Windmill or Wind Turbine- powered boats: how many are out there, and are they viable?

[MPraamsma]

Windmaster,

Here is something to contemplate about the way a duct may eventually be able to surpass a free prop. The only way to extract mechanical (heat)energy from a gas is to let it expand in a confined volume such as a piston and cylinder, or any arrangement that simulates that condition (such as a foil in flow). It may be hard to see the similarity btween a wing and a piston, but they are really the same, except for the volume involved. The surface of the piston is moving away from the expanding gases, and so there is an exchange of momentum TO the piston, and none towards the gases from the piston. The heat from the gases is transfered to the piston as mechanical force that can be used for doing mechanical work. The gas is COLDER after surrendering heat.

In a wing, this expansion is caused by the venturi effect occuring on the upper surface, which is actually one half of a venturi, with the other wall being a virtual one due to the immense (mathematically infinite) distance to it. This is of course a very inefficient venturi, yet it works well enough to benefit from the force developed on the underside which is not (ideally) a venturi surface. The wing is therefore a giant piston, in an infinitely long cylinder, and is actually moving away from the expanding gases on the underside. This motion of the wing is invisible to us because it occurs on the atomic scale, but can be visualized by imagining what would happen if there was no gravity (like in a perfectly vertical dive). Obviously the wing would move briskly in the direction of the upper surface.

Far behind the wing, after everything settles down, the temperature of the air will be somewhat lower, the difference being the mechanical work (heat) extracted to support the wing's load (for now we will ignore the heat introduced to the air from the leading edge shock, which is lost by the way).

In a duct things are different, first of all the leading edge shock cannot escape that easily, and remains part of the internal energy of the flow. Secondly the object is to get the flow to move at the maximum rate possible (which is the local speed of sound in the duct) and then let it expand out the exit and return to the ambient air. As long as this happens before a vacuum can develop it will not cause any retarding force.

How is this possible you ask? Well, in the duct we have almost complete control of all the parameters of flow, temp and density because everything happens in a closed system. It is possible to exchange these factors so that the temp is lower, but the flow velocity is higher, in other words we may have warm air entering at zero flow velocity and colder air at higher velocity exiting. This is the way around the Betz limit ultimately by by discharging the air at a lower temp, higher velocity but same effective pressure.

[Guest625101138]

Originally Posted by MPraamsma

........ I am adding an abreviated diagram to illustrate all of this, so let me know if this seems logical to you. If you want I can elaborate, but I am curious what you see in it so far.

Michael
The vanes on the inlet and outlet runners seem to be arranged incorrectly. My understanding is that there will be less volume out than in. The blades seem to be pitched opposite to this requirement.

I cannot determine the flaw. Simplistically there is a lot of energy in air. Cooling by 1C degree at 3m/s through a 1sq.m duct will give way better energy than I can extract with my 2.2m diameter open turbine.

I have not considered the internal duct drag and this might be significant but intuitively should not be more than a hundred watts or so.

Logically it cannot work because you effectively have free energy. On a moving vehicle you could operate without wind and simply leave a slightly cooler track of air. If there were lots of vehicles then you would make the whole place cooler of course so environmentally there might be issues. In cool, high humidity locations you could run the risk of icing internally.

If it does work, there is no reason that prevents a stationary engine working simply by adjusting the inlet and outlet vanes to provide a pressure difference to get internal air flow without wind.

Rick W

[MPraamsma]

Rick,

I think you may be seeing where I am heading on this thing. In the diagram I sent I show some typical blade angles, the first and last set of blades are the stators, but I only show a typical arrangement. Since at this point I am not sure what those angles should be I have made every blade in the system adjustable by mounting it on a small indexing plate that can be changed or modified. The stators could also be neutral fairings, but that seems to me to possibly ignore some useful aerodynamic function they might serve. It will never be able to run in place by itself in static air (even I am not that optimistic) but REQUIRES the vehicle motion (or wind) to work. If the purpose were just to generate power, the turbine would have to be whirled around on some kind of long arm or something, using some of the power generated to do so.

As far as the 'cooling' effect, remember that whatever energy is generated is ultimately returned to the atmosphere by conduction, radiation, convection etc. (cue the music from Lion King 'The Circle of Life'), so that it is all a zero sum proposition. It is no different from any other cycle, just travels a longer loop to get back to the start point. You are spot on about the staggering amount of energy that is trapped in the atmosphere... it must be directly accessible somehow!

