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Forum Index : Windmills : pressure vs. velocity

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stevet47

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Joined: 12/09/2008
Location: United States
Posts: 7

Posted: 09:04pm 23 Sep 2008

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I know they are hard to distinguish when just thinking about the wind, but what is more important for a wind turbine, the velocity of the wind, or wind's pressure.
I suppose this would vary based on the type of design, IE, a drag-based design like a savonuis would probably benefit from pressure, but a lift-type turbine would probably benefit from velocity.
Has anyone actually researched this?

AllanS
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Joined: 05/06/2006
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Posted: 09:14pm 23 Sep 2008

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The pressure is caused by the air's change of momentum, which is directly related to its velocity. Unless your windmill is on the top of a mountain where the air is thin, wind velocity is all that matters.

But of course, I might be wrong...

stevet47

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Joined: 12/09/2008
Location: United States
Posts: 7

Posted: 01:48am 24 Sep 2008

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Thanks AllanS
Anyone else have any input on this?
I am working on a wind turbine with an enclosure around it, and need to
figure out whether the closure should increase velocity or pressure.

Jarbar
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Joined: 03/02/2008
Location: Australia
Posts: 225

Posted: 02:42am 24 Sep 2008

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Hello,can you describe your idea and to which type of mill you are refering to VAWT or HAWT.

Jarbar.

"Creativity is detirmined by the way you hold your tounge".My Father
"Your generation will have to correct the problems made by mine".My Grandfather.

stevet47

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Joined: 12/09/2008
Location: United States
Posts: 7

Posted: 12:33pm 24 Sep 2008

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Well, I've got a couple of things going, one is multi-directional, so it work work that same as either a VAWT or a HAWT.

The other is a HAWT.

Now that I think about it, I am kind of answering my own question... I suppose of a lift-type design, air pressure doesn't matter, as it is the speed that the air passes the blades that creates the lift and turn the rotor.

But for a drag-type, I am less sure. High velocity is still necessary in order to turn it with usable speed, but I think it would require more pressure to actually turn it, and for the reverse side to push through the wind.

I'm just thinking out loud I guess.Edited by stevet47 2008-09-25

SparWeb

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Joined: 17/04/2008
Location: Canada
Posts: 196

Posted: 02:59pm 24 Sep 2008

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Air pressure isn't directly relevant. Air density is very important. Doing some research, you can find the equation for power collected by a wind turbine. One of the first variables in the formula is air density.

Any wind turbine blades tested at sea level will collect only 90% of the power when installed in an area at 3000 feet altitude (or 1000 meters). I live at 3200 feet altitude, so I experience this effect in all sorts of ways; boiling water, fuel economy of my car, and power through my windmill's rotor blades.

I can't do much about where I live, so I don't have control over the local air density. The site of the wind turbine can have a strong impact on the wind speed it receives, so ultimately, the wind speed is the only thing you have any control over.

Steven T. Fahey

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