OpenFOAM-ESI uses the --oversubscribe flag with mpirun, which instructs MPI to ignore restrictions on the number of processes relative to available CPU cores.
This allows you to run more processes than physical cores, which can be helpful for enabling finer domain decompositions.
For example, a c2d-highcpu-16 machine has 16 vCPUs supported by 8 physical cores. Thanks to --oversubscribe, OpenFOAM-ESI lets you run up to 8 MPI processes on this machine.
⚠️ Note: While this flexibility can be useful, running more processes than available vCPUs is generally not recommended, as it may significantly degrade simulation performance.