KNOWN ISSUE: A steady-state MFX run cannot be restarted as a transient run
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SYMPTOM: A restart of a transient MFX run from a steady-state MFX run does not work correctly. PROBLEM: A typical way to do a steady-state MFX run is to run the CFX part of the run as steady-state, and the ANSYS part of the run as transient with time integration turned off. When such an MFX run is restarted as a transient run (with CFX running as transient) then the initial time for the restart has to be equal to the final coupling time from the original MFX run. The CFX setting for the restart should have an Initial Time setting of "Coupling Initial Time". However, with this setup CFX fails to pick up the correct initial time, and instead starts from 0 [s]. It then runs with no coupling to ANSYS until the final coupling time from the original MFX run is reached, when the CFX and ANSYS solvers start to communicate. At this point the two solvers are out of synch and it is quite likely that the run will fail or diverge. This problem can easily be spotted in the CFX output file, with a message similar to: +--------------------------------------------------------------------+ | ****** Notice ****** | | The simulation time value obtained from the CFX input file | is inconsistent with the Coupling Initial Time value used | for this simulation. Please review results carefully. | CFX input file time : 0.0000E+00 | Coupling Initial Time : 1.0000E+00 +--------------------------------------------------------------------+ before the iterations begin. WORKAROUND: No workaround is currently available. Note that it is not appropriate to try to set the CFX Initial Time using the "Value" option to try to force the correct initial time, as this also resets the mesh (which is inappropriate for this situation). FIXED IN: ANSYS CFX Release 12.1. A custom executable for ANSYS CFX Release 12.0 is available on request. |
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