another idea

The bicycle is just temporary...

...but very useful to subject it to some punishing road tests to make sure it can stand up to higher speeds. It has three speeds, but I have to change them by reconfiguring the chain and all the turnbuckles. I need to change the axle, I made it solid to both wheels, but need to have one freewheel like my earlier model, because this thing is impossible to steer.

 

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

 

Michael: you were a bit sceptical about beating the wind on a downwind course earlier. Check out this thread: http://www.boatdesign.net/forums/sailboats/tacking-downwind-faster-than-wind-24761.html
Of course, it can't be done without tacking so you're quite correct as far as a downwind heading is concerned.

 

ancient kayaker

Sailing on a heavy 40 foot sailboat with a massive keel and draft, one never can get the notion what true downwind possibilities are, however, these land yachts can demonstate it better because they have for all practical purposes three almost frictionless wheels on the ground. I've been sailing for many years, and I'm familiar with the usual wind situations and limitations. What I am attempting to do is to put that insight into downwind performance into a wind collector to harness wind power for forward propulsion. As many of us here have proven to ourselves, by the building of models and such, is that 100% upwind performance is possible. My discovery when testing mine is that the turbine prop starts to look like as someone said here earlier, 'like a spinaker'. I have termed this effect as ADVERSE thrust. In our case, this adverse thrust works against propulsion, and propulsion is what we are trying to achieve. I have proposed an arrangement, where the entire input to a generator is fed into a venturi trough first, then sent spinning through stator blades into a vortex. The turbine blades are then spinning inside a high speed tangential flow. This flow combined with the rotation speed of the blade will allow the torque to be transmitted to the shaft without adverse thrust penalty. These turbine blades are 'flying downwind' to use a sailing analogy, and, and their speed then controls their angle of attack. Drawing off torque will cause the angle of attack to increase in direct proportion, so it can be regulated using generator output. The other advantage of flying downwind is that the blades feather, or luff as we sailors say, at maximum RPM of the turbine, when there is no load and the angle of attack becomes zero degrees.
I have attached a close-up of the turbine as I see it evolving.

If the whole turbine is then turned so that it is spinning in a horizontal plane, any residual thrust is then only capable of lifting or weighing down on the vehicle/vessel weight. Since a freefloating vessel is sensitive to ANY thrusts it sees, they all must be considered when designing a system to produce useful thrust.

 

OK, my opinions on the subject so far (after reading this thread, and the one that ended up becoming a DDWFTTW debate, entirely):

1. When approached with an open mind, DUW & DDWFTTW become obviously feasible "wind-powered" possibilities.

2. A ducted fan (whether energy-gathering, or energy-expending) will, all things being equal, ALWAYS be able to operate more efficiently than the same fan, unducted. (by elimination of tip losses)

Michael:
Good: I like, and thoroughly agree with, your idea of using a venturi-style duct to allow you to improve the angle of attack for your fan blades in order to improve the ratio of torque-produced vs. drag.
Improvement: IYHO, would it be possible to improve the efficiency of this by installing 2 turbines with opposing blade angles (and spin directions) to incite the spin of the stator, and harness a (slight) bit of energy by the first turbine in the process?
Bad: Your idea of reversing your blades at the tips seems to merely be expending unnecessary energy in pursuit of "free energy" to me. From all that I can infer there (sorry, haven't developed an equation to show you) you're trying to use a portion of your energy-harvesting turbine as an energy-spending turbine. The only eventuality I see happening here is an extra loss due to air-friction on the added surface area on the reversed-tip, along with the expenditure of some efficiently harvested energy (from the inner portion of the blade) being wasted to accelerate air that has already bypassed the tips of that section to about the same speed as it's actually moving. Even if you adjusted the attitude of the tips high enough to create real acceleration on the air they touched, assuming your hypothesis worked, couldn't I then design a turbine/prop. that powered itself to move forward by harvesting power from the air in front of it moving backward (relative to the prop's motion)...seems like a free-energy theory to me. (and yes, I know my explanation here sucks)


Everyone:
I found this patent: http://www.google.com/patents?id=XlQDAAAAEBAJ while reading through the link on the ducted wind-turbine patent Michael referenced earlier. What are everyone's thought on the applicability of adapting a design similar to this (patent expired over a year ago, so it's legal now) for a DUW, wind-powered craft?
My thoughts are that it'd be VERY doable for a fixed-position (land-based is misleading, as the cart designs are land-based) generator where drag is a minimal factor, but for our purposes, I'm thinking the drag would be greater than the extra torque it's allow us....

