How to model a free surface with VOF for CFD and CHT?

    • Marie1234


      I'm doing a steady state 3D CFD-simulation in FLUENT with CHT and for modelling the free surface of my tank ( 70mm x 150mm x 100mm) I use VOF.

      In my tank i have 9 cylinder of aluminium with a heater inside with "Energy Source".

      I have an inlet and outlet with e little pipe (diameter 6,5 mm x 40mm).

      The materials are air (phase 1, density: incompressible ideal gas) and oil (phase 2) and the filling level is 85mm (of 100mm).

      viscous model : laminar

      My Operating Conditions are: pressure=101325 Pa, density = 1.225 kg/m^3

      BC : velocity inlet: v = 0.703 m/s, T = 296.95 K

      pressure outlet : 1) outlet: pressure = 0 Pa

      2) atmosphere (opening of the tank) : pressure = 0 Pa

      Solution Methods: presure-velocity coupling : Scheme Coupled (Coupled with Volume Fraction in also enabled.)

      Diskretisation : default

      Solution Controls: default (but Momentum = 0.4)

      The problems:

      • In the beginning, the conti-equation isn't satisfied, so i have more oil coming in than going out, so my filling level increases. But I want a constant volume of oil in the tank. I cannot enable Coupled Level-Set + VOF because I get this Warning : "Level set model is not supported for mesh containing polyhedral cells".
      • I do a pseudo transient simulation with the defaults. After 200 - 300 iterations, the temperatures go crazy ( 1500 °C or -200 °C) --> "Floaing point exception". Should I change the Time scale Factor for a better convergence?

      This is how i initialized the model:

    • DrAmine
      Ansys Employee
      Use unsteady solver if you want to get reasonable results. Do not use Level Set only because you have heard that it might be better: that is not always true. And yeah with polys it is not available. n
    • Rob
      Ansys Employee
      If you want a constant height of liquid you want to check the outlet condition: what's holding the liquid level up? n
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