Fluids

Fluids

Particle tracking, boundary layer resolution and particle diameter sensitivity

    • Suman Sapkota
      Subscriber

      question

    • Rob
      Ansys Employee

      One of the requirements of the DPM model is that the particles are smaller than the cells. The solvers also track a point mass, so a 1mm particle can fit through a 0.1mm gap, and will only contact the walls if the centre point enters the near wall cell.  In your case you may be finding the mesh to be too fine, so the particles are striking slightly down stream. 


      I'll also move this into the Fluids section so hopefully more of the community will see it. 


       

    • Raef.Kobeissi
      Subscriber

      what is your mesh size? (Cell size)


      Regards

    • Suman Sapkota
      Subscriber

      Hello Rwoolu,


      Thank you for replying me. Can I ask how would the "mesh requirement" be based upon if the particles are treated as point mass? Is there any documentation about this dependency? Does the dependency come from the model or the algorithm of cfx developers itself? Because the idea of point mass treatment does not explain the minimum mesh size dependency, I am pretty confused on this problem. If I do not have a good refinement, then I would not be solve the wall functions in flow analysis. This would not give me right variables needed for Lagrangian tracking. Do I have to weigh in the mesh size and particle diameter to perform simulations then?


      Hello Raef, Do you mean the minimum mesh size or the number of elements? The minimum mesh size in X,Y, Z dimension is  0.0129 [dimensionless], 0.06079 [dimensionless] and 0 [dimensionless] in ICEM. The geometry is in metres. The total elements is around 1 million. 

    • Rob
      Ansys Employee

      Sorry, missed this one when I got back from holiday. You've hit on one of the issues with modelling erosion: having enough mesh to get the flow but coarse enough for particles. There are sections in the manual for this (CFX and Fluent and I'd suggest reading both as the model is pretty much the same).


      That's about as far as I can take this as we're not allowed to look at files etc. 

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