Now that the reaction system, chemistry and combustion models are completely
separate from the multicomponent mixture thermophysical properties package that
supports them it is inconsistent that thermo is named reactionThermo and the
name multicomponentThermo better describes the purpose and functionality.
When two phases interact, neither of which can become continuous, only a
general model is appropriate. A warning should not be issued regarding a
general model's use for this configuration.
If the sequence of meshes are decomposed independently the number, order and
potentially type of processor patches is likely to change. Thus the processor
patches and patch fields must be replaced with those of the new mesh.
The topoChanged flag now indicates that the mesh topology has changed at the
start of the current time-step rather than it is changing during the run, for
subsequent time-steps without topology change it is set false until the next
topology change.
For a single particle phase the divDevTau term in fvSchemes is now specified
thus:
divDevTau(U.particles) Gauss linear;
previously:
div((((thermo:rho.particles*nut.particles)*dev2(T(grad(U.particles))))+(((thermo:rho.particles*lambda.particles)*div(phi.particles))*I))) Gauss linear;
// Dispersed phase velocity
// const volVectorField Ud(mixture_.U() + Udm_);
// Use the mixture rather than the dispersed-phase velocity to approximate
// the dispersed-phase acceleration to improve stability as only the mixture
// momentum equation is coupled to continuity and pressure
//
// This approximation is valid only in the limit of small drift-velocity.
// For large drift-velocity an Euler-Euler approach should be used in
// which both the continuous and dispersed-phase momentum equations are
// solved and coupled to the pressure.
const volVectorField& Ud = mixture_.U();
return g_ - (Ud & fvc::grad(Ud));
Now stationary MRF regions may be embedded in moving mesh cases. While in
principle MRF regions moving with the mesh is supported by this development
there is no special handling with the MRF implementation to support the required
specification of the motion of the MRF regions.
The population balance model considers dilatation originating from density
change and mass transfer via source terms describing nucleation as well as
"drift" of the size distribution to smaller or larger sizes. Numerically, the
treatment does not necessarily equal the total dilatation, hence a correction is
introduced to ensure boundedness of the size group fractions.
Patch contributed by Institute of Fluid Dynamics,
Helmholtz-Zentrum Dresden - Rossendorf (HZDR)
and VTT Technical Research Centre of Finland Ltd.
Rather than rely on the MRF rotation the effect of acceleration due to flow
curvature on the dispersed is now handled directly using the Ud.grad(Ud) term
derived from the phase momentum equation. This means that any flow curvature
from bulk rotation to recirulation zones now affect the separation of the
dispersed phase from the continuous phase in a physical manner.
fvMesh::update() now executes at the beginning of the time-step, before time is
incremented and handles topology change, mesh to mesh mapping and redistribution
without point motion. Following each of these mesh changes fields are mapped
from the previous mesh state to new mesh state in a conservative manner. These
mesh changes not occur at most once per time-step.
fvMesh::move() is executed after time is incremented and handles point motion
mesh morphing during the time-step in an Arbitrary Lagrangian Eulerian approach
requiring the mesh motion flux to match the cell volume change. fvMesh::move()
can be called any number of times during the time-step to allow iterative update
of the coupling between the mesh motion and field solution.
This new mapping structure is designed to support run-time mesh-to-mesh mapping
to allow arbitrary changes to the mesh structure, for example during extreme
motion requiring significant topology change including region disconnection etc.
The polyTopoChangeMap is the map specifically relating to polyMesh topological
changes generated by polyTopoChange and used to update and map mesh related
types and fields following the topo-change.
This is a map data structure rather than a class or function which performs the
mapping operation so polyMeshDistributionMap is more logical and comprehensible
than mapDistributePolyMesh.
Added solid particle coalescence model by Adachi, Stuart and Fokkink
(1994), solid particle breakage model by Kusters (1991) and spherical
particle lift force model by Saffman-Mei (1992).
Patch contributed by Kasper Gram Bilde and Institute of Fluid Dynamics,
Helmholtz-Zentrum Dresden - Rossendorf (HZDR)
fvMesh is no longer derived from fvSchemes and fvSolution, these are now
demand-driven and accessed by the member functions schemes() and solution()
respectively. This means that the system/fvSchemes and system/fvSolution files
are no longer required during fvMesh constructions simplifying the mesh
generation and manipulation phase; theses files are read on the first call of
their access functions.
The fvSchemes member function names have also been simplified taking advantage
of the context in which they are called, for example
mesh.ddtScheme(fieldName) -> mesh.schemes().ddt(fieldName)
An optional Function1 can now be supplied to a fixedValueConstraint
which controls what proportion of the constraint is applied. This can be
used to ramp, pulse, or limit the duration of the constraint. For
example, ramping up of the constraint could be specified as follows:
scalarSource
{
type fixedValueConstraint;
selectionMode points;
points ((0 0.1 0));
fieldValues
{
s 1;
}
fraction
{
type ramp;
duration 0.1;
}
}
This required changing the formulation of the relative velocity in terms of a
scalar velocity coefficient Vc rather than the velocity V0 such that
V0 = Vc*g
where g is the acceleration due to gravity. With MRF rotation
V0 = Vc*(g + <MRF centrifugal acceleration>)
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
