Salient White Elephant

May 12, 2009

Practical Artificial Pressure Differential Wind Turbine

Explanation of Artificial Pressure Differential Turbine 1

Explanation of Artificial Pressure Differential Turbine 2

In this way we have brought the low pressure on the downwind side of the parachute to the top of the tower.

Now, in your mind’s eye, eliminate the low pressure tube, and make the parachute whole again. Now attach a high pressure tube to the vertex of the parachute:

Explanation of Artificial Pressure Differential Turbine 3

Now we have techniques for bringing the high pressure of the upwind side of the parachute back to the tower, and for bringing the low pressure of the downwind side of the parachute back to the tower. Next, we build both the high pressure and low pressure extending tubes into the parachute at the same time. The low pressure tube has the smaller diameter, and it connects to the hole in the vertex of the parachute which has the same diameter. The diameter of the high pressure tube is larger than the diameter of the low pressure tube, and it encircles the low pressure tube so that a cross-section of the two tubes makes them look like concentric circles.

The next step is to transmit the high and low pressures to the bottom of the tower using the same technique. The tower is actually two towers – an inner smaller diameter low pressure tube with an outer larger diameter high pressure tube surrounding it so that a cross-section of the two makes them look like concentric circles. The high pressure and low pressure regions are connected at the bottom of the tower and, as expected, a HAWT rotor (with a vertical axis) is positioned between the two. The rotor, gearbox, and generator are at all at ground level.

The only thing I haven’t explained is how the low pressure and high pressure tubes make a right angle turn at the top of the tower. I was planning to draw some pictures of this, but I don’t think it’s really necessary. There are probably a million ways to do this. I will just note here that the parachute part automatically seeks the downwind position, and so it doesn’t require a yaw system. The right angle joint can be yawed, or it can simply be a cylindrical piece with vents positioned radially about its center. The vents have doors in them that can open and close to simulate yawing, though few moving parts would actually be required. (To illustrate, imagine an aerial view of this machine. Suppose the high and low pressure tubes approach the tower near the 9 o’clock position. Then the vents in the cylindrical piece at the top of the tower that are at positions 8 o’clock, 8:30, 9:00, 9:30, and 10 o’clock would all be open, while all of the other vents would be closed tight and aerodynamically sealed.)

The tower supports little weight, and it can be fitted with vents to let storm winds pass through unimpeded. This means the tower can be very light in weight, very inexpensive (relative to a typical HAWT tower), and it can have a large diameter if necessary. The parachute and the fabric part of the low pressure and high pressure tubes may have similar vents so that they also create little drag during storm winds. Maybe the parachute and fabric vents could even be somehow rolled up and stored inside the tower during storm winds.

Finally, note that the tower could be incredibly high. This is true because it supports little weight, has little overturning moment in storm winds, and can accomodate multi-level guy wires that can attach to the tower at any elevation, including at the very top of the tower!

Artificial Pressure Differential Turbine

Yawing Variation

Now we might imagine a long horizontal tube extending from the top of the tower. The supporting cords that tether the parachute are attached to the end of the horizontal tube that is far from the top of the tower. This way, the “vertex” (downwindmost end) of the parachute is right at the top of the tower, and the low and high pressure regions may easily be connected to the vertical (tower) low and high pressure concentric tubes. The horizontal tube yaws to align with the wind.

There are many other variations like this. Maybe we just build something that looks like a giant radio telescope dish, and attach its vertex to the top of the tower. This might not be so ridiculous if the parabolic dish has slats that automatically open when the pressure differential between the upwind and downwind sides of the slats exceeds a safe value.

May 10, 2009

SkyScraper with H-Rotors

This is a very simple idea. Imagine a skyscraper that looks round in an aerial view. Now just put a bunch of disks around the outside walls of the building… (say) one disk every 6 stories or something like that. Now near the outer perimeters of these disks, you cut a slot as described in many of the other posts on this blog. (See for example 20 Megawatt VAWT.) The ends of the airfoils engage these slots. The blades go around the building with each level rotating with the same polarity as its upstairs and downstairs neighbors, or else with adjacent levels rotating with opposite polarity to double the speed difference between the generator rotor and the generator stator:

