Fluids

Fluids

VOF solution with 2nd order momentum not stable

    • fit78
      Subscriber

      Hello,

      I'm working on fluid film on horizontal tube but the solution by using the 2nd order momentum resulted in the breaking of the film as shown in attached figure.

      I tried to decrease relaxation factor of the momentum to 0.01 but to no avail.

      I'm wondering if anyone has any suggestion to go about this.

      I tried to stabilize the film by changing to k-e mid iteration and the film stabilized but didn't work when I changed back to laminar.

      Settings used:

      VOF implicit, laminar, SIMPLE,Body force weighted, compressive volume fraction, second order upwind momentum, the rest is first order.

    • Karthik R
      Administrator
      Hello Firstly, what do you expect to see in this problem? I don't quite understand the problem you are trying to solve?
      Before you change your discretization options, are you making sure that you are converging every single time step? I ask this question because the time-step chosen in your simulation, 0.2 s, seems a bit high for such problems. What is your CFL number? You might need to reduce this further.
      Karthik
    • fit78
      Subscriber
      Hi I'm trying to reduce the film thickness based on some literatures of the same liquid load. I'm using implicit so the CFL number is not an issue I hope. I could get film thickness of within 40% of those in literature but I'm trying to reduce it by using second order momentum. Perhaps this is the limit of implicit solution.
    • Karthik R
      Administrator
      If you are comparing solutions with literature, I'd go the 'Explicit VOF' route and reduce the time-step to keep the CFL number close to 1.
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