Fluids

Fluids

PISO vs SIMPLE & Coupled solvers

    • Lugia_06
      Subscriber

      Hi everyone,

      I developing a transient droplet falling simulation model and play around with the Presure-Velocity Coupling methods, Coupled and SIMPLE both converged at the 3rd time steps and gave good results. However, the PISO method all three residuals are diverging. The Fluent theory guide introduced PISO as a part of the SIMPLE family and the skewness & Neightbour correction factors give higher efficiency. Could anyone assist me understand why PISO is diverging with the other settings the same as SIMPLE & Coupled?

      Best regards,

      Lugia_06

      PISO

    • DrAmine
      Ansys Employee
      SIMPLE is very under-relaxed PISO Not. You might tune Pressure URF for PISO (increase to 0.7) for Mometum (decrease it to 0.3) but I do not recommend doing that all the time.n If Coupled is providing you the required satisfaction then stick to it or does it last long time for your case?n
    • DrAmine
      Ansys Employee
      Just one question: Why CICSAM?n
    • Lugia_06
      Subscriber
      nIt's good to see you on the forum again. The convergence in SIMPLE and Coupled both last for a long time. I will stick to coupled in this case. According to the Fluent theory guide, CICSAM is more suitable for flows with high ratios between phases(water vs air) (https://www.afs.enea.it/project/neptunius/docs/fluent/html/th/node299.htm) and I have tested with Geo-reconstruct as well, there wasn't any difference between them. So I was wondering if you have any recommendations on the discritisation schemes I used in the screenshot?nBest regards,nLugia_06n
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