SkyScraper with H-Rotors

Mechanical energy may be converted into electrical energy in any of several ways. Once again, all of these conversion methods have been described multiple times on this blog, so I won’t repeat them here. I’ll just give a short list of the possibilities:

  • Generator windings are embedded into the slots. A permanent magent is attached to the ends of the blades and the motion of the blades forces these magnets past the windings.
  • Cables are attached to the middle of each rotor blade. These cables are attached to a smaller diameter cable. The diameter of the smaller diameter cable is just large enough to around the building without hitting it. The smaller cable drives the generator. All cables should be designed to carry only the power producing components of the airfoil loads. The larger (non-power producing) loads are carried by the disks that support the blades tips.
  • The slots that engage the blade tips are provided with a great many small wheels inside. Airfoil motion imparts spin to these wheels. All wheels are mechanically linked so that they all rotate at the same rpm. The rotational motion of the wheels (or of their mechanical linkage) drives a generator.

One question is whether blades that are rotating and producing power would be a visual distraction to the people inside the building. I honestly don’t know what the answer to this question would be. Because the building is high, and because the building itself acts as a flow accelerator, you can imagine that the blades might be traveling at a very high velocity indeed. I have no idea what the velocity would be, but let’s say they’re going 200+ miles per hour. Could you even see a blade moving at that speed? Anyway, if this turns out to be a problem, maybe one should explore the opposite approach – a great many blades having a slow, gentle movement.

Direct Drive Counter-Rotating Cat’s Eye Variation

In this variation, each level (each set of adjacent supporting disk-like structures) is provided with two sets of blades. Half rotate clockwise, and the other half rotate counterclockwise. (These blades may or may not be designed to imitate the behavior of the Cat’s Eye Darrieus Rotor.) The ends of all of the blades rotating with one polarity are attached to permanent magnets, while the ends of all the blades rotating with the other polarity are attached to windings. As two blades that rotate with opposite polarity pass by each other, their magnets and coils pass close to each other in a manner similar to what would be witnessed if you could look inside of an electric generator. The magnets and coils are attached to the parts of the ends of the airfoils that are hidden inside the slot, and thus create minimum drag and turbulence. The mechanical tolerances that must be maintained to minimize the air gap that the flux must traverse are acheivable also because these components live within the rigid and tightly controlled confines of the blade guiding slot.

Geodesic Dome Turbine

Start with a Geodesic Dome:

Geodesic DomeNow Cut a hole in the top, and cover the hole with a shroud that can yaw in order to keep its opening pointing upwind. Also add vents near the lower part of the dome can than be either opened or closed:

Geodesic Dome TurbineThe variation depiced above has air flowing into the hole at the top of the dome and out of the vents below. I’m not sure this is the best arrangement. The alternative would be to have air flowing into the lower vents and out of the hole in the top. In this variation, the shroud over the top hole in the diagram would be yawed (rotated) 180 degrees, and (I’m guessing) the left two vents in the diagram would be open, while the other vents would be closed. I guess one of these ideas is probably aerodynamically superior to the other, but I don’t know which is which. It’s worth noting that the real low pressure should be at the top of the dome, since this is where the wind has been accelerated the most. Seems like it might make sense then to let the wind flow in to the lower vents (where pressure is naturally higher), and out through the hole in the top. I don’t know much about the theory of fluid flow, so I’ll leave the rest to those of you who have the academic background to model and solve a problem like this.

Before ending this post, however, I’d like to point out an aspect of this idea that is particularly intriquing. Since you can have lots and lots of vents, but only one hole in the top of the dome, it stands to reason that it should be easy to provide the dome with many square feet worth of vents, given the area of the hole at the top of the dome. This means that the velocity of wind flowing through the vents may be caused to vary by only a small amount relative to the velocity of the wind outside the dome. For this reason, it would seem that the vast part of the lower part of the dome could be made to be quite comfortable for people, and this means the dome can have alternative uses. For example, the dome could house a giant botanical garden for the public to enjoy. If you really wanted to control the environment for the people inside, two concentric geodesic domes could be placed one on top of another, creating a thin (say) 40 foot wide gap between the two ceilings. The gap could be used for wind flow and the harvesting of its energy, while the part inside the lower (smallest) dome could be used for just about anything – commercial office space, a manufacturing plant, basketball court, … you name it!

