increase in effective angle-of-attack when the ground is fixed.

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.