The new fvModels is a general interface to optional physical models in the
finite volume framework, providing sources to the governing conservation
equations, thus ensuring consistency and conservation. This structure is used
not only for simple sources and forces but also provides a general run-time
selection interface for more complex models such as radiation and film, in the
future this will be extended to Lagrangian, reaction, combustion etc. For such
complex models the 'correct()' function is provided to update the state of these
models at the beginning of the PIMPLE loop.
fvModels are specified in the optional constant/fvModels dictionary and
backward-compatibility with fvOption is provided by reading the
constant/fvOptions or system/fvOptions dictionary if present.
The new fvConstraints is a general interface to optional numerical constraints
applied to the matrices of the governing equations after construction and/or to
the resulting field after solution. This system allows arbitrary changes to
either the matrix or solution to ensure numerical or other constraints and hence
violates consistency with the governing equations and conservation but it often
useful to ensure numerical stability, particularly during the initial start-up
period of a run. Complex manipulations can be achieved with fvConstraints, for
example 'meanVelocityForce' used to maintain a specified mean velocity in a
cyclic channel by manipulating the momentum matrix and the velocity solution.
fvConstraints are specified in the optional system/fvConstraints dictionary and
backward-compatibility with fvOption is provided by reading the
constant/fvOptions or system/fvOptions dictionary if present.
The separation of fvOptions into fvModels and fvConstraints provides a rational
and consistent separation between physical and numerical models which is easier
to understand and reason about, avoids the confusing issue of location of the
controlling dictionary file, improves maintainability and easier to extend to
handle current and future requirements for optional complex physical models and
numerical constraints.
A population balance suffix after the phase suffix makes determining the
phase for a given name more complex. The additional suffix is also
unnecessary as a phase can only ever belong to one population balance,
so the phase name alone uniquely idetifies the grouping.
Patch contributed by Institute of Fluid Dynamics,
Helmholtz-Zentrum Dresden - Rossendorf (HZDR)
Field corrections are effectively explicit constraints applied to the field
after solution rather than to the equation and it significantly simplifies the
implementation to treat them as a special case of constraints. To implement
this the fvOption::correct(<field>) function has been renamed
fvOption::constrain(<field>) and uses constrainsField and constrainedFields.
This replaces compressibleInterFilmFoam in a more flexible, general and easily
maintainable form. A compressibleInterFilmFoam script is provided to redirect
uses to the replacement functionality:
The compressibleInterFilmFoam solver has solver has been replaced by the more general
compressibleInterFoam solver, which now supports surface films using the new
VoFSurfaceFilm fvOption.
To run with with surface film create a system/fvOptions dictionary
containing the VoFSurfaceFilm specification, e.g.
VoFSurfaceFilm
{
type VoFSurfaceFilm;
phase water;
}
The paper of Prince and Blanch (1996) contains an error in equation (2),
which computes the collision cross-sectional area and should be using
the bubble diameter rather than the radius. This error also extends to
equation (8) where the coefficient is wrong by a factor of 4. The
current code is correct, but the documentation was still referring to
the wrong coefficient.
Patch contributed by Institute of Fluid Dynamics,
Helmholtz-Zentrum Dresden - Rossendorf (HZDR)
reactingFoam and multiphaseEulerFoam can now both be run with the
frozenFlow switch and multiple outer correctors. This makes their
behaviour consistent with the frozenFlow implementation in
chtMultiRegionFoam.
The previous changes to reactions mean that caching the surface area
density field is no longer necessary. The diameter models have had their
caching functionality removed, which has simplified both the
implementation and the user interface.
A modified Arrhenius reaction rate given by:
k = (A * T^beta * exp(-Ta/T))*a
Where a is the phase surface area per unit volume. The name of the phase is
specified by the user.
Example usage:
oxidationAtSurface
{
type irreversiblePhaseSurfaceArrhenius;
reaction "O2^0 + TiCl4 = TiO2_s + 2Cl2";
A 4.9e1; // The pre-exponential factor is in units
// equal to that in the usual volumetric
// reaction rate **divided by length**, as
// the Arrhenius expression is taken to give
// rate per unit area, not per unit volume
beta 0.0;
Ta 8993;
phase particles;
}
This reaction has been applied to the titaniaSynthesisSurface tutorial,
which avoids the need for explicit caching of the surface area density
field.
