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

[Lin Olen]

Hello Michael,
Thanks for summary of effects on your land machine. You have described very well the rapid increase in Cd along with the sudden rise in power generated. It is awsome because a fixed pitch airscrew becomes a powerful spinnaker at speed. This problem disappears when power input is controlled with a variable pitch mechanism on the airscrew (Rotary Sail). Look up my old posts under Rotary Sails and check out my 22 ft trimaran.
Wish we could meet!
Cheers, Lin

[MPraamsma]

Hello Lin

I have been busy moving to Europe lately, so I have not had the time to report on my test of my wind powered bicycle, so here is what I found out.

I took the rig out to the desert, onto a dry lake bed that has about 5 km of unobstructed open area facing the prevailing wind. This gave plenty of room to run a good test. As I had predicted, it starts up very easy by itself, and can easily outpace a man running, but it won't go over about 12 km/hr no matter what the airspeed (wind). The propeller was producing plenty of power, and was actually skidding the tire, but the adverse thrust produced tended to work directly in opposition to the wheel traction. This differential was great enough to lift the front wheel off the ground, which I corrected by hanging a 20 kg toolbox to the front wheel fork. Unfortunately, I didn't bring my camera, because this rig was somewhat comical, running between accelleration and braking which made it like a galloping gurdy. I think that a variable prop would have helped, but not much, because even then the foils are still at a large pitch angle. The only real solution is to have the blades at a negative angle of attack to the wind heading, and to first direct the flow at right angles with a fixed stator. That way the blades on the turbine are set at an angle that only produces tangential thrust. Another idea I had was to place the turbine in a serpentine shaped tunnel that turned it at right angles to the direction of travel, that way any thrust developed would simply add to or remove weight from the vehicle. I anyone is interested, I could whip up a drawing showing these ideas.

[Rick Willoughby]

Michael
You are hitting the limit of your power transfer capability. If you go to post #234 on this thread you will see my spread sheet. I have nominated a 10kW power limit and you can see that you quickly reach this in the boat application. This is a real limit because things start to fail if it is exceeded. Having ability to alter gearing in any manner can enable a higher speed in stronger wind.

With the bike your limit comes about through traction. The coefficient of friction between tire and surface and the vehicle mass. The maximum driving force on a salt pan is likely to be about 50% of vehicle mass.

Any means of altering the gearing between the blades and driving wheels will allow you to go faster as the wind builds.

Rick W.

[MPraamsma]

Hi Rick

I think you are still missing the point about the adverse thrust. The fact that the wheels spin means that there is another force opposing the wheel torque. That force becomes huge as the prop spins up and has a high tip speed. Even an ideal turbine operating in a sonic flow condition still has an angle of attack, and that means that some of the thrust is exerted in the axial direction. If the entire turbine can be turned so that it rotates in a horizontal plane then none of this force would be detrimental.

[Rick Willoughby]

Michael you have to demonstrate that you can install ducting advantageously. I consider this doubtful. If it was beneficial I expect to see the other machines incorporating ducting rather than just protective cowlings.

My modeling is quite accurate for the open blade configuration. My model takes the thrust on the air turbine into account. I have previously noted that you quickly arrive at the mechanical limits of the power transfer. This is all that you are seeing with your test. If you could alter the gearing between props and wheels by any method you could go a little faster for your given thrust constraint.

Rick W

[Windmaster]

Rick, I think Michael is right. You are missing the point. He's told you many times about the axial force, but you don't seem to take it on board. Maybe you should do some real tests instead of relying on maths.

[MPraamsma]

Ok guys, this is my sketch of what I think is the way to go to solve this thrust problem. It is a serpentine duct that turns the axis around 90 degrees, so that it can spin in a horizontal plane. The first part of the duct and the last part are actually the main passive venturi, and the turbine is located at the throat. The turbine is an active venturi that has a propeller at the inlet, which accelerates and compresses the flow into the annular chamber. Inside this chamber there is a stator that forces the entire flow into a spiral. The turbine, which is now subject to a strong tangential flow, will be actually be flying downwind because of the high rotational speed. This turbine is connected directly to the input prop and rotates at the same speed.

The thrust developed by the input prop is cancelled by the stator thrust. The thrust of the input prop could also be used to support the weight of the spindle/generator/prop assembly, so that the weight on the bearings is minimized.

Keep in mind, that with this type of energy collection, you must have an external means of propulsion in order to create the flow conditions necessary to operate. This can be a marine prop, airscrew, or wheels, but must pull the entire unit into the wind. Since the output might consist of multiple motor, wheels, or props, it is best to make the generator a massive 3 stage brushless variable alternator/motor, and use that generated power to flexibly control power to each actuator electromotor. Electronic traction control for vehicles, or steering for vessels.

[Rick Willoughby]

Originally Posted by Windmaster

Rick, I think Michael is right. You are missing the point. He's told you many times about the axial force, but you don't seem to take it on board. Maybe you should do some real tests instead of relying on maths.

Windmaster you are wrong here. I tried to explain the turbine thrust issue to you previously. Go back to posts #112 and #113. You clearly did not understand what I was pointing out then. Hopefully it is clearer now.

I have also often discussed the power limit previously only his was a limit through the lack of grip rather than a torque limit with mechanical linkage in a boat application. Have a look at post #232 where I explained this to Tcubed. I think it disappointed him because he envisaged being able to build a system and go very fast. I posted the calculator in response to his questions.

The calculator I provided takes axial thrust into account. I could modify the power limit to match the grip limit on Michael's trailer and it would accurately predict what he has observed.

