Fluids

Fluids

Fluent-VOF-Problems reaching convergence

    • wolterj
      Subscriber

      Hey,


      following Problem:
      I try to simulate flow throught a nozzel.


       


      Physics:


      Transient, Pressurebased


      VOF-simulations 2 phases(Water-liquid/Air) Implicit body force, level set, interfacial anti-diffusion. Viscous model is SAS.


      With Sufcae Tension and Wall adhesion


      Boundryconditons is a profil from Simulations of the inlet-pipe(50mm long with a diameter of 3mm)


      Solving:


         PISO


            SC: 2


            NC: 1


            N/C coupling


      Gradient  


         Least Cell....


      Pressure:


         PRESTO!


      Momentum:


         Bounded central Differencing


      Volume-Fraction:


         Geo-Reconstruct


      Turbulence Kinetic energy:


         Second Order


      Rest: first order


      Controls:


         Pressure: 0.8 


         Desity: 1


         Body Forces: 1


         Momentum: 0.7


         Turbulence Kinetic Energy: 0.8


         Specific Dissipation rate: 0.8


         Turbulent Viscousity 1


         Level set Funktion 0.3


       


      This setup were copied from an earlier project. in which somebody simulatet sth similar (simpler geometry of the nozzel)


      Initialization Hybrid:


      1 1.000000e+00


      2 1.483658e-03


      3 2.464239e-04


      4 7.808120e-05


      5 1.954829e-05


      6 2.758029e-05


      7 7.300978e-06


      8 1.637179e-05


      9 3.304232e-06


      10 5.462358e-06


      11 1.297115e-06


      12 2.780550e-06


      13 5.708590e-07


      14 1.221940e-06


      15 2.387166e-07


       


      Time step size:  5e-5s


       im using ANSYS 19.1


      If any more data is needed dont mind to ask.


      Thanks for ur help


       


       


       

    • wolterj
      Subscriber

      Mesh:


         Check:


          Domain Extents:


      x-coordinate: min (m) = -2.298173e-02, max (m) = 7.017803e-03


      y-coordinate: min (m) = -2.199953e-02, max (m) = 8.000000e-03


      z-coordinate: min (m) = -1.910000e-01, max (m) = -1.510000e-01


      Volume statistics:


      minimum volume (m3): 6.296011e-14


      maximum volume (m3): 8.751962e-11


      total volume (m3): 2.268875e-05


      Face area statistics:


      minimum face area (m2): 1.152058e-09


      maximum face area (m2): 4.271876e-07


       


       

    • wolterj
      Subscriber

      Mesh:


      Quality:


         Minimum Orthogonal Quality = 7.22601e-02 cell 351028 on zone 2 (ID: 2859648 on partition: 7) at location (-5.55571e-03 -7.51119e-03 -1.56400e-01)


      (To improve Orthogonal quality , use "Inverse Orthogonal Quality" in Fluent Meshing,


      where Inverse Orthogonal Quality = 1 - Orthogonal Quality)


       


      Maximum Aspect Ratio = 4.45425e+01 cell 354648 on zone 2 (ID: 2850200 on partition: 0) at location (-9.28973e-03 -8.64463e-03 -1.56400e-01)

    • DrAmine
      Ansys Employee

      Check if poor quality is related to some few cells but even some few cells with poor metrics might cause issues. Under solver expert (TUI) enable saving residuals and post-process them to see where they accumulate.

    • wolterj
      Subscriber

      got a better quality but still problems but not as bad as before. Its still converging to slow


       


      Minimum Orthogonal Quality = 2.07948e-01 cell 167471 on zone 2 (ID: 5768309 on partition: 14) at location (-9.47030e-03 -7.19996e-03 -1.59992e-01)


      (To improve Orthogonal quality , use "Inverse Orthogonal Quality" in Fluent Meshing,


      where Inverse Orthogonal Quality = 1 - Orthogonal Quality)


       


      Maximum Aspect Ratio = 1.60527e+01 cell 26041 on zone 2 (ID: 5959628 on partition: 14) at location (-6.47500e-03 -8.72246e-03 -1.59122e-01)


       

    • DrAmine
      Ansys Employee
      What kind of mesh do you have. CLSVOF and surface tension better with structured uniform grid.
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