Cooling Inlet Aerodynamic Performance and System Resistance

This report is a contribution to the understanding of inlet aerodynamics and cooling system resistance. A characterization of the performance capability of a vehicle front-end and underhood, called the ram curve, is introduced. It represents the pressure recovery/loss of the front-end subsystem - the inlet openings, underhood, and underbody. The mathematical representation, derived from several experimental investigations on vehicles and components, has four basic terms:

• Inlet ram pressure recovery; free-stream energy recovered when the vehicle is moving
• Basic inlet loss; inlet restriction when the vehicle is stationary
• Pressure loss of the engine bay
• Engine bay-exit pressure

Not surprisingly, the amount of frontal projection of radiator area through the grille, bumper and front-end structure (called projected inlet area), and flow uniformity play a major role in estimating inlet aerodynamic performance. One experimental investigation demonstrated that the ram curve is independent (essentially) of the fan/shroud system installed in the vehicle. Another experiment showed that the engine-bay pressure loss (which includes the interference of the underhood package on fan performance) might be small compared to the other resistances. The universal characteristic map of fan and system performance can be used to track airflow changes during early vehicle design tradeoff studies.