Retrofit Option

Depending on how attractive this structure could be made to be, and on its cost effectiveness, we might imagine putting one of these things on top of an existing structure. Rooftop wind turbines are generally frowned upon, but I think this is mostly because of the harshly turbulent conditions within which a rooftop turbine must normally operate. The dome solves this problem in several ways. First, it doesn’t have any sharp turbulence producing edges. Second, its rotors are small and therefore less sensitive to turbulence, and they can be located in a short cylindrical shroud that is equipped with the same kinds of turbulence attenuating apparatus as is found in wind tunnels. And finally, if a small rotor does eventually develop a crack due to turbulence-induced fatique, simply replace it. It’s small, and so the cost of replacing it is no big deal.

I saw a medium sized, three story motel the other day that looked like it could easily accomodate a Geodesic Dome Turbine. If the dome had enough vents to open during a wind storm, it would seem likely that the motel could accomodate the turbine in spite of the fact that the building designers had not accounted for the extra load.

April 25, 2009

Spoked Wind Dam

This is an extremely simple idea. Walls are built that radiate like the spokes of a wheel, and a VAWT is placed at the “axis of the wheel”. That’s all there is to it!!!

Spoked Wind Dam

If desired, the lower edges of the walls may be raised up off the ground so that the walls do not impede the movement of the combine. In this case, pillars hold the walls up off the ground.

April 24, 2009

Circular Wind Dam

The Circular Wind Dam first described in this post may not provide much improvement over the current state of the art. However, it lays the groundwork for some variations that I think may be very viable indeed. These variations are presented toward the end of this post, but in case you’re in a hurry, here’s a general idea of the type of machine that we will be working toward:

Circular Wind Dam, Rotated Energy Exchange Variation

Also, make sure you read the section entitled Advantages of the Wind Dam Over Current State of the Art Wind Turbines, as this section presents some very very powerful ideas.

Circular Wind Dam

A circular hallway is made of brick or concrete. It is extremely high, and it has an extremely large diameter. A number of walls block the hallway inside:

Aerial View of Circular Wind Dam, Twelve Walls Block the Inside of the Hallway

Here is a cross-section of the Wind Dam that shows one of the walls that block the hallway. The wall has a hole cut into it, and a wind turbine rotor captures the energy of the wind that flows through the hole:

Cross-Sectional View of Circular Wind Dam Showing Wall and Turbine Rotor

The outside of the Wind Dam has holes cut into it. These holes have sliding doors that are kind of like garage doors. The doors can block the holes, or they can open the holes to the outside air:

Circular Wind Dam

The holes near the upwind side of the dam and the holes near the downwind side of the dam are opened, while all of the other holes are kept closed. Now wind flows through the hallway from the upwind side to the downwind side. The wind turns the turbine rotors that are embedded into the walls that partially block the hallway, and the turbine rotors drive generators to make electricity. The turbine rotors and generators work just like the rotors and generators on a standard wind turbine, except that gearboxes might not be required between the turbine rotors and generators of the Wind Dam. This is true because the Wind Dam and the holes that house the turbine rotors have a concentrating effect on the wind, so that wind flows through the holes and turbine rotors at a much higher velocity than the velocity of the wind outside the dam.

Concentric Hallways Variation

A wall is added inside of the hallway that separates it into two hallways that form concentric rings:

Circular Wind Dam, Concentric Hallways Variation

The previous variation of the Wind Dam had holes in the outside wall – that is, the wall that faces the outside of the dam. In addition to these “outside holes”, the Concentric Hallways Wind Dam has holes that face the inside of the dam (the area enclosed by the dam). The holes facing the inside of the dam are controlled in exactly the same way as the holes that face the outside of the dam. That is, only the holes that are near the upwind and downwind sides of the dam are kept open, and all of the other holes are kept closed. Oddly, wind flows through the inside (smaller diameter) hallway from the downwind side to the upwind side.

