aero effectiveness of roof fins on the evo8
06-02-2005, 11:14 AM
#31
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Originally Posted by platypus
wings work by creating pressure differences between the top and the bottom. The air flow faster over one surface, and thanks to Bernoulli's effect, the pressure is different. On an airplane wing, the top surface is flat and the bottom is curved. This has the effect of making air flow faster over the top, resulting in a low pressure area above the wing, creating lift. On a typical car wing, it's flipped over causing the low pressure area underneath the wing.
Overall, the car will have the same sort of effect, which is why things like air dams and splitters create downforce (less air flowing under the car than over it creates a lower pressure area under the car).
Overall, the car will have the same sort of effect, which is why things like air dams and splitters create downforce (less air flowing under the car than over it creates a lower pressure area under the car).
I was confused for a sec, but now it all makes sense how vortex generators on the roof would effectively kill the Bernoulli effect by slowing/disturbing the air flow (all things being equal and assuming constant flow under the car).
Last edited by wombatsauce; 06-02-2005 at 11:15 AM. Reason: I can't spell and I can admit it.
06-02-2005, 11:42 AM
#32
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ok, having read a bit more (so i can quit talking out of my butt), the curved surface of the wing causes the attached airflow to speed up, which results in a lower pressure area. if that's the case then, anything on the roof of the car which adds turbulence should slow down the air, raising the pressure (although with a drag penalty).
06-02-2005, 11:56 AM
#33
06-02-2005, 12:44 PM
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Originally Posted by platypus
ok, having read a bit more (so i can quit talking out of my butt), the curved surface of the wing causes the attached airflow to speed up, which results in a lower pressure area. if that's the case then, anything on the roof of the car which adds turbulence should slow down the air, raising the pressure (although with a drag penalty).
Exactly what I was saying. Make the assumption that a car is shaped like an airplane wing (which it is, just not a good one). If you make turbulance on the top, you lower the speed and therefore increase the pressure of air above the car.
I'm still almost certain the Evo's spikes help becuase of this increase in pressure and not because of any effect it might throw at the rear wing. The nature of the way down force is meassured, however, makes the spikes look like they make the wing better...but really, they just help raise the air pressure above the car so it has more downforce over all. I think. The spikes definatly add drag though, that's a no brainer.
06-02-2005, 01:34 PM
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Originally Posted by dr3d1zzl3
its all black magic and devils speak
06-02-2005, 01:34 PM
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It looks like the fins direct more fast moving air down the rear window, so that would actually lower the pressure on the rear of the car.
If you look at a race car usually the rear spoiler is slightly lower than the roofline, so it is in the fast stream of air coming off of the roof of the car. The evo's spoiler isn't tall enough to accomplish this by itself, so the vortex generators aid in altering the flow of air down closer to where the spoiler is.
If you look at a race car usually the rear spoiler is slightly lower than the roofline, so it is in the fast stream of air coming off of the roof of the car. The evo's spoiler isn't tall enough to accomplish this by itself, so the vortex generators aid in altering the flow of air down closer to where the spoiler is.
06-02-2005, 02:07 PM
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Originally Posted by platypus
go back to editing your ACL's and leave this to the real engineers.
acl's are for CCNA's foo
im mui l33tAr then that..
in fact i am toying around with meterpreter and passiveX right now.. pretty damn cool stuff...
esp passiveX.. mui ninjah
06-02-2005, 02:25 PM
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Originally Posted by mbquarts
It looks like the fins direct more fast moving air down the rear window, so that would actually lower the pressure on the rear of the car.
If you look at a race car usually the rear spoiler is slightly lower than the roofline, so it is in the fast stream of air coming off of the roof of the car. The evo's spoiler isn't tall enough to accomplish this by itself, so the vortex generators aid in altering the flow of air down closer to where the spoiler is.
If you look at a race car usually the rear spoiler is slightly lower than the roofline, so it is in the fast stream of air coming off of the roof of the car. The evo's spoiler isn't tall enough to accomplish this by itself, so the vortex generators aid in altering the flow of air down closer to where the spoiler is.
I'm not convinced the fins make the air move faster down the window. It seems to me that laminar air flow (big sheet of air not hitting the fins) would be faster and lower pressure than air that has fins stuck into it due to the increase in turbulance, but the article by motortrend seems to say what you're saying.
06-02-2005, 02:43 PM
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if we look at the flow diagrams in the article, the car tested has no spoiler, so we can't really see the difference in flow to the spoiler itself.
06-02-2005, 03:18 PM
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I think you're right on the labeling. I don't really trust those pictures, though, because the red areas in front of where the vortex generators are don't look similar enough...I'm thinking maybe some photoshop data manipulation...
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