This box truck depicts a Cd 0.80+ drag due to the sharp leading edges on the 'trailer.'
An 'optimized' radius will help with separation control
Increasing the single radius may not reduce overall drag
Adding radii to all leading edges really helps
Airstream covers these bases
NASA's research recommends that we use the bulbous pathway to loft the air onto the T.T. roof and around the sides,as AeroStealth is approximating with the up-coming mods.
As to the boat tail,here you can see the 3-dimensional vortex pattern which is part of the drag reduction.
According to Bearman et al' research of 1982,
*the initial 25-degree top angle causes a 14.7% drag increase due to vorticity.,Cd 0.3005.
*the 10-degree diffuser added in creates a 16.8% overall drag reduction,Cd 0.233.
*when the sides are boat-tailed in at 10-degrees,the overall drag reduction rises to 32.8%, Cd 0.176.
*if all the panel intersections are chamfered,the overall drag reduction is 36.6%, Cd 0.166.
Altering any parameter throws the drag right into an unknown quantity.
And,anything we can do to murder the wake will pay deep dividends into the future