[Externet]

Hello all.
Regards, Mr. Worsley; this is Miguel, from San Francisco; it has been perhaps 10 years since we interchanged opinions about Jensa and my model with the stern 'flap'. Very pleased to see your continued activity in the subject.

Lurking at the thread long enough to succumb holding my opinion;
My way of seen this is simplified to overcome static forces. No dynamics/horsepower considered.

The wind pushes a floating boat downwind with a force W related to the area of everything above water level blocking the wind to flow. Everything includes the turbine.
Opposing W is the wet hull drag D transversal to the wind

The propeller pushes the boat with a force F
Opposing F is the wet hull drag d in the fore to aft direction

The propeller must push the boat with a force F greater than W to overcome statics and move against the wind, as directly against the wind, "D" and "d" nearly cancel.

The boat must be very low profile above water surface, exposing as little as possible wind swept structures to incoming wind direction.
The turbine must have a large diameter with little blades area that achieves enough force at the propeller.

The propeller must be geared/sized/pitch chosen very carefully. In electronics, that is called impedance matching. In fluid mechanics, a too large or too small propeller will not perform to its maximum capability.

W-----> <--D < d--> <------F

I believe Rick W is doing it right. A two or three blade turbine should perform better.

Miguel

[Windmaster]

Originally Posted by Externet

Hello all.

The boat must be very low profile above water surface, exposing as little as possible wind swept structures to incoming wind direction.
The turbine must have a large diameter with little blades area that achieves enough force at the propeller.

The propeller must be geared/sized/pitch chosen very carefully. In electronics, that is called impedance matching. In fluid mechanics, a too large or too small propeller will not perform to its maximum capability.

W-----> <--D < d--> <------F

I believe Rick W is doing it right. A two or three blade propeller should perform better.

Miguel

Hello Miguel
Very nice to hear from you again, I still have the pictures you sent me, your "flap" was a good idea and I liked you solar powered receiver. You're quite right about the need to expose as little boat as possible when trying to go into the wind.
Also you are right about the "impedance matching".

The problem is that with a two or three blade propeller is that it needs to turn at high speed, most of your lift is "adverse" thrust, pushing you back and stopping your progress - only a small proportion is used to power you forward and you need to amplify that small force by gearing to overcome the large force pushing you back.

You get a situation of large opposing forces which strains your transmission and is rather frightening and not easy to control.

My aim is to make the whole thing more safe and user friendly, and anyway I've yet to see a small windturbine boat of the "high speed rotor" type work as well as my type.
Maybe Rick can get his working effectively, we will wait and see.

One thing I will say is that he has been very honest in the reporting of his tests and hasn't tried to make it look better than it is.

[Externet]

Hi all.
Had this link sleeping in my favorites folder for almost fifteen years. It is the simplest, eye opening gadget for the agnostics; I think has not been exposed in this thread and will be good to share:

http://www.main.org/polycosmos/silicbar/sailscrw.htm

Built one years ago, tried a few times always on uneasy conditions of too much wind and rough sea. Someday perhaps soon will find proper conditions and a matching propeller to report behavior.
Design is not good to build a boat (that must head in all directions); just to demonstrate the 'directly against the wind' possibility.

The ruler is 15cm, overall length is 85cm, shaft is 8mm ⌀ hollow carbon fiber, aft turbine is 42cm ⌀. The 'fore' 25mm nut is just weight to keep the pulling propeller submerged; the tilt angle varies with wind force and by sliding the 'float' position to avoid splashing. Am a believer

Miguel

[Windmaster]

Nice to see you have built one of these.

That page is quite famous, and dates from about 1994 I think.

Nowadays there are a few more believers, but they just argue about the best way of doing it!

[MPraamsma]

Rick, Windmaster, et al...

