boundaryProcAddressing has been removed. This has not been needed for a
long time. decomposePar has been optimised for mininum IO, rather than
minimum memory usage. decomposePar has also been corrected so that it
can decompose sequences of time-varying meshes.
There is no clear need for a residualAlpha to be defined specifically for Yi and
read from the fvSolution dictionary, the phase.residualAlpha() should be
suitable to stabilise the Yi equations.
The new stabilisation approach avoids any conservation error where the
phase-fraction is greater than residualAlpha by only applying the stabilising
terms to the transport equations in regions where the phase-fraction is less
than residualAlpha.
The handling of the div(phid,p) term for transonic support in the pressure
equation is now consistent such that conservation is achieved at convergence of
the pressure system irrespective of the scheme chosen for div(phid,p) and the
relaxation of the pressure equation.
The rhoSimpleFoam tutorials have been updated and improved.
Solver for steady or transient buoyant, turbulent flow of compressible fluids
for ventilation and heat-transfer, with optional mesh motion and mesh topology
changes. Created by merging buoyantSimpleFoam and buoyantPimpleFoam to provide
a more general solver and simplify maintenance.
In rhoPimpleFoam, rhoSimpleFoam, buoyantPimpleFoam and buoyantSimpleFoam the
density prediction step at the start of pEqn.H is now consistent between these
solvers and the other compressible solvers. If the density is relaxed in the
corrector it is now also relaxed following the predictor which improves
consistency, stability and convergence.
Description
Phase turbulence stabilisation
In the limit of a phase-fraction->0 the turbulence properties cannot be
obtained from the phase turbulence model, coupling to the other phase/phases
is required. The phaseTurbulenceStabilisation fvModel stabilises the phase
turbulence properties by adding transfer terms from the corresponding
properties of the other phases when the phase-fraction is less than the
specified \c alphaInversion. This implementation is a generalisation of
the approach used in the Foam::RASModels::LaheyKEpsilon and
Foam::RASModels::continuousGasKEpsilon models to handle phase-inversion and
free-surface flow and can be used with any combination of RAS turbulence
models.
To stabilise the solution of the phase turbulence equations \c
alphaInversion can be set to a small value e.g. 1e-2, but unless the phase
turbulence model is specifically designed to handle phase-inversion and both
continuous and dispersed regimes it may be useful to set \c alphaInversion
to a higher value, corresponding to the phase-fraction at which transision
from continuous to dispersed happens and effectively use the turbulence
properties of the other phase when the phase is dispersed. This is of
course an approximation to the real system and if accurate handling of both
the continuous and dispersed phase regimes is required specially developed
models should be used.
Usage
Example usage:
\verbatim
phaseTurbulenceStabilisation
{
type phaseTurbulenceStabilisation;
libs ("libmultiphaseEulerFoamFvModels.so");
phase air;
alphaInversion 0.1;
}
\endverbatim
Implementation of the interFoam VoFTurbulenceDamping for multiphaseEulerFoam.
In this implementation no distinction is made between a dispersed phase and the
interface so it is formally only applicable when interface compression is used
between the phase and the other phases. Special handling for dispersed phases
may be added in the future.
Description
Free-surface phase turbulence damping function
Adds an extra source term to the mixture or phase epsilon or omega
equation to reduce turbulence generated near a free-surface. The
implementation is based on
Reference:
\verbatim
Frederix, E. M. A., Mathur, A., Dovizio, D., Geurts, B. J.,
& Komen, E. M. J. (2018).
Reynolds-averaged modeling of turbulence damping
near a large-scale interface in two-phase flow.
Nuclear engineering and design, 333, 122-130.
\endverbatim
but with an improved formulation for the coefficient \c A appropriate for
unstructured meshes including those with split-cell refinement patterns.
However the dimensioned length-scale coefficient \c delta remains and must
be set appropriatly for the case by performing test runs and comparing with
known results. Clearly this model is far from general and more research is
needed in order that \c delta can be obtained directly from the interface
flow and turbulence conditions.
