Salient White Elephant

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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