Video: tuft testing front wheel skirts (Geo Metro)

[MetroMPG]

Originally Posted by Daox

Very nice. I was surprised to see the improvement even above the wheel well. That is quite the difference.

I was too, until I re-read a bit about wheel well/tire aerodynamics:

"The top of the wheel is moving into the air stream at twice the driving speed, and is trying to drag the air forward against the stream." (Contribution of different devices to the total drag - Chalmers University)

So the air being dragged up & forward at the top/outside of the tire collides with the normal air stream flowing aft ... and makes a mess. I think that may be what we're seeing above/aft of the top of the wheel arch.

[MetroMPG]

Originally Posted by lunarhighway

perhaps it would be interesting to use the same setup to test vortex generators behind an open front wheel well.... but perhaps some vortex geneators just aft of the wheel could improve the situation over stock.

I think VG's are a waste of time. They have to be incredibly carefully designed (access to good CFD or a wind tunnel/smoke test) to deliver results that in the end, even when optimized, won't even be detectable in the real world.

the full wheelwell cover will likely be superior

No argument there!

[MetroMPG]

Originally Posted by Daox

Yes, but doesn't flow seperation happen earlier/easier (you know what I mean) at higher speeds?

What I'm not sure is whether it's significant when we're debating a 25 mph difference (between 35 mph and 60). I'm guessing it's not significant, but I'll defer to someone who knows more than I do on this question.

[i_am_socket]

Great video! That is quite the difference. Next you'll have to do some FE quantification without the rack and boom

What I'm not sure is whether it's significant when we're debating a 25 mph difference (between 35 mph and 60). I'm guessing it's not significant, but I'll defer to someone who knows more than I do on this question.

I wouldn't think it is significantly different at that speed considering the angle of the skirt. It might show, but it looks shallow enough to not (but looks can be deceiving). Another test! ;P

[MetroMPG]

If only my cruise control would work reliably, I'd be out there ASAP to get some ABA. I need to trouble-shoot it some more to see if I can figure out what's wrong with it (after replacing it once already).

[fit7ad]

Originally Posted by MetroMPG

I was too, until I re-read a bit about wheel well/tire aerodynamics:

"The top of the wheel is moving into the air stream at twice the driving speed, and is trying to drag the air forward against the stream." (Contribution of different devices to the total drag - Chalmers University)

So the air being dragged up & forward at the top/outside of the tire collides with the normal air stream flowing aft ... and makes a mess. I think that may be what we're seeing above/aft of the top of the wheel arch.

Any chance you can repeat the tuft test with a partial cover? There may be significant improvement just by lowering the wheel arch a bit. That would be really helpful to less ambitious folks like myself. Thanks for the good work.

[NeilBlanchard]

Hi,

Did you solve the wheel clearance on turns; and if so, how? Or was this just a proof of concept?

[MetroMPG]

Originally Posted by Blue Bomber Man

I was thinking of having a flexible fabric of some sort and have a guide bar that was attached around the wheel to the steering mechanism, that would push the fabric clear of the wheel during turns.

I believe Ford did something similar with the Probe V concept. Seem to recall Phil (aerohead) talking about it somewhere...

[MetroMPG]

Here's the raw video, for the hard core aerophiles...

Check out what happens to the airflow around 1:10 (open wheel well) when I turn the wheels slightly to the left (about 1/4 turn of the steering wheel).

http://www.youtube.com/watch?v=xn8bEkriXq0

[MetroMPG]

Originally Posted by NeilBlanchard

Did you solve the wheel clearance on turns; and if so, how? Or was this just a proof of concept?

This was just proof of concept. The tire pushed the skirt off each time I turned the car around to repeat the run, and I stopped at the side of the road & re-taped it. But basjoos already solved the clearance issue: top hinge.

Originally Posted by fit7ad

Any chance you can repeat the tuft test with a partial cover? There may be significant improvement just by lowering the wheel arch a bit.

I think you're right: there's likely a good amount of improvement with a partial cover. I'm guessing approx the top 1/3 or so of the wheel. You'll see this on a number of aero cars (on the rear wheels) like the Mercedes Bionic car (you have to look closely; it's a clear plastic skirt) and their big 4-cyl diesotto concept saloon; even the GM EV1 only covered about half of the rear wheel.

Not going to repeat the test though. It's a lot of time & work! Plus, I'm more interested in the full meal deal.