I thought I might try and explain how I finally got to my ducted turbo-generator concept, which has taken up my thoughts for many years already. I didn't start out looking for a way to sail into the wind, I was actually looking for a way to reduce the coefficient of drag of an automobile body by streamlining and airfoils, just like everyone has already tried. It occured to me that if all the best minds in the business could only make tiny incremental improvements, and these were pretty much exhausted, that what I could do would be a waste of time, sort of like waxing your car so it goes an additional 1 MPH. One day, while bored and browsing the encyclopaedia I stumbled on an article about the Busemann Biplane, and the author had concluded that it was a useless concept, because who needs a wing with no drag and no lift! I was almost offended that somewould declare a principle pointless because they were prejudiced about how it might be applied to a real world situation. However, I was looking for a fuselage, not a wing, so I saw something else in it.

The next few years were spent building all kinds of models out of balsa and fiberglass, trying to see how this 'useless' idea might apply to what I was looking for. As you might expect, and many of you may have also experienced, I was virtually declared to be nuts. The idea would not leave my thoughts, so I figured it was just my mission or something, and pushed through the criticism and self-doubt and kept on keeping on. When I began there was no internet, so it was almost impossible to find anyone else that shared my view, and the only other time I saw anything resembling it was some entrepeneur that made a hollow football that used it to make a football that could be thrown further. Just realizing you are not the only one with a particular idea keeps you going.

The idea rattled around in my head for years, looking for a way to try it out on a larger scale, and then when my daughter turned 4 I thought I would try to make a soapbox racer out of the idea. Despite the objections of my wife, who saw only a good way to waste all our spare houshold funds and a lot of time, I pressed ahead and constructed a vehicle out of thin multi-ply that stuck to all the specifications required. 99.9% of this type of cars are made by others out of plastic or fiberglass, are about the size of a sleeping bag, and have a frontal area of around one square foot, and the pilots are lying down inside them like a luge. It created quite a stir to show up with a giant box 4X8X2 feet on a side, with my kid sitting upright in a very comfortable chair. It performed perfectly (even though people were taking bets whether it could even reach the end of the ramp), no discernable loss of efficiency. I named it the PEGASUS, but my daughter couldn't pronounce it properly, calling it PEGALYS Mark I, and so the new name stuck. I am up the the Mark V on the idea now. I am attaching a PDF with a brief description.

(BTW, the only other application I have ever seen is used by the Pentagon to make hollow kinetic cannon rounds that lose very little energy, and therefore have a much flatter trajectory. http://www.patentstorm.us/patents/49...scription.html)

[Guest625101138]

Michael
I have compared the drag of two 10% thick 5% cambered foils back to back with two similar foils separated by 20% to form a venturi. See attached.

For two vehicles of similar height the ratio of drag is 6 in favour of the back to back. Taking twice the frontal area into account the advantage drops to 3 fold in favour of the back to back foils.

So your observations of similar performance could only be achieved if the volume of air out is less than the volume in. This would increase the tail pressure. The only way this can be achieved is if the venturi process is no longer isothermal. This of course is quite reasonable through adiabatic expansion through the venturi and less than full thermal recovery during the exiting compression.

It would be interesting to measure the temperature difference between inlet and outlet on a venturi in typical wind conditions.

I can see how this process can reduce drag on the vehicle in a gross sense compared with isothermal flow. Also with an internal turbine the vanes see much higher Re# which will improve the L/D of these foils.

My understanding of the principles involved is not sufficient for me to analyse quantitatively but I still have difficulty seeing sufficient benefit in the cooling to offset the higher isothermal drag coefficient. However if they can demonstrate improvements with projectiles then there has to be some net benefit.

One of the problems with my open turbine is that the performance suffers as the windspeed drops because the reduced L/D at lower Re#. I need about 10kts of wind to make way directly to windward with a 3:1 pitch ratio. I need about 20kts to make headway with a 1.6:1 ratio. Anything less and it gets in "irons" and goes backwards.

Rick

[backyardbil]

Mpraamsa

Your account of your Pegalys's is an inspiring story. Since you have done so much work you should have some success. If you what you say is true then it is indeed a significant breakthrough with quite a lot of applications.

I afraid I don't have the technical training to comment precisely on it in a meaningful way. I think maybe that is true for most of the members of this forum (comments invited from those who don't agree)

[backyardbil]

Originally Posted by Rick Willoughby

Michael


One of the problems with my open turbine is that the performance suffers as the windspeed drops because the reduced L/D at lower Re#. I need about 10kts of wind to make way directly to windward with a 3:1 pitch ratio. I need about 20kts to make headway with a 1.6:1 ratio. Anything less and it gets in "irons" and goes backwards.

