h a l f b a k e r y
If you can read this you are not following too closely.
idea:
add, search, annotate, link, view, overview, recent, by name, best, random
meta:
news, help, about, links, report a problem
account:
Browse anonymously,
or get an account
and write.
Login
Create account.
|
|
|
Please log in.
If you're not logged in,
you can see what this page
looks like, but you will
not be able to add anything.
When wind passes through a windmill it comes out with a rotational component... I just want to place a second windmill with thinner blades or possibly fixed vanes, to straighten that out, behind the first... no clue how much it would add to the power output; not much I imagine, but you would be getting
more for the same amount of face.
Wind Turbines Produce 'Green' Energy — and Airflow Mysteries
http://www.jhu.edu/...e07/dec07/wind.html
Aiming Laser at Model Windmills Shows How Clean Power Source Can Stir Up the Atmosphere [baconbrain, Apr 28 2008]
Why windmills have three blades
http://answers.yaho...080407000946AAh2bmE
...or, at least, an odd number. [DrCurry, Apr 28 2008]
Contra-rotating coaxial props
http://en.wikipedia...rotating_propellers
Similar idea, but used for propulsion. [8th of 7, Apr 29 2008]
Newer designs call for only 2 blades
http://www.tfot.inf...e-wind-turbine.html
futuristic offshore wind turbine for the US [rotary, May 16 2008]
Annotation:
|
| |
It would cost so much more that it wouldn't pay for itself. [ ] |
|
| |
A fan or simply a blade? That's the question that needs no answer. |
|
| |
As you are effectively increasing the area, I suspect it would be just as efficient (if not more so) to add the area of the second windmill to the blades of the first. [ ] |
|
| |
Where do you get the impression that the wind downstream has a rotational component to it. As far as i understand it may have a somewhat more turbulent component but it is certainly not rotational. |
|
| |
In a modern windmill, the blades are far more expensive than the rest. In engineering point of view, a single counterweighted blade for a windmill is the most cost-effective that would give economic returns fast - due to the reason that the imparted power transmitted by the wind could be divided to the number of blades sharing the circular sweep area: So, in equivalent wind strength, a singular blade design has more energy captured per blade and more "bang for a buck". |
|
| |
Yet for some reason [rotary] General Electric, one of the worlds leading developers and suppliers of multi megawatt wind turbine(and all the others for that matter) seems to have determined that 3 blades is the magic number. They must all be stupid. |
|
| |
There's a reason they use three blades - see link. Apparently an even number would create undue wobble. |
|
| |
Johns Hopkins University has a project that may show the flow. See link. [Later: Not useful, but interesting, sorta.] |
|
| |
I'm thinking that there will be a rotational component to the downstream airflow, but it won't be worth going after. The rotation is a side-effect of the primary energy capture, so the overall flow is necessarily less than free airflow. |
|
| |
If you had some odd method to stop the rotation, maybe this would be worth doing, as the tower and technology are already there. But to just wish it could be done isn't likely to come up with something better than engineers paid to research windmills. |
|
| |
[rotary] is sort-of right about a single blade's efficiency. A single blade is most aerodynamically efficient, in complicated theory. But it takes a counterbalance, which might as well be a second blade. Then a two-blade rotor needs something to balance it side-to-side, which might as well be a third blade. A three-blade rotor is slightly less efficient, theoretically, but is a lot more practical. (I once saw a video of a single-blade ceiling fan--I wanted to tear it down and beat up the person who made it.) |
|
| |
A 3-bladed design has one obvious advantage: lesser vibration impact caused by the passing of a single blade at the increased air density upstream from the vertical column: The wider the column, the more air slowed down, the greater the air density upstream. Notice that the blade must be close enough to the pole so not to increase cantilever force. Much more, the blade is parallel to the pole at that moment, so a slight increase in density is enough to cause rapid deceleration of that particular blade, limiting the service life of the whole structure due to repetitive stress. The modern Danish and Swedish designs have two blades with active vibration dampening by the use of rapid pitching of the involved blade. It is rightfully so because Denmark and Sweden are pioneers and more experienced in windmill engineering, having harnessed their strong local windpower for centuries. |
|
| |
As for me, I have my own secret windmill design. |
|
| |
I think you have your own secret universe. And I do not wish to visit it. |
|
| |
If you were making a turbine in the sense of a steam turbine or aircraft jet, your idea would have merit. However, in those applications they have found that it is more practical to have a stator (stationary rotor, or more commonly just blades that are part of the casing) between each set of blades rather than counter-rotating axles. |
|
| |
So basically, if you had a tube containing a fan of many blades, a counter-rotating fan may improve efficiency. |
|
| |
ok, what about a stator *before* the windmill ? I'm just stuck on figuring since a blade/stator combination is good in turbines, something similar should be good in windmills. |
|
| |
and how can a single-bladed mill be the most efficient ? even ignoring bearing stress. |
|
| |
Not for cost, but for aero efficiency. The single blade is working in full-speed air, unslowed by other blades. It also has less tip loss, and less skin area than any other number of blades. Think of it as a monoplane versus a biplane, or as the longest possible blade design. |
|
| |
That's all theory. Practically, it's a pain. |
|
| |
The Windmill efficiency problem is one of working with very low velocities of fluid. Billions have been spent researching and building working models and the result is the most efficient, practical example we now see as working and economically viable examples. Adding a second contra rotating set of blade might prove acceptable in some respects...But, if the cost effectiveness / efficiency / structural integrity/etc does not prove practical, it will remain on the trash heap of ideas. Almost certainly, this idea has been tested and is not in production because it presents some violation of the Practicality God's rules. |
|
| |
A pair of contra-rotating blades would minimise twisting forces on the hub, at the price of a more complex gearbox assembly ....... |
|
| |
So what you really need is a cone-shaped windmill or something that actually removes 100% of the movement and turbulence from the wind. |
|
| |
If you some up with the shape, I suggest you patent it. Fast. |
|
| |
There are trade-offs in blade number; among others, fewer blades means a smaller rotational component in the slipstream because fan rotational speed is high and torque low. |
|
| |
I remember a wind turbine concept with a fixed set of blades (stator) in front of the rotational ones. The concept being explored was use of a genetic/evolutionary process to find a good design for the fixed blades. They did produce a large increase in power, but (I think) the conclusion was that it was unnecessarily complex and expensive. |
|
| |