Fluids

Fluids

Torque increases as rotational speed increases

    • motoyama
      Subscriber

      Hi everyone,


      I simulate two blade wind turbine with MRF.


      but as rotational speed 'omega' increase, torque also increase.


      so there is no peak on power coefficient.


      How can I calculate it?

    • Keyur Kanade
      Ansys Employee

      Hi, 


      How are you calculating torque?

    • Keyur Kanade
      Ansys Employee

      Hi


      How are you calculating torque? Please give more details. Please insert some images and explain the problem. 


      In general, you can do following to calculate torque. 


      Please follow the steps below:


       


      Regards,


      Keyur


       

    • Keyur Kanade
      Ansys Employee

      Sorry post is giving some error to me. 


      Please follow the steps below:
      1) Click “Report → Force” to open the Force Reports panel

    • Keyur Kanade
      Ansys Employee

      2) In “Options”, select “Moments”

    • Keyur Kanade
      Ansys Employee

      3) Enter the coordinates of the center point of the rotation for “Moment Center” and the axis at “Moment
      Axis”

    • Keyur Kanade
      Ansys Employee

      4) Select the Wall Zones

    • Keyur Kanade
      Ansys Employee

      that will serve as the plane of rotation from where the torque will be calculated


      5) “Print” will show the results in the Console Window

    • Keyur Kanade
      Ansys Employee

      I am really sorry, I am getting some errors while posting it. May be some maintenance work is going on. 


      Hope you can read these posts. 


      Regards,


      Keyur

    • motoyama
      Subscriber

      I know the procedure.


      but I've already checked the reference values, no problem.


      and moment itself converged.


      but when rotating speed increase, the torque also increase.


      anyone can help?



    • DrAmine
      Ansys Employee

      Your torque is constant from the plot. Can you please add some more information here? If there is a linear momentum then the torque will change even at constant angular velocity.

    • motoyama
      Subscriber

      Hi Amine, 


      thanks for your reply.


      below is example of angular velocity and torque and Cp values


      what do you want else?


    • Rob
      Ansys Employee

      OK, why should torque be the same for different speeds? Ie, what is the definition? 

    • motoyama
      Subscriber

      Hi , rwoolhou


      the torque value means half of the moment that i calculate


      well, I think torque is not same as for different speeds.


      from the tip speed ratio, there should be a Cp peak.


       

    • motoyama
      Subscriber

      I add the data.

    • Rob
      Ansys Employee

      I'm not sure I understand.  If you expect the torque to change with speed, what is the problem? 

    • motoyama
      Subscriber

      the problem is that torque increase and decrease as the rotational speed increase.


      so Cp=torque x omega should have peak.


      but this data shows torque only increases but not decrease. 

    • DrAmine
      Ansys Employee

      From the data you are mentioning I do only detect  single trend: torque is increasing as the angular velocity is increasing (due to linear mometum). So now: What is the problem?

    • motoyama
      Subscriber

      Hi Amine


      I searched the similar examples


      please refer below


      https://www.cfd-online.com/Forums/cfx/160097-problem-torque-calculation.html


       


       

    • Rob
      Ansys Employee

      That's not the problem, you need to define & explain why you think your answer is wrong. As you've read through the whole of that thread, have you also found the same problem with a finer & much finer mesh? 


      Note, as ANSYS staff we can't download and/or open project files. 

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