Class 3 Error

If the CFX Interpolator is used to interpolate the results from a multi-component flow onto a new definition file, then it is possible for the initial values created in the definition file to have the mass fractions for the components mixed up. For example, in a gaseous mixture, it may be that the mass fraction of oxygen is initialised to the mass fraction of nitrogen from the initial values file. This may not be obvious, particular for combustion cases where there may be a large number of components all with fairly small mass fractions.

A similar effect can be seen if the interpolator is used with results from a multiphase flow, where the initial values of volume fraction for the different fluids may be mixed up. This is usually obvious, because the initial conditions are so badly wrong (due to the fluids usually having such different volume fractions) that the simulation often crashes or has difficulty converging.

These problems cannot be seen by looking at the interpolated results in the definition file in CFX-Post, but can be seen by post-processing a backup or transient file that is written before the first timestep of the run.

The CFX Solver works with fixed internal names for the mass fractions and volume fractions of the components and fluids. For the restart to work correctly, the user names of the components or fluids (e.g. Water.Volume Fraction or N2.Mass Fraction) must be mapped to the same internal names in the restarted runas they were in the original run. For some interpolated runs (particularly those where the components or fluids have changed), this mapping is n

For problems with volume fraction initial conditions being mixed up, the workaround is to swap the order of the fluids in the fluids list in the CFX Command Language (CCL). For example, if the CCL contains "Fluids List = Air, Water" and the volume fraction initialisation is incorrect, then using the CFX Command Editor to change the CCL to read "Fluids List = Water, Air" should resolve the problem.

For problems with mass fraction initial conditions being mixed up, it may help to re-order the Materials List in the CCL for the fluid in the same way, and making sure that any new components appear at the end of the list.

ANSYS CFX Release 12.0.

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