Quote:
Originally Posted by JohnForde
Seeking advice.
Today I thought for sure I would see an appreciable decrease in drag. My sample was only 15 miles but any improvement was negligible. I have a 4 sided box 66" long at 16 degrees. The entry cuff is curved HDPE at about 11 degrees. The top is 16 degrees. There are vortex generators on top & both sides.
The Zevo is 84" W. The WT doors 'aperture' @ 50"W.
I cannot do a tuft test because I do not have a partner/chase vehicle.
Included are 6 photos and a video. Thoughts?
https://photos.google.com/photo/AF1Q...YZmJw5oCr5sSsJ |
* The VGs just may not be capable of inducing reattachment onto the 16-degree slope.
* A study of the Mitsubishi Lancer Evo's effective back-light angle would 'tell' us something about their VG's capability to reattach flow onto the boot/trunklid of that vehicle.
* Vortex-drag is the most 'powerful' type of drag known.
* A 'squareback' trailing edge already produces vortex-drag.
* From Bearman's research on angled aft-bodies, a 16-degree slope would have increased vortex-drag by over 300%, compared to the 'flat' roofline.
* Another 'unknown' has to do with the exposed, down-facing 'winglet' formed from the upper panel.It may be behaving as a 180-degree out of phase 'capping plate' that you'd find on the wings of an Indycar, or Formula One. Very 'draggy'!
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* If we presume that ATDynamics wind tunnel, or CFD tested ( or both ) their 'Trailer Tail,' then observation informs us that they weren't willing to push their aft-body slope angle beyond 12.5-degrees. This may be the 'GO, NO GO' for a simple body type. And we're not led to believe that Trailer Tail has 'attached' flow over it's 48-inch span, only that it's tearing edge has 'intercepted' the 'reversal point', where the flow just barely reattaches before it reaches the trailing edges of the tail.
* Shooting from the hip, I'd be inclined to ignore everything between 16-degrees and 12.5-degrees, and go straight to 12.5-degrees for a re-test.
* The result would would be instructive either way. ( aerodynamicist Alex Tremulis referred to this as conducting 'pick and shovel work').
* If you saw 'pay dirt' at 12.5, you could always 'back off' until the drag trend 'reversed', indicating the slope 'limit.'