Continuty convergence problem

    • omidFSI

      Hi everyone,


      I am simulating a simple flow over a cylinder with a circular domain shape in 3D with Fluent.
      For continuity I am not getting a good convergence and the residual is close to 0.1 while I expect it to be much lower.

      The drag coefficient is also not accurate especially for high Re. I have tried different RANS models , mesh is fine enough (O-type) though y+ getting from ANSYS is somehow high more than 100 which don't know why since my mesh is structured and very fine!
      Re: 2e4-1e5
      Transient solver with Time step~0.005-0.05 (s)

      Any idea in this regard?

      Thanks in advance!

    • Vishal Ganore
      Ansys Employee

      How is your orientation of cylinder with respect to flow direction? Could you please show your geometry?

      Are you doing similar to following tutorial but extending your domain to 3D? I would keep Y+ value close to 30 and use k-e standard wall function model.

    • omidFSI

      Thanks for the reply!

      I have a similar flow simulation where the cylinder is perpendicular to the fluid flow. The only difference is using circular fluid domain.
      (D: diameter of cylinder, flow left to right, domain diameter:40D, domain depth=3D-5D)

      My y+ as I calculated is good and around 5. I am using Spalart-Allmaras and SST- k-omega as later I wanna use these models for more complex geometry.

      For high Re (like 88000) and domain depth of around 5D (D-diameter of cylinder), the values of drag coefficient I get is not accurate at all and for all the cases the continuity residual is around 0.1. My previous simulation for a coarser mesh or 2d case had really good result which I don't understand at all!

      Any help is appreciated!

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