I am interested in what Michael is doing from the point of view of ducting. There may be some point where ducting provides a benefit and this will be interesting to see as I have not yet modeled ducting. There is potential to get better turbine efficiency in light winds by increasing velocity over the blades. It also overcomes the Betz limit applicable to unducted turbines. So it is a matter of these benefits outweighing the cost of extra drag on the ducting and extra weight to carry around.

So far his unducted testing verifies what I calculated.

Rick W

[MPraamsma]

I also wanted to elaborate on my desert floor tests of my wind powered cycle/bicycle, as we had a unique experience with some land yacht enthousiasts that were there the same day. They saw us running this obvious mechanical wind contraption directly windward, and offered us a ride in their craft on the same salt lake bed. These were tricycle gear two seater on aircraft tires, with about a 3 meter sail. These things went about 80-100 km/hr top speed, and really demonstrated the power of the downwind leg. As a sailor of a 40 foot sailboat, I am used to downwind feeling slow and powerless, and the upwind feeling powerful and fast. These things however have the opposite performance, they go to wind only grudgingly, and with a lot of noise and tension, and don't like to get too close to the wind. Downwind is an entirely different story, we were flying! I couldn't believe how much speed we were able to get to, many times the wind speed. This made me realize that the secret to getting as much power as possible is to get the entire blade area to be rotating at such a high speed that it is 'flying downwind faster than the windspeed'. Of course this means that the flow over it must also be traveling at a high rate of speed so that the resultant dynamic angle of attack is in a flight regime. In this mode, slowing it down causes the angle of attack to effectively increase in proportion to the load. By keeping the blade planform a simple square shaped foil, where the effective airflow can be considered to be uniform, there is no need for blade twist, or dealing with the effects of tip speed/root speed issues.

In the sketch you can see the turbine blades are actually at a negative angle of attack to the flow (assuming the other propeller elements were not present), and by itself would drive the turbine BACKWARDs. However, the flow past it (due to the stator system) would be at an angle of attack of almost 80-90 degrees at startup, but would be only a few degrees at cruise speed, when every thing is flowing and rotating at a maximum rate. Even though the flow could be exiting the stator blades at sonic speed, they pass over the turbine blades subsonically because they are traveling along with the flow (downwind).

[Windmaster]

Originally Posted by Rick Willoughby

Windmaster you are wrong here. I tried to explain the turbine thrust issue to you previously. Go back to posts #112 and #113. You clearly did not understand what I was pointing out then. Hopefully it is clearer now.

Rick W

Yes, I confess, I did not understand, and to be honest, I don't really understand now. Your posts are too technical and I can't always see what you are trying to achieve. Can you try and explain more simply for the layman? Maybe I don't have enough brain cells to get it all in place!

The ducting argument is very interesting, I would have thought that ducting would carry more of a penalty than an advantage, due to parasitic drag. In the past ducted propellers and ducted turbines have never superseded unducted ones. Were all previous designers wrong?

[Windmaster]

Originally Posted by MPraamsma

This made me realize that the secret to getting as much power as possible is to get the entire blade area to be rotating at such a high speed that it is 'flying downwind faster than the windspeed'. Of course this means that the flow over it must also be traveling at a high rate of speed so that the resultant dynamic angle of attack is in a flight regime.

I don't think this is going to allow you to go directly into the wind successfully.

[Windmaster]

Some doubters of the possibility that a Rotary Sailing craft can go directly into the wind claim that you are getting "something for nothing" and it is impossible.
Although they are wrong, it is quite possible to see where they get this idea from.
To them, the thought that something can move in the completely opposite direction from the force that powers it seems impossible.
(However, if they gave it deeper thought they would realise that it is simply the application of the lever and fulcrum or seesaw - you press down on one end and the other end rises in the opposite direction!

Sailing in the opposite direction of the powering wind is simply based upon the remarkable feature of an aerofoil (airfoil) to produce many times more lift than drag.

Consider a high-performance sailplane being towed by a tug aircraft.
If the glider weighed 1000 lb and the lift to drag ratio of the whole glider (not just the wings) was 20:1 (most are better than this) then the pull on the tow rope would be only 50lb (1000 devided by 20).
So in this case you would have a force of 50lb supporting a weight of 1000lb - sounds impossible, but it is a fact. Something for nothing?

[MPraamsma]

...and that something is the boiler-like atmosphere we live in. The atmosphere is the boiled off vapors of liquid air, for another way of looking at it, and can release some of this latent heat through expansion. This is the same principle as the steam engine, where the atmosphere is hot steam. You are not getting anything for nothing, but you are harvesting a form of heat energy that is contained in the atmosphere at normal temperatures. This energy is replenished by sunlight all day long, so it is an inexhaustable source. The release of latent heat can also provide mechanical force.

[MPraamsma]

Originally Posted by Windmaster

The ducting argument is very interesting, I would have thought that ducting would carry more of a penalty than an advantage, due to parasitic drag. In the past ducted propellers and ducted turbines have never superseded unducted ones. Were all previous designers wrong?

The touble with ducted fans is that they try and provide all the thrust by sucking air in with a propeller that is inside the duct. This will only work up to a point, because it is more important to get a huge flow over the duct first due to vehicle motion. This is better achieved by driving wheels or a marine propeller that is not connected to the turbine directly, but can independently drive the turbine system up to operating speed. The vehicle speed then becomes part of the pumping system for the energy system into the duct. This allows the duct to function as an energy collector, not a propulsion system.

[Windmaster]

There is an interesting video of a wind-turbine powered boat on Youtube.

Its on: http://www.youtube.com/watch?v=NNbNNSDljGI