New study on wind energy

Page 7 of 9  


I dunno. Someone posted an interesting site a while back about why an all-powerful God who makes miracle cures each minute of each day has never regrown a severed limb. I had my (sadly dying) evangelic cousin tackle that and she responded "there have been cases of fingertip regeneration." If there is a God, he/she/it seems strangely limited to effecting cures that random chance could just as easily explain. The fact that there are so many different versions of God tends to prove that there isn't any true one. A "true" God should have been revealed a long, long time ago but just the reverse is happening - religions split all the time, splintering even further the concept of one all-knowing God.
-- Bobby G.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Higgs Boson wrote:

That's just not true. There were 200,000 witnesses to God's revelation at Sinai (plus countless women, children, slaves, and asses). And an unbroken oral tradition retelling the tale to subsequent generations. As such, that fact is as acceptable and believable as a news story in the New York Times.
No, wait...
Never mind.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

for us agnostic/atheists can you provide proof of this?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 7/27/2011 2:05 AM, harry wrote: ...

That's certainly not what polling data indicates...while historic organized denominations (of all stripes) are losing market share to the nondenominational and that ilk, individuals indicate a personal belief at roughly 70% overall US population. Down some, but not "most" on the side of no belief or belief in none by any stretch.
[No value judgment implied either way, simply observation...]
--
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 7/29/2011 2:17 PM, harry wrote: ...

Or at least the ones _you_ choose... :)
--
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Actually, the Cheney-instigated invasion of Iraq (neglecting the REAL target, Osama's refuge in Afghanistan) was to put down that insolent rascal of a Saddam Hussein who actually thought he could bust the sacrosanct US.-Saudi oil relationship and replace it with his cartel. Tsk, tsk! And then to have the chutzpah to plan denominating his oil in Euros instead of the sacred Dollar! Man's gotta go...
HB
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Higgs Boson wrote:

Uh, we invaded Afghanistan before we invaded Iraq.
It was never the policy of the Bush administration to kill or capture Osama ben Laden.
Don't get me wrong, if OBL HAD been captured or killed, that would have been a plus, but the stated goals of the Bush adminstration was to disrupt or destroy the ability of terrorists to train, have sanctuary, get financing, recruit, or organize. These goals were substantially achieved.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
HeyBub wrote:

Hi, Every coin has two sides. Been to Denmark? They have hundreds of wind turbines along their coast line. Denmark is not a country of children, is it?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
HeyBub wrote:

When you look at an ordinary fan, it has large blades that occupy a significant portion of the cross-sectional swept area.
When you look at a wind turbine, the blades are very thin, occupying a very minimal amount of swept area, allowing much of the wind energy to flow right through or between the blades.
If a fan has fan blades that are designed to *efficiently move air*, then why won't that same basic blade design also be *efficiently moved by air* ?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

That's not true. Look at a propeller airplane. It's blades move air and they are long and thin.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Wed, 20 Jul 2011 06:09:59 -0700 (PDT), jamesgangnc

I feel an aerodynamics lesson coming.
Jim
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

One word.......plastics. er, no, I mean feathering.
--Vic
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
jamesgangnc wrote:

The cross-sectional area of a plane's propellers are a hindrance (drag) to forward motion. So while a fatter blade can provide more thrust at a lower rpm or with a lower swept area, a fatter blade will present more drag to counter a plane's forward movement. The slower a plane is designed to fly, the slower a plane's engine is designed to operate, the more sense it makes to use a fatter blade, or more blades (3 or 4 vs 2).
A helicopter develops lift because it's blades are really air foils that just like wings develop a low pressure area on their upper surface as they are moved forward (ie - as they are rotated).
When you look at the constraints of a typical house fan (low speed, inefficient motor, small design envelope or package) what you get are wide, fat blades. If wide fat blades are best at being turned by motors of low power to generate a breeze that consumers demand out of a small package size, then I'd have to assume that wide, fat blades would also be most easily and efficiently rotated by a breeze or flow of air passing through them.
If it doesn't take much motor force or motor power to turn wide/fat blades to generate an acceptible air flow, then the converse must also be true - that wide/fat blades are more easily turned by a given breeze vs long/narrow blades.
The energy potential in a wind field is measured in terms of the swept area of the blades.
So how can you capture a respectible fraction of this energy by using thin blades that "see" or experience only a small fraction of this swept area, vs using fatter blades that expose themselves to a greater percentage of this wind field?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Fat and thin. They are all airfoils. Do you think they woudn't use fat blades if they worked better? You think engineers didn't design the blades on wind turbines?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
jamesgangnc used improper usenet mesage composition style by full-quoting:


A typical air foil is an airplane wing. The "foil" is cross-sectional profile - curved upper surface, flat lower surface. The foil is what gets you life when it's moved forward through the air. You create a low-pressure area on the upper surface.
I can move air with flat blade angled at 45 degrees. The blade doesn't need a foil-shaped cross section - instead it can be flat. When a flat blade is angled (any angle other than 0) and rotated, it is pushing air out of the way as it turns.
Similarly, wind that wants to move past the blade must push it aside, and in doing so it will rotate the hub. The more surface area you present to the wind (ie the wider the blade) the more rotational force you transmit to the hub.

