Can air be forced into an ideal path using fences ?

[RunningStrong]

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?

[kach22i]

Originally Posted by Cd

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 ?

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


I think the above does, and will work.

Opinions?

[aerohead]

Originally Posted by Cd

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.

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.

[Cd]

Aerohead, this is a question for you :
How would this Kach22i idea work out ?

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.

[RedDevil]

What a coincidence...
From today's thread http://ecomodder.com/forum/showthrea...res-27852.html :


I think they work. The 60s had something going after all. Happy days are here again

[Cd]

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 ?

[RedDevil]

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.

[kach22i]

Originally Posted by RedDevil

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:

Popular culture

Harley Earl arranged for several of his designers to view a YP-38 prototype shortly before World War II, and its design directly inspired the tail fins of the 1948–1949 Cadillac.[120]

The P-38 was also the inspiration for Raymond Loewy and his design team at Studebaker for the 1950 and 1951 model-year Studebakers.[121]

The whine of the speeder bike engines in Return of the Jedi was partly achieved by recording the engine noise of a P-38, combined with that of a North American P-51 Mustang.[122]

[ron22]

It did not seem to help on the Fiero

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

[aerohead]

Originally Posted by Cd

Aerohead, this is a question for you :
How would this Kach22i idea work out ?

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.

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.
-------------------------------------------------------------------------
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.
-------------------------------------------------------------------------
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.
------------------------------------------------------------------------
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.
--------------------------------------------------------------------------
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.