h a l f b a k e r yPoint of hors d'oevre
add, search, annotate, link, view, overview, recent, by name, random
news, help, about, links, report a problem
browse anonymously,
or get an account
and write.
register,
|
|
|
While this Idea is being posted to the Windmill area, it will also work as a water-power device. And, of course, it could be used backwards like a fan, taking power to force the movement of air or water.
Synopsis:
) ) ) ) ) ) ... ) ) ) ) ) ) [motion-->]
( ( ( ( ( ( ... ( ( ( ( ( ( [<--motion]
Edge
view. At each end (left and right above) is an axle and appropriate other mechanism to allow the blades turn around, making an endless loop. Relative to the portrayed orientation, fluid flows from top to bottom or vice-versa. Power is transmitted through either or both of the (unshown) axles, of course.
Details:
Every gadget that extracts power from a moving fluid (or imparts power to is) uses one or more of a specially shaped interaction device usually called a "foil" (airfoil, hydrofoil, etc) Propeller blades and aircraft wings and steam-turbine blades all have that basic foil shape, which is similar to the parentheses-symbol ) or (.
One of the mysteries of modern windmill-manufacturing is the number of foils used. Some really large ones only have a single foil (balanced by a counterweight), while some old-fashioned ones have many (see link). It bothers me that if you want to extract as much power from the wind as possible, then why does anyone design a windmill with only a few foils (only the INTERCEPTED/interacted wind can yield power, see)? I'm sure cost has something to do with it, but mass production is supposed to reduce costs! (Also, I greatly doubt that birds ever fly into a many-blade windmill...)
Well, a few-foil windmill can intercept more wind if it rotates faster than a many-foil windmill. It still won't intercept as much wind as the many-foil type, but the difference can be considerably reduced. However, now a new problem enters the picture: Turbulence. Foils that move rapidly through a fluid never move as smoothly as slower-moving foils; energy is lost as the fluid becomes agitated. Scientists have a special term, "laminar flow", to describe a fluid moving smoothly. In water, when laminar flow is agitated into turbulence, "cavitation" (production of bubbles) happens that can be destructive to ship propellers. Turbulent air around a windmill isn't quite as destructive, but it still represents wasted energy.
One other problem with ordinary windmills is also speed-related. The centrifugal effect limits their size, which in turn limits the total area of wind that can be intercepted.
So, How About Deliberately Desiging a Device to Overcome The Problems of Small Area and Turbulence? The Venetian Turbine is the answer!
According to the Wikipedia definition of a "Venetian Blind" (see link), it could be that I am misusing the label somewhat for this Idea. Nevertheless, assuming most people reading this know what typical Venetian Blinds are, I shall proceed.
It happens that a modern Venetian Blind incorporates a large number of foils (see first OR second line of Synopsis above), and not simple straight slats. So, it is easy enough to imagine fluid flowing through the foils of an ordinary Venetian Blind and causing the whole Blind to lift. An endless loop of foils could continuously be lifted by moving wind or water. And very conveniently, if the foils in the other half of the endless loop are oriented in the opposite direction, then the same direction of moving wind or water causes the foils to descend rather than rise.
The preceding makes a Venetian Turbine double-acting, not only intercepting the entire area-of-the-plane ("planar" area) of fluid passing through it, but also intercepting it twice, to extract even more energy from it. Finally, the speed of motion of all those foils need not be large, which means that the fluid flow can be nicely laminar. I have chosen to coin a new word "planimar" implying a planar area through which laminar flow occurs. Thus "Planimar Turbine" would be the technical term for this Idea, while the popular name can be "Venetian Turbine".
