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ICHEC Software

Information about software packages installed on the ICHEC systems.

ANSYS CFX & Fluent

Versions Installed

Fionn: 15.0 / 16.0


ANSYS CFX is supported in the ANSYS Workbench interface, with all the stages of a full CFD simulation existing within a single environment. The technology in CFX includes, coupled multigrid linear solver technology, meshing flexibility, parallel efficiency and pre and post-processing capabilities.

ANSYS FLUENT is a general purpose commercial package for Computational Fluid Dynamics (CFD). It's modelling capabilities include acoustics, heat transfer, reacting flow, multiphase flow and dynamic mesh motion.


In order to use CFX or FLUENT a user must contact the Helpdesk and request that they be added to the CFX group.

For ANSYS products of version 12.0 and higher, new users have to specifically request the licensing system to use an academic license as opposed to a commercial license (the default). The most convenient way do this is to download the following license configuration file and copy it to ~/.ansys/v1XX/licensing/ (you will need to create this directory if it doesn't exist) where v1XX corresponds to the version of ANSYS you are using (~/.ansys/v150/licensing/ for ANSYS 15.0): license.preferences.xml



CFX Job Submission Example

Like other jobs on ICHEC systems, CFX jobs must be submitted using a PBS script. The following is an example PBS script for running a CFX job on 48 cores of the Fionn system with a maximum walltime of 25 hours (the CFX definition file is called test.def):

#PBS -l nodes=2:ppn=24
#PBS -l walltime=25:00:00
#PBS -N MyCFXJobName
#PBS -A MyProjectName

#Load the ansys module - CFX is then accessible
module load apps ansys/15.0


#Create a list of available nodes for the CFX executable:
nodes=`cat $PBS_NODEFILE`
nodes=`echo $nodes | sed -e 's/ /,/g'`

#Partition + Solve:
cfx5solve -def test.def -par-dist $nodes -start-method 'HP MPI Distributed Parallel'

This job can be submitted using the command

qsub scriptname.pbs

Where scriptname.pbs is the filename of the sample PBS script

Fluent Job Submission Example

Like other jobs on ICHEC systems, Fluent jobs must be submitted using a PBS script. The PBS script should launch the Fluent executable with the Graphical User Interface (GUI) disabled. This can be achieved by specifying the -g argument on the command line. When the GUI is disabled, Fluent commands can be issued using the Fluent Text User Interface (TUI). A series of TUI commands can be saved to a text file, which can subsequently read by the Fluent solver using the -i command line argument. The following is a minimal example PBS script for running a steady-state 3D Fluent job on 24 cores of the Fionn system for a maximum walltime of 5 hours (the Fluent case file is called "example.cas.gz"):

#PBS -l nodes=1:ppn=24
#PBS -l walltime=5:00:00
#PBS -N myJobName
#PBS -A myProjectName
#PBS -W x=GRES:aa_r_hpc+8

module load apps ansys/15.0

#Run the fluent executable:
fluent 3ddp -g -ssh -pinfiniband -cnf=$PBS_NODEFILE < FluentCommandFile.txt >myJob.log 2>&1

The following is a summary of Fluent command line parameters used in the above PBS script:

  • 3ddp: Run a 3D simulation in double precision (remove dp for single precision).
  • -g: Run Fluent without the GUI
  • -ssh: Use ssh to login to the available nodes (rsh is the default, which is not supported)
  • -pinfiniband: Use infiniband interconnect
  • -cnf=$PBS_NODEFILE: Provides the Fluent solver with the list of nodes allocated to the PBS job
  • < FluentCommandFile.txt: Read Fluent commands from FluentCommandFile.txt . This is a plain text file containing the commands that will be executed by the Fluent solver.
  • >myJob.log 2>&1: Redirect the Fluent output information to "myJob.log"

For this example, FluentCommandFile.txt contains the following Fluent commands (comments in this file begin with a semicolon (;)):

; Read the Fluent case file
; Initialise the flow field
; Run the solver for 200 iterations
/solve/iterate 200
; Write the results to a data file
/file/write-data example.dat
; Exit Fluent

This job can be submitted using the command

qsub scriptname.pbs

where scriptname.pbs is the filename of the sample PBS script

Checking License Availability in PBS

On Fionn users are required to specify the number of tokens required per job so that jobs will only be started if there are enough tokens available. The number HPC tokens required is the number of cores - 16. For a single node job this is 8 tokens:

#PBS -W x=GRES:aa_r_hpc+8

For larger jobs add 24 tokens per node: two nodes is 32; three nodes is 56. It is important to note that this means that smaller single node jobs are a more efficient use of the license tokens and should be used where possible.

Additional Notes

Further information can be obtained in the CFX documentation and at www.ansys.com.

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