Quote:
Originally Posted by Engeu1
@JSH, yes that's the sort. Side skirt is in the pipeline, but priority has to be rear now because of a forthcoming non-aero change. Anyway, looks like U-Haul didn't fit a deflector on the overcab part of the box and left it square.
@freebeard, I hadn't seen the vortex traps (though not applicable) or strakes.
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Wolf-Heinrich Hucho made a comment about commercial vehicles which pertains to the deflector.
At the large scale, reflected in commercial trucks, a leading edge radii equal to 5% of the square-root of the frontal area is all that is necessary to achieve flow 'SATURATION.'
No additional softening of the leading edges will result in lower drag.
If true ( highly probable considering the source), then the NASA / U-HAUL box configuration would yield drag characteristics on par with a box with deflector.
A stagnation bubble travels ahead of the box, of which the surrounding air deflects around as if it were a solid, bulbous structure. Smoke images from wind tunnels clearly illustrate this phenomena, labeled ' Prandtl surfaces of discontinuity,' after Ludwig Prandtl's aerodynamic research which 'discovered' them.
Since the front of a truck constitutes only 5.8% of the overall drag, the gaps, sides, belly, and rear become the target for drag reduction.
Leyland DAF, in 1988, had a box truck with Cd 0.325, by Besco Bodies, Northhampton, England.
In 1986, Renault had a semi-trailer,'V.I.R.A.G.E.S.', with Cd 0.254, with cab-to-van gap-filler and 32-inches ( 813 mm ) of boat-tail.
If you simply mimic'd what NASA had done by 1980, your truck could have the drag of the 2020 Porsche Taycan Turbo S.
