Learning Forum

[nicko627]

Hi,

I am attempting to run a steady-state, incompressible, turbulent simulation on a mesh of about 18 million cells. The coupled Pressure-velocity solver is enabled. I am solving with energy eqn and k-omega turbulence model enabled. I am running this simulation on a Linux machine with ~49 GB of available RAM and 12 available cores.

The above simulation overloads the machine and forces it to use the Hard drive during iterations, but there was no issue with a 14 million cell mesh. Furthermore, the same 18 million cell mesh can solve perfectly fine on a windows machine with 8 cores and 32 GB of RAM. Is there a strong reason that the Windows machine works, but the Linux one does not? Also, Is there a way to find out how much RAM is necessary to run a simulation from Fluent?

The Windows application is run using the GUI, the Linux process is started with the CLI command: "fluent 3ddp -g -t 12 -i ./journal.command -cflush"

The journal.command file is listed here:

/file/read-case/

"CaseName.cas.h5"

/solve/initialize/initialize-flow/

/solve/iterate/ 200

##It is at this point, the simulation gets stuck

[Rob]

You typically need 2-3 GB per million cells with the PBCS solver, so you're probably just over the limits. Drop to SIMPLE and see if that helps. The old guide was 1GB per million cells but with the solver speed and robustness improvements that's no longer the case. I'm surprised the same 18M cell case ran on the Windows machine without paging, can you double check the RAM use as it could just mean the Win10 box has an SSD drive.
There's not a memory estimator (yet) for Fluent. Given the combination of models, cell types, material properties and boundary conditions that's not an easy task.