Quote:
Originally Posted by Engeu1
See figure 12 in
2012 Khalighi et al. Unsteady Aerodynamic Flow Investigation Around a Simplified Square-Back Road Vehicle With Drag Reduction Devices J. Fluids Eng. Jun 2012, 134(6)
for a very good approximation of a rectangular body induced vortex ring.
In any case, to some degree a rear tail could transition the flow away from rectangular -some tails are well radiused.
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I had to check, but I've had that paper for years.
Again, their work corroborates Hucho's claim that, only box cavities and boat tails produced drag reductions. 18% in the case of their box-cavity, and 30% in the case of the boat-tail.
And both these devices are longitudinally ' non-ventilated'.
The first device incorporates locked-vortices to accomplish flow deceleration and pressure recovery, while the second provides the actual, solid deceleration ramp.
The investigators are from General Motors Corporation, which conceived the ' OPTIMUM TAIL', which graduate student Scott Funderburk and Professor Carver included in Scott's Masters thesis investigations of boat tails in the 1990s.
Unlike the Ahmed body boat tail, the GM Optimum Tail incorporated generous all-edge radii, for vortex-free flow, of special interest to Funderburk. Myself included.