A simulation of a micro centrifugal compressor using Air, P-P gives a reasonable result compared to test data, but trying M-P or P-M does converge, but gives a difference in inlet/outlet mass flow. The project is actually for a Steam compressor, but running with steam never converges - using any combination of I/O boundary condition (P.envir-P.envir, Static P in and out either equal or based on expected dP, Pin and MassFlow out etc.).
Screen grab of both Air and Steam under identical conditions attached. Intended to use saturates steam at about 100C at inlet, in both simulations, the boundary conditions have been set to 120C to ensure clearance form the saturation curve. I have tried rotating region, averaging and sliding - in all cases the Steam model runs nominally for a short while, but usually the temperature increases rapidly to >800C and / or I get mass flow inward from both openings. Any guidance most welcome.