Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - View Single Post - Managing vortexes off the back of a partial boattail

aerohead · 03-20-2012, 06:42 PM

From Hucho,Buchheim's research took two directions,one the simple hard-edged model work,and curved surface research.
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On the hard-edged bodies the optimum angle was a direct function of the length of the slanted portion of the body.Angles can only be taken in the context of the slant length.
Cars with the largest slant length can sustain the greatest angle.
*a 9% aft-body min is @ 13.2-degrees
*a 18% aft-body is 15.3-degrees
*a 27% is 17.4-degrees
*a 36% is 18.5-degrees
*a 45% is 22.5-degrees ( halfway between Mair's 22-degree limit and Hucho's 23-degrees.
When you look at the minimum drags for the data presented,they always occur when at 'Template' tangent angles.
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For the curved body Buchheim's research demonstrated minimum drag also at 'Template' angles.His Fig.4.60,at drag minimum is a dead match to the 'Template.'
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I would recommend that all your contour be based on the 'Template.' You have less to work with on the sides,so you'd just pick up where Ford left off with respect to plan taper.
For the roofline I would stay as close to the 'Template ' as you can.22-23 degrees of slope is the maximum or you're looking at separation.
I wouldn't sweat the vorticity,it becomes a real problem at over 30-degrees of slope.You won't be going anywhere near there.
If you had a notchback you might do things a little different.

03-20-2012, 06:42 PM	#2 (permalink)
aerohead Master EcoModder Join Date: Jan 2008 Location: Sanger,Texas,U.S.A. Posts: 16,330 Thanks: 24,452 Thanked 7,393 Times in 4,788 Posts	the back From Hucho,Buchheim's research took two directions,one the simple hard-edged model work,and curved surface research. ---------------------------------------------------------------------------- On the hard-edged bodies the optimum angle was a direct function of the length of the slanted portion of the body.Angles can only be taken in the context of the slant length. Cars with the largest slant length can sustain the greatest angle. a 9% aft-body min is @ 13.2-degrees a 18% aft-body is 15.3-degrees a 27% is 17.4-degrees a 36% is 18.5-degrees *a 45% is 22.5-degrees ( halfway between Mair's 22-degree limit and Hucho's 23-degrees. When you look at the minimum drags for the data presented,they always occur when at 'Template' tangent angles. -------------------------------------------------------------------------- For the curved body Buchheim's research demonstrated minimum drag also at 'Template' angles.His Fig.4.60,at drag minimum is a dead match to the 'Template.' -------------------------------------------------------------------------- I would recommend that all your contour be based on the 'Template.' You have less to work with on the sides,so you'd just pick up where Ford left off with respect to plan taper. For the roofline I would stay as close to the 'Template ' as you can.22-23 degrees of slope is the maximum or you're looking at separation. I wouldn't sweat the vorticity,it becomes a real problem at over 30-degrees of slope.You won't be going anywhere near there. If you had a notchback you might do things a little different.