If they prove worthwhile I may go buy a sheet of polycarbonate and cut some out of that. I have also been dreaming up a spoiler/boattail out of polycarbonate. I think it could be done to look fairly good.
The CDs only work if they are Earth, WIND and Fire
2006 Jeep Liberty CRD...Founder of L.O.S.T.
OME 2.25" Lift w/ Toyo Open Country HTs 235/75/16s
ASFIR Alum Eng/Tranny/Transfercase/Fuel Skids
2002 Air Box Mod...Air Tabs (5) on Roof...(3)each behind rear windows
Partial Grill Block with Custom Air Scoop and 3" Open Catback Exhaust
Lambretta UNO150cc 4 Stroke Scooter
Well the initial drive with them has provided no feedback at all. I had to drive 35-45 mph for about 80 miles of my 150 mile trip due to the snow and idiots over the pass yesterday. The rear window did not stay any cleaner with them on. I ran a steady 65 when I got over to I-5 and my trip computer says i was running better mpg than I have the last few tanks but the weather has been completely different.
One negative I have found with them is the guy with the lifted 4x4 must have thought they looked cool in his high beams as he put them on several times while right behind me in the right lane of a passing zone.....
I think I will leave them on for a few more tanks of fuel and try to do some A-B testing when I take them off.
At this point I am going to call this attempt a failure. I did not go into doing this with a good enough plan and the weather has not cooperated this week so I have no idea if it made any differnce in FE. The rain and snow and wind finally detached 3 of the 6 VG's after 400 miles. It made no difference on how dirty my rear window got.
I think I will talk to the VW dealer and see if there is a kit for deleting the roof racks. Probably a much better chance of seeing an improvement.
Dang Zuq, The time stamp says you replied at 3:07AM!
I need to take the time to be more serious with my testing. I have been looking at adding a spoiler to extend the roof anther 6". It looks like it would be even easier to make than the VG's.
I still may look into VG's for my 4x4 dodge and various tralers.
I'm a truck driver and have been researching the vg's for my use. This is how I came acrossed this thread. From what I have read the Votex generated is 4 times the height of the vg. This leads me to think the reason for your failure of proof of concept is the cd in unaltered form is too big. A 1 inch vertical vg will create a 4 inch vortex. That's all you need. Spaced 3 inches apart. As large as those CDs were I might even hypothesize that they distorted under load and possibly lost functionality. Love the effort keep it up.
I drive a 2013 peterbuild and currently average 7.5 to 8 mpg weekly avg. many variables to account for but for every 50 gals a week I can save is between 175 to 200 dollars increased income per week. Needless to say I take this subject seriously.
There was also a paper on them I found that went extensively into the science and experimenting. The author concluded with ideal dimensions for a delta shaped VG. I gotta google it if anyone wants the link.
But in my experiments using tuft testing I have found that these air tab shaped VGs have done very well. Admittedly, I grew tired of the aesthetics which is why I switched to delta VGs.