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.

Jet Stream Ram Air Wind Turbine

In earlier posts I have mentioned that a turbine capable of harvesting the energy of jet streams would probably be better for newspaper headlines than for an economical approach to wind electricity, since it would probably be cheaper and more effective to build several smaller low altitude turbines than a single monster that could tap into the jet streams. But it got me to realize that there are no jet stream turbines on the Salient White Elephant. This is Salient, to be sure, but is it White Elephant? Certainly not! And already I can hear not a little hubbub from the Canadian Parliament behind me patting their tables and gushing heah heah! So let’s just round things out with a couple of jet stream turbines before tensions run too high and one of the hairs on the head of the Right Honourable Stephen Harper springs noticeably out of place, shall we?

Jet Stream Ram Air Wind Turbine

For some reason, I’m usually biased toward using suction rather than high pressure in my flow accelerator ideas. But one advantage of using ram air pressure in the machine proposed here is that it would keep the long fabric tube inflated. This is very significant of course, since one of the biggest challenges in designing an airborne turbine is keeping weight to a minimum. Using high pressure might eliminate any rib-like supporting structure that would otherwise be required for the tube. I guess you’d have to stabilize the fabric tube by attaching it to the tethering cables at various intervals, but who knows… maybe somebody can design a way around this requirement.

Triple Tethered Variation

Jet Stream Ram Air Wind Turbine, Triple Tethered Variation

Multiple Blimps Variation

There are many variations of the ideas proposed here, but let me discuss one in particular. This idea emphasizes a technique I’d like to use to bring these pie-in-the-sky airborne turbines a little closer to feasible. Imagine eight blimps. Each is tethered by at least three cables to keep the blimps from moving around too much. An aerial view would reveal that the blimps are situated at the vertices of a gigantic octagon. It is important to note that the “diameter” of the octagon is far from insignificant. I can’t give you a number… maybe two or three football fields? Each blimp has a parachute and a high pressure tube, just as described above. All of the high pressure tubes converge at the center of the octagon, where they connect to a single larger high pressure tube that takes the jet stream wind down to the ground.

What’s so great about this variation? Well… let me first list what I believe may be the salient objectives of airborne turbine design:

  • If possible, no moving parts in the air.
  • If possible, no fiberglass, electrical cable, gearboxes, drive shafts, or electrical generators in the air. (Ever notice how the components of a wind turbine that have to do with mechanical and electrical power are about the most dense (heaviest) things known to engineering kind?!)

So the idea here is that instead of having eight different tubes, we attempt to minimize weight by having a single large tube carry wind from the jet stream to the ground. This is desirable because the really long distance is from the jet stream to the ground. Once at the center of the jet stream octagon, it isn’t much further to the blimps. So could we use this trick to reduce the overall weight of the machine?

Well, whether this trick will work or not… I think you see my point. What is needed is a kind of linear programming style optimization that minimizes weight of fabric per kilowatt of capacity.

Can We Really Reach the Jet Stream?

No. The jet streams are like 30 to 40 thousand feet off the ground. (The cruising altitude of jet airplanes!) So we can’t reach the jet stream with the design proposed in this post. But we can certainly reach a higher altitude than today’s state of the art wind turbines! If you want to see a more practical configuration that uses the principles described in this post, check out the Practical Artificial Pressure Differential Wind Turbine.

April 27, 2009

Blimp Supported Linear Turbine

Filed under: Airborne Wind Turbine, Linear Wind Turbine — Tags: , — Salient White Elephant @ 8:40 pm

Blimp Supported Linear Turbine

There’s not much detail in the diagram, and much has been omitted. But I’ve drawn all the mechanisms involved so many times on this blog that I don’t think I’ll draw them again. But let me explain how it works. Heavy cables connect the blimps to the ground and carry the large loads. The symmetrical airfoils travel from the ground to the blimp and then back to the ground again. These airfoils are supported at either ends by moving cables (not shown) that turn a bunch of pulley wheels. The pulley wheels are suspsended from the heavy cables. Power is transmitted from the airfoils through the pulley system to a couple of generators at ground level. Each rail car has one of these generators on top of it.

Alternatively, replace the airfoils in the diagram with relatively small diameter Darrieus or H rotors. Power is still transmitted to the ground mechanically with a pulley system.

Airborne Wind Turbine Energy Multiplier

Filed under: Airborne Wind Turbine — Tags: — Salient White Elephant @ 6:22 pm

Suppose an airborne turbine can choose its altitude, as in the various blimp supported turbines proposed on this blog. In this case, the blimp may choose to hover in the clouds if it’s a cloudy day. Since the air in the clouds is wet, won’t its density be greater? And since the energy in the wind is proportional to density, then won’t this mean that the wind in the clouds will have more energy? Of course, the blimp may not be able to reach that altitude, but if it can, then here’s a possible option for increasing the amount of energy harvested.

About an hour after I posted this, I read in Wikipedia that the density of air actually decreases as a function of humidity. I was quite surprised to read this, but if you don’t believe me, check out the Wikipedia article for yourself. The reason it decreases is that “the molecular mass of water (18) is less than the molecular mass of air (around 29)”. One of my earlier posts suggested increasing the energy density of wind approaching a turbine by injecting a fine mist into the wind in some upstream location. (I was thinking of those misting devices they have to cool people down on the patios of some coffee shops and restaurants.) The Wikipedia article raises an interesting question. Is air that carries a fine mist “humid air”, or is it air that is carrying droplets of water? Because for the Wikipedia analysis to apply, the water must be in a gaseous state. And what about clouds? The stuff that falls on our heads on a rainy day certainly isn’t a gas. Well… it’s late, and I hope you guys will be able to sleep without knowing the answer to this compelling mystery… because I’m going to sleep! More on this later…

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.)

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