The Ansys Fluent environment

Overview

In-order to use Ansys Flutent a VNC session is need. Execution can be done in batch mode, but that is beyond the scope of this guide.

There are three versions of fluent installed on octopus:

  • 17.2

  • 18.2

  • 19.0

to load the latest version, the following command can be used in a terminal:

$ module load ansys/fluent/19.0

Job script template

The following job script template can be used (for a VNC session):

#!/bin/bash

## specify the job and project name
#SBATCH --job-name=my_fluent_job
#SBATCH --account=abc123

## specify the required resources
#SBATCH --partition=normal
#SBATCH --nodes=4
#SBATCH --ntasks-per-node=8
#SBATCH --cpus-per-task=1
#SBATCH --mem=64000
#SBATCH --time=0-06:00:00

### DO NOT EDIT BEYOND HERE UNLESS YOU KNOW WHAT YOU ARE DOING
source ~/.bashrc

VNC_HEAD_PORT=$(random_unused_port)
echo "VNC_HEAD_PORT = ${VNC_HEAD_PORT}"

JOB_INFO_FPATH=~/.vnc/slurm_${SLURM_JOB_ID}.vnc.out
rm -f ${JOB_INFO_FPATH}

VNC_SESSION_ID=$(vncserver 2>&1 | grep "desktop is" | tr ":" "\n" | tail -n 1)
echo ${VNC_SESSION_ID} >> ${JOB_INFO_FPATH}

ssh -R localhost:${VNC_HEAD_PORT}:localhost:$((5900 + ${VNC_SESSION_ID})) ohead1 -N &
SSH_TUNNEL_PID=$!
echo ${SSH_TUNNEL_PID} >> ${JOB_INFO_FPATH}

slurm_hosts_to_fluent_hosts

sleep infinity

Running Ansys Fluent

Fluent in shared memory mode

In this configuration, Fluent can be run either in serial mode (one core) or in shared memory (SMP) mode using up to the max number of cores and all the available memory of a compute node.

To run Fluent in local mode using one or multiple cores on the same machine, execute:

$ module load ansys/fluent/19.0
$ fluent

in a terminal, the Fluent launcher should open in the desktop

Note

use #SBATCH --nodes=1 in the job script.

../_images/fluent_local.png

Fluent in distributed mode

For simulations that do not fit in a single node, Fluent can automatically allocate resources on multiple nodes. In this case the following steps must be followed:

  • open the fluent laucher in the same procedure done for shared memory mode

  • select the number of cores (step 1 in the figure below)

  • click on the Parallel Settings tab (step 2 in the figure below)

  • set the File Containing Machine Names (step 3 in the figure below). Each job will have a different file name that is prefix by the slurm job id.

Note

For example to use four nodes use #SBATCH --nodes=4 in the job script to use for node. To run a simulation on 128 cores you can use:

  • #SBATCH --nodes=4 and #SBATCH --ntasks-per-node=32, this will allow you to use up to 1024 GB ram.

  • #SBATCH --nodes=2 and #SBATCH --ntasks-per-node=64 will grant you access to 512 GB ram.

../_images/fluent_multi_node_1.png