Multiphase simulation taking too long

allenpv · February 14, 2021, 13:44

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,

Mesh:
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.

ViLaks · March 3, 2021, 07:09

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!!!!

February 14, 2021, 13:44	Multiphase simulation taking too long	#1
allenpv New Member Allen Join Date: Feb 2021 Posts: 3 Rep Power: 5	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, Mesh: 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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March 3, 2021, 07:09		#2
ViLaks Member Vignesh Lakshmanan Join Date: Nov 2016 Posts: 79 Rep Power: 10	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!!!!