Usage
Example usage:
\verbatim
interfaceTurbulenceDamping
{
type interfaceTurbulenceDamping;
libs ("libmultiphaseEulerFoamFvModels.so");
phase water;
// Interface turbulence damping length scale
// This is a required input as described in section 3.3 of the paper
delta 1e-4;
}
\endverbatim
Replaces the local definition of the omega function in
functionObjects::turbulenceFields.
Will also be used in interfacial transfers and coupling in multiphase turbulence
modelling where different turbulence models are used in different phases.
For some cases, in particular those with very small cells created by snapping in
corners for example, it may be beneficial to convergence rate to limit the
minimum LTS time-step, the new minDeltaT control provides this.
to limit the time-step by comparing the film Courant number with the maximum
Courant number obtain from the optional maxCo entry in the system/<film
region>/fvSolution file. If maxCo is not provided the film model does not limit
the time-step.
See tutorials/multiphase/compressibleInterFoam/laminar/cylinder as an example
demonstrating this functionality.
Alpha contact angle boundaries are now specified in the following way
for multiphase solvers (i.e., multiphaseInterFoam,
compressibleMultiphaseInterFoam, and multiphaseEulerFoam):
boundaryField
{
wall
{
type alphaContactAngle;
contactAngleProperties
{
water
{
// Constant contact angle
theta0 90;
}
oil
{
// Dynamic contact angle
theta0 90;
uTheta 1;
thetaA 125;
thetaR 85;
}
}
value uniform 0;
}
}
All solvers now share the same implementation of the alphaContactAngle
boundary condition and the contact angle correction algorithm.
If alpha contact angle boundary conditions are used they must be
specified for all phases or an error will result. The consistency of the
input will also be checked. The angles given for water in the alpha.air
file must be 180 degrees minus the angles given for air in the
alpha.water file.
Blending of sub-models has been extended so that it provides the
necessary functionality for the simulation of three or more phases.
Models now, by default, blend within the two-phase subset. So, the
functions which specify blending coefficients are evaluated using
`alpha1/(alpha1 + alpha2)` and `alpha2/(alpha1 + alpha2)`, rather than
just `alpha1` and `alpha2`. This ensures that the functions behave
consistently in multiphase configurations as the combined fraction of
both phases reduces.
Additional "displaced" categories of model are now available. These
allow the interface modelling to change as a third phase fraction
becomes significant and displaces the phases associated with the
interface in question. These can be specified using displaced phase
interfaces. If they are not supplied then the non-displaced models apply
instead.
Additional "general" categories are also now available. These span the
entire range of the subset's phase fraction space and apply if models
for the more specific configurations (i.e., displaced and segregated)
are omitted.
For example, to specify standard SchillerNaumann droplet/bubble drag
modelling outside of a solid bed, and the bed-specific AttouFerschneider
drag model within the bed, the following specification could be used:
drag
{
air_dispersedIn_water
{
type SchillerNaumann;
residualRe 1e-3;
}
water_dispersedIn_air
{
$air_dispersedIn_water;
}
air_water_displacedBy_solid
{
type AttouFerschneider;
gas air;
liquid water;
solid solid;
E1 280;
E2 4.8;
}
solid_dispersedIn_air
{
$air_water_displacedBy_solid;
}
solid_dispersedIn_water
{
$air_water_displacedBy_solid;
}
}
The "air_water_displacedBy_solid" model shown above is a
"general-displaced" model, in that its application does not depend on
dispersal of the air-water system; it only depends on the level of
displacement by the solid. Alternatively, a set of three
"dispersed-displaced" and "segregated-displaced" models could have been
provided with the following syntax:
air_dispersedIn_water_displacedBy_solid
{
...
}
air_segregatedWith_water_displacedBy_solid
{
...
}
water_dispersedIn_air_displacedBy_solid
{
...
}
The blending methods themselves have changed slightly. There are now two
new methods; "segregated" for churning configurations in which no phase
is ever considered dispersed in another, and "continuous" where a
specified phase is always considered to be continuous and all other
phases are considered dispersed. These models replace the "none" model.
