[aerohead]

I GOOGLED this topic, which took me over to a Cal Tech article.
Most of it was for 'contained' 2-dimensional flow within a pipe, in compressible flow, not something germane to automobiles.
What it said with respect to un-bounded, 3-dimensional flow, and a turbulent boundary layer had no bearing on automotive aerodynamics that I could discern.
A parting thought with respect to 'Rocketail', it will be interesting to see what product liability attorneys do when a motorcyclist slides into the back of an over-turned 18-wheeler with 'Rocketail' and their body is bifurcated with the trailing edges of the vanes.