Openfoam - pisoFoam only uses one core

Question

I use openfoam Version 1606+ When I run pisoFoam, in htop (to show CPU Usage) I can see that pisoFoam only uses one core (of course usage 99%). What do I have to modify if I want to use all cores of my CPU?

Best regards

Answer 1

To run pisoFoam parallel, roughly the following steps need to be taken:

• Decompose the grid and fields via the command decomposePar (assuming you set system/decomposeParDict file appropriately).
• Execute pisoFoam in parallel mode via this example command: mpirun -np X pisoFoam -parallel >& logFile(SampiyonCanakkaleDardanel), i.e. X is the integer number of processors being used. Say you have 4 cores in your workstation, then X = 4.

Please note that you do not need to modify anything within pisoFoam to perform a parallel task.

Answer 2

This is the typical workflow (after you generate your mesh):

• checkMesh > log.checkMesh.1 2>&1
• decomposePar > log.decomposePar 2>&1
• renumberMesh > log.renumberMesh 2>&1
• checkMesh > log.checkMesh.2 2>&1
• mpiexec -n 5 pisoFoam -parallel > log.pisoFoam 2>&1
• reconstructPar

Notes:

• Tested on v2.4.
• I used 5 as the number of cores in this example. Replace by the number you want. You may want to test using hyperthreading; it may or may not be useful.
• Don't forget the -parallel flag.
• renumberMesh is useful in cases of large meshes.
• Try to use functionObjects as much as you can, as saving time directories can consume a lot of disk space.
• See the OpenFOAM tutorials for examples of all that is mentioned above (e.g. pitzDaily, channel395, damBreak, motorBike etc. etc.)