Wall to wall airfoil in a wind tunnel

  • #1
John Mcrain
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Does wall to wall airfoil produce downwash in wind tunnel ?
 

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  • #2
rcgldr
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Depends if the wind tunnel has a ceiling and a floor, and if it does, how close to the ceiling and floor are to each other. If the wind tunnel is vertically "short", only a tiny amount of downwash occurs as air flows across the wing. For example, the amount of downwash over an airfoil with a 1 foot chord in a 1 foot tall wind tunnel will be tiny, while the amount downwash from that same air foil with a 1 foot chord in a 20 foot tall wind tunnel will be significant.
 
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  • #3
John Mcrain
407
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Depends if the wind tunnel has a ceiling and a floor, and if it does, how close to the ceiling and floor are to each other. If the wind tunnel is vertically "short", only a tiny amount of downwash occurs as air flows across the wing. For example, the amount of downwash over an airfoil with a 1 foot chord in a 1 foot tall wind tunnel will be tiny, while the amount downwash from that same air foil with a 1 foot chord in a 20 foot tall wind tunnel will be significant.
Wall to wall airfoil has "wingspan" same as wind tunnel width, high pressure can't leak to low pressure at tips.No wingtip vortices.
In wall to wall airfoil in closed test section downward movement of air will create a void above it(walls/vacuum stop this action), and the air below has to make place for that downward moving air,but again walls stop this action.
How then this is possible in fully closed wind tunnel even test section is very big/tall compare to airfoil?
Upper(ceiling) and lower(floor) walls don't allow that air circulation which downwash requier.
downwash .jpg.png



You say that downwash(like this on picture below) is possible in tall wind tunnel for wall to wall airfoil.
* to make that possible ,air behind center of airfoil must go down and air at side walls must go up,this air circulation must produce two roll-up vortices,Why I don't see described air DOWNWARD MOVEMENT in any wall to wall airfoil wind tunnel video?
cyr0c.jpg



downwash behind wing video:
https://fyfluiddynamics.com/2014/04/Newtons-third-law-says-that-forces-come-in-equal/
 
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  • #4
rcgldr
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Wall to wall airfoil has "wingspan" same as wind tunnel width, high pressure can't leak to low pressure at tips.No wingtip vortices.
In wall to wall airfoil in closed test section downward movement of air will create a void above it(walls/vacuum stop this action), and the air below has to make place for that downward moving air,but again walls stop this action. How then this is possible in fully closed wind tunnel even test section is very big/tall compare to airfoil?
Upper(ceiling) and lower(floor) walls don't allow that air circulation which downwash requires.
A fresh stream of air is flowing into the wind tunnel. For a tall wind tunnel, in order for a pressure differential to be created, part of that air flow has to be diverted downwards, it will eventually recover, but there will be downwash in the vicinity of the wing.
 

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