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Old 09-03-2011, 04:41 PM   #1 (permalink)
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Simple Reduction of Drag due to the Wheels of Road Vehicles : Regert

This link is apparantly a poster session, mostly graphics. The fun part is on pp. 17-20, wherein he suggests one might benefit from different wheel coverings front and rear.
http://www.cfd.hu/pdf/10%20Dr.Regert...2010.11.11.pdf

Anyhow, this stuck me as prime Ecomodder material, deserving of it's own thread. Also, here's a more detailed paper with some cool CFD pix of vortices around wheels.

http://www.ara.bme.hu/~regert/public...s_cmff2003.pdf

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Old 09-03-2011, 08:00 PM   #2 (permalink)
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Many thanks for finding/posting this.

It is interesting to note that the maximum drag reduction, 8.4% resulted from running an open rim front wheel and a closed rim rear:

Click image for larger version

Name:	Wheel Drag Reduction.jpg
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ID:	9390

It is notable that in the previous tests of different underbody air dams the front
rim had been closed!!!

Can it be that "open rim" means the rim types that come OEM?

I wonder , to what extent would rear wheel skirts stand in for the "closed rim?"
I take it that a closed rim is essentially an aero wheel cover.
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Old 09-03-2011, 08:27 PM   #3 (permalink)
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Wow. Might have to try just doing the backs. And I had an idea that I got little response to. Closing off the inside area of the rim so as not to make the air going under the car turbulent. I think one member here did it with a Jetta, i think.

I wonder also why the guy doing those experiments didnt try skirting that extends down closer to the ground. Like this
Quote:
Originally Posted by AndrewJ View Post
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Old 09-03-2011, 08:34 PM   #4 (permalink)
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More interesting wheel stuff.
There is a fascinating paper by Morelli, citing Cogotti's research (SAE 2001-01-0491), which I'll try to summarize. It's copyrighted. You need to see the pix.

Adding a centrifugal fan to the rear wheels so as to draw air from the outside through the wheel yields a 5kW savings for the 240 W expended (20.8:1 advantage) by the following:

a: narrower wake due to air suction
b: a major decrease in base drag
c. suppression of jetting vortices by means of the Coanda effect.

I'd love to see someone try this.
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Old 09-04-2011, 12:08 AM   #5 (permalink)
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Originally Posted by autogyro View Post

Adding a centrifugal fan to the rear wheels so as to draw air from the outside through the wheel...
Where does that air that has been grabbed go to?
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Old 09-04-2011, 02:18 AM   #6 (permalink)
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Rokeby -

Quote:
Originally Posted by Rokeby View Post
Many thanks for finding/posting this.

It is interesting to note that the maximum drag reduction, 8.4% resulted from running an open rim front wheel and a closed rim rear:

Attachment 9390

It is notable that in the previous tests of different underbody air dams the front
rim had been closed!!!

Can it be that "open rim" means the rim types that come OEM?

I wonder , to what extent would rear wheel skirts stand in for the "closed rim?"
I take it that a closed rim is essentially an aero wheel cover.
Wow, that is interesting. Curiouser and curiouser.

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Old 09-04-2011, 06:26 AM   #7 (permalink)
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Quote:
Originally Posted by Floordford View Post
Wow. Might have to try just doing the backs. And I had an idea that I got little response to. Closing off the inside area of the rim so as not to make the air going under the car turbulent. I think one member here did it with a Jetta, i think.

I wonder also why the guy doing those experiments didnt try skirting that extends down closer to the ground. Like this
I extended the skirting closer to the ground on my car.

80MPG Honda Civic :: IMG_0350.jpg picture by MikeMariettaSC - Photobucket
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Old 09-04-2011, 06:52 AM   #8 (permalink)
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Quote:
Originally Posted by Rokeby View Post
It is interesting to note that the maximum drag reduction, 8.4%, resulted
from running an open rim front wheel and a closed rim rear:
I'm beginning to wonder if the "open rim" is purely a computer-based
phenomena. The picture shows only a center hub cylinder and a thin rim
cylinder with nothing in between.

Click image for larger version

Name:	Open Wheel.jpg
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Size:	8.3 KB
ID:	9392

Taken literally, this would mean the results are meaningless!

Quote:
Originally Posted by cfg83 View Post
Curiouser and curiouser.
Indeed.

But, hubless, spokeless wheels do exist. Enter the Osmos Hubless Wheel.
It, or something like it, has apparently been around since the '80s and is much
beloved by futuristic motorcycle and bicycle designers:



Cost? I can't find it, and I dunno.

The Osmos people say that their design has real-world automotive benefits
and applications, but make no claims to increased aero efficiency:

A FORMULA 1 chassis fitted with OSMOS wheels has shown that experimentation and applications are numerous but are not limited to the field of competition.

At this stage, we can provide the details that confirm the three strong points of our product: Safety, Performance, Reliability.

Accurate steering : The increased precision is due to the use of the new front and rear wheel axles, with their large diameter bearings providing a high degree of resistance during tilt, and with the layout of the ball joints reducing the angle allowance.

Reduced forces and structural stress : In a traditional configuration, the dynamic forces acting at the tyre/road interface are increased in terms of torque and stress as they pass through the midwheel, thereby allowing an indirect passage. Up to now this has always been considered as unavoidable.
The advent of the orbital wheel means that these forces are transmitted directly to the suspended elements.
Reduced unsprung mass : The optimised front and rear axles specially designed to meet the new requirements will lead to a significant reduction in terms of unsprung mass: up to 40% compared with traditional systems.

Braking efficiency : LThe use of single or multiple peripheral ring brakes opens up the possibility of producing lightweight wheels with a higher capacity for absorbing kinetic energy due to a large nominal diameter and virtually unlimited ventilation.

Rigidity and Solidity : The new front and rear heel axles provide excellent rigidity (a more "rational" layout of parts, elimination of give and structural strain). The forces, no longer amplified by complex chanelling, are transmitted directly. The unit as a whole is perfectly solid.

Resistance to wear : The reduction of specific pressure means that the bearings in particular will be extremely long-lasting: up to 100,000 km.

Future developments : Future tests on operating prototypes will enable the performance of the original orbital wheel systems to be checked.
There is no doubt that the field of application will be extended as long as there are design engineers engaged in finding new sources of inspiration.


More irrelevant examples

Last edited by Rokeby; 09-04-2011 at 08:31 AM..
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Old 09-04-2011, 11:41 AM   #9 (permalink)
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The air would go through the wheel, and exit out under the rear of the car, filling in some of the "vacuum" at the back.
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Old 09-04-2011, 12:37 PM   #10 (permalink)
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Quote:
Originally Posted by CFECO View Post
The air would go through the wheel, and exit out under the rear of the car, filling in some of the "vacuum" at the back.
You almost nailed it. The air is drawn inward through the wheel, directed up and back over the top of the tire, pointing outwards, and then bent back, down and rearwards to jet out the back through narrow horizontal slots on the underside.

They did this to a stock Fiat Punto. Talk about extreme aeromodding!

Of course it does help if you've the University of Turin windtunnel, and a few unemployed supercomputers to do your Navier-Stokes

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