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Convergence problems when changing the roughness of a centrifugal pump

    • July 25, 2019 at 11:40 am
      MrFCA
      Subscriber

      Hi!


      I am simulating the performance of a centrifugal pump.


      First, I simulated the centrifugal pump without roughness to have a approximate results, but when I have simulated it with roughness, the convergence becomes disastrous.


      Any idea why this happens?



       


      For the solid boundaries, the no-slip condition with relative roughness is 100 micron. I know that the setup asks for roughness in "Sand Grain Roughness". Fo this reason I put 0.0005863 m.


      I attach the photos of convergence without roughness ad rougnhness.


    • July 26, 2019 at 1:41 pm
      Rob
      Ansys Employee

      Check the time step and/or substepping (I don't use CFX). It's possible the roughness has triggered a change in the flow field (separation point or similar) so a smaller step may be needed? 

    • July 27, 2019 at 11:07 am
      Raef.Kobeissi
      Subscriber
      Are you using second order for your equations?
    • July 29, 2019 at 7:45 am
      MrFCA
      Subscriber

      Yes!

    • August 1, 2019 at 12:26 pm
      MrFCA
      Subscriber

      Any more idea?

    • August 1, 2019 at 1:24 pm
      Rob
      Ansys Employee

      Assuming it's transient, can you see any changes in the flow field?

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