Tuft Testing - "Vortekz" vortex generators on 2003 Jetta Rear Window
 

I've seen a few people attempt to find fuel economy improvements using vortex generators. However most folks were using "Airtabs", which are a larger flow disturbance vs. a smaller delta-wing style VG. In addition many folks were also placing them at the very rear edges of their bluff body style vehicle, or at the trunk-lid edge of sedans/hatchbacks. That doesn't seem like the ideal application to me.

I went with the "Vortekz" delta-wing type: Welcome to Vortekz.com

Their website is not too impressive to say the least.

Nevertheless, I bought some. The only other person I saw using these post on a forum such as this was a thread over on gassavers with a Mazda 6 sedan. I think he's getting the best documented mileage of anyone with this car. Otherwise, these VGs mimic the type used on Mitsu Lancer EVOs and Subaru WRX STIs to direct air down and around the rear spoiler. I don't think anyone could deny that they work in this context. If we can visualize them bending down the airflow, and accept the Mistu paper on drag reduction (with the spoiler), then it can't hurt to give this a try.

Those looking for measured fuel economy impact of my application will be disappointed here. Sorry. Too many mods going on, and 700 mile tanks just last to long to do them one at a time. In any case, I did what I could with some tuft testing.

The array:
http://i287.photobucket.com/albums/l...z/IMG_1731.jpg

Stock roof

http://www.youtube.com/watch?v=0DBnJn1MWQ8

http://i287.photobucket.com/albums/l...ckTuftTest.jpg

So there is obviously detached flow in most of the center of the car. I was a little surprised with how well flow stayed attached down the sides. Or at least visually "attached". You can see one of the center trunklid tufts just dancing straight up into the air though. Other window glass tufts turn front to rear. But it appears to me that the flow definitely comes over the roof and partway down the rear glass before severely separating. This was a good find for my selected VG location.

Installation:
http://i287.photobucket.com/albums/l...z/IMG_1734.jpg

http://i287.photobucket.com/albums/l...z/IMG_1736.jpg

Back onto the road for a quick test at speed:

http://www.youtube.com/watch?v=98gsuMJRQMk

http://i287.photobucket.com/albums/l...GsTuftTest.png

The still image with the VGs looks a little blurrier as the sun was setting. Obvious flow attachment improvement down the rear glass and deck. Cool. Whether this saves me fuel or not may remain difficult to ascertain. I think I'll refill 'er with bio asap so I can try to asses them on the next tank vs the current one.

These things really don't add much in the way of frontal area. Technically none, but the if the airflow is attached when it hits them, there is obviously going to be an impact on drag.

http://i287.photobucket.com/albums/l...z/IMG_1747.jpg

http://i287.photobucket.com/albums/l...z/IMG_1748.jpg

View from interior:
http://i287.photobucket.com/albums/l...z/IMG_1749.jpg

http://i287.photobucket.com/albums/l...z/IMG_1746.jpg

http://i287.photobucket.com/albums/l...z/IMG_1754.jpg



I also threw some tufts onto my passenger side glass where I recently did a flush mirror delete. I'll post up the results of that vs. a small safety mirror over in my general build thread.

Man, over 40 views and no comments. :rolleyes: Here I thought I was doing something useful, too...

I remembered Trebuchet's CFD thread from a while back and decided to compare my results. I'd say he was doing some pretty good modeling!

I drew a line of my estimated flow separation point on this shot:
http://i287.photobucket.com/albums/l...TuftTest-1.jpg

Vs:
http://ecomodder.com/forum/attachmen...1&d=1226637053

I'm also now more encouraged to do my decklid extension, since he got these results with one modeled:

http://ecomodder.com/forum/attachmen...1&d=1226793943

If the VGs are drawing more flow down the rear glass and onto the decklid, further airflow smoothing via an extension should help minimize the total wake, too, no?

So what do you guys make of all this?

Actually, it kinda looks like the decklid extension is creating a much larger wake, but then I could be wrong.

Definitely improved flow to the rear window there. I wonder if there's a way to figure out how far ahead of the flow separation you need to put the VGs for optimal benefit.

