When a fluid is a variable composition mixture, set the initial mass fractions for
each of the components in the fluid. If modeling combustion, setting a mass fraction
of 0.232 for Oxygen, and then setting all other components to
Automatic is a good initial guess. For details, see Combustion Modeling.
For non-combusting reactions, Automatic is a sensible initial
guess method if you do not know the initial concentrations of components at the
start of the simulation.
Note: When restarting a calculation, you can rename a defined material component, or add (define) a new material component in the solver input file. For the renamed and/or added material components, there is no initial condition information stored in the initial values file; therefore, these component mass fractions are initialized using user-specified values and/or automatically generated default values.
Since a combination of initialization options may be used to initialize all of
the component mass fractions, it is likely that the component mass fractions
(including the Constraint mass fraction) will no longer sum
to 1. If this is the case, the solver scales the defined mass fractions and/or
recalculates the Constraint mass fraction to enforce a
component mass fraction sum of 1. The solver also issues a warning explaining
that the initial component mass fractions that were produced may not be
precisely those defined by the initial condition information in the initial
values file.