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FAO: Gabriel- Giant generator windmills aerodynamics

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  • #31
    3BS applies cow manure to his corn and then runs a mechanical harvester through it.

    Some of the nitrogen in the manure volitalizes and some of it is taken up by the corn. We analyze the manure for total nitrogen available and analyze the corn similarly.

    Th nitrogen in the corn divided by the nitrogen in the manure is the nitrogen use efficiency. The volatilized nitrogen is part the denomonator even thought it can be used later.

    The corn harvester has a blower to separate grain from chaff. But some of the corn is blown out the back. The total corn available divided by the corn harvested is the harvest efficiency. The wasted corn on the ground is part of the denominator even though it could be picked up and used later.

    The power company puts up a windmill. But Gabriel, the hell better aeroengineer, says that they can't divide the energy harvested by the total energy available to get an efficiency rating on how well the blades pull energy from the air and evaluate if adding additional blades would be worthwhile. You can't include the the unharvested energy because it can be used later.
    Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

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    • #32
      By the way- I get it that you are focused on energy obtained divided by energy harvested which is the effecieny of the process if you will. Yeah this includes drag and turbulence and other stuff.

      I still say than an evaluation of how much energy you pull per unit disk area is valid- and then to put that relative to the total energy available is also valid.
      Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

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      • #33
        Isn't the easiest way to describe all this like this....

        Someone makes a generator that generates variable amounts of power to be supplied to electricity users via the national grid. This generator will operate up to a maximum design speed past which it will destroy itself.

        The generator is mounted on top of a pole on wind direction controlled gimbals to allow it to always face into the wind.

        The generator has a conical hub fitted to it.

        The conical hub has a certain number of blades fitted to it (Normally 3). Those blades are designed to be as cheap as possible while being aerodynamically efficient enough to turn the hub, and hence the generator up to its maximum design speed limit. Average wind speeds in the location will be part of the equation in designing the profile of the blades.
        Another handy factor is that the moving mass of air that we call "Wind" is provided at absolutely no cost to us at all. It doesn't matter how much we do or do not use. Trust me, there will be more along in a moment.

        If the generator gets to its maximum design speed the blades will feather and the generator will be brought to a halt to prevent self destruction.
        Electricity supply to customers will then come from other types of generation. (Nuclear, Gas powered, Coal fired and even steam powered produced by water desalination plants which have the happy side effect of producing vast amounts of free steam).

        If wind speed increases to very high speeds so much so that cows, motor vehicles, houses and humans become airborne then the owners and designers of the wind farms will adopt a kneeling position, place their hands palms together and pray to whichever God that floats their boat that the fruits of their labours don't turn into just so much horizontally placed scrap metal and composite plastic !

        In the meantime, I will be coming home to watch the latest F1 Grand Prix on TV. To do so requires a supply of electricity so I throw various switches, push various buttons on the remote control (once I've prised it out of the wifes' hand !!) and all is well in my world. It's even better with a glass of whiskey in my hand. I am a happy man, my life is fulfilled. I am at peace in my world...

        .....and I don't leave one single, solitary thought to where that electricity came from.

        Last edited by brianw999; 2014-07-05, 15:16.
        If it 'ain't broken........ Don't try to mend it !

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        • #34
          Indeed..three blades fit nicely and efficiently on the hub.

          Except my cattle want water, not amps and volts.

          You need a lot of blades to pump water.
          Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

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          • #35
            Originally posted by 3WE View Post
            Indeed..three blades fit nicely and efficiently on the hub.

            Except my cattle want water, not amps and volts.

            You need a lot of blades to pump water.
            Sure...But may I direct the honourable farmer to the the subject topic of this thread which refers to Wind Turbine Generators.......although it is true that your cows are producers of prodigious amounts of their own ozone layer damaging wind !!!

            If it 'ain't broken........ Don't try to mend it !

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            • #36
              Originally posted by 3WE View Post
              By the way- I get it that you are focused on energy obtained divided by energy harvested which is the effecieny of the process if you will. Yeah this includes drag and turbulence and other stuff.

              I still say than an evaluation of how much energy you pull per unit disk area is valid- and then to put that relative to the total energy available is also valid.
              Efficiency and similar performance indexes (productivity, etc.) always have a measure of what you get on top and a measure of the effort, resources, investment, etc. in the bottom.

              The analogies that you propose are not valid.
              You had to put the nitrogen in the manure or, if it's some kind of natural manure, you had to produce or collect it somehow.
              Producing corn takes a lot of money, time, effort, natural resources, energy. Of course that all the corn that is blown out the back with the chaff is a waste. It is not there available to harvest as you did the first time.

              Let's do this: You keep your very efficient many-blades, small diameter windmill. I'll keep my few-blades, big diameter windmill.
              Yes, my windmill let go a lot of energy between the blades. Yours let go even more energy around the disk.

              There is ONE case where you would get a point. You are space-constrained. You cannot go beyond this disk that's available to you and you can't put another windmill behind the first one. Your goal is to extract as much energy as possible from this scarce resource (the wind flowing through this rare disk) as you can. The result will look very much like an aeromotor. Now go and tell me that this was ever a constrain for a farmer.

              However, I do think that there is a good reason why aeromotors look like they do: cost. Doing long blades with an optimized chord distribution, twist distribution and airfoil distribution is much more expensive, not only for the blades but also for the supporting structure. Aeromotors work well enough, are cheap enough, and no farmer cares about how much more water could have been pumped with the energy actually exctracted from the wind. They don't have to pay for the wind.