I have to wonder if you could use fewer VGs and get close to the same improvement. Your original air flow near the sides of the rear window was pretty well attached.

I believe it was MetroMPG who did a similar test on another car using Airtabs. Seperation results were the same as yours.
He also tested airtabs on a minivan of some persuasion. In both cases there was no difference in mpg.
Putting the VG's in an area of seperated flow (Maybe the back edge of your deck lid) would be useless.

I cannot tell a difference between extension & not from the pictures.
Are you planning on making the extension adjustable for testing or putting VG's at the rear of the extension?

I notice similar flows on my 07 Civic. We often get misty rain in the Pacific NW, and any wind starts to produce drops which then flow in the path of the wind. There's always a "dead spot in the lower middle of the rear window.

One thing I was wondering about was if the wind noise would be reduced if the airflow is smoother. Did you notice any difference?

Very interesting thread.
Nice cfd, however i think you actually need to make everything correct with wheels and flow into engine since that changes alot.

From the decklid extension I dont see that he got any improvement. Most likely alot of air will pressure bellow the decklid. However with an diffuser you might have another result

Its intresting with these vortexes that separates air and also with different irregularity that causes air to slow down so it more easily follow edge etc. It works for golfballs atleast:)

Yeah I wondered that too right after I stuck the last VG on. doh. I am contemplating pulling the very outer ones back off. As you say the airflow out there was already fairly well attached, so VGs out there can only be causing extra drag...

As per the deck lid extension, well, I guess I'm not so sure. But the CFD pics above were done with NO vortex generators. I pleaded with Trebuchet to run some of those in a simulation but his interest waned before it happened. Not sure whether the CFD could properly model those, but it would be interesting.

Only got one rainy day of commuting with these on, but the drive to work was my best ever scan gauge reading. Also a downpour that forced slower driving. Drive home was clear, and only average mileage. Have not noticed any less wind noise, but seems like that would only be noticeable in the back seat anyway, since my airflow up front is unchanged.

What you are seeing on the sides of the rear glass are C pillar vortices IMHO.

Good experimenting, Deezler.

I wouldn't expect to see any MPG improvement show up - it'll probably be too small to see above the normal statistical noise of tank-to-tank variation. Recall that Mitsubishi estimated a drag reduction of just -0.006 in their study.

I like your idea of putting the VG's aft of the physical "peak" of max frontal area projection. And they still clearly influence airflow placed at the top of the window!

The $60,000 question is whether their additional induced drag (from their vortices) is greater/equal/less than the potential for drag reduction because of a smaller wake.

In each case where I tested VG's, I felt there was more noise when they were in place. Subjective though. Take 2 grains of salt and call me in the morning.

Ah ha. Meaning that the flow is truly less attached than it appears? Either way I suppose there isn't much you could do about it other than put some VGs on the side of the vehicle. Wonder if my roof VGs on the edges can sort of "over ride" the C pillar vortices.

Tas, how did you get the green machine up to 55 mpg? Driving style? Quite the jump from the 44 mpg I recall you having earlier.

Thanks metro, and yes, that is the real question here. Probably will never know. I think I need to just clean up the underside of my vehicle a bit more, build some rear wheel skirts, and focus on driving style. Then be content with my results. hopefully.

Winter blend has quite a lot less BTU than straight ULSD. My daily commute is also only 7 miles each way, so outside temps play a big role there. I deleted my passenger side mirror and replaced my driver side mirror with a DTM cup style mirror, added some grill blocks and wheel deflectors also.

Good luck on the experiments but I've not found any evidence of a measurable drag reduction with my 03 Prius. I observed the flow attachment with the vortex generators but it looks like the rotary motion at the base of the glass is not a major drag source.

My interest has moved on to reducing excessive cooling drag at the air inlet.

Bob Wilson

Another indication of these difficult economic times?

So are they worth what they cost? will you get it back in better FE savings?

wouldn't VGs on the side only increase the C pillar vortices ?

Gotta see some pics Tas! Or did I just miss your thread?

