Wheel well vents

[freebeard]

The top of the fender is a simple case, the interior of the wheelwell not so much. I'm reminded of the https://duckduckgo.com/?q=hollow+cylinder+shear+test.

The top of the tire is moving twice as fast in the opposite direction. The shape and free space inside the wheelwell cavity will have a lot of influence. As will the presence or absence of an air curtain or skirt.

[kach22i]

Originally Posted by kach22i

https://www.r8talk.com/threads/wheel...21641/#replies


I found this location diagram of interest because I thought the wheel well vent was to be located aft of the center hub, and not over the top or forward of it.

Not sure where the original diagram came from, no source cited.

EDIT: Think I found the source, 350rsracing.wordpress.com?

https://350rsracing.wordpress.com/20...et-fender-mod/

Follow-up:



I wonder why they closed off the front half of these wheel well vents.

https://sportscardigest.com/2009-24-...porsche-riley/


Green lines added to study placement.

[freebeard]

Thanks for posting. The followup contradicts the original post?

[aerohead]

Originally Posted by freebeard

The top of the fender is a simple case, the interior of the wheelwell not so much. I'm reminded of the https://duckduckgo.com/?q=hollow+cylinder+shear+test.

The top of the tire is moving twice as fast in the opposite direction. The shape and free space inside the wheelwell cavity will have a lot of influence. As will the presence or absence of an air curtain or skirt.

* The 'surface-feet-per-minute' of the tire tread is identical to the ground speed of the vehicle.
* That puts the top of the tire, 'if exposed' to the airstream, attacking the surrounding calm air, at the same speed as the vehicle, while the bottom of the tire is retreating away from the surrounding air mass.
* With an 'enclosed' body, airflow conditions within a wheel cavity would be highly 'conditional,' as mentioned, so no 'one-size-fits-all' characterizations allowed.
* Wheel-related aerodynamics could be reduced to 'windage'- ' ventilation drag .'
* Caveats .

[aerohead]

Originally Posted by kach22i

Follow-up:



I wonder why they closed off the front half of these wheel well vents.

https://sportscardigest.com/2009-24-...porsche-riley/


Green lines added to study placement.

From the image, the greatest supervelocity ( lowest static pressure ) would not occur until the flow reached where the slots begin. So their placement is 'logical,' if the intention is to scavenge as much air volume as possible.

[freebeard]

* That puts the top of the tire, 'if exposed' to the airstream, attacking the surrounding calm air, at the same speed as the vehicle, (while the bottom of the tire is retreating away from the surrounding air mass.)

So then the axle is moving at half the speed of the vehicle?

[kach22i]

I think that I figured out those three diagrams originally posted, and why car #58 is as it is.

1. Diagram one; no air entering though other sources, as in most street cars.

2. Diagram two; works best when brake cooling air, engine cooling air (front engined cars), and or radiators vent into wheel well (ie water cooled Porsche 911 & Boxster).

3. Diagram three; works when no external air is being vented through wheel well that would otherwise mess with or shift internal wheel well pressures.

.................................................. ........................................

Originally Posted by aerohead

From the image, the greatest supervelocity ( lowest static pressure ) would not occur until the flow reached where the slots begin. So their placement is 'logical,' if the intention is to scavenge as much air volume as possible.

Yes I agree, thank you for confirmation.

[Vekke]

If you want efficiency I would recommend looking answers from efficiency cars. In race cars you cannot know what is there for downforce and what is to lower drag.

But what you can know is that MB EQXX with Cd 0,17 has those rear vents. They help I have also some studies on my computer. If you plan to build ones look for a car that has similar width tires etc and copy first dimensions from that.

https://www.youtube.com/watch?v=leR56nqGSgk

In my Audi A2 bodykit there will come those vents as well. 3d printed parts are easy and fast to try.

[aerohead]

When the car made it's debut, M-B reported Cd 0.1816 for it. If they now claim Cd 0.17, is there a link to an explanation for the more liberal drag coefficient?
Also, MOTOR TREND reported that the A-pillars and side mirrors did not meet EU safety standards, and to meet them, the Cd would have to be downgraded to a higher value.