KNOWN ISSUE: Inconsistent default temperature range for real gas specific heats (Class 3 Error)
Incorrect specific heat values can be obtained in calculations with real gases. These errors will not be large, but will be relatively larger at low temperatures compared to high temperatures. These errors in specific heat should not affect the rest of the solution, provided it is fully converged. The specific heat is used in the linearisation of the energy equation, and so convergence rates may be affected.
The default table range for real gas materials (if not specified by the user) should be 100 K to 1000 K. For Cp and Cv the CFX-Solver incorrectly sets this to 100 K to 5000 K, which is inconsistent with the other properties.
The workaround for this is to set the table range explicitly in CFX-Pre. CFX-Pre should give a warning that no table range is specified, for both user-specified materials, and materials from the real gas databases.
ANSYS CFX Release 12.1. A custom executable for ANSYS CFX Release 12.0 is available on request.