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-   -   Simple Reduction of Drag due to the Wheels of Road Vehicles : Regert (https://ecomodder.com/forum/showthread.php/simple-reduction-drag-due-wheels-road-vehicles-regert-18716.html)

autogyro 09-03-2011 05:41 PM

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

Rokeby 09-03-2011 09:00 PM

1 Attachment(s)
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.

Floordford 09-03-2011 09:27 PM

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 (Post 5554)


autogyro 09-03-2011 09:34 PM

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.

Floordford 09-04-2011 01:08 AM

Quote:

Originally Posted by autogyro (Post 259470)

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?

cfg83 09-04-2011 03:18 AM

Rokeby -

Quote:

Originally Posted by Rokeby (Post 259466)
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.

CarloSW2

basjoos 09-04-2011 07:26 AM

Quote:

Originally Posted by Floordford (Post 259469)
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

Rokeby 09-04-2011 07:52 AM

1 Attachment(s)
Quote:

Originally Posted by Rokeby (Post 259466)
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. :confused:

Attachment 9392

Taken literally, this would mean the results are meaningless! :(

Quote:

Originally Posted by cfg83 (Post 259496)
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:

http://i.i.com.com/cnwk.1d/i/bto/200...01_610x436.JPG

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

CFECO 09-04-2011 12:41 PM

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.

autogyro 09-04-2011 01:37 PM

Quote:

Originally Posted by CFECO (Post 259526)
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

autogyro 09-04-2011 01:59 PM

I found a link to the paper.

Powered by Google Docs

This is through google docs. If you want a direct link, search "Morelli Centifugal Fan Rear Wheels" and a non-linkable PDF will show up under the paper's title

CFECO 09-04-2011 02:09 PM

It seems that it has nothing to do with the body of the car at all, just making the tire more aero efficient. This could be done with fairings in front of the tire, and use the air coming through the wheel, to exit out the rear of the car to fill in the low pressure area behind the car.

autogyro 09-04-2011 02:31 PM

Quote:

Originally Posted by CFECO (Post 259538)
It seems that it has nothing to do with the body of the car at all, just making the tire more aero efficient. This could be done with fairings in front of the tire, and use the air coming through the wheel, to exit out the rear of the car to fill in the low pressure area behind the car.

Not exactly. The major benefit and energy pickup, as pointed out in the paper, comes from the suppression of the jetting vortices squirting out of the front of the tire contact patch. This is done by "unwinding" the vortices through the use of the Coanda Effect.
These vortices turn out to be a major source of drag .You will have seen these spinning out from under the wheels of a vehicle you are overtaking when there is a light rain or mist. Look for it.

Floordford 09-04-2011 02:37 PM

Quote:

Originally Posted by CFECO (Post 259526)
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.

I had an idea of how I would do it, I just wanted to hear your thought.

My idea was bladed spokes that grab air from the rims face and pull air toward the back of the rim. But then have an aluminum panel to keep the air in the rim. And then have a 2" port attached to a hose and channel the air to the back of the car to break up the vacuum.

cfg83 09-04-2011 06:54 PM

Rokeby -

Quote:

Originally Posted by Rokeby (Post 259510)
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. :confused:

Attachment 9392

Taken literally, this would mean the results are meaningless! :(


...

Yeah, it seems to be mostly CFD, but page 21 and 22 imply a scale model with axles to turn wheels in a wind tunnel. On page 23 it says "Validation was carried out based on a 'classic' Ahmed body but with moving ground plane, results were acceptably good", but I wonder what acceptably good means.

CarloSW2

gone-ot 09-04-2011 06:57 PM

...acceptably good is often equated as 90% correlation coefficients.

JasonG 09-05-2011 11:15 PM

Quote:

Originally Posted by Floordford (Post 259543)
I had an idea of how I would do it, I just wanted to hear your thought.

My idea was bladed spokes that grab air from the rims face and pull air toward the back of the rim. But then have an aluminum panel to keep the air in the rim. And then have a 2" port attached to a hose and channel the air to the back of the car to break up the vacuum.

Right track, but you will need a larger air passage.

Breaking the vacuum has shown benefits before.
This company for example :
https://lh4.googleusercontent.com/-f...20airwedge.JPG

NASCAR uses a slight propeller shape to their rims for this same reason :
https://lh4.googleusercontent.com/-1...0/IMAG0065.jpg

Its hard to see, but there is a slight pitch to the spokes.

Floordford 09-06-2011 10:28 AM

I just threw 2" out there because I figure the rim wouldn't make that much pressure with a bladed spoke.

Rokeby 09-06-2011 08:16 PM

I'm not certain that I understand the visualizations of the standing vortexes
around a spinning wheel in a "wheel house"/fender well in contact with the
ground. :confused:

Having said that, I hope this question makes sense: :o

With respect to enhancing getting air from the rear tires to fill in the low
pressure area behind the body, would "mud flaps" on the rear wheels help or
hinder the process?

autogyro 09-06-2011 08:43 PM

Quote:

Originally Posted by Rokeby (Post 259845)
I'm not certain that I understand the visualizations of the standing vortexes
around a spinning wheel in a "wheel house"/fender well in contact with the
ground. :confused:

Having said that, I hope this question makes sense: :o

With respect to enhancing getting air from the rear tires to fill in the low
pressure area behind the body, would "mud flaps" on the rear wheels help or
hinder the process?

This issue is, as always, how do you handle the transition from low pressure areas to higher pressure ones? For this reason Prii and such use as mudflaps little vertical "boatails" which mate with the width of the rear tires to manage the pressure transition to the rear.

The demon here is at the front of the tire where the airflow gets squished downwards and sideways, and then merges with the outside airflow, forming a vortex.

I hope this is useful.

Rokeby 09-06-2011 10:58 PM

Well, now I'm really confused. :eek:


My Prius, and I think all Prii, came with little OEM wind deflectors in front of
both the front and rear wheels.

And as I understand it, these little jobbies are meant to start vortexes that
spin around the wheels and as you say, are intended to "manage the
pressure transition to the rear."

All well and good, and I think we're together up to this point.

From the article I understand that what then happens to the vortexes, after
the wheel is also important.

My question has to do with mud flaps that are installed behind the wheels.

Floordford 09-07-2011 01:34 AM

Has any one payed any attention to the wheels of a Mercedes SLR?
Mercedes-Benz SLR McLaren wallpaper # 170 of 243, Wheels / Rims, MY 2004, 800x600
Its like it pulls air past the brakes from under the car.

JasonG 09-07-2011 08:48 AM

That is for brake disc cooling.


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