Quote:
Originally Posted by Blacktree
Can you explain this in more detail? My brain isn't firing on all cylinders, at the moment.
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1) In the best case, underbody airflow would pass along a full, smooth belly pan, then decelerate up a gentle diffuser, experiencing pressure recovery, and injecting higher pressure air, vectored into the base, directed into the wake, for an overall base pressure increase, overall reduced pressure drag, overall reduced drag.
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2) Extending a Baumann scoop into the flow below the body, to harvest ram-air to pressurize the 'duct', would rob air from the downstream belly and diffuser.
3) Since the duct has more wall surface area than the belly pan where it would otherwise flow, you've introduced surface friction at an average duct velocity, with a Cd 0.003 coefficient of surface friction drag ( for a perfectly-smooth ) surface, and total wall area of the interior of the duct.
4) There will be viscous shearing losses within the air itself as it decelerates in the duct system.
5) The lowest drag Baumann scoop is Cd 0.05. Along with its projected frontal area. CdA. Which increases the overall frontal area of the vehicle. A step backwards.
6) A NACA submerged-inlet ( preferred over a scoop ) would not be a candidate for use because of the Tahoe's deep, ladder-type frame
crossmembers.
7) On an Audi 100-III for instance, the presence of the scoop(s) could increase drag by Cd 0.015 right where they're mounted, and another Cd 0.025 by destroying the efficacy of a low-drag diffuser downstream. A potential Cd 0.04 drag increase.
8) Add the drag of the flow perturbation, the scoop, aggravated frontal, plus the increased surface friction within the ductwork, and you've shot yourself in the foot. A numericalized guess.