Rick

Rick
How can you get over this problem? I think the natural wind is pretty variable all the time. Could you adjust the pitch ratio easily? or would changing the mechanical gear ratio do the trick.
P.S. did you do any more testing yet?

[MPraamsma]

Rick,

I also did a million plots with JavaFoil and others, and I started to get the suspicion that the programs were just looking at standard tables to predict drag based on the flow velocity over the surface. Obviously the venturi goes supersonic pretty soon compared with the external foil, and by their reasoning is producing a lot of drag. I tried to throw a curve ball at the program by putting two objects in the flow field adjacent to each other, and the results were very questionable. In the diagrams attached, I put an automobile shaped body next to a venturi body, and it clearly shows the extent of the disturbed air ahead and behind the car, and the undisturbed air near the venturi. All the dark areas represent lost energy. Yet calculated separately they showed similar Cd. I'm not sure these programs take the reflected wave into proper consideration, otherwise, where is the lost energy evident in the venturi plot.

You might also try feathering the inlet and outlet more to avoid the abrupt changes in direction, and also make the external surfaces totally flat and parallel. You may notice that the slightest pertubation on the outer surface produces far field effects.

[MPraamsma]

Gusting is a problem for any wind generator, that is why I am focussing my efforts also on the design of the alternator to collect the power. I ran across what I consider to be the best configuration to handle the problem, it is the brushless design by Electrodyne. http://www.electrodyne.com/operation.html

This is a very clever design, it has only staionary coils for armature and stator, and the magnetic field is induced into a rotor that runs inbetween two gaps in a toroidial field. The output voltage is controlled by varying the field voltage. This can be done very rapidly, and can act as a speed regulator as well, as long as you have somewhere for the excess power to go, like a battery.

Your point about gusts is one of the reasons I am pursuing the internal arrangement, because it feathers automatically at it's highest speed under no-load conditions. This leaves it spinning harmlessly at very high RPM, and conserves it's rotational momentum. Exciting the field coil causes the armature to draw power, and lowers the RPM, but in this case that causes the effective angle of attack to increase and the turbine to develop more torque. Of course drawing too much will cause it to stall, just like any flying wing.

[Windmaster]

Originally Posted by Rick Willoughby

Michael

One of the problems with my open turbine is that the performance suffers as the windspeed drops because the reduced L/D at lower Re#. I need about 10kts of wind to make way directly to windward with a 3:1 pitch ratio. I need about 20kts to make headway with a 1.6:1 ratio. Anything less and it gets in "irons" and goes backwards.

Rick

I've certainly never had any problems with them going backwards. They always want to go forwards so much I have to restrain them. That applies for all windspeeds.
As a matter of fact I have just uploaded a video to youtube showing this - I hope you can see the piece of wool that shows the wind direction.
Its http://www.youtube.com/watch?v=iygLgI25WOg

Secondly, can you really believe that these aerodynamic prediction programs are the gospel truth? After all, they are only as good as the data put in them. Many still agree that Aerodynamics is a "Black Art". Mpraamsa is right to question them.

[MPraamsma]

A while back, I had a long internet conversation with someone who knew about, and had actually seen this invention working as a young boy, but was surprised later that it never became a practical machine in widespread use. The patent drawing shows the basic principle, and the working model that the original inventor made was fairly large, the 'cups' were around one meter in diameter. It apparently ran as a demo for months and months, but the idea was killed by the hydropower interests that prevailed (in Austria). This style of wind energy harvesting uses pure drag as the driving force, and the cups develop no lift at all. The cups are always travelling downwind, therefore they develop little to no adverse thrust.

My internet friend was a sailor and was mostly interested in creating a silent mast-top auxilliary power generator (if you have ever spent much time as a slip neighbor to someone with the regular noisy bladed prop version, you realize this is a noble goal), but I was also interested in the way it might help my work. I sketched out some ideas, and for the first time I started to see if it was possible to incorporate a generator inside a duct, because I was still thinking that anything placed in the duct would destroy the flow, and this seemed to be a way around that. Looking back these sketches are naiive but served to make me aware of the need to make sure that all the thrusts and forces have to be aligned so they cannot inhibit the vehicle motion.