Your Guys' Thoughts???
(I'll try to post drawings later, if I can ever get them to match the confused jumble of images in my head...lol)

 

i dunno, seems a bit complicated. the math involved in crafting a duct that would be efficient at any single wind speed(and that's how it'd be, only one wind speed, unless you use a stepped concept, or had multiple ducts you could install), well, that's a lot.

why not contrarotating blades on the turbine? they eliminate tip loss inefficiencies also(and they're an order of magnitude simpler to build), and if you got fancy with your shaft arrangement(rather than make the second set of blades free-spinning), you could extract even more energy from the wind.

just thought i'd bring that up.

 

Very unlikely a nozzle of any sort will perform better than the best unducted design.

The sort of applications where duct offer an advantage is where there is a constraint on prop or turbine diameter. If these are not an issue then run unducted.

You have to include any ducting in weight and drag components as well.

Any direct mechanically connected system of propeller to wheel or turbine propulsion is of limited use.

1. In the upwind case the power handling ability of the transmission quickly becomes a constraint.

2. In the down wind case you are looking at a very narrow angle of operation. Outside that range you are better off using the turbine and making use of the apparent wind. I believe DDWFTTW is of curiousity value only as a concept. It might have limited practical merit for a land vehicle constrained to travel on roads. But you can still get along here with a turbine vehicle just going a bit slower.

3. The propeller for the DDWFTTW case will not resemble anything required for the turbine to go upwind. They are fundamentally incompatible particularly where you have substantial drag such as a hull or slight incline on land.

4. To get anywhere near the best range of performance you need variable transmission. At minimum you need two gears if you want to use upwind and DDWFTTW potential on the same platform.

All this considered I believe it only makes sense to combine these ideas in a vehicle with electric transmission where you can store energy even when stopped and release it as required. In periods of high wind you store energy and don't waste it going just a tad faster. In light winds you release stored energy to keep up a good average. You can add solar cells for a little extra boost in dead calm air. Such a system also gives the ability to achieve bursts of speed at any time.

As a practical means of getting about current sails offer much greater utility than propeller/turbines, at least on water, unless the latter is tied into energy storage.

Rick W

 

I think Michael is in transit. He has not been active here for some time.

Rick W

 

Yes, I was thinking of combining that with the ducting, but at least we're thinking on the same page here. I'm in (partially) complete agreement!

Yeah, I kinda figured the nozzle would be worthless for our purpose here, but wanted to bring up the option, see what everyone else thought.

Yes, I agree here, I only mention the two together as they seem to follow inherently linked thinking patterns, though I also see few uses, other than curiosity, for DDWFTTW tech.

 

robherc et al,

Actually I am stilll active here, but no-one commented for some time on this concept, so I have been silent until someone offers something I can respond to. I will compose something to address your questions and get back. I am in Holland now.

 

robherc,

I'm not sure if you caught the discussion we had on this some months ago, but the reverse blade tip idea was just a way to do something with one blade system that I later realized needed to be done by several co-operative fan wheels and a stator. Those ideas ended up in the 'turbo ducted turbine' or enhanced duct. I will repeat the total concept diagram here that was on the other thread. My main point to make was that we need to carefully separate what causes a force in a system of blades, and where these forces are exerted. These total forces consist of various contributions from friction, drag, and most importantly, the force developed by lift but vectored in a direction adverse to the thrust we are trying to utilize to power the vessel/vehicle. This force can quickly swamp any useful output, as my bicycle experiment clearly proved. The thrust (torque at generator) and the adverse thrust are on intersecting curves, and when that point is reached, the vehicle stops accelerating.

In the full (ducted) concept, the air is accelerated by a duct (I use this term acceleration with hesitation, because the air molecules never actually travel any faster in a venturi, they are simply more likely to be travelling in the flow direction the closer to the throat they are), then the air enters the high pressure area of the turbine. Before the air can strike the turbine, and produce thrust, it needs to be re-directed so that any forces developed are perpendicular to the plane in which the vehicle has freedom. Since vehicles/vessels (aircraft excluded for now) have no degree of freedom in the vertical plane (since they are on wheels or they are afloat), that is the axis on which the turbine must operate. In other words, the entire flow needs to be turned 90 degrees before we try and extract any energy.