In the field, a Venetian Turbine would consist of segments. One segment would consist of two vertical posts, with an axle connecting them at top and bottom. The posts can be as high as -- or higher than -- any ordinary windmill (hundreds of meters); guy wires for support would also be employed, of course. Pulleys or sprockets would be mounted near the ends of the axles (in-between the posts), and two vertical belts or chains would be adjacent to the two posts. Many foils would cross the space between the posts and connect to the belts or chains. A two-segment version would only need three posts, because the central post can be shared by the segments (and the two axles can just be twice as long). A kind of "wall" of segments can be built, stretching across hundreds or even thousands of meters of landscape. Power can be extracted from the lower axle in more than one place (via additional pulleys or sprockets). A particular wall-of-turbines should be oriented at right angles to the prevailing wind --let's pretend it stretches north/south -- and in this case it will work quite well if the wind comes at it from almost any direction except due north or due south. (A variant construction, in which each segment mounts the axles vertically and the foils sweep horizontally, is less forgiving with respect to arrving wind direction, so let's not consider that variant further.)
The only real problem with this Idea involves the way the foils are turned around at each end of the plane through which they sweep. The inner arc is shorter than the outer arc, after all. This can be solved as simply as attaching the MIDDLE of the end of the foil to the belt or chain, instead of attaching the edges of the foil (as might be implied by looking at an ordinary Venetian Blind).
Many-foil windmill
http://internal.mat...ndmill/howmany.html
As mentioned in the main text [Vernon, Sep 06 2005]
Wikipedia article on Venetian Blinds
http://en.wikipedia...wiki/Venetian_blind
As mentioned in the main text [Vernon, Sep 06 2005]
Betz' Law: The 16/27 limit
http://www.windpowe.../tour/wres/betz.htm
from the Danish Wind Industry Association [Laughs Last, Sep 07 2005]
The good old Wiki
http://en.wikipedia...m_and_wake_rotation
"At high tip speed ratios three blades are sufficient to interact with all the air passing through the rotor plane" [TheLightsAreOnBut, Dec 11 2007]
Cross-flow Fans
http://www.xoxide.c...-crossflow-fan.html
Zoom in on (click) the first thumbnail to see [neutrinos_shadow, Dec 12 2007]
Sail Turbine
Sail_20Turbine
Here's the original inspiration behind this Idea. It also indicates something of how (with difficulty) a directional bias can become part of the Idea, which is the key to running it in reverse, as a fluid-pusher. [Vernon, Feb 02 2012]
D-Dalus
http://www.google.c...jdOP7KWxz1hNXSujpZQ
And here's the proof, that fluid can be moved by gadgets in the same class as this Idea, and the Sail Turbine. [Vernon, Feb 02 2012]
Natel Energy
http://www.natelenergy.com/technology/
A few extra stators, but essentially this idea. [neutrinos_shadow, Mar 13 2016]
Tesla turbine
https://en.wikipedi.../wiki/Tesla_turbine
[not_morrison_rm, Mar 14 2016]
Magnetohydrodynamics
http://mysite.du.ed...alvert/phys/mhd.htm
Another foil-less way for energy to be extracted from or imparted into a fluid. [Vernon, Mar 14 2016]
Wind and electrically charged water droplets
http://www.gizmag.c...wind-turbine/26907/
Another foil-less way for energy to be extracted from or imparted into a fluid. [Vernon, Mar 14 2016]
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.
