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Old 03-31-2012, 05:38 PM   #1 (permalink)
Cd
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Can air be forced into an ideal path using fences ?

Is it possible to add aerodynamic fences to direct the airflow around the side of the cars A pillar ?
Will the airflow just trip over the fence and result in more drag ?
I ask because i noticed the sides around my windshield have a raised 1/4" channel that i would have thought would snag the sideways traveling air and direct it upwards.
However, when i did my tuft test i found that the air just tripped over the obstruction and continued onward, resulting in a large A pillar vortex.

Below is an image of wing fences used on a MIG fighter jets wings to direct airflow

Wing fence - Wikipedia, the free encyclopedia

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Old 03-31-2012, 05:56 PM   #2 (permalink)
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fences

Quote:
Originally Posted by Cd View Post
Is it possible to add aerodynamic fences to direct the airflow around the side of the cars A pillar ?
Will the airflow just trip over the fence and result in more drag ?
I ask because i noticed the sides around my windshield have a raised 1/4" channel that i would have thought would snag the sideways traveling air and direct it upwards.
However, when i did my tuft test i found that the air just tripped over the obstruction and continued onward, resulting in a large A pillar vortex.

Below is an image of wing fences used on a MIG fighter jets wings to direct airflow

Wing fence - Wikipedia, the free encyclopedia
You might,but you're splitting hairs.
Ferrari spent hundreds of hours in the wind tunnel refining the C-pillar wiglets on their 599XX car.That's at $2,000 /hour in nothing less than a full-scale tunnel.These could not be evaluated as a model.
If you do anything wrong,the interference drag will offset any gains made.
I really believe that this sort of thing is outside the realm of what we as amateurs could do.
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Old 03-31-2012, 07:25 PM   #3 (permalink)
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How much drag results from an A pillar vortex anyways ?

Nissan used it to their advantage by having it reduce some of the wind noise on their Leaf side mirrors.
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Old 03-31-2012, 07:31 PM   #4 (permalink)
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Quote:
Originally Posted by Cd View Post
Is it possible to add aerodynamic fences to direct the airflow around the side of the cars A pillar ?
You'd need something like an aircraft's leading edge slat to do that.
The idea is being used on European cab-over-engine lorries.

Quote:
I ask because i noticed the sides around my windshield have a raised 1/4" channel that i would have thought would snag the sideways traveling air and direct it upwards.
Same on my car.
I'd say their purpose is more to keep water off the side windows in the rain / when using windshield washers (they're not very successful at that either)

At best, they'd keep some part of the boundary air on the car, flowing aft - with the rest spilling over the fence.
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Old 03-31-2012, 08:14 PM   #5 (permalink)
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I'm not sure of the purpose, but 1969 Charger Daytonas and 1970 Plymouth Superbirds had a chrome trim piece at the A pillar that was not fitted to standard Chargers and Road Runners.

The piece appears to wrap around the sides of the windshield and back to the A pillar.
It looks to small to do anything good, but it has me curious about its purpose.

Everything added to the cars had some sort of aero functionality. The backwards facing scoops on the fenders had a cut out to exit high pressure air on the racing versions of the car.



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Old 04-02-2012, 12:16 AM   #6 (permalink)
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Interesting topic Cd. I have wondered about this ever since I installed a set of A-pillar fairings on my old 84 Jetta GLI (for those who wonder, yes, they did exist) and they were said to cut drag 10%. They also had a small channel that ran up the length of the windshield. But I wasn't curious enough about airflow back then to ask the question "why".
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Old 04-02-2012, 05:43 AM   #7 (permalink)
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Cut drag by 10 % ? More like 1 %.

There is already attached flow around the windshield. As aerohead mentioned, redirecting airflow around the A pillar isnt a magic bullet.

Something I found strange is that when Chrysler ran one of their wing cars at Bonneville, they removed the trim pieces.
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Old 04-02-2012, 10:13 AM   #8 (permalink)
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Quote:
Originally Posted by Cd View Post
Is it possible to add aerodynamic fences to direct the airflow around the side of the cars A pillar ?
Your proposal is a little different than my studies, starting with post 16. The prevailing opinion was that adding a fence between the side and roof would only delay and offset the vortex formation, not do anything to make it less of a problem.

http://ecomodder.com/forum/showthrea...a-19525-2.html

As already mentioned, those European super racing trucks use air fences, which might be adapted to your A-pillar.

Automobile 2 - Odds and Ends pictures by kach22i - Photobucket


I say just go for it and have fun experimenting. Who knows, you might come up with something new and useful.

Just do it.

EDIT: I've also looked into putting fences elsewhere, but that was a NO_GO as well.


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Old 04-02-2012, 10:41 AM   #9 (permalink)
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Quote:
Originally Posted by kach22i View Post
As already mentioned, those European super racing trucks use air fences, which might be adapted to your A-pillar.
Not just racing trucks, but just about all Euro cabover trucks.



And looking at the different truck models on the MAN website, it looks like they too have gone for blocked grilles
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Old 04-02-2012, 11:30 AM   #10 (permalink)
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Quote:
Originally Posted by euromodder View Post
Not just racing trucks, but just about all Euro cabover trucks.


And looking at the different truck models on the MAN website, it looks like they too have gone for blocked grilles
Also note shape of front fender, they have extended top to continue straight back instead of traditional arc, door is shaped to let air go from gate and follow top of fender, bumper is wide and shaped so that it might direct air over wheel area and there seem to be small air dam too.

Our trucks need to comply with EURO norms and those are getting tighter and tighter by every revision, there is really tight policies so truck makers are forced here to take great measures of aero too, engine emissions are very limited, also noise, tire noises too and there are limits of rolling resistances of tires you can use on trucks, next 20 years will bring much bigger restrictions so they have to take actions to improve aero.

Rear ends however here are same as they were at 80's, more or less

If you think about these air fences, wouldn't those small airdams at front of wheel classify as air fence too?

Front bumper edge and area from bumper to front wheels underside of car could be considered perhaps some sort of aerofoil, there is typically rounded edge, shape above, hood, nosecone are kind of aerofoil as air travels greater distance above than it does at below, so maybe in that way one could think that fences really would work.

Mercedes was probably first one to use those fences at front corners of cab, I think that I saw those 20 years ago already and felt they were common and normal back then, they might been there already at 80's, but my memory is not so great that I could say for sure when they did appear and what their function was, reduce noise or improve aero, either way it is probably improving aero:


Thing is of course different with windshield being angled, but for van or truck front corners, maybe something to test?

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