Engine Compartment Venting

[arcosine]

Interesting paper.

The red looks better than the blue. I don't know why the square back and notch back are so different, very strange. The blue defiantly had more air flowing, because of the bigger opening.

I don't think this paper applies completely, since my wheel wells are covered the air can not escape through the sides, but must exit under the body through the tire clearance holes in the belly pan.., my grill opening is minimal, I will be keeping most of the blue closed.

[ConnClark]

well you might consider you could be doing more harm than good. On the other hand the biggest difference it made was 0.004 in Cd over or under the base line.

[arcosine]

I would like to keep the flow smoother under the car to try to get better pressure recovery on the boat tail bottom surface.

[ConnClark]

The question is does smother flow on the under side of the boat tail really going to get a net gain by disrupting air flow some where else?

What I think you are trying to say is that flow around the wheels is already disrupted and that a bigger disruption there won't matter. In this paper they show for both the notch back and the square back that isn't the case as drag increased when they blocked off the transmission tunnel. If this is the case for your car I can't say and I don't think any one else will be able to unless they have a wind tunnel that can measure Cd to the 3 digit after the decimal point.

[arcosine]

My car doesn't have a transmission tunnel.

"None of our men are 'experts.' We have most unfortunately found it necessary to get rid of a man as soon as he thinks himself an expert because no one ever considers himself expert if he really knows his job. A man who knows a job sees so much more to be done than he has done, that he is always pressing forward and never gives up an instant of thought to how good and how efficient he is. Thinking always ahead, thinking always of trying to do more, brings a state of mind in which nothing is impossible. The moment one gets into the 'expert' state of mind a great number of things become impossible.” " ... Henry Ford

[ksa8907]

Over the hood. Will help reduce lift from air under the car.

[jime57]

Very interesting study. Slightly at odds with Buchheim, et. al., but interest anyway.

One take away was that the aero drag from cooling is linear with the amount of cooling air. Ecomodders have been proving that for a while

[AndrzejM]

Maybe you could consider NACA vents on your belly pan, those should reduce the turbulences under the car siginificantly, comparing to grill like vents you've mentioned in a first post.

[arcosine]

NACA vents are low drag intake vents, not meant for exhaust.

http://en.wikipedia.org/wiki/NACA_duct

I am considering streamlining the engine compartment, ducting the flow so it expands from the slit in the bumper to the radiator (diffuser) and then narrowing again to the exit and try to match the external flow velocity with minimum turbulence. I don't know if it can be done in practice, but I had something similar on an earlier saturn and that car would blow leaves out the back. I'll post progress on sc1 aeromods thread. I ordered more rivets, hopfully they will arrive today.

[AndrzejM]

Check out google for "reverse NACA duct"



Bring back the NACA duct..... - PistonHeads

NACA can work both ways. I've seen NACA-like outlet working as an exhaust tip, but can't find a photo right now to link it. It was just build as reverse of NACA inlet. So it was wider at the very end of the outlet and it was tapering to the front and the actual exhaust pipe. I'm hoping you get the idea from my description.