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 http://www.maquetland.com/v2/images_...ingFencing.jpg

Wing fence - Wikipedia, the free encyclopedia

fences
 

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.

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.

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.

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.

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.

http://www.dodgecharger.com/forum/in...ch=67305;image

http://t2.gstatic.com/images?q=tbn:A...XrXmhHHtmqxrJA

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".

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.

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
http://i184.photobucket.com/albums/x...it-truck-1.jpg

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.

http://i184.photobucket.com/albums/x...dit-Camaro.jpg
http://i184.photobucket.com/albums/x...ite-Camaro.jpg

Not just racing trucks, but just about all Euro cabover trucks.

http://www.mantruckandbus.co.uk/man/...height_182.jpg

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 :D

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:
http://upload.wikimedia.org/wikipedi...edes_Truck.jpg

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

I've noticed the air fences on the front of trucks for a while, but was unsure as to whether they where aerodynamic or sacrificial plastic in case of bumps and scrapes.


Regarding fences in general I think in the vast majority of cases they are a waste of time, certainly when you are not actually using the air for anything and simply trying to maintain a clean flow.

Winglets on plane wings are functional but take 100s if not 1000s of hours in wind tunnels to perfect as they are very specific to each wing design. Earlier "bolt on" designs were of limited benefit economically as the added weight and cost actually gave little economical benefit over fuel savings but did allow airliners to appear more modern. Winglets that are integrated into new design (787 and A380) are far more effective from what I've been told in my studies.

Multiple fences on flat surface are simply increasing frontal area and can possibly cause more turbulence that they prevent. Don't forget you are creating further edges which will lead to further issues at the edge were the two separate air flows meet again.

And then finally there's the side profile, greatly increased but for what real gain?

Did you originally mean a fence not like the MIG-15, but more of a spoiler perpendicular to the air flow?

Automobile 2 - Odds and Ends pictures by kach22i - Photobucket
http://i184.photobucket.com/albums/x...edes_Truck.jpg

I think the above does, and will work.

Opinions?

how much
 

The amount will vary from vehicle to vehicle of course.A HUMMER H-1 will have unrecoverable vorticity destroying greenhouse flow the full length of the vehicle.
The D-B,M-B,C-111 record car probably has zero A-pillar vorticity.Ditto Renault Vesta II.Lots of factors affecting this sort of thing.
I think Hucho would have you look elsewhere for savings.
I do believe the bright metal on the Daytona helped,Hucho was involved in this kind of research at VW.I believe he addresses this drag with the Audi 100 and Golf.

Aerohead, this is a question for you :
How would this Kach22i idea work out ? http://i184.photobucket.com/albums/x...dit-Camaro.jpg

This is actually exactly what I had in mind by the fences.

Normally the air starts to spill over the sides and meets at the back of the car in one huge vortex. I would think that fences like the one illustrated by Kach22i would minimize the size of the vortex since the main air spilling over the cars roof would not mix with the spiraling air on either side of the car.

What a coincidence...
From today's thread http://ecomodder.com/forum/showthrea...res-27852.html :
http://ecomodder.com/forum/attachmen...1&d=1388267247

I think they work. The 60s had something going after all. Happy days are here again ;)
http://2.bp.blogspot.com/_Sqh2Lxf8d9...0/000_0806.jpg

I have read in the past that the fins on cars such as those in the above image resulted in large vortices. Much larger than if none were present.
Want to chime in on this Aerhead ?

The tails on the 50's and 60's car were never meant for reducing drag of course. They just came into fashion when one of the designers of an American motor corporation saw the double tail of the Lockheed P-38 Lightning fighterbomber.

I checked out the link, at first thought it was oddly specific - guess not.

From the link:

It did not seem to help on the Fiero

1986-88 Fiero GT....................0.365 Cd.
1986-87 Fiero SE....................0.350 Cd.

how would?
 

