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Old 7th February 2009, 11:28 PM   #1
windsomniac
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Default Windsurf Sail Wind tunnel data Cl Cd

Does anyone have any windsurf sail lift/drag vs alpha data?
Maybe Jim Drake. I don't know how to get in touch with him.
I'd prefer not to get into deriving cl and cd purely from theory as
this is difficult in 3-d without some type of check.
My math model is severely limited using generic sail data from Marchaj.
Thanks
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Old 8th February 2009, 12:05 AM   #2
mim
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Default hi,

I kind of doubt that...wind tunnel testing would be theoretically possible...but the problem is dynamic behaviour of the sail (no) real wind is stready one.

In car industry or turbine theory it is not an issue, because the wind gusts are still negligible compared to speed generated flow.

this is a bit tricky, even if there would be a measurement in wind tunnel, personally I think the actually values looks a bit different.
The biggest problem generally I see in the model it self...if you assume only a steady flow, the model will be very bad. If there is a stochastic part of wind (flow) the model will not be good either (because the values the coefficients will be again for a steady state).

Hope this ain't that messy, and you could understand what i am trying to say.

Hang loose,
Ciao Michal.
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Old 8th February 2009, 01:09 AM   #3
windsomniac
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I understand what you are saying. Point taken. I take issue with my model will be very bad. Simplified mathematical models are used in all engineering disciplines to predict physical behavior. Even though they may be incomplete, these simplified models can give much insight. For example I'm not going to solve unsteady navier-stokes to figure out what the head loss is in 100 ft of 1/2 inch pipe with three 90s.
In fact, I'm pretty surprised at how reasonable my existing model is at predicting velocities, planing, optimal sheeting angle and sail heel. Yes the model is steady state. The model uses generic sail data from Marchaj. Just looking for some more sail data that is closer to the windsurf sail plan form. If there is some test data taken at the proper reynold number it would be very useful. Solving for lift and drag of the windsurf plan form purely from theory is daunting no matter the method (including CFD). But, besides your words of encouragement got any data?
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Old 8th February 2009, 01:34 AM   #4
mim
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Default data

sorry i have nothing, I understand flow physics till a certain level (deeper I could go if your questions concern plasma physics and molecular flow of ionised fluid in E-B field...), but I definetely have no data sails aerodimac coeff.

But you´ve got my attention...would be intereted for your present work...any chance of sharing?

Ciao M.
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Old 8th February 2009, 09:44 PM   #5
davide
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Quote:
Originally Posted by windsomniac View Post
But, besides your words of encouragement got any data?
Gastra (http://www.gaastra.com/) years ago had a set up where they put a sail on top of a truck with a bunch of sensors to simulate and measure different conditions. Maybe you could contact them ...

Last edited by davide; 8th February 2009 at 09:47 PM.
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Old 8th February 2009, 11:01 PM   #6
mim
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Default wow

that definetely is pretty close to the reality...
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Old 9th February 2009, 12:29 AM   #7
steveC
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Relative to davide's post where a sail was mounted on a truck to study design and performance related issues, it's my recollection that Bruce Peterson (now of Sailworks) was one of the principals involved in the testing. I think that he would be the best source to contact.
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Old 9th February 2009, 02:01 AM   #8
Farlo
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Hi Windsomniac, 25 years ago I tested a wing in a wind tunnel at school. This wing's shape was close to an old fashioned windsurf sail but with two masts (I can't describe it easily). Would it be of interest for you? The results are still at home somewhere, but I won't be back before next Sunday.
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Old 9th February 2009, 03:18 AM   #9
windsomniac
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Farlo, i'd like to see your data. Yes that would be terrific!
Davide and SteveC, I'll try to get in touch /w gaastra and Bruce, thanks!
mim, i don't think my model is user friendly enough at this stage to share, but I'll keep you posted. i will eventually need some peer review.
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Old 9th February 2009, 03:40 AM   #10
windsomniac
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Thinking out loud here, I guess I might be able to back out lift and drag coeffcients out my model by analyzing really good time stamped video. I would need to know the sailor's weight, equipment size, and the wind speed in the video. This would probably about as accurate as full CFD, but maybe more work.
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