Annotation:
|
| |
It would help if you could sketch a few views of this, because I'm not sure that I understand. If I do understand, then you are suggesting making an array of Darrieus-type windmills connected mechanically? |
|
| |
No, Darrieus windmills only have a few foils. A single Venetian Turbine segment can have hundreds of foils. |
|
| |
Go to a window equipped with a Venetian Blind. Open the blind midway. Imagine a second identical Blind behind the first, only with the foils upside-down. Imagine the two Blinds connected at top and bottom, going around rollers. Imagine wind blowing through. The shape of the foils causes vertical motion. All the foils of the front Blind go up together, and one-at-a-time roll over to join the rear Blind. All the foils in the rear Blind go down together, and one-at-at-a-time roll under to join the front Blind. |
|
| |
I may try to draw a picture later, but I thought this Idea was simple enough that it wasn't necessary. |
|
| |
One of the main limitations of existing turbines of all kinds is blade flutter. There are specialist small engineering companies that do nothing else but compute, model, design and consult around the issue of turbine blade flutter. Your design will need to incorporate elements that severely restrict any non-linear movements of the blades, or it will destroy itself in a short time. |
|
| |
I appreciate the ease with which your masts can be stayed against the wind. |
|
| |
Because wind is stronger as you get further from the ground, I would expect that the foils near the top would receive more force than the ones at the bottom. They will push/pull the lower foils, but I suppose a like condition is true in other designs. |
|
| |
Also, the rotating mass of traditional designs acts as a flywheel. This can absorb micro-gusts and micro-lulls, smooth over rough spots on the bearing and generator. |
|
| |
[ConsulFlaminicus], I agree. But please note that I did not say anything in the main text about how big and how separated-from-each-other the individual foils needed to be. I was aware that in practice, if a wide spacing between the vertical posts is used, then the foils needed to be fairly robust. They might also be more wing-shaped/constructed, with an actual flat side instead of an open concavity. |
|
| |
[Laughs Last], Regarding flywheels, consider the amount of MASS that would be in motion here, if hundreds of foils occupied a two-hundred-meter-high segment. Just because simple rotation isn't involved, that doesn't mean there is no equivalent of the flywheel effect here. |
|
| |
Vernon, I like the idea, but have you come across the proof which shows the maximum power which can be extracted from the wind?
For example, a brick wall intercepts all of the wind...
+ |
|
| |
[Ling], no, I haven't. I wouldn't be surprised if it had something to do with why modern windmills mostly have only a few foils. And I wouldn't be surprised if this Idea implies a greater need for lots of foils than is actually true. AND I wouldn't be surprised if a more efficient "unidirectional" foil-design would work even better than the simple bidirectional type described here. (That is, a regular airplane wing cross-section is intended to cut through air in a particular direction, so that makes it "unidirectional".) I am aware that using such a foil would require some extra mechanical trickery, with respect to angling the foil to the wind (different when going down than when going up). There are ways to do such trickery; I just didn't bother trying to describe it here. |
|
| |
As [Ling] mentions, the maximum energy that can be extracted from a flow by a turbine can be proven to be 59.3%. |
|
| |
This would certainly work, but why would it be better than existing designs? |
|
| |
[Pa`ve], in water this would be a rather slow-moving turbine, with incredible torque. With decent spacing between the foils, fish may be able to go through it just fine. In air, the problem with birds is that an ordinary windmill looks like a blur, and THROUGH the blur you can see behind the windmill. So birds ignore the blur and get sliced. Here I expect the number of foils to pretty much block out the view through the turbine. Birds have good enough eyesight that they don't usually try to fly through something that resembles a wall. |
|
| |
[lurch], as described in the main text, you are correct. But as mentioned in my prior anno, a directional bias CAN be added. With some difficulty. |
|
| |
[david scothern], if one of these is built on the same amount of ground as reserved for an ordinary wind turbine, well, it can interact with more moving air than can the ordinary windmill (from the prevailing direction). That means greater power extracted, given similar conversion efficiencies.
