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Questions about VAWT Design

  1. Nov 2, 2008 #1
    Hello :smile: ,

    I have two questions about VAWT Design o:)

    1- If you are designing a full scale turbine theoretically and decided to test a small scale model to check the value of Cp, what things you should take in mind to make the results and performance of the model reflects the full scale turbine?

    I understand for example in wing design the Reynolds number, Airfoil and Aspect ratio should be the same, but in VAWT case what parameters should be equal in model and full scale?

    2- When you want to measure the power of the turbine , what are the steps?

    I understand you need to measure angular velocity and torque but my question is how should I measure torque ? do I need to full stop the turbine by a weight to get the torque ? or should I apply a load on the turbine but not to stop it then measrue torque and speed?


    Thank you :smile:
     
  2. jcsd
  3. Nov 3, 2008 #2
    1. This is not a easy question. The most important variable for turbine operation is the top speed ratio. This means that your model will need to spin much faster than the real thing which will introduce all kinds of different affects, like the Reynolds number like you stated. In practice I don't believe this is ever really done for larger 600kw+ machines.

    For turbo-machinery, its usually best to define the performance of the machine by non-dimensionalizing everything. But be aware, that most coefficients for open fluid turbines are not the same for closed fluid turbines.

    2. Getting the torque from your model is pretty simple. You could just use a torque transducer or you can get it from what ever type of electrical machine you are using to generate power. If your using and induction or a PM machine which already has flux and torque estimators then its even easier. You want to measure the torque and its operating speed since the torque produce is a function of a tip speed ratio. If you stop it, your not going to get the actual amount of torque at its operating point(s).
     
  4. Nov 5, 2008 #3
    Thank you Topher925 for your response :)
     
  5. Nov 5, 2008 #4
    Whisper, you may find the answers at www.windstuffnow.com
    Mr.Ed Lenz has some formulas and software he has written
    He also sells small scale kits.

    But a twisted helix VAWT will generate @ lower speeds, designed with a genny on
    top & bottom of the shaft. Peace Out
     
  6. Nov 5, 2008 #5
  7. Nov 6, 2008 #6
    mel67 thanks for the links, indeed it will help
    thank you very much :)
     
  8. Nov 11, 2008 #7
    Agreed, the torque MUST be measured precisely at the real operating speed. If you know the momentum of inertia of you rotor, just open brutally the generator and observe with a video camera how quickly the rotor accelerates. Or buy a sensor, yes.

    Identical Reynolds numbers would be nice, but identical surroundings might be more important: scaled model of the hill, similar turbulence before the turbine... Surface cleanliness and roughness should be scaled as well, not really easy.
     
  9. Jun 2, 2010 #8
    Hi Deathwhisper:

    I am doing the simualtion and wind tunnel experimental for straight blade VAWT with 4 blades currently. What you have mentioned is really interesting for me and I ahve this doubts also. So i really hope that you can share the few things with me:

    First, for the Re, how you calculated that one, if i am doing the small scale one, it seems the turbine need to rotate very faster than the real one, and the effects will be different also since there is the tunnel wall there. So how you define the Reyonds no, and is there any parameters that i need to pay attention on it?

    Second, I am using torque detector to measure the rotating torque in order to study the power performance of the turbine. Of course, the induction machine will be there to function as the motor to staring the turbine, it will automatically become like the generator when the turbine rotates.

    Thirdly, I need to optimiaze the turbine also, I think I will try the different blade shape, I am using SD8020 for the current testing. I plan to try naca4415 since the camber much more thicker than SD8020. Or am I right?

    Anyone have good suggestion? Am really new to this.

    Thanks a lot for the suggestion and help!
     
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