The linear and hyperbolic blending methods now support a "none" entry,
which can be set for parameters for phases that cannot become
continuous. For example, in an air-water-particles simulation the air
and water may become continuous, but the particles may not. A suitable
linear blending specification for this scenario might be as follows:
blending
{
default
{
type linear;
minFullyContinuousAlpha.air 0.8;
minPartlyContinuousAlpha.air 0.2;
minFullyContinuousAlpha.water 0.8;
minPartlyContinuousAlpha.water 0.2;
minFullyContinuousAlpha.solid none;
minPartlyContinuousAlpha.solid none;
}
}
The blending now provides far more feedback in terms of warnings and
errors when invalid or inadvisable specifications are made.
It is now also possible to visualise the various models' utilisation of
the phase fraction space. If the keyword "format" is placed in the
blending section of constant/phaseProperties then a plot (1 or 2 phases)
or surface (3 or more phases) file will be written out which shows the
phase fractions and the coefficients with which various models are
combined.
A new class, phaseInterface, has been added to represent interfacial
configurations between pairs of phases. This class and its derivations
explicitly represent different configurations (e.g., dispersal,
segregation, displacement) by type and provide a run-time selection
mechanism so that these configurations can be uniquely named and
intuitively selected for sub-models to apply to.
For example, drag models can be selected for an air-water system with
full phase inversion with the following syntax in
constant/phaseProperties:
drag
{
air_dispersedIn_water
{
type IshiiZuber;
}
air_segregatedWith_water
{
type segregated;
m 0.5;
n 8;
}
steam_dispersedIn_water
{
type SchillerNaumann;
residualRe 1e-3;
}
}
As well as the entries now being underscore separated, note also that
the sub model sections are now dictionaries ("{ ... }"), rather than
lists ("( ... );"). If a list is provided instead, then the input will
be considered to be in the old syntax, and will be read in a backwards
compatibility mode.
The new dictionary syntax permits substitution and therefore reuse of
settings, reducing the workload associated with setting up a large case
with many model combinations. In future it may be possible to introduce
wildcards to further reduce the verbosity of the input.
The new phase-interface classes and keywords and the phase-pairs and
keywords that they replace are listed below:
Default/General: phaseInterface "<phase>_<phase>"
replaces phasePair "(<phase> and <phase>)"
Dispersed: dispersedPhaseInterface "<phase>_dispersedIn_<phase>"
replaces orderedPhasePair "(<phase> in <phase>)"
Segregated: segregatedPhaseInterface "<phase>_segregatedWith_<phase>"
replaces phasePair "(<phase> and <phase>)"
Sided: sidedPhaseInterface "<phase>_<phase>_inThe_<phase>"
replaces orderedPhasePair "(<phase> in <phase>)"
Displaced: displacedPhaseInterface "<phase>_<phase>_displacedBy_<phase>"
is new
Interface combinations are also possible. There can be, for example, an
interface which is both dispersed and sided. This class is the
dispersedSidedPhaseInterface and can be selected with the keyword
"<phase>_dispersedIn_<phase>_inThe_<phase>". This is needed, for
example, in two-resistance heat transfer modelling, where a different
model can be selected to represent heat transfer within the fluids on
either side of an interface.
A full list of all available phase interface relationships can be
generated by specifying an incorrect name, and viewing the output of the
error message that results.
The "displaced" interface is not currently used, but will shortly be
utilised to allowing the user to control how models between phases
change as the fraction of a third phase becomes significant and
displaces the phases associated with the interface in question.
Notes for developers:
There is no centralised storage of phase interface relationships in the
phase system any more; the table of phasePairs has been removed, and
there is no correcponding table of phaseInterfaces. Models now locally
store their own phaseInterface objects, or a derivation thereof, rather
than a reference to a centrally stored object. These phaseInterface
classes hold only references so there is no cost associated with their
duplication in multiple sub models.
If a model requires an interface of a specific type, it has to down-cast
the interface provided to it. There is a `phaseSystem::modelCast` method
for this purpose which also provides meaningful error messages in the
event that an inappropriate interface was specified and the cast fails.
