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 29, 2009

Small H Rotors Perimeter Yawing Flow Accelerating Shroud Atop High Guyed Tower

Filed under: Wind Turbine Flow Accelerating Shroud — Tags: , , , — Salient White Elephant @ 10:12 pm

Small H Rotors Perimeter Yawing Flow Accelerating Shroud Atop High Guyed Tower

Small H Rotors Perimeter Yawing Flow Accelerating Shroud Atop High Guyed Tower

Small H Rotors Perimeter Yawing Flow Accelerating Shroud Atop High Guyed Tower

I guess if the shroud were octagonally shaped then that would probably come close enough to an approximate circle to eliminate really counterproductive flow patterns near the corners of the square:

Octagonal Shroud

Flow Accelerator that Yaws by Force of Drag

VAWT with Shroud that Yaws by Force of Drag

HAWT with Shroud that Yaws by Force of Drag

April 27, 2009

Practical Small Scale Airborne Kite Turbine

Practical Small Scale Airborne Kite Turbine

There’s a hole in the middle of the kite that the tube connects to so that the tube can reach the low pressure behind the kite.

Wind Turbine With Blimp Supported Flow Accelerator

Wind Turbine With Blimp Wind Turbine With Supported Flow Accelerator

Wind Turbine With Blimp Wind Turbine With Supported Flow Accelerator

Ultra High Altitude Low Visual Pollution Variation

There are a few problems with the turbine just described:

  • The weight of the suspended tarp may be prohibitive.
  • The tarp resource is poorly leveraged because much of the wind it redirects is low-energy wind that is close to the ground.
  • The blimp resource is poorly leveraged because much of its size and weight stems from the need to support the large part of the tarp that is close to the ground.
  • The blimps are not able to fly at high altitude because the tarp would simply be too heavy to lift to high altitude.
  • The exceedingly powerful suction developed by such a large flow accelerator may reverse the flow that is near to the ground and not too far above the turbine and the lower edge of the tarp.

This variation proposes to solve these problems and permit extremely high altitude wind to be harvested:

Wind Turbine With Blimp Supported Flow Accelerator, Side View, High Altitude Variation

Wind Turbine With Blimp Supported Flow Accelerator, Side View, High Altitude Variation

Now the blimps and tarp may be separated from the turbine by a very large vertical distance, and the suction is carried to the ground through light-weight fabric tubes that are supported on the guy wires. As an alternative to the design shown above, one tube can be fixed to carry high pressure and the other can carry low pressure. The turbine is then placed between the openings of these two tubes at ground level.

I wonder if this design or something like it would be capable of reaching the jet streams? I guess that’s pretty outrageous, and probably not even necessary. (It may be more economical to harvest lower altitude winds using several machines than to build a single gigantic machine that reaches the jet stream. Plus you’d have the safety issue – what if a cable breaks? Of course, I guess you could always put it out in the ocean. Another potential problem with extremely high altitudes is that the wind direction up there might not be the same as on the ground. But then again, if you’re getting so much energy from altitude, you could just put the turbine rotor inside the tube, and also put the rotor on the ground so that it doesn’t have to yaw. This way the wind velocity near the ground would be insignificant compared to the velocity of air moving through the tube, and so it wouldn’t matter which way the rotor were pointed, or which way the opening of the tube were pointed. In fact, you could use a HAWT rotor that spins about a vertical axis, and let the tube extend from the rotor in the vertical direction.)

VAWT Forest With OmniDirectional Flow Accelerators

This post describes a field of stationary flow accelerators that I hope will be effective for any wind direction. Flow accelerators, or shrouds, are generally regarded as closer to science fiction than to a practical and economical idea. I think this may be due to the following problems:

  • It is difficult to yaw a large structure.
  • If the yaw system fails during high winds, the structure will fail.
  • The complexity and cost of the structure are probably greater than the complexity and cost of simply scaling up a more conventional and well understood design.

The VAWT Forest with OmniDirectional Flow Accelerators attempts to solve these problems as follows:

  • The flow accelerators are fixed. They do not yaw, and they rest on the ground.
  • The flow accelerators are equipped with vents that allow high winds to pass through the structures without generating much drag.
  • The cost and complexity is low. The flow accelerators are basically nothing more than oblong shaped brick walls.

The diagram shows Savonius rotors, but the design might work with other types of VAWT rotors. However, because of the relatively unpredictable and complex flow patterns that are likely to be created with this design, I am assuming that the Savonius might be a good choice, because it is mechanically and aerodynamically robust, and because it is relatively insensitive to turbulence:Savonius Forest With OmniDirectional Flow Accelerators

What’s so great about this idea? It seems incredible that you could develop a fixed flow accelerator that is equally (or almost equally) effective for every wind direction. The trick here, of course, is that only the accelerators that are in the interior of the forest are equally effective for every wind direction. The ones on the periphery of the forest may not accelerate flow at all for certain wind directions! But the design is effective because we can make the forest very very large – with many accelerators and many turbines. In this case, the number of turbines and accelerators that are at the periphery of the forest account for only a very small fraction of the total number turbines and accelerators.

