How do I set up a compressible flow in the segregated solver for a stable solution process?
There are several steps which will work under most circumstances:
In the Material Properties panel, set the density to be "ideal gas".
Initialize the flow domain to near stagnation properties. In other words, the static pressure should be set to the inlet total pressure, the temperature to the inlet total temperature, and the velocity to nearly, but not exactly zero (say 1 m/s). Initialize the turbulence values to something characteristic of the inlet (using the "compute from" option).
Set the under-relaxation factor for pressure to be 0.4 and for momentum to be 0.3.
Turn the energy equation off in the solvecontrolssolution panel for the first 50 iterations.
Turn the energy equation back on and slowly increase the pressure under-relaxation up to approximately 0.7 or as high as it will stably go, always save data files before making any changes.