drove in the rain today and notice.... - Fuelly Forums

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Old 06-27-2008, 04:40 AM   #1
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Question drove in the rain today and notice....

that the water was not moving or evaporating in the middle of my rear window. i have a picture of it in my garage and marked the area in black. if i understand aerodynamics correctly. shouldn't it be even in the back with the wind pushing it down or evaporation,etc..?? and it always has the swirl look to it. like hurricane shape. so what is excately wrong here or is there something wrong with the aeros of the car? there are no aero mods in the front, but it does have a OEM spoiler on it.
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Old 06-27-2008, 08:26 AM   #2
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Looks about the same as mine. The rear window is too steep, and the airflow detaches from it. Hopefully your spoiler is in the right place to catch the attached flow, otherwise you have a huge trailing wake. It's a design compromise between rear seat headroom and airflow, and in our cases, headroom won. Look at a Prius to see the right way to do it.
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Old 06-27-2008, 12:59 PM   #3
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I had the same condition, then I replaced the seal to stop the leak onto the inside of the window....
The detachment of the laminar flow might not be a bad thing. The Kamm design principle takes steps to produce this delamination, but the glass is nearly perpendicular to the air stream, not nearly parallel to it. It seems that either extreme of angle is acceptable, but there is some relative orientation between these extremes that is not.
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Old 06-28-2008, 10:27 PM   #4
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John Cobb's land speed record Railton - Mobil Special was regarded as close to an ideally teardrop shaped speed vehicle. It was about 9 metres (28 - 29 ft) long; most of the back half was the fast back, the pointy tail. This is too long to be practical added to a road vehicle. The Kamm tail it seems. perhaps tries to keep the delamination, the angle of separation, minimized, whilst hoping that the disturbed, low pressure air zone behind the vehicle will assume the shape of a pointy tail.

A spoiler on top of a Kamm - like tail is often seen, what this may do is to prevent the laminar/turbulent flow boundary dipping too sharply, which could put some laminar flow in to the low pressure zone. That might increase drag: hence a spoiler, not so much to reduce drag, but prevent more of it occurring.
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Old 06-30-2008, 02:30 AM   #5
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hey Pale i'm not sure if the spoiler is in the right spot. i have no i idea really. how would one figure out if it is?
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Old 06-30-2008, 07:49 AM   #6
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Try some tuft testing. If the tufts go straight back, you're good. If they flutter all over, it's bad.
http://www.gassavers.org/showthread.php?t=4004
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Old 06-30-2008, 09:07 AM   #7
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You're pretty much always gonna have a stagnant spot right in the middle of a rear surface, but I guess that should be happening lower down, not on the window.
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Old 06-30-2008, 10:12 AM   #8
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hmmm is there another way that does not have a strimmer all over the car?lol
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Old 06-30-2008, 10:29 AM   #9
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Quote:
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hmmm is there another way that does not have a strimmer all over the car?lol
have seen oil used
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