You are correct, the first set of blades uses some power from the turbine to further speed up the flow, and to force a prefered direction to the vortex entering the turbine. Jets do this all the time, it is called power feedback, and occurs entirely within the machine, with no loss. It is important to get the flow up as high as possible first, because the power in the flow goes up exponentially with speed. The maximum speed is therefore when shocks start to form inside the duct. However, shocks only form if the relative velocity of air and blade are near the speed of sound. If the blade is rotating in such a manner that it is moving 'downwind' so to speak, the effective air velocity is then considerably lower.

The diagram was on this page, review our discussion to see how this was evolving.

http://www.boatdesign.net/forums/pr...-how-many-out-there-they-viable-14182-18.html

 

hmmm...read the other thread (from where you came in)...considering the data...dug out my "Aircraft Engines and Gas Turbines" textbook...will get back with you once I've reached any theory-level conclusions

 

robherc

Looking forward to your input. Let me know if you have questions.

 

1st thing that comes to mind: the "power feedback" you're referring to in jet engines (at least according to this book, and my understanding) is actually a compressor stage. Unfortunately for us, when you're not burning any fuel later, the compressor just wastes energy...wanna inject some alcohol & make a ramjet boat? (hmmm...now there's an Idea...lol)

Also, the idea of turning the turbine vertically in the duct doesn't seem to me to accomplish anything benenificial. Although you ARE changing the plane on which the TURBINE experiences drag (from horizontal to vertical), the vehicle will still experience the drag on the horizontal plane because your "bent venturi" shroud is still facing fore & aft. I.E. there will be a stagnation pressure (or temperature, if you will) fore (the energy being used to turn the turbine), and a lower-than-atmospheric pressure (or temperature) aft (energy was harvested). This pressure differential fore-aft will create slightly more drag (due to friction losses inside the figure "S" venturi duct) than the design with the turbine mounted on the horizontal plane.
I still think it was an excellent idea, and kudos to you for thinking outside the box there, but I don't think that one's workable.

I'm still loving the idea of enclosing the turbine in a venturi though, and I'd still like to hear what you guys think on the movable stator/counter-rotating turbine idea...be able to harvest a little energy from the stator/forward turbine spinning, in addition to the energy harvested by the second turbine.

Any thoughts?

 

robherc,

This is more than just an idea that came to me in a flash one day. This is a technology I have been working on for many years. I'll try and answer some of your objections and doubts about the viability. First, feedback means taking some of the power output and re-routing it AHEAD of the input. This way, the energy is always caught in a loop, and is not wasted. All the compressor does for us here is to increase the pressure slightly so it will flow into the next venturi stage. At each stage the venturi gets narrower, and the flow inches closer to the speed of sound. Part of this flow is that caused by the vehicle motion, and is also power returned by feedback. By driving the wheels the vehicle moves forward and causes a flow which is maintained by the mass and momentum of the vehicle.

You need to revisit the idea of air friction to see it more as an acoustic wave that dissipates energy into the surrounding atmosphere as heat. As I pointed out in other posts, this acoustic loss becomes very obvious when you approach the speed of sound. However, a properly designed internal body reflects this wave in on itself and captures that energy in an enclosed space, and forces the flow to behave exactly as defined by an idealized flow channel. While the flow is in the venturi section, it barely makes contact with the wall, as a measurement of the static pressure at the wall will show.

The other point to make is that the external flow is unaffected, and the amount of air in the tunnel has no direct relationship to it. The transit time in the tunnel can be longer than the external path. In plain speak this means the turbine chamber itself can be 'pumped up' to higher than ambient pressure while in the dynamic operating state. The best analogy to this is the LASER, where there is a lot more energy trapped inside the cavity than makes it out to the outside world.

We don't want to confuse drag and lift force, because any lift force directed along the same vector as drag will be hard to distinguish from drag. Since we don't have the luxury of a fixed pedestal to oppose the drag axis, we have to subtract this force from the useful output. I can assure you that the adverse thrust developed on a turbine prop with a high tip velocity is considerable, and turning the turbine 90 deg is necessay to avoid this force becoming the determinant factor in output.