BMW cooling duct

[fabrio.]

some pictures of radiator/cooling exhaust of an BMW 320 D

I am sure interests to you.

Sorry for the bad quality, but I used a cellphon!





last photo, from rear car:



note the quality of smooth underbody...very good.

the car it is standard!

[tjts1]

Cool. Is this an E46 or E92?

[trebuchet03]

Looks NACA ish Also note the wheel deflectors

[fabrio.]

I think to remember an E46!

[Peter7307]

Fabrio,
Thanks for posting these great photos.
Some great details to study.

Cheers , Pete.

[diesel_john]

i am saving that pic

[Otto]

Notice the radiused surface on the aft side of the outlet. NACA did studies of cooling inlets and outlets during WWII for piston aircraft, using the best methods found on both our and German/Japanese aircraft. Outlets are as important as inlets for good aerodynamics. Actually, you need matched inlets, internal ducting, and outlets to get the lowest drag. This BMW has some comparativelygood outlet geometry, but could be better.

Google for "AR-5 aircraft" by Mike Arnold, who studied these methods when building his fine little plane.

[fabrio.]

hi Otto, I have find the mike arnold's site, but I do not "have tried this interesting page.
Could you send me the correct adress please?

from "Race Car Aerodynamic by Joseph Katz":


By fabrio

[aerohead]

The photo exhibits very good design on the part of BMW.This is exactly the sort of technology race teams have used for decades,and what Walter Korff of Lockheed Aircraft was advocating for passenger cars back in the 1960s.Glad to see that Rip van Winkle is waking!

[Otto]

I wish I knew how to post scanned images here. If so, I could show you illustrations out of Dr. S. Hoerner's "Fluid-Dynamic Drag" page 9-16, with cites and sources.

The optimum outlet is not as shown in the BMW photo, or anything close. It is more like the bottom drawing D in the above illustration, but with the outlet channel as close to parallel to outside flow as possible, and with the downstream intersection radiused.

Fast flow of the outside air means low pressure, which in turn sucks the outlet discharge into the free stream. If the outlet is as close to parallel with the free stream as possible, and the downstream intersection radiused, the outlet air can merge with the free stream with the least possible turbulence and greatest efficiency. Think of it as an on-ramp to a freeway, where the cars represent air molecules.

BTW, some folks use NACA submerged inlets and turn them around backward as outlets. Ungood. These NACA arrowhead-shaped inlets look sexy and work pretty good as inlets, but are not efficient as outlets.

Bottom line: If outlets and internal ducting are good, the stagnation point inlet at the nose can be quite small.