The pre-exponential factor provided to this reaction rate is assumed to
relate to surface area, so the units are kmol/m^2/s/(kmol/m^3)^sum{exp}.
A standard volumentic reaction, by comparison, (e.g., Arrhenius) would
have pre-exponential factor units of kmol/m^3/s/(kmol/m^3)^sum{exp}.
The use of the surface-area-volume ratio has been corrected to conform
to this definition.
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.
For transient solvers which support steady operation using the steadyState ddt
scheme the ".*Final" solver settings are now only used for the final PIMPLE
iteration when running transient; for stead running the standard solver settings
are used for all PIMPLE iterations for compatibility with the equivalent steady
solvers. This makes it easier to maintain both transient and steady cases for
transient solvers.
This allows changers to access geometry from the fvMesh on construction.
It also prevents a crash that occurs when a changer loads a field in
which there is a cyclic boundary condition.
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.
This permits forward declaration of the boundary and internal fields.
References and pointers to boundary fields and sliced internal fields
can now be used in situations where full instantiation of the geometric
field is not possible due to cyclic dependencies.
It has been possible as a result of this change to type the pointer to
the cell volumes field in fvMesh. Previously this was done with a void
pointer and explicit casting.
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.
when evaluating the external total pressure from the static pressure and
tangential velocity. This improves numerical stability and solution smoothness
for compressible cases.
The external pressure p0 is now formally the static pressure in the presence of
tangential flow and the corresponding total pressure is calculated from this
static pressure using the tangential velocity obtained from the
pressureInletOutletVelocity boundary condition if available. In the case that
there is no external tangential flow the external total pressure is equal to the
static pressure p0 as before.
Description
Inflow, outflow and entrainment pressure boundary condition based on a
constant total pressure assumption.
For outflow the patch pressure is set to the external static pressure.
For inflow the patch pressure is evaluated from the patch velocity and the
external total pressure obtained from the external static pressure \c p_0
and external velocity \c U_0 which is looked-up from the the optional \c
tangentialVelocity entry in the \c pressureInletOutletVelocity velocity
boundary condition for the patch if that boundary condition is used,
otherwise \c U_0 is assumed zero and the external total pressure is equal to
the external static pressure.
The patch pressure is evaluated from the external conditions using one of
the following expressions depending on the flow conditions and
specification of compressibility:
1. incompressible subsonic:
\f[
p_p = p_0 + 0.5 |U_0|^2 - 0.5 |U|^2
\f]
where
\vartable
p_p | pressure at patch [m^2/s^2]
p_0 | external static pressure [m^2/s^2]
U | velocity [m/s]
U_0 | external velocity [m/s]
\endvartable
2. compressible subsonic:
\f[
p_p = p_0 + 0.5 \rho |U_0|^2 - 0.5 \rho |U|^2
\f]
where
\vartable
p_p | pressure at patch [Pa]
p_0 | external static pressure [Pa]
\rho | density [kg/m^3]
U | velocity [m/s]
U_0 | external velocity [m/s]
\endvartable
3. compressible transonic (\f$\gamma = 1\f$):
\f[
p_p = \frac{p_0 + 0.5 \rho |U_0|^2}{1 + 0.5 \psi |U|^2}
\f]
where
\vartable
p_p | pressure at patch [Pa]
p_0 | external static pressure [Pa]
\psi | compressibility [m^2/s^2]
\rho | density [kg/m^3]
U | velocity [m/s]
U_0 | external velocity [m/s]
\endvartable
4. compressible supersonic (\f$\gamma > 1\f$):
\f[
p_p = \frac{p_0 + 0.5 \rho |U_0|^2}
{(1 + 0.5 \psi G |U|^2)^{\frac{1}{G}}}
\f]
where
\vartable
p_p | pressure at patch [Pa]
p_0 | external static pressure [Pa]
\psi | compressibility [m^2/s^2]
\rho | density [kg/m^3]
G | coefficient given by \f$\frac{\gamma}{1-\gamma}\f$ []
\gamma | ratio of specific heats (Cp/Cv) []
U | velocity [m/s]
U_0 | external velocity [m/s]
\endvartable
The modes of operation are set by the dimensions of the pressure field
to which this boundary condition is applied, the \c psi entry and the value
of \c gamma:
\table
Mode | dimensions | psi | gamma
incompressible subsonic | p/rho | |
compressible subsonic | p | none |
compressible transonic | p | psi | 1
compressible supersonic | p | psi | > 1
\endtable
Usage
\table
Property | Description | Required | Default value
U | Velocity field name | no | U
phi | Flux field name | no | phi
rho | Density field name | no | rho
psi | Compressibility field name | no | none
gamma | (Cp/Cv) | no | 1
p0 | External pressure | yes |
\endtable
Example of the boundary condition specification:
\verbatim
<patchName>
{
type totalPressure;
p0 uniform 1e5;
}
\endverbatim
For most multiphase flows it is more appropriate to evaluate the total pressure
from the static pressure obtained from p_rgh rather than from p_rgh directly.
The flow rate to the disk is now (dHat & U_o) and the momentum source
orientation dHat where dHat is the unit disk direction (orientation).
Constant values for momentum source for actuation disk
\f[
T = 2 \rho A (\hat{d}\dot U_{o})^2 a (1-a) \hat{d}
\f]
where:
\vartable
A | Disk area
dHat | Unit disk direction
U_o | Upstream velocity
a | 1 - Cp/Ct
Cp | Power coefficient
Ct | Thrust coefficient
\endvartable