HypeNoob, that question is hard to answer. But at $20 for the set of VGs, I only need to improve my FE by 0.2 mpg, or 0.5% if I drive another 80k miles with them on. So it seems plausible that they could pay off. But since I may never really answer the question of whether they are even beneficial in the first place, who knows.

Conn, good question. I am picturing attached flow over the roof edge and down the glass at the edges "buffering" against the vortices, so to speak. But I think we all know how terrible most people's aerodynamic imagination is....

No Thread yet, but I added pics in the garage entry.

Hey! That was me with the Mazda 6! :D And yes, I never saw anyone ever hit the mileage that i got from that car- 45mpg in the freeway was the top... till I sold it :(

Anyway, a few observations. You should place the VG's further up at the edge of the roof, not at the start of the window. This is because you want them at the edge of the turbulent flow, not at the start of the flow (if that makes sense- ie. a little before it starts).

I LOVED my VG's on my mazda, always got comments on the "cool" factor and set the car apart. They held up through anything that I put them on (power washes, automatic drive through car washes, ice, etc). I also LOVED how they kept my rear window clean most of the time.

Now, everybody look out for new testing with my new car (an Audi TT Quattro with 500hp which suprisingly gets 28mpg combined right now, and it has 275 tires in the back! Look out, who says you cant get a super gas saving sports car!

Again, thanks for YOUR testing! It really helps to add to the truth and fakes out there and to me these (NOT the airtabs) are a real gain.

Interesting. Anyone have any updates from when this was posted a year ago?

Updates? none to be had, really. The 3-M adhesive tape these VG's come with rocks, they are still on super strong. They are still bending the airflow, but fuel economy benefit is still negligible.

This is definitely not the magic easy way to cut drag though. Focus on grill blocks, flat under-tray/underbody panels, and wheel covers, mirror deletes, etc.

But, do they keep the rear window cleaner?

Anybody tried vortex generators on a belly pan? Might get some downforce.

I started doing a little research on VGs after I started noticing them on a number of large trucks. Seems they are most useful in getting airflow to smooth out when crossing some kind of gap, like that between the back of a truck's cab and the front of it's trailer. But I did find an interesting video on the subject and some pictures that may help understand their effects and applications better. I think that I'll probably be adding some to my towcar. Just a matter of deciding the best type to try and the best place to put them. Since I go through an entire tank on a daily basis I should be able to provide a fair bit of practical use data on them.

https://www.youtube.com/watch?v=9Whd_KnsLKE

All the Kyle Drives videos are good.

Have you thought about air dams and Coanda nozzles?

I have a pilot friend who races Long EZ airplanes. His advise on vortex generators was to paint used engine oil on the surface you would like to add them to. Then go drive on the highway for a few miles. The air washing over the oiled panel will define where the air flows, and thus where you need to put the generators to create separation for cleaner aero flow. It does work but its messy....

This is not his EZ, but one like his.

https://s-media-cache-ak0.pinimg.com...642f3b74e6.jpg

Not coanda nozzles, as they'll likely interfere with my towing equipment, but definitely considering air dams. I'm thinking of doing a trunk lid extension that will be something of a bonneville type flat spoiler and something of a partial boat tail, the VGs should help prevent the angle of the back glass from causing premature airflow separation, that way I'll get the most benefit out of the trunk lid extension.

Ugh......VG's are borderline unicorn corral material. Airplane aerodynamics do not matter much for cars & trucks. Besides, by the very nature of flight, if you increase lift you increase drag....Think about that. If you came up with something that increased lift AND reduced drag you could have airplanes powered by 50 HP engines flying at 500MPH getting 60 MPG.

The only way to reduce aerodynamic drag is to change the shape of the vehicle, adding things that stick out increase drag. Any benefit from the vortices will only be a tiny bit better than the drag created, at best, and only in very rare circumstances.

