### 7.17.6. Convergence

If convergence stalls completely or becomes very slow, check the conservation and imbalances at the end of the output file. If these are acceptable, plot the residual fields. It may be that the residual fields are good almost everywhere except for a few ‘hot spots.’ In this case, the solution is valid. You can also monitor some important quantity; for example, in a bubble column you can monitor if gas hold-up has reached steady-state.

For a case with a very dilute phase, the continuous phase will have a volume fraction very close to unity everywhere. Rounding errors will affect the residuals at a much higher level for the continuous phase in this case. By default, the volume fraction residual target is 10 times the global target residual.

For some multiphase simulations, notably free surface and interphase mass transfer cases, using the double precision solver executable can improve convergence significantly. For details, see Advection Schemes for Multiphase Volume Fractions.

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