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 Post subject: Gusty Wind and Upwind Obstructions
PostPosted: Wed Mar 17, 2004 4:35 pm 
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Joined: Mon Feb 11, 2002 1:00 am
Posts: 8254
Location: Florida
windowguy wrote:
anybody got expierience going under tall bridges.
for instance...is it best to have wind at 90 degrees so u can just make a downwind run out of it,
also is the turbulence on the other side crazy or do-able.


I would guess that you are thinking about the Skyway Bridge in Tampa. I have only driven over it and have not ridden in the area before. I know you guys hit that area a lot as the wind seems to favor the area.

Image
from: http://www.figgbridge.com/

Lacking any practical experience with riding in the area of the bridge, some ideas come from a fluid mechanics perspective. I would imagine that you would have a lot of vortical shedding or eddies cast off downwind of the road bed which is "foil-like" in section. These eddies could extend downwind for a considerable distance and might behave a bit like rotor downwind of land based obstructions. Rotor gusts and lulls are a pain to kiteboard in. Then look at the mass of suspension cables, I am not sure what kind of disturbance field they would setup but it looks like it could be significant. Finally the primary span supports are large enough in diameter to shed some major eddies all on their own.

Image
An eddy field set up by a cylinder
From: http://www.tecplot.com/

Your kite would be flying in that messy stuff to the right of the cylinder. You might get some big air though, for a short time, if an eddy carries your kite up. Of course it will likely stall it and dump it shortly after that, ouch!

Image
Another view, the darker blue blobs represent faster moving fluid or air in our case, intermixed with the slower moving green blobs and more pronounced lulls.
From: http://www.software.aeat.com/

Being a bridge "wind dummy" or the first person to test these conditions may not be all that fun, particularly if some bizarre flow occurs in the area of the bridge. If the wind is side or side on to the bridge, the flow and eddy corridor could be quite wide and whip over a substantial area. Your kite would be closer to the eddy corridor cast off from the road bed, i.e. that is the area of higher wind speed and direction shifts. I think I would pass on it myself though it is an interesting problem to consider.

Originally posted at:

http://www.kiteforum.com/phpbb/posting. ... t&p=107664


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