Next, remember, this is the HalfBakery. I'm surprised nobody so far has derided this with the obvious "too many moving parts" problem. Nevertheless, there is an interesting possibility here. See the link that [Laughs Last] added? On that page is this quote, regarding the fraction of energy that can be extracted from wind: "It is quite surprising that one can make such a sweeping, general statement which applies to any wind turbine with a disc-like rotor." --this gadget DOES NOT HAVE a disc-like rotor! |
|
| |
The proof linked off [Laughs Last]'s page is independent of the shape of the swept area. There is just an area term, F, which is cancelled out in the calculation to give the ratio of extracted power to available power. We're happily bereft of any references to Pi or R for the purposes of calculating this limit. |
|
| |
OK, I accept the cancelled area "F" in the calculation. Still, that site seems to make a big deal about the way a rotary mill centrifugally expands the airflow with which it interacts. A Venetian Turbine would not do that (or would do something else to a lesser extent), and may gain something thereby. I guess the most important question is, "Just how close to a 2/3 wind-speed drop does an ordinary windmill achieve?" (I've been looking around that site for that tidbit, but haven't found it yet.) |
|
| |
I like this idea - we could line the borders between the US and Mexico with a bunch of these that go all the way to the ground. Any illegals trying to climb over/through would instantly become fajita meat! This would solve two problems at once! |
|
| |
My Interpretation of Betz' law may be flawed but if you put enough of these in a line would there be no water/air movement at the end of the line? |
|
| |
If you stuck these in a tunnel and used gravity to force water through, all of the blades would spin. |
|
| |
Similarly if you funneled the air into a windsock type tube - you could eliminate some of this energy loss. |
|
| |
Saw the (((((((((((((((((( and ))))))))))))))))
and knew it was Vernon. |
|
| |
I recently read Stephen Baxter's Manifold series, in which the explanation of Venus was that some aliens wrapped superconductor wire around it and tapped the energy to slow it's spin. Or something. |
|
| |
[Vernon], that about the expansion of the airflow will happen whatever turbine you use. The mass flow in and out must be constant, but as you extract kinetic energy from the flow, it will slow down. Consequently the cross-section of the flow will increase. |
|
| |
[david scothern], thanks. For air, though, it could also come out of the turbine a bit denser than it went in...ONLY because it is so compressible. However, I can also think of a reason or two why it might not become any denser. Thanks, again! |
|
| |
I like the idea, but it has some design hurdles: 1. inefficient airfoil shape, since you are using the same wing for propultion in both directions you'd have to use a symetric cross section, or some kind of bending wing design for efficiency; 2. As mentioned, lots of parts that all move and move in relation to one another. 3. non rotary design makes internal friction tougher to deal with, like a tank tread vs.a tire. 4. Very hard to steer into the wind. I realize the system will work off wind, but not as well, like solar panels. |
|
| |
None are deal breakers but the last is close depending on the prevailing winds. |
|
| |
[MisterQED], your (1) objection has the same solution as I wrote in an earlier annotation, in reply to [lurch]. I didn't feel the need to go into that much detail, though, in a basic HalfBakery Idea, because even if inefficient, simple parentheses-shaped foils will work. Regarding (2), at least so many parts are identical, which means economy-of-scale mass-production factors come into play. Regarding (3), this IS a semi-rotary design, since at each end of the "wall" of foils is a rotating thing for making the foils do U-turns. Enormous torque gets applied to the axles of those rotating parts. And one thing NOBODY likes about ordinary rotating designs, especially when using the device in reverse, to push fluid, is the centrifugal effect (not all the fluid is pushed directly in the desired direction). Regarding (4), though, I basically agree. That's why if a miles-long wall of Venetian Turbines is built, it needs to catch the PREVAILING wind, and not worry about day-to-day variances. |
|
| |
I'm sorry, I assumed that the airfoils would be set to always face the same edge into the wind and only their angle of attack changed, so that is why I hadn't understood the "parentheses-shaped foils" idea found no purchase when I read it. |
|
| |
So if we assume the front vanes move upward and then flip and go down the back, the bottom should be shrouded to allow the vane to flip back. This might not be an issue as wind near ground level is lower than higher up. |
|
| |
Also I think the maximum efficiency figure is wrong for this design because it assumes that air can move around the mill. In this design air cannot go below, so the overall aerodynamics are different. I'm not saying better, but certainly different. Like comparing the aerodynamics of a car on the ground to a plane in flight.
