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Old 10-03-2017, 08:25 PM   #1 (permalink)
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In cabin wind/"redneck a/c" aerodynamics

Any clue how to improve this to increas
aerodynamics while ventilating the cabin?
I am curious if the rear roof angle is ideal and if there is an ideal hole placement/size in the back to empty air into the vacuum behind the car from the cabin.

Edit this is **not** for an existing model car, but for a prototype I have built from scratch (see pic, which I have repost outside of Facebook to ensure it is visible)



https://1drv.ms/i/s!ApZC8QFk-svmgXIZdrsgSxXP-kV8


Last edited by mikesheiman; 10-06-2017 at 12:23 PM.. Reason: Add image
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Old 10-04-2017, 11:37 AM   #2 (permalink)
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Old 10-04-2017, 02:37 PM   #3 (permalink)
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Not touching a Facespook link. At least tell us the make and model.

Meanwhile, fabricate or simulate a wind wing.
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Old 10-04-2017, 04:07 PM   #4 (permalink)
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Does not compute:
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Old 10-04-2017, 05:37 PM   #5 (permalink)
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Old 10-05-2017, 09:52 AM   #6 (permalink)
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Updated/fixed image

Sorry about that, just updated the image link. Will upload a wind tunnel analysis sketch soon showing where internal air ducting is now (wheel well tops and upper back of car).
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Old 10-05-2017, 12:12 PM   #7 (permalink)
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I just have both the windows down 2 inches on the passenger side of the car and amazed at how much the air circulates without the use of a fan or A/C. The front and rear windows must be down and equal amount though or it doesn't work.
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Old 10-05-2017, 02:37 PM   #8 (permalink)
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Thanks.

If the sketch includes the window area and door cut-lines that will disallow things that couldn't work.

The wake is stagnant, low-pressure air. Look at the engine cooling on the Edison2. It is a vertical slot at the maximum camber (widest point of the body). The air is moving fastest there and you can intake or exhaust most efficiently there. For cabin ventilation the window height is prolly adequate.


Edison2 - Very Light Blog - Edison2, Local Motors & Siemens: The VLC Design*Challenge

My Superbeetle's flow through ventilation exhausts in the C-pillar. Opening to the wake could allow exhaust gases (if not electric) to intrude into the cabin.
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Old 10-05-2017, 05:00 PM   #9 (permalink)
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Quote:
Originally Posted by freebeard View Post
The air is moving fastest there and you can intake or exhaust most efficiently there.
So would exhausting out the middle back of the car, literally dead center, be ideal? Or is there a reason I'd want to exhaust via the c-pillar area further forward, even if I have a tapered rear end behind that?

Still trying to wrap my head around it...my gut reaction is it would be easier
to push exhaust air into the low-pressure area behind the car than the fast moving area beside it. Or, on my car body/pic, could you circle potential areas you'd recommend to exhaust cabin air through? I'd really appreciate it.
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Old 10-05-2017, 07:40 PM   #10 (permalink)
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I'm no expert, despite the tag somebody put under my user name. I think that's based on number of posts. See if you can lure aerohead into the thread.

Basically, fluids like air have a pressure and a velocity at any given point. You can no more push air than you can push a rope.

https://en.wikipedia.org/wiki/Bernoulli%27s_principle

The most you can do is pool it in a plenum and suck it out through a port.
IMHO, the stagnant low-pressure air in the wake will be no more effective than the high-velocity air moving over the sides of the body. think of a reverse Coanda nozzle:

https://en.wikipedia.org/wiki/Coand%C4%83_effect

The picture is poorly lighted. How close is the sketch? Three-views would be nice. Is it gas/diesel or electric?

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