Quote:
Originally Posted by kach22i
Aerohead, can you post some visuals on this?
I did find the below, and it is different than the boundary layer I had imagined you were describing.
I imagine that the first layer of boundary air can cause all sorts of drag, lift and vortex formation so we better not ignore it, right?
https://www.google.com/amp/s/www.res...1_30496832/amp |
1) You're looking at a 'laminar' wing section in 2-D flow.
2) The 'center-most' structure, all in white is the actual wing.
3) The black region around it is both the thin laminar boundary layer ( LBL ), then, where the wing is thickest, the air the fastest, and pressure the lowest, you see the immediate jump to thicker turbulent boundary layer ( TBL), which continues to thicken with distance, caused by the higher skin friction of a TBL.
4) For a wing, the TBL aggravates drag due to the higher surface friction.
5) The outer inviscid flow travels over the boundary layer as laminar flow.
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A) In a road vehicle, Earth's boundary layer turbulence almost completely prevents the existence of a laminar boundary layer. One paper published for a full-scale RAM pickup determined that the truck had 30mm of LBL, right at the leading edges.
B) A TBL can withstand a higher positive pressure gradient in the direction of flow, so it's actually an advantage for a motor vehicle.
C) Since road vehicle drag is dominated by pressure drag, and pressure drag is a function of separation, the whole point of streamlining is to minimize, or totally eliminate separation.
D) Lift is solely a function of pressure.
E) Pressure is solely a function of local velocity.
F) Vorticity is a function of intersecting flows of varying velocity ( pressure). You might witness a fast moving storm-swollen stream enter into a slow-moving river, and where the two meet you'll see swirls, eddies, gyres, and turbulence, which can actually eat away at the riverbank. This is happening in the Antarctic ice sheets right now. And Clear Creek, along our property.
G) Streamlined shapes don't have pressure increases ( especially spikes) of sufficient magnitude to overcome the TBL's ability to adhere to the surface it's flowing over at any point.
H) Kamm and Fachsenfeld took a full-length streamliner and then just started chopping away the tail and recording the changes.
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I'll have to figure out something about images. I lost over $770 worth of pictures when photobucket decided extortion was going to be their new business model.