Cd,I'll try 'n do your question justice.
*The fence itself does nothing to alter the tranverse pressure gradient which drives the higher pressure air from below and on the sides towards the backlight/boot area.
*The fence WOULD in effect,limit the air's open access up top,just as the capping plates do on racing spoilers,and winglets on aircarft wings.
*One risk,is that the backlight area may already 'optimized' by the manufacturer (as with the Dodge Charger Daytona) and the fin will destroy the C-Pillar flow onto the boot, which is part of the drag/lift equation and balance.
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On my CRX I extended the contour of the rear slope essentially with two-fences which followed the 'Template' ,however they were embedded within side fairings sculpted to match the C-pillars outer contour,blending the flow while gently boat-tailing in.
Spanning the 'fences' were an upper Kamm-wing extension over the glass to extend the roofline camber,directing the 'jump' towards a low wing spoiler below.It also provides some shade to the cabin.
This contraption sequestered a bird-bath if you will,of vorticity and dead air for the outer flow to 'jump,' while preventing any really weird CG/CP effects.The CRX is un-phased by gust or crosswind.
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By the time the air from below reaches up top,the upper flow has slowed and gained pressure to match the side flow,killing the attached vortices in their crib.
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Volkswagen's Lamborghini division is doing this today so they don't have to add crap to the car top kill rear lift.The basic shape of the rear is incapable of generating lift as it is generally understood.
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So George's idea has merit.But I would take it to the next level,fully sculpting them into the rear slope to help regain what is lost on the C-Pillars.Chevrolet Division has finally,after 60-years,killed the drag in this area of their Corvette,filling this area in.

fins
 

We would want to take the cars on a case specific basis I suppose.
Alfa Romeo got some tasty Cds with their 3-car B.A.T.series of show cars.
Chrysler did some tests and reported directional stability benefits attributed to fins.The 'fin'/wing on the Daytona does add up to 36% added drag in strong crosswind.
Kamm was seemingly obsessed with fins and put them on all his own cars,up to his last project for the DKW/Audi notchback of the 1960s.
Some of the Citroens,due to their forward weight bias,are so stable without fins,that one may cruise all day at 127-mph with nary a care.
Morelli put them 'under' his banana car behind the rear wheels.
Ford claimed that the dorsal fin on their Probe-V,Cd 0.137 concept helped it achieve outstanding directional stability in gusts and crosswinds.
We could go on forever.
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The fin was a 'styling' gimmick for the most part.
When used as a palliative for stability issues,aerodynamicists figured that the car's body could be reconfigured so as not to create the situations needing 'fixing' with fins, as Lamborghini is doing today.

I understand the need for air fences on swept wing fighters, but as jtbo asked, what is the purpose of those on the front of Euro- cab-over tractors?

That question crossed my mind, to a degree. Would there be anything to be gained with air fences running lengthwise? I would think little would change, except at the roof/door edges perhaps.

Which reminds me, air streaking down the sides of the vehicle has a pretty bumpy path, with wheel wells, door handles, window trim and all. Over the roof seems a little better, but that's just from looking. I guess some tuft testing would be in order...

[edit] as I stew on this more, I could see how these curved air fences may serve similar to a recent rear spoiler or Kammback design I saw here last week. It was shaped a bit like some wing flap airfoils, and was said to reduce drag. The page escapes me at the moment though...
Found it!! http://ecomodder.com/forum/showthrea...tml#post271093

The wing fences on Mig fighters was an aero "band aid" installed to mitigate bad stall characteristics, not to reduce aero drag. The wing fences keeps the detached airflow that first appears at the wing root of swept wings as the Mig approaches stall speed from spreading out to the wing tip where it would hamper the roll response of the ailerons.

basjoos is currect. Wing fences are used on aircraft to get the wing to stall the way they want to. Nothing to do with drag.

Euro Cab Over Tractors
 

I'm going to take a stab at the structure on the tractor,and say that I believe that they are harvesting ram-air pressure from the stagnation footprint to create a 'jet' below the side glass and mirrors,to protect them in a rain from splash and spray,which would create a blind-spot for the driver.
There's already enough leading edge radius for attached flow,and concerning that,the turning vanes would be superfluous.

While we're on the subject, what about the recessed rear windows with side extensions on cars from the 60s like the Charger? More or less drag than a flush window? http://www.jmooneyham.com/rear-tail-...ge-charger.jpg

Compare that Charger to the Daytona version with a flush window. I thin kthey also made a 500 version that had a flush grilleand rear window before the Daytona version.

regards
Mech