A number of fvOptions that apply to a user-derined field can now
automatically work what primitive type they apply to. These options can
apply to any field type, and in some cases even multiple fields of
differing type. Example usage of the options to which this change
applies are shown below:
codedSource1
{
type codedSource;
name codedSource1;
field h;
...
}
fixedValueConstraint1
{
type fixedValueConstraint;
fieldValues
{
R (1 0 0 1 0 1);
epsilon 150;
}
...
}
phaseLimitStabilization11
{
type phaseLimitStabilization;
field sigma.liquid;
...
}
Previously to apply to a given type, these options had to be selected
with the name of the type prepended to the option name (e.g., "type
symmTensorPhaseLimitStabilization;") and those that operated on multiple
fields were restricted to those fields being of the same type.
A number of other options have had improvements made to their handling
of user specification of fields. Where possible, the option will now
attempt to work out what field the option applies to automatically. The
following options, therefore, no longer require "field" or "fields"
entries:
actuationDiskSource
buoyancyEnergy
buoyancyForce
meanVelocityForce
rotorDiskSource
volumeFractionSource
constantHeatTransfer
function2HeatTransfer
variableHeatTransfer
Non-standard field names can be overridden in the same way as in
boundary conditions; e.g., the velocity name can be overridden with a "U
<UName>;" entry if it does not have the default name, "U". The name of
the energy field is now always determined from the thermodynamics
model and should always be correct. Some options that can be applied to
an individual phase also support a "phase <phaseName>;" entry;
fvOptions field-name handling has been rewritten to increase its
flexibility and to improve warning messages. The flexibility now allows
for options that apply to all fields, or all fields of a given phase,
rather than being limited to a specific list of field names. Messages
warning about options that have not been applied now always print just
once per time-step.
multiphaseEulerFoam now supports the "frozenFlow" setting in
system/fvSolution/PIMPLE. With this switch on, the pressure-velocity
system is not solved. Energy and species transport are simulated using
fixed velocity and pressure fields. Non-transport effects on the phase
fraction, such as mass transfer or fvOption sources, are also included.
Note that this setting does not enforce conservation. In general, any
processes that alter the phase fraction have to be set up carefully in
order to avoid generating an inconsistent set of phase fractions.
This switch has been enabled in two zero-dimensional test cases which
are designed to operate at a constant pressure. The "frozenFlow" switch
now enforces this constant pressure directly. Previously the pressure
equation was being solved, but the system was not well posed, and the
cases were failing to run as a result.
Mesh-motion with or without topology change or AMI is now supported in
multiphaseEulerFoam for both cell- and face-momentum algorithms.
The new tutorial case mixerVesselAMI2D is provided which is the AMI version of
the 4-phase MRF mixerVessel2D case. It is setup with the cell-momentum
algorithm but also runs fine with the face-momentum algorithm although the
results are noticeably less accurate, particularly when the case is run
single-phase and compared directly with those from pimpleFoam.
Further testing is in progress.
I2D/constant/thermophysicalProperties.water
The new compressible form of the twoPhaseChange library including cavitation
models Kunz, Merkle and SchnerrSauer provides compressibleInterFoam with
optional phase change functionality specified in the optional
constant/phaseChangeProperties dictionary, e.g.
phaseChangeModel SchnerrSauer;
pSat 2300; // Saturation pressure
All function objects now re-read as a result of run-time modifications
to the system/controlDict.
Function objects that write log files (via the logFiles class) will now
generate a new postProcessing/<funcName>/<time> directory as a result of
either restart or run-time modification. Log files will therefore never
be overwritten by restart or run-time modification, except for when a
case is restarted at the same time as a previous execution (e.g.,
repeated runs at the start time).
The phase-change functionality in interPhaseChangeFoam has been generalised and
moved into the run-time selectable twoPhaseChange library included into
interFoam providing optional phase-change. The three cavitation models provided
in interPhaseChangeFoam are now included in the twoPhaseChange library and the
two interPhaseChangeFoam cavitation tutorials updated for interFoam.
interPhaseChangeFoam has been replaced by a user redirection script which prints
the following message:
The interPhaseChangeFoam solver has solver has been replaced by the more general
interFoam solver, which now supports phase-change using the new twoPhaseChange
models library.
