Video: tuft testing front wheel skirts (Geo Metro)

[tasdrouille]

Darin, awesome work as always.

Regarding partial cover, I'm confidend that anything you do to close the gap between the wheel and fender will benefit the aero of your car.

[MetroMPG]

OK, so I'm sold on the tuft testing.

Next step: Designing/building front wheel skirts v.1.0 (Geo Metro)

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[Xringer]

Originally Posted by lunarhighway

perhaps it would be interesting to use the same setup to test vortex generators behind an open front wheel well.... front wheel skirts are not really an option for everyone,

but perhaps some vortex generators just aft of the wheel could improve the situation over stock.
some people claim they should be placed in front of a wheelwell so that might be tested as well.

the full wheelwell cover will likely be superior, but it would be interesing to see where vortex generators are positioned betwee these two extremes

Or, maybe some jumbo zig-zag tape fore-&-aft of the wheel wells??
(but not this JUMBO)!



I can see where adding VGs/ZZ tape forward of the wheel well might help some if you had moon disc wheel covers..
But, I wonder if they would help the turbulent air coming off the rear of the wheel well??
Does turbulent air get settled down when it hits a VG?

[MetroMPG]

Xringer: do you have any info about the effectiveness of that kind of tape or VG's ahead of wheel arches? I know the AirTabs web site recommends that particular positioning, but I'm skeptical it does anything. They certainly don't offer any quality information about them.

I'm going to stick with things I know that work.

[Xringer]

I think that Zig-Zag tape works, after reading the sailplane info/study and seeing what Neal Blanchard did with his DIY ZZ tape.

The wing-oil-flow pictures were impressive. It's hard for me to understand how something that thin can have such a positive affect. Preventing flow separation/ maintaining smooth air flow. (Like golf ball dimples?)

Since it seems to be doing something down about 1mm off the steel, I'm not sure exactly what it would do 'ahead of wheel arches'..
It might cause the flow to hang on to the metal and flow around inside the wheel well. (Making things worse?).

I think you are right about the airtabs. Sticking them 'ahead of wheel arches' would likely just cause more drag. Since they are so large..

I wouldn't put anything in around those arches. (Except maybe a wheel skirt)..


My crazy thinking about suppressing turbulence around the front wheel,
is to use a skirt (like in the above pic), or try a moon disc and some heavy duty ZZ tape 'ahead of wheel arches'.. Nothing too big. Maybe 1 or 2 MM thick. Nothing that will add more sq inches to the frontal area..
A ZZ patten that would generate a curtain of small vortexes, one every few mm.

In my day dream, these small vortexes off the ZZ tape would flow over the wheel well gap to the top of the moon disc. Spinning across the disc just above it's surface. Smooth!!
Then, there's the problem of the rear wheel arch gap..
Maybe confused air at that point could be helped out by some more ZZ tape.

Like Neil used on his A-pillar.. But on the leading edge of the arch..?.
Scion xA aero mods

Maybe some before-and-after yarn testing just forward of the door would tell you something. I'm a novice at this stuff. Just trying to learn the ropes..

Good luck!

[basslover911]

That tape is what i was looking for AFTER the wheel, it would help A LOT. But I may use dimple tape instead since it would look much better on the car.

Oh and I have VG's on my car ("Vortekz?) and I beleive that they do work. NOBODY with my car has been able to even get close to my mpg highway rating, even hypermillers. I did some testing (--- "vortekz" Generators Tested!! --- Pictures!! - GasSavers.org - Helping You Save at the Pump) and it showed MUCH better flow attatchment on the window which only leads to a better simulated teardrop shape.

BUT, i dont think airtabs work because they have way to much frontal area, as "vortkez" are extremley slim and have probably 1/20th the frontal area, so the net aero gain is negative as compared to the "Vortkez". Now if think ZZ tape is even better as it has practically NO added frontal area (But I didnt know about zz tape when I put my VG's on).

[NeilBlanchard]

Hi,

Since zigzag tape is so thin, it cannot help reattach turbulent air. The pictures of the zigzag tape in the wind tunnel have it in the high pressure air on the leading part of the wing, and it helps create a slip layer near the surface.

It can't pull turbulent air in from a distance away.

[aerohead]

Originally Posted by MetroMPG

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.

Seems like the big-dogs are going to argue that flow separation ,if it occurs,will be constant over the entire speed range above 20-mph,as at that velocity,Reynold's Number is fixed along with Cd.

[aerohead]

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. That would be really helpful to less ambitious folks like myself. Thanks for the good work.

I don't have any independent mpg numbers for partial covers but what I will tell you,is that if they're more than a couple inches deep ( 50 mm+) they'll tend to rub the tire,as I discovered on my Volkswagen, Honda,Dodge,and Toyota, and will need to be articulated as basjoos and MetroMPG have done.------------------------ For all the trouble,seems like we're better off doing the full,articulated skirt.Some early high-mpg concept cars began with fractional wheels skirts only to be superceded by full skirts in later endeavors.I think there's a big lesson there.

[trebuchet03]

Originally Posted by NeilBlanchard

Hi,

Since zigzag tape is so thin, it cannot help reattach turbulent air. The pictures of the zigzag tape in the wind tunnel have it in the high pressure air on the leading part of the wing, and it helps create a slip layer near the surface.

It can't pull turbulent air in from a distance away.

That's the thing about any sort off VG - which includes zigzag tape, dimples, etc... The whole theory behind it never involves turning turbulent flow into attached flow - it's taking turbulent energy and transferring a bit into flow about to detach.

Furthermore, I'm not convinced comparing a sailplane to a car is of any use. The ASK 21 sailplane has a max speed (where this tape would have most effect) of 175mph (if you can find minimums, that'd be great) and is a streamlined body to begin with. Maybe the lower pressure offsets the velocity discrepancy - I'll have to do a quick calc a bit later