Vortex Generators / Hmmm Airtabs

[zpiloto]

Originally Posted by ZugyNA

Using the Mitsu research and ultralight info...I made 5 vgs from alum flashing material 2 1/2" long....with 2 vanes each 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.

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. Have you thought about adding a couple more to decrease the space between VG's?

[ZugyNA]

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.

[zpiloto]

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.

[ZugyNA]

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.

[MetroMPG]

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.

[JanGeo]

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.

[MetroMPG]

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

[JanGeo]

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.

[zpiloto]

Originally Posted by MetroMPG

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.

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.

[ZugyNA]

Originally Posted by MetroMPG

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.

>> 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"?)?