Quote:
Originally Posted by GaryBIS
Hi,
I got a set of Vorblade vortex generators and installed them on my 2014 ProMaster van and have done an MPG test on them using the methodology described on this site.
I mounted them temporarily on the van so I could do the A-B-A thing and also not have to keep them if they did not work.
I did an A-A-B-B-A-A test with the two B's being with vortex generators. Each loop was a 65 mph drive down the freeway for 17 miles and then back in the opposite direction for 17 miles. I kept track of MPG using: 1) the onboard trip computer, 2) and OBDLink logging data to my laptop, and 3) fillups at a very nearby gas station after each two loops.
I guess I can't include links until I've made a few posts, but the full results of the test are available on my "Build A Green RV" website (just google it), then on the site search for "Vorblade". There are lots of pictures, plots, and details -- maybe someone who can post links can include the URL in a comment?
The results on the trip computer were:
First two A loops (noVGs): 21.6 and 21.1 MPG
The two B loops (with VGs): 21.1 and 20.4 MPG
The last two A loops (noVGs): 20.4 and 20.7 MPG
I can't see any reason to think the VGs resulted in any improvement.
I'd be very interested to hear...
- Any problems with the test method I used?
- Is anyone surprised by the result?
- Any suggestions for improvements?
- Any thoughts on the simpler alternate test procedure that is described at the link above?
I want to thank all the folks who contribute to the website and make it easier to come up to speed on doing valid tests easily!
Gary
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VGs are a technology borrowed from aeronautical use. Since aircraft typically 'rotate' to achieve an angle-of-attack dependent coefficient of lift,both in takeoff and landing, it's extremely important to maintain elevator, aileron,and slat/slot/flap authority to control the plane.
At 'flight' conditions, at operational altitude, air density, and trimmed for level flight, the VGs are just a constant source of drag. A compromise for takeoff and landing safety.
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When aeronautical engineer,Gary Wheeler, popularized vortex -generators on his Honda Accord notchback ( they became 'Airtabs' ), the context for their operation hinged upon the fact that, there would be a surface in separated flow behind the VGs which would experience reattached flow, due to the delta-wing-like momentum transfer of energy into the turbulent boundary layer of the boot ( trunklid).
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If VGs are placed at the back of a van, truck box, or trailer van, they're violating the premise of a VGs primary function. Without some surface to reattach to, other than alter the flow back there, there will be no flow attachment, captured vortex, flow deceleration around the vortex, and pressure regain; all hallmarks of drag reduction.
Hucho commented long ago that, we'd only expect real drag reduction from either a box cavity, or boat-tail, as these are the only two technologies capable of performing the flow deceleration, pressure regain, and increased base pressure associated with pressure-drag related total drag reduction.
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If you're flying a Lockheed C-130 Hercules, then by all means, put some VGs under that horrible up-swept, high-drag tail. Otherwise, leave them to the gullible, non-critical thinkers.