Vortex Generators / Hmmm Airtabs
 

Wanted to see if installing vortec generators on the roof, trunk and front fender would improve FE. Did 4 runs on a 7.5 mile north south section of highway with cruise control set at 60. Did runs with a clean car, with VG on roof, VG on roof, trunk, and front fenders. Temperature was 93 and winds were out of the south at 15mph. VG's were made from hand out of aluminium.

#1N #2S #3N #4S
Clean car 42.0 38.4 42.1 39.0 AVG 40.38

VG on roof 42.6 39.2 42.8 39.1 AVG 40.93

VG/roof/trunk/ff 42.9 39.1 42.9 39.0 AVG 40.98

That's only a 1.5% increase in FE and it looks like the VG anywhere but the roof are ineffective.

https://members.cox.net/zpiloto/101_0070.JPG

On the front wheel well

https://members.cox.net/zpiloto/101_0071.JPG

Cool. So were they hard to make? Seems like tin snips, a vice, and some kind of glue is all that is needed.

I think the roof is the only place you're going to see an improvement, since the rear window is at a greater than 11 degree angle, the boundry layer seperates from the window and causes greater drag. Or so says the things I've read and studied. =)

That's kinda what I figured out. The gain not really worth the effort. Do you think that it might show a better improvement on a box vechile or mini van placed on the roof and sides on the rear end?

Definitely better on a boxier vehicle. You might try moving the VGs from the front fenders to the rear, just before the curve to the rear bumper and I use the term bumper loosely.

vg
 

Well I know a really boxy vehicle that shows greatly reduced MPG at higher speed that needs to be tested . . . my xB

a set of vortex generators
 

I like. If you were to sell a couple of those vortex generators to a fellow gassaver for his roofline, what would you charge him?

And my Tahoe!

I know it may be some trouble to try the test again, but your vortex generators might be too close to the trailing edge to be of benefit. On plane wings, the generators are closer to the front of the wing, to keep the air attached over the surface of the wing. You might want to try moving them forward a few inches, and see if there is any difference.

One thing that might be of interest is this quick doc on the generators, on the wikipedia (https://en.wikipedia.org/wiki/Vortex_generator), where it says they actually increase drag.

I don't have any left to sell. I have 2 left over and I would just give them to you if I had a bunch extra any way. If you want PM me your address and I can send you the paper pattern I used to make them. Just copy the pattern on to cardboard(for durability) then use the carboard cutout to copy on to the aluminium. Then cut out the pattern and bend with a pair of plyers. The whole shooting match was less then ten bucks at Lowes or Home Depot and took about 3 hours to make 45 of them. The aluminum was $6.00 for a ten foot roll and the 2 sided tape was under $5.00.

I don't think I'll test them again. It a pretty small gain. With such a small amount of data it really a toss up that they help at all on this car. The roofline is where they have them on the new cars and my cars rear end is rounded on the top and the sides so not much help there.

VG
 

Yeah but what percentage of your fuel consumption is to air drag compared to other drags of your vehicle? I know my xB gets better MPG at lower speeds and drops off over 40mph. Also think about AirTabs for $2.50 each in clear, black or white which have been wind tunnel tested.

I've thought about Airtabs in the past but then thought about making some and then people post other cool stuff and I start thinking about that and I procrastinate and get nothing done!:rolleyes:
With the brush guard stuff on the Tahoe, which I don't want to take off, I know aerodynamic mods would help, but I'm having problems deciding what to use that won't change the looks too much. Clear Airtabs are a definite possibility. I've wondered about belly pans but are they effective on vehicles with large ground clearances? I never use the luggage rack so I could remove the cross bars. Then I could add a Ram Implosion Wing!

Do you know anybody that tested that thing. It looks pretty hokie.:eek: It would be the ultimate whale tail. https://www.electrifyingtimes.com/Rob...Patterson.html

I've studied the vg thing and have installed some.

I'd have to guess that the ones on the roof are in an area where the boundary layer has already separated to some extent....probably reducing their effectiveness. Maybe try moving them forward about a foot?

The ones on the deck lid are at a place where the air has pretty much separated for sure from the sharp drop at the window.

I had some on the roof of a hatchback with less slope...slightly different design of vg though...similar to the Mitsubishi kind. Found that silicone caulk is best for permanent mounting.

Good to see the accurate testing....and some positive results.


Here is a similar car with similar flows:

https://www.mitsubishi-motors.com/cor...004/16E_03.pdf


vgs:

https://www.thirdshift.com/jack/firefly/firefly18.html

https://www.thirdshift.com/jack/firefly/firefly19a.html

Notice that he has his version of vg mounted the other direction? This plane cruises at around 60 mph.