I read this 20 years ago, but I think you could double the frontal area because the shape is really the car and it's negative. The whole shape is aerodynamically like a two cars with tires touching. |
|
| |
Aerofoils will give you limitations on how close together the vanes can be as they work by creating a pressure difference between the upper and lower surfaces. The lower surface of a vane must therefore be a certain distance away from the upper surface of the vane below in order to work. |
|
| |
It would be much simpler and efficient to use flat blades at an angle (a slight curve may prove to be ideal). You could then create an area where you cannot see through either row horizontally. An added bonus would be that the wind hitting the second row would already have been deflected to hit it at a better angle. I suspect that something around 30 degrees would be the best angle (at 45 degrees, the wind would be perpendicular to the second row). |
|
| |
There is no reason why this can only be a loop. You could arrange it in a concertina (the shape, not the instrument) with the bottom-back running underneath to the bottom-front. There will of course be diminishing returns from each iteration, but there may be a way of altering the angle of each row by using cogs with a different gap between the inner and outer runners used for the front and back vanes. |
|
| |
Is it wrong that I knew that this was a Vernon idea by the time I got down to the fifth paragraph? |
|
| |
[MisterQED], yes, it's a reasonably sensible thing to shroud the place where the foils would move against the wind. I didn't mention it in the main text because it's such a small part of the total surface area that interacts with the wind. |
|
| |
[marklar], I agree that the foils shouldn't be too close together. I suspect there will be a pretty simple correlation between the breadth of a foil (not its longest dimension) and the spacing between foils. |
|
| |
Using flat blades at an angle requires the angle to be changed; a simple U-turn (a 180-degree rotation) leaves the blades at exactly the same angle. Changing the angle during the U-turn can be done, but this is the extra complexity I didn't want to talk about much, in the main text, and which I've mentioned in other annotations. A simpler way to increase efficiency is to turn the parentheses shape ) into a more ordinary airfoil shape, something like a tall skinny capital D. |
|
| |
Basically, you have a cross-flow fan (linky), running as a turbine with some modifications (the linear track instead of circular). This would seem to indicate that it would probably work, to some degree.
The spacing between the front and the back 'sets' of vanes would be an important design consideration, as if they are close, you would get an interaction of the airflow from the front set onto the back (like rotor/stator in a jet engine); but if they are far apart (back towards the fan cylinder style) they would be independent (and therefore easier to design).
It really needs a scale model to be built, but that is going beyond its 'halfbaked' status... |
|
| |
//It really needs a scale model to be built//[neutrinos_shadow] Indeed, I've been eyeing up the blinds for a couple days now. |
|
| |
[Vernon] Stop coming up with ideas I want to bake, I've got a backlog. |
|
| |
[neutrinos shadow], the end view of that cross flow fan looks very much like the end view of a "blower" type of fan, where air travels from the circumference toward the axle (or vice versa). I think that to use that design for cross flow is inefficient, partly because a fair amount of shrouding is needed to force cross flow, and partly because the blade angles change constantly during rotation. By contrast, the long linear stretches covered by Venetian Turbine blades maximizes efficient interaction with the air. |
|
| |
I agree that it's probably not wise to have the two moving sets of blades too close together, but this directly depends on the diameters of the U-turns at each end of the straight movement path, so it's an easy thing to manage. |
|
| |
[marklar], thanks. "So many ideas, so little money...." |
|
| |
search for reference to the "Schneider Lift Translator" in wind energy texts (such as Paul Gipe's 'Wind Energy Comes Of Age'). It didn't work then, and we're still working under Physics 1.0 ... |
|
| |
I guess if you close the blinds it stops spinning. Using a vertical shaft would be more practical, and you may need to consider pulling the blind in a storm if you use them to power boats. |
|
| |
Seems some-one has been reading the halfbakery. Natel Energy are making water turbine generators based on pretty much this exact idea. See linky. |
|
| |
It was quicker to read the annos than the idea. |
|
| |
[Vernon], if you could just bring the first and last
words of your ideas a little closer together, they
would be better. |
|
| |
[neutrinos shadow], thanks for the link! |
|
| |
<puts on uber-pedant hat> "Every gadget that extracts
power from a moving fluid (or imparts power to is) uses one
or more of a specially shaped interaction device usually
called a "foil" (airfoil, hydrofoil, etc) Propeller blades and
aircraft wings" |
|
| |
Errr, the Tesla turbine doesn't. |
|
| |
[not_morrison_m] Okay, I admit I didn't think about the
oddball techniques that are not widely used. (Like, there's
a variant of magnetohydrodynamics that uses electrostatics
instead of magnetism.) |
|
| |