              --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
              --- Defend what you say with arguments, not by imposing your credentials ---

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              • #37
                Originally posted by brianw999 View Post
                ......although it is true that your cows are producers of prodigious amounts of their own greenhouse gases wind !!!

                Fixed

                --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
                --- Defend what you say with arguments, not by imposing your credentials ---

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                • #38
                  A question: It seems in this debate that the concept of torque and speed must come in to play.

                  Farmer John wants his water pump to deliver high torque to pump the water at quite low RPM. After all he is a farmer and has not built it out of carbon fiber airfoils. If the darn thing goes round too fast it will fly apart. Thus he has lots of wide blades because he wants lots of torque at low speed. In fact the more wide blades the better, since they will interfere with each other at high speeds and will will self-limit the speed of rotation. The "diesel engine" of wind turbines.

                  Engineer Gabriel is in it for the money. He wants the wind turbine that gives him the biggest return on his investment. Long blades built out of space age carbon fiber sweep a huge disk. And they rotate fast, so that they are extracting a significant amount of the energy out of the air that passes through the disk. The "turbine engine" of wind turbines.

                  pothole
                  You just can't avoid the potholes.

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                  • #39
                    Originally posted by pothole View Post
                    A question: It seems in this debate that the concept of torque and speed must come in to play.

                    Farmer John wants his water pump to deliver high torque to pump the water at quite low RPM. After all he is a farmer and has not built it out of carbon fiber airfoils. If the darn thing goes round too fast it will fly apart. Thus he has lots of wide blades because he wants lots of torque at low speed. In fact the more wide blades the better, since they will interfere with each other at high speeds and will will self-limit the speed of rotation. The "diesel engine" of wind turbines.

                    Engineer Gabriel is in it for the money. He wants the wind turbine that gives him the biggest return on his investment. Long blades built out of space age carbon fiber sweep a huge disk. And they rotate fast, so that they are extracting a significant amount of the energy out of the air that passes through the disk. The "turbine engine" of wind turbines.

                    pothole
                    It's rather the opposite.
                    Aeromotors of water pumps tend to turn fast and deliver a somehow low torque.
                    Wind turbine generators turn very slow and provide a very high torque.
                    In any event, torque times RPM = power, and once you have the power in the shaft you can convert it to another combination of torque times RPM with a gearbox, that's what both the aeromotor and the wind tubine generator do.

                    --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
                    --- Defend what you say with arguments, not by imposing your credentials ---

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                    • #40
                      Originally posted by Gabriel View Post
                      Say that you want to make a 777 tuboprop. Do you think that you could fit props bigger than the fan disc the 777 already has?
                      Yes

                      As with the majority of turbo props, put the engine on top of the wing and then the blades can reach down to where the bottom of where the turbofan would be and then you have the same distance on the up side...

                      Easily 2x the diameter / 4x the effective disk.
                      Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

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                      • #41
                        Originally posted by 3WE View Post


                        By the way- I half suspect that in 1920 or so, Bubba and Goober took ag mechanization and never went on to airoknoticks at collage and just figgered you oughta have a bunch of blades to be sure you catch all that passing wind...

                        And lookey thar- it shore does pump water!

                        Let's patent it and call it Aeromotor!
                        And, it has a special spring loaded vane that turns the turbine sideways if the wind gets too strong...

                        If only airplanes could provide such protections....
                        Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

                        Comment


                        • #42
                          Originally posted by 3WE View Post
                          Yes

                          As with the majority of turbo props, put the engine on top of the wing and then the blades can reach down to where the bottom of where the turbofan would be and then you have the same distance on the up side...

                          Easily 2x the diameter / 4x the effective disk.
                          Uhm, yes, well. I didn't mean for geometric constrains but to blade tip speed constrains. Of course, make it fly at helicopter speeds and you can have an helicopter-sized prop. Osprey comes to mind.

                          --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
                          --- Defend what you say with arguments, not by imposing your credentials ---

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                          • #43
                            I got ever so slightly west today and studied some generator's...

                            I estimated about 4 seconds/turn or 15 RPM or 1.33 seconds between blade swipes.

                            If the wind is blowing 20 MPH that means about 40 feet of air passes between before a blade swings by to harvest energy.

                            Seems to me a LOT of wasted energy that could be harvested...

                            Seems to me putting another three (or 6 or 9) blades on that hub would largely double the wind you catch while adding very little additional costs in terms of additional towers, generators, wind-direction sensing, and aiming mechanisms......

                            I guess it must have something to do with the hubs only having room to bolt on three blades.
                            Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

                            Comment


                            • #44
                              Originally posted by 3WE View Post
                              I got ever so slightly west today and studied some generator's...

                              I estimated about 4 seconds/turn or 15 RPM or 1.33 seconds between blade swipes.

                              If the wind is blowing 20 MPH that means about 40 feet of air passes between before a blade swings by to harvest energy.

                              Seems to me a LOT of wasted energy that could be harvested...

                              Seems to me putting another three (or 6 or 9) blades on that hub would largely double the wind you catch while adding very little additional costs in terms of additional towers, generators, wind-direction sensing, and aiming mechanisms......
                              Ok, good luck. Those the hell better aeroengineers don't understand no crap about how to design an aerogenerator. How didn't they note that they could harvest more energy with more blades, instead of wasting all that valuable wind?

                              PS: Are you EC?

                              --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
                              --- Defend what you say with arguments, not by imposing your credentials ---

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                              • #45
                                Gabriel,

                                You don't understand... they're all using secondhand hubs they got at a local pawnshop that have only 3 attachment points... so they can't add more blades!
                                Be alert! America needs more lerts.

                                Eric Law

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