Fluent is used for computational fluid dynamics (CFD).

Meshing tool

The meshing tool in Fluent is called ICEM. You can start ICEM with the command icemcfd.

Submit a Fluent job

You can run a Fluent job interactively on ALICE using the qsub command. However it is more sensible to run Fluent as a non-interactive job.

To run Fluent as a non-interactive job you need to:

  • Store instructions including locations of input and output files in a Fluent journal file. A journal file is a simple text file containing Fluent Text User Interface (TUI) commands.
  • Use the -i option followed by the name of the journal file to make Fluent execute the commands in a journal file.
  • Use the -g option to disable the graphical user interface (GUI) since this isn't required.
  • Use a submission script to submit the Fluent job to the job scheduler. The scheduler uses this to execute the Fluent command.


In the example below the case and data files simulation.cas and simulation.dat will be processed over 10000 iterations by Fluent by reading instructions from the simulation.jou file.

Example journal file simulation.jou:

; Read case and data files
file read-case-data simulation.cas
; Do 10000 iterations
it 10000
; Write output back to data file
file write-data simulation.dat
; 'yes' here allows the existing .dat file to be overwritten

Example submission script submit.sh:

This example requests one hour of walltime, uses 16 processor cores and 120GB of memory (the job requests exclusive use of an entire node, then runs 16 parallel threads as this is the limit imposed by the fluent license).

#PBS -N Fluent
#PBS -m bae
#PBS -M username@leicester.ac.uk
#PBS -l walltime=01:00:00
#PBS -l nodes=1:ppn=28
#PBS -l vmem=60g
#PBS -q parallel

# Load the Fluent module module load fluent/18 # nprocs is the number of cores to use
# note that the number of processors is limited to 16 by the fluent
# license, though the node has 28 available
nprocs=16 cd $PBS_O_WORKDIR # Start fluent using the specified journal file fluent 3d -pib -ssh -g -mpi=ibmmpi -t16 -cnf=${PBS_NODEFILE} -i $HOME/fluent/fluent3dles.jou

Submit the Fluent submission job to the queue:

> qsub submit.sh

Create your own submission script

You will usually only need to make small changes to the example submission script:

  • Walltime
  • Memory limits
  • Fluent grid (this is 2ddp in the example above).

The current Fluent licence allows parallelism up to a maximum of 16 cores, which can be distributed across multiple nodes in the cluster. Such a run will use only one Fluent licence. Fluent does not co-exist well with other jobs sharing the same node. If you are running more than a few cores, please request an entire node as above, run using -pshmem and submit the job to parallel queue (-q parallel). Fluent also supports GPU acceleration in some cases. Please take a look at the fluent documentation and contact rcs.support@le.ac.uk if you would like to take advantage of this.

Find out more

You can find details of the TUI commands in the Fluent documentation.

CFD Online is a very useful resource, particularly its section on Journal Files and TUI.

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