Your right about the direction. I don't know how I screwed that up. I'll have to swing them around and retest. Mybe this weekend. I was disappointed with the original results. Maybe this will get it around 3%.:D

Box drivers might be better served by adding a boat-tail to break up the inevitable turbulence behind the vehicle:

Some now well-known articles:
https://www.greencarcongress.com/2005...at_tail_d.html
https://www.maxmpg.org/the_cap.html

PDF warnings:
https://www.nasa.gov/centers/dryden/p...ain_H-2283.pdf
https://www.osti.gov/fcvt/2000-01-2209.pdf

On a vehicle with a blunted rear end (as opposed to the back of a pickup cab), it seems that the air space created by some plates does more to reduce drag than their angle of taper.

You are right, at least with my application. I turned the VG's around and ran the same test protocal as before with the same results:mad:.

I got "inspired" by your 1.5% gain and made up some vgs for use above the rear window on my hatchback. I combined the Mitsubishi research and the vg design from the ultralight. Also some some oil flow testing to determine air flow direction. Will post some specifics and a pic when I get them finished.

I have some vgs on the sides of the same car (3 per side)...they are oriented the same as your roof vgs...2 vanes that point to the rear in a "V" shape.

The Mitsu research shows that mounting them around 4" from where the rear window starts was the ideal position on that car.

"Vortex generators (VGs) were studied to install
immediately upstream of the flow separation point
in order to control separation of airflow above the
sedan?s rear window and improve the aerodynamic
characteristics. It was found that the optimum
height of the VGs is almost equivalent to the thickness
of the boundary layer (15 to 25 mm) and the
optimum method of placement is to arrange them
in a row in the lateral direction 100 mm upstream of
the roof end at intervals of 100 mm. The VGs are not
highly sensitive to these parameters and their optimum
value ranges are wide."

Keep us posted with the results.:D

Using the Mitsu research and ultralight info...I made 5 vgs from alum flashing material 2 1/2" long....with 2 vanes each set 3" apart. The vanes are about 5/8" high.

Did an oil flow test first by drawing a line 3-4" back from where the roof starts to slope down...marked 7 different points along this line...had an eyedropper of engine oil...put a good sized drop in all 7 places and drove about a mile and a half down the road at 60 and stopped. Found the center 3 flowed straight back...the 2 points in one from the ends angled in around 8* towards the centerline of the car. The 2 places right near where the roof dropped off to the side had a pretty disturbed flow...lot of buffeting here?

So they are mounted about 3" back from the "break line"...the two vgs on the ends are angled 8* inwards...glued on using silicone caulk. Each vg is 4 1/2" apart.

Expecting that each vane creates a vortex that rotates conterclockwise on the right side and clockwise on the left (looking to the back)...so that they don't tend to cancel each other out.

https://www.cpu-net.com/host/gaxir/gpics/zvgs.jpg

That's nice do you have any data on FE increase? Your methology is better than my stick it on there and lets see what happens.:D Have you thought about adding a couple more to decrease the space between VG's?

Just got them on there...and am also testing other things...like the FA2000...so no mpg results.

The Mitsu research says that a spacing of 4" is ideal...mine are spaced 3" and 4.5"...Mitsu has 8 vgs...I have 10. Ideal for that car was 4" back from the "break"...mine are 3" back. I was planning on using 7 of them instead of 5.

I can't do the research they did...but I can generally duplicate what they say is ideal. I think they compromized for production by putting them too far back.

Though as they say..."The VGs are not highly sensitive to these parameters and their optimum value ranges are wide."

I made some previously pretty much exactly the same dismensions they used...but the doublesided tape wouldn't hold in the rain. Didn't test for flow. Didn't put them back on because of the very low reduction in CD they mention.

Sounds like IDEAL would be 4" back...spaced 4"...none at the edges....angled 15* to the tested flow...they say 1" high vgs are OK. Theirs were 2" long.

Nice job. I tried a FA 2000 knockoff that I manufactored myself with no luck. Do you have an EFIE on your O2 sensor? Without it I don't think you'll have much luck with the ECU making adjustments.

Yep...got an EFIE. Somehow the FA2000 was set back to a lower setting where no gas was flowing...either somebody was messing with it...or I'm getting careless...but testing goes on.

Have had a problem with liquid gas building up under some conditions...got that solved by adding an extra PCV jar to catch it.