Since wind flows through the hallways in opposite directions, we can replace the horizontal axis rotors with a vertical axis rotors. There are many ways to do this, but for the sake of making the diagram easy to draw, let’s use Savonius rotors with flat vanes. Notice that wind will always flow in opposite directions through the hallways regardless of which direction the outside wind is blowing:

Circular Wind Dam, Concentric Hallways VariationHere’s a diagram that shows how wind flows through the dam:

Circular Wind Dam Concentric Hallways Variation Showing Approximate Flow of Wind

Advantages of the Wind Dam Over Current State of the Art Wind Turbines

  • Most of your investment in a current State of the Art Horizontal Axis Wind Turbine (SOTAHAWT) is used to purchase sensitive, short life components that are difficult to design and that are easy to break. The majority of an investment in a Wind Dam purchases the structure itself – basically just a pile of bricks – and this investment will probably still be productive 100 years from today. (Think of the great hydro-dams in the NorthWestern United States.) And if somebody knocks a hole into the wall… big deal – just fill it in with a few more bricks. But suppose instead that an expensive component on one of your SOTAHAWTs fails. Suppose have to replace a turbine blade that is 150 feet long! You buy a new blade, wait 3 months for it to be manufactured, somehow get that 150 foot blade to the site and then weave it in between the other turbines, hire a crane, take the old blade down, put the new one up. You see what I mean – most of your investment might as well be stored in a crystal goldfish bowl that is balanced on top of a 300 foot FM radio tower. My goodness… how can you even sleep at night!? I don’t know how large the turbine rotor blades will be in the Wind Dam, but even if they are 20 feet long… so what? They don’t represent a significant fraction of your investment, and repairing and replacing them are no big deal.
  • The Wind Dam is virtually indestructible. It can assume a very low drag profile during storm winds by opening all of the doors in the inside and outside walls of the dam. Its drag profile may be further reduced by installing sliding doors into the wall that separates the two concentric hallways. These sliding doors may also be opened during storm winds to keep the drag profile to a minimum. No large sensitive components (rotor blades, etc) are required to withstand storm wind drag forces.
  • Wind turbine rotors, gearboxes (if required), and generators are all located inside the Wind Dam. Thus, these relatively sensitive components are well protected from wind, rain, snow, and other weather. And it would be easy to provide heating for these components during cold weather.
  • The Wind Dam is very quiet because noisy components are located inside the dam.
  • Electrical components are virtually immune to lightning strikes. This is true because these components are housed inside the dam, and because the dam has lightning rods on top to direct lightning strikes away from sensitive components.
  • The life of a Wind Dam will probably far exceed the 20 or 30 year lifespan of your typical SOTAHAWT. It is obvious that this would hold true for the structural part of the Wind Dam (the bricks). What is less obvious is that smaller rotors that turn at higher speeds that drive higher voltage electrical equipment, all of which live in the luxurious indoor environment of the wind dam, will also last much longer than the massive SOTAHAWT components that are stressed, fatigued, and pounded by wind, rain, snow, ice, cold temperature, humidity, and lightning year after year after year. Also, smaller components last longer than larger components because they are easier to design and because they are subjected to less vigorous mechanical abuse than are larger components.
  • Since the wind turbine rotors and electrical equipment live inside the Wind Dam, it’s hard to imagine the machine posing any danger whatsoever to the public. Can you imagine what would happen if a 150 foot rotor blade became detached from a SOTAHAWT? I wouldn’t be surprised if it could pierce through the roof of an enclosed baseball stadium. This also reflects in the cost of wind generated electricity. Because of the danger of accidents, SOTAHAWT components are quite significantly over-engineered. But normal safety margins could easily be justified in the design of the Wind Dam, and this will significantly lower costs.
  • An oft cited disadvantage of wind energy is that it has a very low energy density. The wind dam solves this problem. I don’t know what the water pressure is at the bottom of a hydro dam, but I know it’s huge. Water is heavy. But the fact that the energy density of water is high means that you need a lot of concrete to hold it back. Maybe your hydro dam is only as long as a couple of football fields, but it has 50 million dollars worth of concrete in it. But the wind dam is holding back something that is much lighter, so the walls do not have to be so massive. Maybe the circumference of the wind dam is 75 football fields, but since the walls are thin, they still have the same total amount of concrete: 50 million dollars worth. Warm up to the idea that the density of investment capital is directly proportional to the density of energy. Spreading energy out over a larger area does not raise the capital cost of the structure required to harvest that energy, it merely spreads the same capital cost out over the same larger area. Getting uptight about the low energy density in wind is like worrying about whether you should stack your money in a pile when you count it, or whether you should lay your dollar bills end to end across the bedroom floor. Actually, if you carpet your house with dollar bills, it looks like a lot more money than if you just put them in a greasy old stack with a rubber band. (But what about storms? Won’t the wind dam have to be massive and expensive in order to withstand storm winds? No. Consider the hydro dam. If more precipitation falls than you expected, you simply open the gates and let the water run through the dam. But exactly the same approach works for the wind dam. If there’s a hurricane, you simply open all the doors and let the wind pass through unimpeded. And if you have trouble making this approach work, remember that the light weight surfaces of a wind dam may be folded up, rolled up, retracted, or even laid down on the ground.)

