Quote:
Originally Posted by yabert
Thanks for all details. I guess 13% penalty in nothing and don't worth the extra fabricating effort.
1-Is it possible to see this?
2-What about the other axes. I guess it's better to be smaller to the rear, but how to know the best shape?
3-How about the final transition ''blending into the metal roof''? Is the best shape go down at the rear, is it go straight (let say down 17.5°) or is it better to go parallel to road a bit like the rear of a Tesla Model 3?
I have all those question because I have limited aerodynamic experiment.
I think I can do something with Solidworks flow express. I don't know how it work and I don't know if this flow express have enough features to calculate the best shape I'm looking for.
|
1) you've essentially depicted it in your #2 image, excepting that, you'd have a 2-D flow apparatus, instead of 3-D, with no facility for a '3D relieving effect', described by Goro Tamai.
2) as to 'best' shape, that would be the conjoined, nose-less, double-tailed, 3-D 'blister/ canopy', with a 100% 'aft-body', both in elevation and plan-view, however, that's off the table as far as your fabrication goes.
3) 'qualitativley', it could have 35% lower drag than the 'classic' bubble canopy, but since it's being used as a 2-D structure, it remains an unknown quantity.
--------------------------------------------------------------------------------------
If we want to back-pedal a bit, we could discuss the 'two' Vanagons you're driving. In road vehicle aerodynamics, we must consider the 'form' of the vehicle's body, 'above' and 'below' the ground, in mirror image ground reflection, as it would appear in free flight.
Combining to two provides what the air 'sees.' We drive the 'right-side-up' version, while the air also sees the 'upside-down version.' ( this is built into the code of all CFD software ).
--------------------------------------------------------------------------------------
If you wanted, you could scale the Vanagon, with each roof mod to fit under the apex of the aerodynamic streamlining template gen-3 tool, here at the Aerodynamics Forum, and 'see' how it compares. ( if you watch the wind tunnel video of the Audi E-Tron GT, you'll see the Cd 0.04 streamline body of revolution which the 'template' is based upon. Hucho used it in his 1986 textbook, although it dates to the 19-teens, and is shared by Sighard Hoerner in his book, 'AERODYNAMIC DRAG', published in 1951, and 1965).
This contour/silhouette is a known quantity, and is presently used for the lowest drag concepts and production cars.
--------------------------------------------------------------------------------------
If I had the facility, I'd print out your CAD drawings and go ahead and do the comparisons.
--------------------------------------------------------------------------------------
The angled roof of the DON-BUR TEARDROP TRAILER channels the roof flow downwards into the base ( wake ), and although it may produce some vorticity, it doesn't appear to be a drag liability. So all of your 'aft-body' portions of the roof extension, in theory, should be okay.
-------------------------------------------------------------------------------------
You might consider fabricating a full-scale mockup for one of the 'teardrop' roofs out of 1/2-inch ( 13mm ) polyisocyanurate rigid foam insulation board and duct tape, then drive the 'transbolt' like you're going to, capture the 'miles/ kWh' from the 'guess-o-meter', then using what you've already tested, carefully deconstruct the roof, re-cut the sides, to create the 'double-tailed' #2 shape, tape the roof back on, and re-test at the same conditions, as best you can, and see if you can discern a 'winner.'
Think Flight has a great YouTube for his Subaru Impreza aero project, Gen-II, version-4 that you might get a kick out of .
--------------------------------------------------------------------------------------
if this takes, you're looking at an under-slung, add-on cargo pod, seen in 'Flying Wild Alaska'. The leading edge has little significance, whereas, the 'aft-body' is given a lot of attention.
https://www.bing.com/images/search?v...t=0&ajaxserp=0