Simple Reduction of Drag due to the Wheels of Road Vehicles : Regert

[autogyro]

I found a link to the paper.

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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]

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]

Originally Posted by CFECO

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]

Originally Posted by CFECO

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]

Rokeby -

Originally Posted by Rokeby

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.

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]

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

[JasonG]

Originally Posted by Floordford

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 :


NASCAR uses a slight propeller shape to their rims for this same reason :


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

[Floordford]

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

[Rokeby]

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.

Having said that, I hope this question makes sense:

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]

Originally Posted by Rokeby

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.

Having said that, I hope this question makes sense:

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.