Model generation is now hierarchical. Wrapper models (blended and sided)
are constructed with the same interface as non-wrapper models (drag,
virtual mass, etc...). The wrapper model constructors call the
constructors of their sub-models directly, rather than requiring model
pointers to be passed in.
Sub-model lookup has been significantly generalised and simplified.
There is now just one `phaseSystem::lookupInterfacialModel` method which
takes a phaseInterface as its argument. Looking up a model for a
specific configuration just requires providing the appropriate
phaseInterface. E.g., this call will return the virtual mass model for
gas bubbles in liquid:
lookupSubModel<virtualMassModel>(dispersedPhaseInterface(gas, liquid))
Whilst this call will return the drag model for the segregated regime:
lookupSubModel<dragModel>(segregatedPhaseInterface(phase1, phase2))
And this call will return the complete blended heat transfer model:
lookupSubModel<blendedHeatTransferModel>(phaseInterface(phase1, phase2))
currently without strain-rate dependency.
Class
Foam::mixtureViscosityModels::Quemada
Description
Quemada viscosity model for for colloidal dispersions.
References:
\verbatim
Quemada, D. (1998).
Rheological modelling of complex fluids. I.
The concept of effective volume fraction revisited.
The European Physical Journal-Applied Physics, 1(1), 119-127.
\endverbatim
Usage
Example usage:
\verbatim
viscosityModel Quemada;
alphaMax 0.6; // Maximum dispersed phase-fraction (packing fraction)
q 2; // Exponent, defaults to 2
rho 1996;
\endverbatim
The lookup been fixed to prevent failures when a field is looked up with
the wrong type, and it now also provides warnings when a field cannot be
found for any type.
This model will generate an error if the diameter is requested. This
will happen if another sub model is included that depends on the
diameter of the continuous phase. It therefore provides a check that the
sub-modelling combination is valid.
Patch contributed by Institute of Fluid Dynamics,
Helmholtz-Zentrum Dresden - Rossendorf (HZDR)
This utility initialises the U, k and epsilon fields (if available) to
the output of the atmBoundaryLayer model. This is the same model as used
in the atmBoundaryLayerInlet.* boundary conditions and in the
waveAtmBoundaryLayer wave model.
The settings for the initialisation are read from a
system/setAtmBoundaryLayerDict file and are identical to the settings
required by the other use cases. An example of the settings required
within a system/setAtmBoundaryLayerDict file is shown below:
zDir (0 0 1); // Vertical direction
flowDir (1 0 0); // Direction of far-field flow
Zref 20; // Reference height
Uref 10; // Speed at reference height
z0 uniform 0.1; // Roughness height
zGround uniform 0; // Ground height
Now that Cp and Cv are cached it is more convenient and consistent and slightly
more efficient to cache thermal conductivity kappa rather than thermal
diffusivity alpha which is not a fundamental property, the appropriate form
depending on the energy solved for. kappa is converted into the appropriate
thermal diffusivity for the energy form solved for by dividing by the
corresponding cached heat capacity when required, which is efficient.
Following the addition of the new moments functionObject, all related
functionality was removed from sizeDistribution.
In its revised version, sizeDistribution allows for different kinds of
weighted region averaging in case of field-dependent representative
particle properties.
A packaged function has also been added to allow for command line solver
post-processing.
For example, the following function object specification returns the
volume-based number density function:
numberDensity
{
type sizeDistribution;
libs ("libmultiphaseEulerFoamFunctionObjects.so");
writeControl writeTime;
populationBalance bubbles;
functionType numberDensity;
coordinateType volume;
setFormat raw;
}
The same can be achieved using a packaged function:
#includeFunc sizeDistribution
(
populationBalance=bubbles,
functionType=numberDensity,
coordinateType=volume,
funcName=numberDensity
)
Or on the command line:
multiphaseEulerFoam -postProcess -func "
sizeDistribution
(
populationBalance=bubbles,
functionType=numberDensity,
coordinateType=volume,
funcName=numberDensity
)"
Patch contributed by Institute of Fluid Dynamics,
Helmholtz-Zentrum Dresden - Rossendorf (HZDR)
