For a multiphase simulation, the initial conditions for some variables must be the same for all fluids. For example, in CFX, the pressure is assumed to be common for all fluids. However, for other variables, the initial conditions can be specified for each fluid individually.
Initial conditions for parameters common to both fluids are set in the same way as
for single-phase simulations. The initial conditions that are fluid specific are set
on the Fluid Specific Initialization frame. For details, see
Fluid Specific Initialization in the CFX-Pre User's Guide. As
with single-phase simulations, the initial conditions can be set to
Automatic or Automatic with Value. For
details, see Modeling Advice for Multiphase Flow.
If a CFX-Solver default value is used for the Fluid Volume
Fraction, it is distributed evenly among the fluids for which a
volume fraction has not been assigned. For example, for two phase flow, an
initial Fluid Volume Fraction of 0.5
would be assigned to each fluid if the defaults are used. For many simulations,
including those containing a dilute fluid, using the Solver default values is
not recommended. Instead, set a sensible value for the initial Fluid
Volume Fraction using Automatic with Value.
Solver default values are used when the Automatic option is
selected without an initial values file, or when Default is
selected. If values are entered for the Fluid Volume
Fraction, they must sum to 1.