Vortex Generators / Hmmm Airtabs

[zpiloto]

Originally Posted by Silveredwings

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.

[ZugyNA]

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.

[zpiloto]

Originally Posted by ZugyNA

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.

[ZugyNA]

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.

[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.