Fluids

Fluids

Regarding boundary conditions

    • Adidash97
      Subscriber
      Is it mandatory to apply velocity conditions on all walls for formulating a Multiple reference model?. What is the difference between stationary wall motion and absolute wall motion with zero RPM
    • DrAmine
      Ansys Employee

      Stationary wall settings is always relative to the adjacent cell zone. Setting the wall to Moving and using zero RPM you will need to set whether it relative to absolute system or just relative to the adjacent cell zone. If the adjacent cell is rotating and you set Stationary wall then the wall will be rotating relative to the absolute system. If you want the same but using "Moving Wall" option then use "Relative to Adjacent CEll zone" and give 0 RPM.


       


       

    • Keyur Kanade
      Ansys Employee

      Hello, 


      Perfectly explained by Amine. 


      Also you can have a look at following. 



      Also, please like the answers which have helped you move forward and in the end, once your issue is resolved, please mark the most appropriate solution (most useful advice) as 'Is Solution'. This will help others who are using this thread to find answers to similar questions.


      Regards,


      Keyur

    • Adidash97
      Subscriber

      Then what is the meaning of this message?

    • Raef.Kobeissi
      Subscriber

      Is it possible to upload the file to understand better the simulation?


      Regards

    • Keyur Kanade
      Ansys Employee

      please insert some images of mesh and set up explaining the situation. 


      it is the warning message which need attention or can be ignored depending on your setup. 

    • Adidash97
      Subscriber


      This is the blade wall condition which is rotating



      This is the inlet pipe which is stationary and not rotating



      This is the impeller wall which is rotating w.r.t to the adjacent cell zone

    • Adidash97
      Subscriber

      So as per the solution given by abenhadj that the stationary wall setting is relative to the adjacent cell zone, the impeller wall which is rotating can be assigned as a stationary wall. Then also I still receive the message I had posted earlier "Review wall motion. Stationary wall motion adjacent to cell zone detected". What is wrong with the boundary conditions?

    • Rob
      Ansys Employee

      The cell zone around the impellor is set to rotate (I think you've done that). The impellor wall should be moving at zero speed relative to that zone. The outer casing may need setting to stationary if the rotating zone also touches it.  

    • Adidash97
      Subscriber

      But why am I receiving that message? What is the correct way of providing a stationary boundary condition? Is it "stationary wall" or "Moving wall with zero velocity"? I am really confused with these two?

    • DrAmine
      Ansys Employee

      If the wall is not moving in absolute system then set it as moving in absolute system and give zero angular velocity. 


       


      Stationary wall settings is always relative to the adjacent cell zone. Setting the wall to Moving and using zero RPM you will need to set whether it relative to absolute system or just relative to the adjacent cell zone. If the adjacent cell is rotating and you set Stationary wall then the wall will be rotating relative to the absolute system. If you want the same but using "Moving Wall" option then use "Relative to Adjacent Cell zone" and give 0 RPM.

    • Adidash97
      Subscriber

      I did the same but getting the message.

    • DrAmine
      Ansys Employee
      Then ignore the warning message already mentioned here at first and check results afterwards. Check what has been suggested thoroughly. Default behaviour is stationary relative to a adjacent cell zone. Walls of rotating impeller can be then set stationary relative to impeller zone or rotating with zero rpm relative to the same zone.

      Global stationary wall which does not rotate better made through zero rpm relative to absolute frame.
    • yalin
      Subscriber

      Thank you all for the great discussion. Let's say we have two concentric cylinders and the inner cylinder is rotating while there is fluid in between (rotor and stator can be a good example for this). To calculate the heat transfer through the fluid between cylinders we can have two scenarios:


      1- We use moving reference and rotate the whole inner cylinder.


      2- Only define the rotating wall for the OD of the inner cylinder.


      Could you please explain the difference between these two approaches in the results? 


      Thank you.

    • Rob
      Ansys Employee

      Please post the results, what difference are you seeing? 

    • srivastavatanuj
      Subscriber

      But why am I receiving that message? What is the correct way of providing a stationary boundary condition? Is it "stationary wall" or "Moving wall with zero velocity"? I am really confused with these two?


       


      Try initializing from the absolute reference frame. I just found this thing. It may help.


       


      Cheers,


      Tanuj 


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