That's a thought that's certainly worth considering. However in circumstances where changing the shape of the vehicle would be impractical, one takes their improvements where they can find them. A thousand minute gains can do the same as a single large gain, if one simply has the ability to see the big picture.

oiled panel
 

here,you can see Pininfarina doing this with the CNR car they developed between 1976 and '78
http://i1271.photobucket.com/albums/...itled13_13.jpg
here,GM use lamp-black and kerosene to sort out their 1963 Sting Ray
http://i1271.photobucket.com/albums/...head2/2220.jpg

It was chilly and humid when I went to work the other day, so the car was covered in condensation. When I stopped for gas I looked at the way the airflow had affected the moisture on the car, and took some pictures with my cell phone. Sorry they're not very good, but it's a cheap phone that I only have because I need it for work. But what seems to be going on is that the airflow over the roof is about what you'd expect, until about three inches from the back glass, which is where the roof curves down to meet the back glass, at which point the moisture on the roof is completely undisturbed. The moisture on the back glass is likewise completely undisturbed. In fact it's not until you get to about the middle of the trunk lid that the moisture shows signs of airflow again. Which would seem to indicate that the airflow is detaching from the roof at the point where it begins to slope down towards the back glass and does not reattach until approximately the middle of the trunk lid. Which presents the question: Is it better to encourage the airflow to remain attached, such as with some VGs? Or is it better to encourage the airflow to remain detached by putting some sort of extension onto the roof so that the downward moving air misses the back of the car entirely?

Makes you wonder where cars would be today if car makers had continued along this line of development. Since cars became decidedly less aerodynamic in the late 70's early 80's and it seems that only now, over the last ten years or so, have they started getting rounded out and made more aerodynamic again.

I'd say just the opposite. Review this: An Illustrated History Of Automotive Aerodynamics: Part 3 (1960 – Present)

The 80s is the 'jelly bean' era, precipitated by the Ford Taurus/Mercury Sable. The first American cars with the headlight reflectors mounted in aerodynamic buckets, following (of course) the VW Beetle in the 30s.

Contemporary cars have lost the 'jelly bean' look, especially in the back, and have more sculpted sides.

As for your question posted three minutes earlier; depends on the installation, a Kammback is probably the winner.

You're probably right, on both counts. But I was thinking about how cars went from being rounded and sleek, to boxy and angular. I've got a '74 Buick Apollo, and while compared to either of the vehicles pictured above, it's a brick, compared to my grandmother's '83 Chevy Impala it possesses a dart like sleekness. And the difference is even more pronounced when looking at SUV type vehicles. An 80's era Jeep Grand Cherokee looks like a box on wheels, while the current 2017 Jeep Grand Cherokee looks like it was modeled after a space craft from some futuristic sci-fi series, very sleek and aerodynamic.

I agree about the Kammback, and I think that in the near future I may build a test model out of cardboard, with the miles I drive every day it shouldn't take long to get an idea as to how well, or poorly, it's working.

P.S. The Aptera, pictured in the article you shared, looks a lot like the Elio that just started selling this year.

HAVE they actually *sold & delivered" ANY vehicles yet?

On further investigation, no they have not. In fact despite the 65k+ paid reservations, they've pushed the launch date back to 2018 and are claiming financial problems as the reason why. What a shame.

The thread on this runs 172 pages since 2013-01.

http://ecomodder.com/forum/showthrea...ing-24513.html

Photobucket
 

Looks like Photobucket has changed their services and I can no longer share or link any of my 71-pages of aero images without paying them an annual fee.
At first blush,I can't conceive of paying out any new expenses.After Medicare kicked in,my monthly income is equivalent to around $4/hour.

Is it better to
 

It depends.
Hucho suggests that for the optimum drag reduction,you'd convert the notchback to a Kammback.
However,there is evidence that it's not a one-size-fits-all solution.
Evidently,we'd have to consider each vehicle on a case-specific basis.And there's no apriori way to predict any specific outcome.Which sucks!

https://www.google.com/search?q=photobucket+3rd+party+hosting

PCMag reports it 6hrs ago, Ghacks Technology News 9hrs ago. :eek:

If you still have access of your own, it's not ransomware. Be looking for a download manager or utility to suck down everything behind your log-in page.

https://www.google.com/search?q=website+downloader