Originally Posted by aerohead
I've mentioned that we have no direct analogue to Zevo, as related to reported test data.
P. T. Bearman did test a prismatic 'Windsor' saloon body square-back in 1984, which included 11-degrees, through 16-degrees rear slant ( roof only, no sides, nor 'diffuser' ) :
1) 'Any' slant created vortex-induced drag.
2) 'Profile drag' DID fall between, zero-degrees and 5-degrees, then rose again.
3) At 11-degrees, vortex-induced drag was Cd 0.01428
4) At 16-degree, vortex-induced drag had risen to Cd 0.04693 ( a 328% increase ).
5) For 'ALL' slant angles, drag increased.
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6) The Ahmed body ( van ) 'square-back' experienced a drag minimum, with a rear slant angle of 9-degrees.
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7) The soft-sided, 'Windsor body' square-back, achieved a drag minimum with a boat tail of 8-degrees, top and sides, with soft sides.
8) As slant angle increased to anything beyond 8-degrees, 3D trailing vortices pushed vortex-induced drag higher, increasing the total drag.
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9) Revisiting Lawrence Livermore's research:
A) The #1 tail, with the 'LARGEST' wake, had lower drag than the two tails with the 'smallest' wakes.
B) The #2 tail, with the 2nd-largest wake, had the lowest-overall drag.
C) The tearing edge of the #2 tail would constitute the 'intercept' with the 'reversal point' of a 'streamlined' contour, at which flow would reattach, a captured-vortex would form, and a compromised pressure recovery would be realized, plus Hoerner's 'Angle of Flow', towards the wake would be 'optimum
;' and base pressure the highest.
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