Aerodynamic Discussion Thread
03-05-2013, 12:00 AM
#84
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The reason for guys removing the rear window in the hardtop has to do with the fact that they found that the wing was more effective this way. No way without a wind tunnel to say if it's because it alters the air's flow as it comes off the top towards the wing, or if the wing is actually getting airflow that is coming out of the rear window hole, but either way, the whole reason is because it aids the wing.
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03-05-2013, 12:05 PM
#86
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Yeah I understand that's it's not a nice pretty bubble of pressure inside like having the windows up, it's very turbulent, but the 'parachute' effect is an exaggeration - I don't think the guys who pulled the rear window out were seeing significant MPH changes at the end of straights, from what I have heard it was much more differences in wing performance.
I run a rear lexan window though, so I cannot comment from personal testing. I've considered doing some sort of quick disconnects on it such as Dzus fasteners so that I could do back to back tests.
How high the wing is mounted plays a big role in that too though. The APR GTC-200 for example mounts pretty low, and IIRC even with the 2.5" risers still isn't at the roofline, so the no-rear-window configuration might benefit those wings much more than it would for someone who has gotten their wing up higher..
-Ryan
I run a rear lexan window though, so I cannot comment from personal testing. I've considered doing some sort of quick disconnects on it such as Dzus fasteners so that I could do back to back tests.
How high the wing is mounted plays a big role in that too though. The APR GTC-200 for example mounts pretty low, and IIRC even with the 2.5" risers still isn't at the roofline, so the no-rear-window configuration might benefit those wings much more than it would for someone who has gotten their wing up higher..
-Ryan
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03-05-2013, 12:50 PM
#87
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It seems to me that with the back window removed,
a) there is high-velocity air coming off of the rear roof lid meeting slower air
b) this is going to tend to pull air out the rear windshield opening, thus pulling air through the cabin windows.
c) this is also going to form a vortex with the axis of the vortex along the pitch axis of the car. The downward side of the vortex is going to hit the rear wing, effectively increasing its angle of attack.
This is from my 5 minutes of coffee & M&M's fueled cereberal CFD. Feel free to discuss.
a) there is high-velocity air coming off of the rear roof lid meeting slower air
b) this is going to tend to pull air out the rear windshield opening, thus pulling air through the cabin windows.
c) this is also going to form a vortex with the axis of the vortex along the pitch axis of the car. The downward side of the vortex is going to hit the rear wing, effectively increasing its angle of attack.
This is from my 5 minutes of coffee & M&M's fueled cereberal CFD. Feel free to discuss.
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03-05-2013, 02:24 PM
#88
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I think you're right, without the rear window much more air is going to flow thru the cabin. Poor man's AC. 
Though I agree it may have more air hitting the wing, it's going to be highly turbulent and likely not beneficial. That's my guess anyways.
Why doesn't someone windtunnel Miatas already?
Though I agree it may have more air hitting the wing, it's going to be highly turbulent and likely not beneficial. That's my guess anyways.
Why doesn't someone windtunnel Miatas already?
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03-05-2013, 10:16 PM
#90
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With the rear window removed, the air moves forward through the hole and into the cabin from the rear, then exits out of the side windows. Anybody who has ever had a zip-down plastic rear window can attest to this.
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03-05-2013, 10:25 PM
#91
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Maybe when my schedule clears up, or if somebody wants to pay to have it done (and allow me to share), it can be moved up the list.
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03-05-2013, 11:07 PM
#92
It seems to me that with the back window removed,
a) there is high-velocity air coming off of the rear roof lid meeting slower air
b) this is going to tend to pull air out the rear windshield opening, thus pulling air through the cabin windows.
c) this is also going to form a vortex with the axis of the vortex along the pitch axis of the car. The downward side of the vortex is going to hit the rear wing, effectively increasing its angle of attack.
This is from my 5 minutes of coffee & M&M's fueled cereberal CFD. Feel free to discuss.
a) there is high-velocity air coming off of the rear roof lid meeting slower air
b) this is going to tend to pull air out the rear windshield opening, thus pulling air through the cabin windows.
c) this is also going to form a vortex with the axis of the vortex along the pitch axis of the car. The downward side of the vortex is going to hit the rear wing, effectively increasing its angle of attack.
This is from my 5 minutes of coffee & M&M's fueled cereberal CFD. Feel free to discuss.
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03-06-2013, 08:15 AM
#96
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Ya Tage Evanson, I was following him after this inspiring article "Anatomy of A Giant Killer"
1995 Honda Civic - 11 second Civic - Import Tuner Magazine
Sad what happened to his car, but now the car is a Phoenix
1995 Honda Civic - 11 second Civic - Import Tuner Magazine
Sad what happened to his car, but now the car is a Phoenix
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