View Single Post
Old 09-22-2018, 02:45 PM   #8 (permalink)
aerohead
Master EcoModder
 
aerohead's Avatar
 
Join Date: Jan 2008
Location: Sanger,Texas,U.S.A.
Posts: 13,046
Thanks: 20,917
Thanked 6,377 Times in 3,961 Posts
thrust

Quote:
Originally Posted by hat_man View Post
Ok after re reading that maybe it's low pressure under the tonneau and a higher pressure (still low but not as low as under the half tonneau) behind the truck at the tailgate, causing the pressure differential and the idea of 'thrust"?
*Without the tonneau cover,there's nothing but turbulence back there.All the kinetic energy is lost forever,and there's no chance for any re-attachment.A lot of drag and a lot of lift.
*The tonneau provides a surface of re-attachment for the separated flow,allowing for a much smaller wake,and it kills most of the rear lift.
*The half-tonneau is a peculiar animal.It allows a locked-vortex to be captured behind the rearward facing step of the cab.
*The inviscid (streamline flow) follows over the vortex as if it were more a solid body,strikes the tail end's upper surface,really killing lift.
*The extremely low pressure of the 'eye' of the vortex is transferred to the inner face of the tailgate.This inner face is at a lower pressure than behind the gate,creating a pressure differential which 'pushes' the gate forwards,something which doesn't happen with a full tonneau.
*If you cut ducting through the gate,you lose the differential,and the 'push.'
*Also,air would actually go through the hole.from the back to the front,tripping up the flow and creating drag.
__________________
Photobucket album: http://s1271.photobucket.com/albums/jj622/aerohead2/
  Reply With Quote
The Following 2 Users Say Thank You to aerohead For This Useful Post:
hat_man (09-23-2018), slowmover (04-10-2019)