09-07-2013, 03:56 AM
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#1 (permalink)
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Lots of Questions
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Making a "Kammback" with the Sunroof and Rear Window
Lester has a sunroof and rear window. I was wondering what would happen to the aerodynamics of the truck if I were to open both of them. Does anybody have any idea what that would do or can anybody do one of those airflow diagrams to see how it would work?
Thanks! 
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09-07-2013, 09:14 AM
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#2 (permalink)
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Cyborg ECU
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I think it would hurt the aerodynamics, especially with the sunroof open. Not sure what to think with just a rear window open. Assuming it is the kind that retracts into the door, I guess it starts to look a little like a box cavity back there, but box cavities have to be carefully tuned and their benefit is very small and highly interactive with other aero features, apparently.
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See my car's mod & maintenance thread and my electric bicycle's thread for ongoing projects. I will rebuild Black and Green over decades as parts die, until it becomes a different car of roughly the same shape and color. My minimum fuel economy goal is 55 mpg while averaging posted speed limits. I generally top 60 mpg. See also my Honda manual transmission specs thread.
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09-07-2013, 11:16 AM
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#3 (permalink)
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EcoModding Apprentice
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Don't open the back window while driving unless you also have side windows open. You will be sucking your exhaust fumes into the vehicle.
If you want to try it do so on a gravel road, it will be obvious if you are sucking the wake into the cabin by the dust levels well before you get any CO poisoning.
I miss my 4Runner.
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09-07-2013, 03:21 PM
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Master EcoModder
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open
I'll vote 'don't also.
The lowest pressure outside the vehicle is near the windshield.If you open the sunroof and rear glass,the low pressure above the roof will telegraph through the cabin,bringing air and exhaust fumes forward towards that low pressure as it attempts to equalize the static pressure between the two areas.
It not only ruins the airflow,but it poisons you to boot! 
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09-07-2013, 04:16 PM
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Ultimate Fail
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STOCK : 
SUNROOF OPEN / BACK WINDOW OPEN : 
SIDE WINDOWS OPEN / BACK WINDOW OPEN :  |
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09-07-2013, 04:21 PM
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#6 (permalink)
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Ultimate Fail
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I had pondered the same thing before on this forum. Thanks for the idea to test it in CFD.
Last edited by Cd; 09-07-2013 at 04:44 PM..
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09-07-2013, 04:30 PM
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#7 (permalink)
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Ultimate Fail
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I'll test the coefficient of drag later to see how bad it gets with the windows open.
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09-07-2013, 04:41 PM
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Cyborg ECU
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Quote:
Originally Posted by Cd
In all instances, the flow at the rear was sucked inward into the cabin. ( Appeared to at least. I can continue to test this )
I had pondered the same thing before on this forum. Thanks for the idea to test it in CFD.
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This will sound uninformed, but why does the graphic seem to show slower air flow at the front of the vehicle when the windows are opened downstream? Is it because the open windows slow the ari around the greenhouse which in turn makes the flow at the front of the car slower?
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See my car's mod & maintenance thread and my electric bicycle's thread for ongoing projects. I will rebuild Black and Green over decades as parts die, until it becomes a different car of roughly the same shape and color. My minimum fuel economy goal is 55 mpg while averaging posted speed limits. I generally top 60 mpg. See also my Honda manual transmission specs thread.
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09-07-2013, 04:46 PM
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#9 (permalink)
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Ultimate Fail
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Actually the flow appears to be moving out of the cabin. Here is a video :
http://www.flickr.com/photos/60376566@N00/9693089745/
I'm multitasking here and getting ahead of myself.
Last edited by Cd; 09-07-2013 at 11:06 PM..
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09-07-2013, 04:50 PM
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#10 (permalink)
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Ultimate Fail
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Quote:
Originally Posted by California98Civic
This will sound uninformed, but why does the graphic seem to show slower air flow at the front of the vehicle when the windows are opened downstream? Is it because the open windows slow the ari around the greenhouse which in turn makes the flow at the front of the car slower?
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This has me puzzled too.
I will test this later as well. I think it's the fact that my computer is bogged down from having too many things going and it is causing everything to act screwwy.
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