Quote:
Originally Posted by MTrenk
I don't believe that bumps would work. Dimples create low pressure zones that keep the boundary layer attached for as long as possible. Bumps won't really create that effect.
aerohead:
I know about the Reynold's numbers and blah blah blah.
--> A flat panel will have a short laminar attached boundary layer, then an attached turbulent layer, then lose any attached flow.
--> A dimpled (flat) panel will keep the attached turbulent flow, reducing drag compared to the flat panel.
Sure things are different based on how big your object is vs. how large your dimples are and stuff, but in no way can you say that a flat panel will be the same as a dimpled panel.
Still the best way is to not have a flat panel; an airfoil shaped bottom is ideal.
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*the laminar boundary layer is about 25mm long with a passenger car.
*then it transitions to turbulent boundary layer.
*the flow remains attached,with growing boundary layer thickness until it encounters the end of the car,where,in the absence of a diffuser, it separates,joining the wake turbulence.
*with the addition of a slow or up to 11-degree 'fast' diffuser,the air regains pressure,separating at a lower velocity,increasing base pressure,reducing pressure drag.
*Bumps,nubs,and an assortment of vortex-generators could actually perform better than dimples.The only reason that they're not used on golf balls,is that they'd be deformed or destroyed every time they were struck by the club head.
*any discontinuity in the aerodynamic pathway increases drag.
*Aerodynamically,a smooth panel would be preferred.
*Other considerations might compete.
*the most simple airfoils (Clark Y) have a smooth flat bottom