Real Estate Sharing Variation

The wind dam can be built near areas that have residences or commercial activity, since there’s no possibility whatsoever of an accident, and since the noise is probably mostly contained inside the hallways. Holes can be cut into the walls so that roads can go through. In this case, the air is simply routed over the passageway in an aerodynamically friendly way. You could put a wind dam around a cornfield, and make a passageway big enough for a combine to get through.

Wind Vane Doors Variation

Instead of garage doors that roll up into the ceiling, maybe curved doors could be used instead to further concentrate flow in the hallways:

Circular Wind Dam Concentric Hallways with Wind Vane Doors

Very High Altitude Variation

Imagine an extremely tall (500 feet?) circular wind dam. It may have a single internal hallway, or it may have two concentric hallways. The very-high-altitude very-high-velocity wind causes the air inside the hallway(s) to also move at high velocity. This action may be accomplished in any of the ways depicted above: doors that open and close, curved vanes, or via some other appropriate aerodynamic components. However, once inside the hallway, the energy is transferred from the highest part of the hallway to a lower altitude region of the inside of the hallway. This may be achieved by blocking all altitudes within the hallway except for those that are (say) 300 feet or lower. Or it may be achieved by using nearly horizontal airfoils that direct the high-altitude energy downward toward the earth, or by some other kind aerodynamic hanky-panky. Bringing the high energy to the lower elevations allows the turbine rotors, gearboxes, and generators to be positioned at a lower altitude.

As stated in another post on this blog, Synopsis of the Best Design Tricks Developed to Date, if you can’t put the turbine up into the high altitude high energy wind, then bring the high altitude high energy wind down to the turbine. (I wrote that synopsis of best design tricks post in a hurry… don’t be disappointed because it’s actually not a very good post. Hope to have time to rewrite it later.)

Energy Exchange Variation

Circular Wind Dam, Energy Exhange Variation

For ideas on how to design a very tall H Rotor (Straight-Bladed Darrieus), see High Speed Centrifugally Stable VAWT. Of course, any VAWT may be used with the energy exchanging version of the Wind Dam, and the Savonius may be a good choice as well.

Another approach would use H Rotors with a horizontal axis. One end of a rotor’s axis would be anchored to the smaller diameter wall, and the other to the larger diameter wall. The rotor’s axis should be parallel to a line that extends radially from the center of the circle formed by the smaller diameter wall segments. (This is, or course, the same point that is the center of the circle formed by the larger diameter wall segments.) And, or course, the H Rotor’s axis would also be parallel to the ground. Anyway, you stack these horizontal axis H Rotors one on top of the other so that they form an “aerodynamic barrier” that extends from the ground to the height of the two walls (smaller and larger diameter walls). Since the axes of these rotors are all parallel, they can all be connected with a common chain drive. The chain extends to a sprocket which is on the generator shaft, and the generator shaft is on the ground.

Furthermore, if it is determined that HAWT rotors would provide better efficiency or this design, simply replace the 3 bladed H Rotors above with walls that can rotate through an angle of 180 degrees. Now cut round holes in these walls, and install HAWT rotors in the holes. Now rotate the wall by 180 degrees if the wind passes through the holes in the direction that is opposite the direction that the HAWT rotors are intended to act upon.

Two Concentric Circular Wind Dams, Energy Exhange Variation

Rotated Energy Exchange Variation

Circular Wind Dam, Rotated Energy Exchange Variation

I wonder if you could put some kind of a smooth geodesic dome structure on top of a Walmart to smooth out all the turbulence generated when wind pushes up vertically from the walls and tries to make the right angle turn to flowing across the roof. And I wonder if you could build a wind turbine that looks a little like the one above and put it on top of that dome roof.