Here’s a simpler way to make the flow accelerators that might be less expensive and that still avoids making the wind flow around sharp corners:

Alternate Design for Flow Accelerators

I think this idea looks pretty good as is, but we can experiment further by putting circular shaped energy exchangers over the large empty places formed by the flow accelerators. These energy exchangers are able to rotate in order to align with wind direction. The slotted channels cause the oncoming (high energy) wind to flow down into the empty areas between the flow accelerators, and they also cause low energy air that has already flowed through the rotors to flow up and out of these empty areas in the downstream direction:

Counter-Sloping Energy Exchange Channels

Savonius Forest With OmniDirectional Flow Accelerators and Rotating Energy Exchangers

Another variation has a tarp lying across the roofs of all the flow accelerators, and places towers along the four edges of the Savonius Forest that support angled tarps. The following diagram omits the towers and the tarps that would be in the front and the rear of the view shown. (That is, only the towers and tarps on the right and left are shown – the ones in the front and back are omitted.)

Savonius Forest With OmniDirectional Flow Accelerators and Guyed Tower Supported Flow Accelerators

I am not an aerodynamicist, but I have always had the feeling that ducted rotors waste a lot of the accelerated flow created by the shroud. Wind tends to veer around obstructions. This is the reason for the Betz limit – the more energy you extract from the wind, the more you are slowing it down, the greater is the obstruction to flow, and the more the oncoming wind veers to avoid the obstruction. The idea proposed here is that more rotors should be placed in the path of the wind that is attempting to make its way around the turbines. Now I realize that this smacks of an “eternal motion” kind of logic. Isn’t it true that all of the turbines and all of the flow accelerators may be regarded as a single energy harvesting device, and that the Betz limit will apply to this large composite “turbine” just as well as to a single ducted rotor? Well… I’m not sure. The situation is complicated somewhat because the rotors are dispersed in the upwind and downwind directions as well as in the cross-wind directions. But let’s just suppose that the dispersed nature of this design is indeed subject to the same limitations as a single ducted turbine. Doesn’t it still enjoy the advantage of being omnidirectional? And isn’t it easier to design and build a number of small rotors instead of a single giant one? And isn’t it nice that the small rotors will spin at high rpm, thus reducing torque? And there is an aspect of the omnidirectional nature of this machine that I can’t quite wrap my mind around. It is as though the energy is filtered through the turbines like the way you might imagine rainwater making its way down to the aquafer. That is, if the pressure becomes unbalanced for some reason, the wind just might decide to flow in the crosswind direction. This seems possible since once inside the maze of flow accelerators, air has no “direct contact” with the wind outside the maze. (If this doesn’t sound very scientific, then you are obviously not a graduate, as I am, of the Billy Mays two week engineering correspondence course with complimentary “Senior Engineering Manager Your Name Here” wall plaque.)

There is another feature of this design that appeals to me as well. It seems to me that in the past, designers of ducted machines have assumed that a flow accelerator must be symmetrical. This seems like a critical mistake to me. One of the problems with flow accelerators is that they are huge, unweildy, expensive, and vulnerable to damage in storm winds. But the dispersed “Forest” idea shows that you aren’t constrained to expanding in symmetrical directions – you can simply ignore the vertical direction and spend your money expanding in the horizontal direction alone. Or, more likely, you can develop mathematical design techniques that can predict the optimal aspect ratio.

April 26, 2009

Flow Magnified VAWT Forest

Flow Magnified VAWT Forest

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.

Underground Wind Turbine

The two diagrams below show aerial views of the underground wind turbine. The first diagram omits the doors that cover the trenches.

Underground Wind Turbine

The doors are visible in the following diagram. The doors may be opened so that either long edge may be raised, while the opposite long edge remains at ground level. Because the diagram isn’t three dimensional, it might be a little hard to comprehend at first. But it is easier to understand if you keep in mind that the width of the doors is exactly the same as the width of the trench that it covers below:

Underground Wind Turbine Showing How Doors Open to Capture Wind

Tipi Cross-Section Circular Wind Dam

This wind dam is made of fabric, and is supported by very tall guyed towers. Its cross-section is shaped like an American Indian Tipi:

Tipi Cross-Section Circular Wind Dam

The fabric on either side of the tower may be rolled up to the top of the tower or rolled down to ground level. The fabric on both sides of all towers can be rolled up or down to minimize the drag profile during storm winds. The fabric on the upwind sides of the towers that are on the upwind side of the dam is rolled up to concentrate the flow. The fabric on the downwind sides of the towers that are on the downwind side of the dam is rolled up to further concentrate the flow. The operation of the machine is very similar to the operation of the Circular Wind Dam. Two wind dams may be constructed as described here so that they form concentric rings. In this way, the concentric rings variation of the Circular Wind Dam may be mimicked.

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