Population balance size-group fraction 'f<index>.<phase>' fields are now
read from an 'fDefault.<phase>' field if they are not provided
explicitly. This is the same process as is applied to species fractions
or fvDOM rays. The sum-of-fs field 'f.<phase>' is no longer required.
The value of a fraction field and its boundary conditions must now be
specified in the corresponding field file. Value entries are no longer
given in the size group dictionaries in the constant/phaseProperties
file, and an error message will be generated if a value entry is found.
The fraction fields are now numbered programatically, rather than being
named. So, the size-group dictionaries do not require a name any more.
All of the above is also true for any 'kappa<index>.<phase>' fields that
are constructed and solved for as part of a fractal shape model.
The following is an example of a specification of a population balance
with two phases in it:
populationBalances (bubbles);
air1
{
type pureIsothermalPhaseModel;
diameterModel velocityGroup;
velocityGroupCoeffs
{
populationBalance bubbles;
shapeModel spherical;
sizeGroups
(
{ dSph 1e-3; } // Size-group #0: Fraction field f0.air1
{ dSph 2e-3; } // ...
{ dSph 3e-3; }
{ dSph 4e-3; }
{ dSph 5e-3; }
);
}
residualAlpha 1e-6;
}
air2
{
type pureIsothermalPhaseModel;
diameterModel velocityGroup;
velocityGroupCoeffs
{
populationBalance bubbles;
shapeModel spherical;
sizeGroups
(
{ dSph 6e-3; } // Size-group #5: Fraction field f5.air2
{ dSph 7e-3; } // ...
{ dSph 8e-3; }
{ dSph 9e-3; }
{ dSph 10e-3; }
{ dSph 11e-3; }
{ dSph 12e-3; }
);
}
residualAlpha 1e-6;
}
Previously a fraction field was constructed automatically using the
boundary condition types from the sum-of-fs field, and the value of both
the internal and boundary field was then overridden by the value setting
provided for the size-group. This procedure doesn't generalise to
boundary conditions other than basic types that store no additional
data, like zeroGradient and fixedValue. More complex boundary conditions
such as inletOutlet and uniformFixedValue are incompatible with this
approach.
This is arguably less convenient than the previous specification, where
the sizes and fractions appeared together in a table-like list in the
sizeGroups entry. In the event that a substantial proportion of the
size-groups have a non-zero initial fraction, writing out all the field
files manually is extremely tedious. To mitigate this somewhat, a
packaged function has been added to initialise the fields given a file
containing a size distribution (see the pipeBend tutorial for an example
of its usage). This function has the same limitations as the previous
code in that it requires all boundary conditions to be default
constructable.
Ultimately, the "correct" fix for the issue of how to set the boundary
conditions conveniently is to create customised inlet-outlet boundary
conditions that determine their field's position within the population
balance and evaluate a distribution to determine the appropriate inlet
value. This work is pending funding.
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