The Qdot field has been removed from all reacting solvers, in favour of
computing on the fly whenever it is needed. It can still be generated
for post-processing purposes by means of the Qdot function object. This
change reduces code duplication and storage for all modified solvers.
The Qdot function object has been applied to a number of tutorials in
order to retain the existing output.
A fix to Qdot has also been applied for multi-phase cases.
Now for transient simulations "Final" solver settings are required for ALL
equations providing consistency between the solution of velocity, energy,
composition and radiation properties.
However "Final" relaxation factors are no longer required for fields or
equations and if not present the standard value for the variable will be
applied. Given that relaxation factors other than 1 are rarely required for
transient runs and hence the same for all iterations including the final one
this approach provide simpler input while still providing the flexibility to
specify a different value for the final iteration if required. For steady cases
it is usual to execute just 1 outer iteration per time-step for which the
standard relaxation factors are appropriate, and if more than one iteration is
executed it is common to use the same factors for both. In the unlikely event
of requiring different relaxation factors for the final iteration this is still
possible to specify via the now optional "Final" specification.
coneInjection has been extended to include the functionality of
coneNozzleInjection, and the latter has been removed.
Some parameters have changed names. The "positionAxis" entry from
coneInjection has been removed in preferance of coneNozzleInjection's
single "position" and "direction" entries. This means that only one
injection site is possible per model (dictionary substitutions mean that
only minimal additions are required to add further injection sites with
the same parameters). The name of the velocity magnitude has been
standardised as "Umag" and "innerDiameter" and "outerDiamater" have been
renamed "dInner" and "dOuter" for consistency with the inner and outer
spray angles.
Velocity magnitude and diameters are no longer read when they are not
required.
The randomisation has been altered so that the injections generate a
uniform distribution on an cross section normal to the direction of
injection. Previously there was an unexplained bias towards the
centreline.
An example specification with a full list of parameters is shown below.
injectionModels
{
model1
{
type coneInjection;
// Times
SOI 0;
duration 1;
// Quantities
massTotal 0; // <-- not used with these settings
parcelBasisType fixed;
parcelsPerSecond 1000000;
flowRateProfile constant 1;
nParticle 1;
// Sizes
sizeDistribution
{
type fixedValue;
fixedValueDistribution
{
value 0.0025;
}
}
// Geometry
positions (-0.15 -0.1 0);
directions (1 0 0);
thetaInner 0;
thetaOuter 45;
// - Inject at a point
injectionMethod point;
// - Or, inject over a disc:
/*
injectionMethod disc;
dInner 0;
dOuter 0.05;
*/
// Velocity
// - Inject with constant velocity
flowType constantVelocity;
Umag 1;
// - Or, inject with flow rate and discharge coefficient
// This also requires massTotal, dInner and dOuter
/*
flowType flowRateAndDischarge;
Cd 0.9;
*/
// - Or, inject at a pressure
/*
flowType pressureDrivenVelocity;
Pinj 10e5;
*/
}
model2
{
// The same as model1, but at a different position
$model1;
position (-0.15 0.1 0);
}
}
To switch-off radiation set
radiationModel none;
in radiationProperties which instantiates "null" model that does not read any
data or coefficients or evaluate any fields.
The entries for liquid and solid species can now be simply be the name unless
property coefficients are overridden in which are specified in a dictionary as
before e.g. in the tutorials/lagrangian/coalChemistryFoam/simplifiedSiwek case
the water is simply specified
liquids
{
H2O;
}
and solid ash uses standard coefficients but the coefficients for carbon are
overridden thus
solids
{
C
{
rho 2010;
Cp 710;
kappa 0.04;
Hf 0;
emissivity 1.0;
}
ash;
}
The defaultCoeffs entry is now redundant and supported only for backward
compatibility. To specify a liquid with default coefficients simply leave the
coefficients dictionary empty:
liquids
{
H2O {}
}
Any or all of the coefficients may be overridden by specifying the properties in
the coefficients dictionary, e.g.
liquids
{
H2O
{
rho
{
a 1000;
b 0;
c 0;
d 0;
}
}
}
using a run-time selectable preconditioner
References:
Van der Vorst, H. A. (1992).
Bi-CGSTAB: A fast and smoothly converging variant of Bi-CG
for the solution of nonsymmetric linear systems.
SIAM Journal on scientific and Statistical Computing, 13(2), 631-644.
Barrett, R., Berry, M. W., Chan, T. F., Demmel, J., Donato, J.,
Dongarra, J., Eijkhout, V., Pozo, R., Romine, C. & Van der Vorst, H.
(1994).
Templates for the solution of linear systems:
building blocks for iterative methods
(Vol. 43). Siam.
See also: https://en.wikipedia.org/wiki/Biconjugate_gradient_stabilized_method
Tests have shown that PBiCGStab with the DILU preconditioner is more
robust, reliable and shows faster convergence (~2x) than PBiCG with
DILU, in particular in parallel where PBiCG occasionally diverges.
This remarkable improvement over PBiCG prompted the update of all
tutorial cases currently using PBiCG to use PBiCGStab instead. If any
issues arise with this update please report on Mantis: http://bugs.openfoam.org
so that the specification of the name and dimensions are optional in property dictionaries.
Update tutorials so that the name of the dimensionedScalar property is
no longer duplicated but optional dimensions are still provided and are
checked on read.
For multi-region cases the default location of blockMeshDict is now system/<region name>
If the blockMeshDict is not found in system then the constant directory
is also checked providing backward-compatibility
The old separate incompressible and compressible libraries have been removed.
Most of the commonly used RANS and LES models have been upgraded to the
new framework but there are a few missing which will be added over the
next few days, in particular the realizable k-epsilon model. Some of
the less common incompressible RANS models have been introduced into the
new library instantiated for incompressible flow only. If they prove to
be generally useful they can be templated for compressible and
multiphase application.
The Spalart-Allmaras DDES and IDDES models have been thoroughly
debugged, removing serious errors concerning the use of S rather than
Omega.
The compressible instances of the models have been augmented by a simple
backward-compatible eddyDiffusivity model for thermal transport based on
alphat and alphaEff. This will be replaced with a separate run-time
selectable thermal transport model framework in a few weeks.
For simplicity and ease of maintenance and further development the
turbulent transport and wall modeling is based on nut/nuEff rather than
mut/muEff for compressible models so that all forms of turbulence models
can use the same wall-functions and other BCs.
All turbulence model selection made in the constant/turbulenceProperties
dictionary with RAS and LES as sub-dictionaries rather than in separate
files which added huge complexity for multiphase.
All tutorials have been updated so study the changes and update your own
cases by comparison with similar cases provided.
Sorry for the inconvenience in the break in backward-compatibility but
this update to the turbulence modeling is an essential step in the
future of OpenFOAM to allow more models to be added and maintained for a
wider range of cases and physics. Over the next weeks and months more
turbulence models will be added of single and multiphase flow, more
additional sub-models and further development and testing of existing
models. I hope this brings benefits to all OpenFOAM users.
Henry G. Weller
