### 11.1.2. Convergence Tips

For high speed compressors and turbines, where the machine mass flow is choked, it is generally not possible to specify the specified mass flow at the outlet to match the numerical choked mass flow value. For choked flow conditions, you can either specify static pressure or exit corrected mass flow at the outlet. Both these conditions allow the mass flow through the machine to adjust to the numerical choked mass flow value.

If you have trouble converging a simulation involving real gases, try to obtain a solution first using an ideal gas. Ideal gases are available in the real gas library.

If you have trouble converging a problem with many stages, you may find that solving for a reduced number of stages can give you a better understanding of the physics, and may allow you to restart a multi-stage problem with a better initial guess. You can also try ramping up boundary conditions and the RPM.

Low pressure ratio Gas compressors (1.1 or less) can be treated more like liquid pumps. For details, see Liquid Pumps and Turbines.

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