Vortex Generators / Hmmm Airtabs

[zpiloto]

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.



On the front wheel well

[kickflipjr]

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

[Bunger]

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. =)

[zpiloto]

Originally Posted by Bunger

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?

[GasSavers_katman]

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.

[JanGeo]

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

[Silveredwings]

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:
http://www.greencarcongress.com/2005...at_tail_d.html
http://www.maxmpg.org/the_cap.html

PDF warnings:
http://www.nasa.gov/centers/dryden/p...ain_H-2283.pdf
http://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.

[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.