To run with with phase-change create a constant/phaseChangeProperties dictionary
containing the phase-change model specification, e.g.
phaseChangeModel SchnerrSauer;
pSat 2300; // Saturation pressure
See the following cases for an example converted from interPhaseChangeFoam:
$FOAM_TUTORIALS/multiphase/interFoam/laminar/cavitatingBullet
$FOAM_TUTORIALS/multiphase/interFoam/RAS/propeller
Description
Thixotropic viscosity momentum transport model based on the evolution of
the structural parameter \f$ \lambda \f$:
\f[
\frac{D\lambda}{Dt} = a(1 - \lambda)^b - c \lambda \dot{\gamma}^d
\f]
The viscosity is then calculated using the expression
\f[
\nu = \frac{\nu_{\infty}}{{1 - K \lambda}^2}
\f]
Where the parameter K is given by:
\f[
K = 1 - \sqrt{\frac{\nu_{\infty}}{\nu_{0}}}
\f]
Here:
\vartable
\lambda | structural parameter
a | model coefficient
b | model coefficient
c | model coefficient
d | model coefficient
\dot{\gamma} | stress rate [1/s]
\nu_{0} | limiting viscosity when \f$ \lambda = 1 \f$
\nu_{\infty} | limiting viscosity when \f$ \lambda = 0 \f$
\endvartable
Reference:
\verbatim
Barnes H A, 1997. Thixotropy - a review. J. Non-Newtonian Fluid
Mech 70, pp 1-33
\endverbatim
In multi-specie systems the calculation of Cp and Cv is relatively expensive due
to the cost of mixing the coefficients of the specie thermo model, e.g. JANAF,
and it is significantly more efficient if these are calculated at the same time
as the rest of the thermo-physical properties following the energy solution.
Also the need for CpByCpv is also avoided by the specie thermo providing the
energy type in the form of a boolean 'enthalpy()' function which returns true if
the energy type is an enthalpy form.
This simplifies and standardises the handling of radiation in all solvers which
include an energy equation, all of which now support radiation via the
'radiation' fvOption which is selected in the constant/fvOption or
constant/<region>/fvOption file:
radiation
{
type radiation;
libs ("libradiationModels.so");
}
The radiation model, parameters, settings and sub-models are specified in the
'radiationProperties' file as before.
with frozenFlow set true in the PIMPLE sub-dictionary of fvSolution the p-U
system is not solved and the energy-composition system including reactions is
solved with the fixed flow.
cpp is no longer used to pre-process Make/files files allowing standard make '#'
syntax for comments, 'ifdef', 'ifndef' conditionals etc. This is make possible
by automatically pre-pending SOURCE += to each of the source file names in
Make/files.
The list of source files compile can be specified either as a simple list of
files in Make/files e.g.
# Note: fileMonitor assumes inotify by default. Compile with -DFOAM_USE_STAT
# to use stat (=timestamps) instead of inotify
fileMonitor.C
ifdef SunOS64
dummyPrintStack.C
else
printStack.C
endif
LIB = $(FOAM_LIBBIN)/libOSspecific
or
or directly as the SOURCE entry which is used in the Makefile:
SOURCE = \
adjointOutletPressure/adjointOutletPressureFvPatchScalarField.C \
adjointOutletVelocity/adjointOutletVelocityFvPatchVectorField.C \
adjointShapeOptimizationFoam.C
EXE = $(FOAM_APPBIN)/adjointShapeOptimizationFoam
In either form make syntax for comments and conditionals is supported.
It is better to not select and instantiate a model, fvOption etc. than to create
it and set it inactive as the creation process requires reading of settings,
parameters, fields etc. with all the associated specification and storage
without being used. Also the incomplete implementation added a lot of
complexity in the low-level operation of models introducing a significant
maintenance overhead and development overhead for new models.
TableBase, TableFile and Table now combined into a single simpler Table class
which handle both the reading of embedded and file data using the generalised
TableReader. The new EmbeddedTableReader handles the embedded data reading
providing the functionality of the original Table class within the same
structure that can read the data from separate files.
The input format defaults to 'embedded' unless the 'file' entry is present and
the Table class is added to the run-time selection table under the name 'table'
and 'tableFile' which provides complete backward comparability. However it is
advisable to migrate cases to use the new 'table' entry and all tutorial cases
have been updated.