More info I've found about VG's...

zpiloto: yours are/were not on backwards, at least according to the old web site of Gary Wheeler, an Indy car designer/aerodynamicist who originally popularized VG's for use on regular cars (if I'm not mistaken). His were oriented the same way as your photos show.

zugyNA: what's that flat black thing on the top of the rear window downstream of your VG's? It's not a spoiler is it? (Would kind of negate the VG's.)

3rd party tests: I still haven't found anything good that supports using these at the trailing edge of a vehicle (vs. the roof)... but I did hear back from the airtabs company with a report of a study done in the UK using them ahead of the tractor/trailer gap, and it appears legit.

You guys need to put a fan on the roof and have it blow backwards over the VGs and then spray a mist of water or smoke and see the air flow to check for the VGs working and the proper spacing and never mind the road testing . . . you need to actually see it working up close. Maybe a thread tell tail off of the tips of the VGs would help too.

I thought of using a shop vac hooked up to the outlet port. ... and then immediately realized it would only generate turbulent flow, since it's blowing into still air. Same deal with the fan. Unless it's a really big fan, like, say, in a wind tunnel :)

I don't think you can cover the entire roof line but you should have a pretty good air flow at 1 inch height along the roof line if the fan is at the start of the roof - by the time the air gets to the rear of the roof it should be pretty smooth flow - not looking for 60 mph wind either - just some 10-20mph air flow. I was looking at the bottom end of my xB on a windy day and could feel the air flowing under the rear ground effect. Maybe a windy day would show the vortex created. I also have to wonder about using sheet metal for the VGs instead of a smooth aero shaped VG like the Airtab.

I've tested both directions with the same results. I've also tried them at different spacing with the same results. It looks like VG just need to be there to help the flow. The spacing and orientation don't seem to make too big a difference. I saw a 1.5% increase with a 40 MPG base. I personally don't think it worth the trouble as far as bang for the buck but your base is a lot higher than mine. I spent about 8 hours on the whole project including getting material making the VG installing and testing, but then again every little bit helps.:D

>> Could you upload a copy of that report? <<


* maybe with some vgs...direction isn't that important

* flat (?) black thing is one of those 3rd brake lights...does mess up the flow

* the kind of vg I put on the ZX roof is a different design than the airtab clones made of alum. The basic vg is just a single vane usually set at a 15* angle to the air flow....the ultralight type I made for the roof just combines 2 vgs in the same piece of metal....these create 2 vortexes.

the airtab clones are made so that the air is focused and made into a non vortex type higher pressure stream...while maybe there is a low pressure area between them.

the kind used on the roof should likely be the actual vortex generators (spaced at 4"?)...while those used at the back should be the airtab clones (spaced at 1"?)?

I will if the airtab guy says it's OK. Waiting to hear back.

That seems to be the case, doesn't it.

Could you show me a pic of this non-vortex type? This is the first I've heard of that behaviour. My understanding is that the airtab style also creates vortices.

The Airtabs have a definate direction to face and create a clockwise vortex and counter clockwise vortex and should be placed 4 inches apart. The idea is to prevent reverse air flow back against the rear of the vehicle which represents drag and turbulance. I wish the improvement was greater to justify the cost but I guess at some point I will get a few and try them.

Vortex Strakes
 

Here's an SAE paper that describes how "vortex strakes" can be used to create an "aerodynamic boattail" behind semitrailers. See p. 13 for pics.

https://www.solusinc.com/pdf/2003-01-3377.pdf

Blue skies,

Patrick

a pic and the pattern for the airtab clones is here:

https://www.gassavers.org/showthread.php?t=1351

I don't think the airtab type create vortexes...since the vanes oppose one another....


the vgs I used on the roof are a different pattern....and do create vortexes.

According to the airtabs website (in "How do they work"), they create vortices.

Yes. Metro, I've been running my airtabs for sometime now, and when I drive through the rain, and a vehicle is behind me with thier lights on...I can significantly see the votices. Also, whenever I cruise down a dirt road above 40mph I can see them.

All I can say is that they are symetrical, but the air hitting between the vanes is bumped up...might create a spin? Maybe there is an interaction between this higher pressure and the lower pressure air between the airtabs?

the typical vg obviously creates a spin.....

FYI: Porsche 914 club forum - racer claims use of airtabs cut 1/2 second off his lap times by reducing rear lift:

https://www.914club.com/bbs2/index.php?s=&showtopic=52170

vgs for Vettes:

https://www.greenwoodcorvettes.net/gc4/vortex.htm

https://www.greenwoodcorvettes.net/gc...structions.htm

Info given to me by Ron Davidson at Airtabs. (Posted with permission)