I am a university student, and have been using Fluent for a while on a desktop, using up to 12 threads (processes) without issue. I recently started trying to use an older server for HPC, and am running into problems. The server is running Windows Server 2012 R2, has four AMD Opteron 6380 processors for total 32 hyperthreaded cores, and 256 GB RAM. Ansys 18.2 is installed, and I am using Workbench for a fuel injection case. The system works fine, and seems to scale properly, with up to 9 processes, and Fluent appears to see the system as having a single 64 thread CPU. The problem comes with 10 or more processes.
With the default settings, which appears to be using the ibmmpi MPI type, Fluent crashes after getting to the point where it says "...spawning node 0 on machine..." with a Windows error saying mpirun.exe has stopped working, and once Fluent is closed, Workbench gives the error "The FLUENT application failed to validate the connection." For the sake of trial and error, I changed the MPI type to msmpi, which gives a slightly different error in Fluent, saying that it is unable to find the file for the msmpi type. Workbench gives the same error as before. When using the intel MPI type, on the other hand, Fluent loads with 32 processes without apparent issue, and even appears to run correctly, crunching through iterations much faster than with 9 processes, but invariably, with this setup, the residuals jump after a number of iterations and Fluent gives the "Divergence detected in AMG for pressure coupled, protective actions enabled!" and "...temporarily solve with BCGSTAB!" warnings.
If the error occurred with more than 8, or with more than 16 processes, I would suspect that it has to do with the fact that the server has 4 CPUs, but the fact that it occurs with more than 9 is confusing. Please advise, and thank you for your help.