Circular Wind Dam, Rotated Energy Exchange Variation

Circular Wind Dam, Rotated Energy Exchange Variation

Circular Wind Dam, Rotated Energy Exchange Variation

Circular Wind Dam, Rotated Energy Exchange Variation with Alternating Diffusor Concentrators

Circular Wind Dam, Rotated Energy Exchange Variation with Alternating Diffusor Concentrators

Circular Wind Dam, Rotated Energy Exchange Variation with Alternating Diffusor Concentrators 2

Circular Wind Dam, Rotated Energy Exchange Variation

Circular Wind Dam

Controlling Vortex Shedding

Circular Wind Dam, Control of Vortex Shedding

Circular Wind Dam, Control of Vortex Shedding (closeup)

High Altitude Variation

Suppose the wind turbine blades extend from an elevation of 50 feet up to an elevation of 150 feet. We would like for the walls of the wind dam to reach an altitude of 300 feet. This allows us to extract some of the energy from higher energy density wind at altitude. There are a variety of ways I can think of to do this, but I’m wondering if all that is necessary is to make the walls of the wind dam lean in one direction or the other:

Wall Leans to Access High Energy Density Wind at Altitude

At first, this solution would seem to be sensitive to wind direction. But I’m wondering if maybe that isn’t the case. Imagine, for example, wind flowing from right to left in the diagram above. Intuitively, it would seem that high energy high altitude wind would be driven downward towards the earth by the slanted portion of the wall. This is reminiscent of a flow concentrator. But if instead wind flows from the left to the right, high energy high altitude wind ramps over the slanted portion of the wall, reminiscent of a flow diffuser. In this later case, wouldn’t some of its energy still be transferred to lower altitude wind, albeit through the action of suction rather than through the action of compression?

Of course, it is also important to note that a certain amount of the high energy high altitude wind will be deflected downward (toward the earth) even if the entire wall is vertical (rather than having the upper part slanted).

In any case, if a leaning wall proves to be useful, note that it is easy to build one by anchoring fabric to the guy wires of a tower:

Making Leaning Fabric Wall with Guyed Tubular Tower

Better Diagrams of High Altitude Variation?

I’m not much of an artist, and I’m using 2D software to boot. But here’s an attempt at rendering one of the variations that captures energy from high-altitude winds without using tall turbines:

Aerial View of Pseudo-High-Altitude Circular Wind Dam

One Section of Polygon of Pseudo-High-Altitude Circular Wind Dam with Darrieus Rotors

Side View of Pseudo-High-Altitude Circular Wind Dam with Darrieus Rotors

Circular Wind Dam Pseudo-High-Altitude Variation #2

Aerial View of Pseudo-High-Altitude Circular Wind Dam Variation #2

Side View of Pseudo-High-Altitude Circular Wind Dam Variation #2 (wind blowing from right)

Side View of Pseudo-High-Altitude Circular Wind Dam Variation #2 (wind blowing from left)

Circular Wind Dam Pseudo-High-Altitude Variation #2 Stacked on top of Rotated Energy Exchange Variation

Just stack the high altitude part:

High Altitude Part

On top of the low altitude part:

Circular Wind Dam, Rotated Energy Exchange Variation

Put the towers inside the brick walls, and make the lower ends of the tarps come approximately to the tops of the brick walls.

Circular Wind Dam Pseudo-High-Altitude Variation #3

Aerial View of Pseudo-High-Altitude Circular Wind Dam Variation #3

Using HAWTs instead of VAWTs

Of course, HAWTs may be substituted for VAWTs in the above designs. Just block the regions of accelerated flow with walls, cut holes in the walls, and put HAWT rotors into the holes. The only other necessary modification is that you’d have to figure out a way to “yaw” the HAWT by 180 degrees. This is so because the wind may flow in either direction through the hole, depending on the direction of the ambient wind.

Non-Circular Variation

Non-Circular Wind Dam Rotated Energy Exchange VariationIf a non-circular path is properly designed, the wind dam will still be equally effective (or almost equally effective) regardless of wind direction. For an explanation of how to design a non-circular path, see the earlier post 20 Megawatt Direct Drive Darrieus.

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