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Multiphase simulation taking too long

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Old   February 14, 2021, 13:44
Default Multiphase simulation taking too long
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I am studying the effect of change in gravity on a tank that is filled up to 1/3rd of its volume with liquid N2. The tank has baffles and I am trying to study the sloshing effects. These are the settings I have enabled,

Number of cells: 1,226,345
Polyhexacore mesh generated within Fluent watertight geometry
The mesh is kept as coarse as possible for initial simulation

Fluent Setup:
  • Multiphase
    • Volume of Fluid
    • Explicit forumulation
    • Implicit body force enabled
    • Sharp interface modelling
    • 2 Eulerian phases
      • Phase1: n2gas
      • Phase2: n2liquid
      • No surface tension between them
  • Viscous: Laminar
  • No inlet or outlet BC
  • Cell register region defined for region to represent n2liquid
  • Initialized the whole domain with n2gas = 1, patched defined region with n2liquid = 1
  • Methods
    • Scheme: PISO
    • Gradient: Least Squares Cell Based
    • Pressure: Presto!
    • Momentum: Second Order Upwind
    • Volume Fraction: Geo-Reconstruct
    • Non-Iterative Time Advancement has been enabled
    • Warped Face Gradient Correction has been enabled
  • Controls
    • Pressure: 0.5
    • Momentum: 0.5
    • Density: 0.5
    • Body Force: 0.5
  • Solver Settings
    • Type: Adaptive
    • Method: Multiphase Specific
    • Duration specification method: Total time
    • Total time: 12seconds
    • Global Courant Number: 2
    • Initial time step size: 1e-05
    • Fixed time step, reporting interval, time step update interval, profile update interval: 1

I am running the simulation parallelly on 30 processors of Intel Xeon 4216 CPU @ 2.10 Ghz & 1 GPU NVIDIA GeForce RTX 2080Ti. 64GB 2400MHz RAM and 42GB GPU Memory

The simulation is taking a very long time (around 0.25 seconds of flow time has been simulated in 24 hours, 1%). Is there something I am doing wrong? Is there some way I can improve my timings.
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Old   March 3, 2021, 07:09
Vignesh Lakshmanan
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I guess the time step size is too small. Probably you can gradually increase time steps size as the simulation progresses.

Though I dont have much exposure in multiphase flows, I guess your settings are ok

Hope it helps!!!!
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fluent - parallel, multiphase

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