Maybe it's all a scam. Maybe wind turbines don't need to cost a few million each, and be hundreds of feet tall with blades made from exotic materials and methods.

Explain what's wrong with my concept.
How much cross-sectional area is occupied by the blades in a water turbine as water flows past them in a hydro-electric station?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
harry used improper usenet message composition style by full-quoting:

Well shit.
If a conventional airplane wing is a foil, and if a flat plate can be a foil, then fuck, everything and anything can be a foil according to you. So where does that get us?
No matter which way you cut it, you're still left with capturing a lateral force (ie = wind pressure) and convert it into rotational energy. A flat blade angled at 45 degrees will probably get you the most torque and rotational speed out of a given breeze of air (but it's totally possible that optimal blade angle is a function of RPM), and the more surface area your blade has, the more of that wind energy it can convert into rotational energy.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

If you look at the old stereotypical "prairie" style windmills, that's how they are. A disk with pie-shaped blades angled at 45 degrees, facing directly into the wind with the help of a fin.
All that surface area catches a lot of wind, but it also creates a lot of aerodynamic drag which makes it require higher wind speeds to turn. The air pushing through the "fan" creates rotational energy, but the air AROUND the fan is creating drag as the tips of the blades contact it.
The reality is that what makes a good propeller or helicopter rotor also makes a good windmill blade. Maximum lift with minimum drag. THAT is why we have thin blades. The cross-section of a modern wind turbine blade is a high lift, low drag airfoil that will catch air and turn the rotor at far lower wind speeds than a solid disk of 45 degree flat plates.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@rochester.rr.com wrote:

I believe that drag is a function of the surface area of either the front or rear (or maybe both) trailing edges of the blade.
Which if you look at the ratio of blade area to frontal or trailing edge area, the conventional long thin blades have a horrible ratio.

Those blades are operating in a wind-speed regime that far exceeds the design profile of capturing low-speed terrestrial wind currents. So again I don't know why airplane propeller blades (or in general the long, thin blades) are being thought of as the most optimal to capture energy from 5 to 25 mph wind currents.
Look at the cross-sectional area of a jet turbine. Lots of surface area there. Ever sit on a jet parked at the gate and watch it's turbine rotate as it catches the calm breeze wafting by?
I think that in the future your going to see more of these helical-based turbines:
http://www.caleta2.com/video/spiralairfoil-wind-turbine-spiralairfoil-com-/4vSD8z4fzNg /
http://www.bnet.com/blog/energy/three-bright-new-ideas-in-biofuels-solar-and-wind-power/2827
http://www.groovygreen.com/groove/?p 60
http://www.azocleantech.com/news.aspx?newsID 611
http://www.mywindpowersystem.com/2009/05/the-most-amazing-wind-turbines-designs /
"Helical structured wind turbines are the future of wind mill technology. These amazingly unique looking twists and turns will replace those long and boring blades which represent the conventional image of a windmill. These new and sleek looking windmills are designed much like the old ones when it comes to converting their circular motion in to mechanical work, but it is the structural design that makes them unique and special. In fact, they logically should function better than the traditional windmills as the helical structures seems to not just utilize the energy of the wind, but maximize it by containing the wind."
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 7/21/2011 1:29 PM, snipped-for-privacy@rochester.rr.com wrote:

Have you seen the eight bladed props on the Airbus A400M Military transport plane? The propellers look quite a bit different from what you'd expect to see on a turboprop engine. I remember seeing pictures of NASA developing such a prop years ago.

http://www.youtube.com/watch?v=h-V5jzSslZo


http://www.youtube.com/watch?v=fTFitHATBWc

TDD
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 7/21/2011 1:29 PM, snipped-for-privacy@rochester.rr.com wrote: ...

...
None I've seen were actually flat, though. All ours had a curve built into the blades; steeper front attack angle than rear. Dated from roughly 1910 on thru the 20's...
The old Delco Windcharger (mid-1910s when ours installed; not sure when they were actually introduced) did have a three-bladed hub; not quite so aerodynamic as current but certainly reminiscent.
--
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Related Threads

    HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.