Fluids

Fluids

Species Mass Transfer – results keep diverging

    • b404957074
      Subscriber

      Hi everyone,

      I am trying to simulate the natural evaporation of a thin water film. Basically, there is dry air passing through above the water liquid film, and the water liquid is expected to evaporate into the dry air. Basically, I wanna reproduce the simulation in this link (

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      ).

      I used the Eulerian Multi-Fluid VOF model, with the first phase being a mixture of air and water vapour, the second phase is also a mixture but only contains water liquid. I used the species mass transfer and kept the saturation pressure as default. The pics show the settings and boundary conditions. The result diverged almost immediately after the simulation began. The time step is 0.00005 s, so the courant number is no way greater than 250.

      If I did not patch the water liquid in the domain, it worked without any errors.

      Please help me!! Thank you!

      The errors show below:

      Error at Node 2: Global Courant

      Error at Node 4: GlEE

      Error at Node 5: Global Courant number is greater thr number is greater rothan 250.0an 250.00 The

      vel0 The

      velocitocityyr field atrror a Nod f is probably diverging. Please cheeield is pt 1 Node ck the solution

      0: Global Couraand reduce the time-stent number is greater p if necessthan 250.: Global Cary.

      00 ouobal Courarnt nant number is greumber isater t ghan 250.00 The r

      velocity fe ield isThe

      velocit probablyy fiel divergid is probng. Pleaseably d check tiverging. Plehe solution

      and redase check the solution

      and reduce the time-step if necessary.

      uce the time-step if necessary.

      ater than 250.00 The

      velocity field is probably diverging. Please check the solution

      and reduce the time-step if necessary.

      robably diverging. Please check the solution

      and reduce the time-step if necessary.

      Error at Node 3: Global Courant number is greater than 250.00 The

      velocity field is probably diverging. Please check the solution

      and reduce the time-step if necessary.

    • Karthik R
      Administrator
      Hello What are your boundary conditions? Can you double-check to make sure that the correct phases are applied.
      Regarding the time-step, what is your Courant number if you use your current time-step? Please remember that you are solving an explicit Eulerian model.
      Karthik
    • b404957074
      Subscriber
      Hi Karthik Thanks for the comments. The courant is around 0.025, the boundary conditions are shown in figure 4. I don't think there is any problems about the phrases setting...
    • b404957074
      Subscriber
      New errors found here:" Divergence detected in AMG solver: pressure correction Stabilizing phase-2-species-0 to enhance linear solver robustness.
      Stabilizing phase-2-species-0 using GMRES to enhance linear solver robustness.

      Divergence detected in AMG solver: phase-2-species-0 Stabilizing temperature to enhance linear solver robustness.
      Stabilizing temperature using GMRES to enhance linear solver robustness.
      temperature limited to 1.000000e+00 in 6000 cells on zone 3 in domain 2
      temperature limited to 1.000000e+00 in 6000 cells on zone 3 in domain 3
      Stabilizing vof-1 to enhance linear solver robustness.
      Stabilizing vof-1 using GMRES to enhance linear solver robustness."

      When I used the Mixture multiphase model, everything seems fine. However, after switching to the Eulerian VOF model, this error pops up.
      I have tried to lower down the standard state enthalpy of water vapour and also set a constant temperature of all the walls, but it did not work...
    • jao4817
      Subscriber
      Hello! Did you later find a solution to the problem, i'm facing a similar issue.
    • Rob
      Ansys Employee
      It's possibly a combination of time step and mesh quality. All I can see from the above is the solver not being very happy about something.
    • b404957074
      Subscriber
      Not yet. I gave up.
    • b404957074
      Subscriber
      I do not think it is because of the time step or mesh, since the time step I used is 0.00005 s, and the geometry is just a rectangle, the mesh is quite straightforward.
    • Rob
      Ansys Employee
      How quickly does the flow pass through a cell?
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