Okay, after 4 years of FSAE, I give up trying to understand FSAE radiator ducting.
Convention is to have a diverging inlet (slow the air down), radiator, and then converging outlet (usually with a fan at the outlet). We've typically followed this convention
Design judges support this, the Smith books support this, everyone seems to support this.
However, everyone's support for this seems to stem from WWII heat exchanger research for aircraft flying at 400 mph.
WWII aircraft Goals: Reduce Drag
FSAE Goals: Don't melt the engine, screw drag
What I mean by this is, in FSAE (at least for our team), our primary concern is making sure we don't overheat the engine when we are reaming on it at 25 mph for extended periods. Saving 4 lbs of drag at 29 mph by having a small entrance to the radiator duct means nothing.
I guess it just frustrates me because every calculation I know how to do from fluids/heat transfer/common sense, tells me to make the entrance AT LEAST the same size as the radiator if you are concerned about mass flow rate and not drag.
I just finished a CFD study of external flow over the body/ducting and it also shows highest mass flow rates at the radiator with a duct entrance area at least equal to radiator area.
What are other's thoughts on this?