The majority of input parameters now support automatic unit conversion.
Units are specified within square brackets, either before or after the
value. Primitive parameters (e.g., scalars, vectors, tensors, ...),
dimensioned types, fields, Function1-s and Function2-s all support unit
conversion in this way.
Unit conversion occurs on input only. OpenFOAM writes out all fields and
parameters in standard units. It is recommended to use '.orig' files in
the 0 directory to preserve user-readable input if those files are being
modified by pre-processing applications (e.g., setFields).
For example, to specify a volumetric flow rate inlet boundary in litres
per second [l/s], rather than metres-cubed per second [m^3/s], in 0/U:
boundaryField
{
inlet
{
type flowRateInletVelocity;
volumetricFlowRate 0.1 [l/s];
value $internalField;
}
...
}
Or, to specify the pressure field in bar, in 0/p:
internalField uniform 1 [bar];
Or, to convert the parameters of an Arrhenius reaction rate from a
cm-mol-kcal unit system, in constant/chemistryProperties:
reactions
{
methaneReaction
{
type irreversibleArrhenius;
reaction "CH4^0.2 + 2O2^1.3 = CO2 + 2H2O";
A 6.7e12 [(mol/cm^3)^-0.5/s];
beta 0;
Ea 48.4 [kcal/mol];
}
}
Or, to define a time-varying outlet pressure using a CSV file in which
the pressure column is in mega-pascals [MPa], in 0/p:
boundaryField
{
outlet
{
type uniformFixedValue;
value
{
type table;
format csv;
nHeaderLine 1;
units ([s] [MPa]); // <-- new units entry
columns (0 1);
mergeSeparators no;
file "data/pressure.csv";
outOfBounds clamp;
interpolationScheme linear;
}
}
...
}
(Note also that a new 'columns' entry replaces the old 'refColumn' and
'componentColumns'. This is is considered to be more intuitive, and has
a consistent syntax with the new 'units' entry. 'columns' and
'componentColumns' have been retained for backwards compatibility and
will continue to work for the time being.)
Unit definitions can be added in the global or case controlDict files.
See UnitConversions in $WM_PROJECT_DIR/etc/controlDict for examples.
Currently available units include:
Standard: kg m s K kmol A Cd
Derived: Hz N Pa J W g um mm cm km l ml us ms min hr mol
rpm bar atm kPa MPa cal kcal cSt cP % rad rot deg
A user-time unit is also provided if user-time is in operation. This
allows it to be specified locally whether a parameter relates to
real-time or to user-time. For example, to define a mass source that
ramps up from a given engine-time (in crank-angle-degrees [CAD]) over a
duration in real-time, in constant/fvModels:
massSource1
{
type massSource;
points ((1 2 3));
massFlowRate
{
type scale;
scale linearRamp;
start 20 [CAD];
duration 50 [ms];
value 0.1 [g/s];
}
}
Specified units will be checked against the parameter's dimensions where
possible, and an error generated if they are not consistent. For the
dimensions to be available for this check, the code requires
modification, and work propagating this change across OpenFOAM is
ongoing. Unit conversions are still possible without these changes, but
the validity of such conversions will not be checked.
Units are no longer permitted in 'dimensions' entries in field files.
These 'dimensions' entries can now, instead, take the names of
dimensions. The names of the available dimensions are:
Standard: mass length time temperature
moles current luminousIntensity
Derived: area volume rate velocity momentum acceleration density
force energy power pressure kinematicPressure
compressibility gasConstant specificHeatCapacity
kinematicViscosity dynamicViscosity thermalConductivity
volumetricFlux massFlux
So, for example, a 0/epsilon file might specify the dimensions as
follows:
dimensions [energy/mass/time];
And a 0/alphat file might have:
dimensions [thermalConductivity/specificHeatCapacity];
*** Development Notes ***
A unit conversion can construct trivially from a dimension set,
resulting in a "standard" unit with a conversion factor of one. This
means the functions which perform unit conversion on read can be
provided dimension sets or unit conversion objects interchangeably.
A basic `dict.lookup<vector>("Umean")` call will do unit conversion, but
it does not know the parameter's dimensions, so it cannot check the
validity of the supplied units. A corresponding lookup function has been
added in which the dimensions or units can be provided; in this case the
corresponding call would be `dict.lookup<vector>("Umean", dimVelocity)`.
This function enables additional checking and should be used wherever
possible.
Function1-s and Function2-s have had their constructors and selectors
changed so that dimensions/units must be specified by calling code. In
the case of Function1, two unit arguments must be given; one for the
x-axis and one for the value-axis. For Function2-s, three must be
provided.
In some cases, it is desirable (or at least established practice), that
a given non-standard unit be used in the absence of specific
user-defined units. Commonly this includes reading angles in degrees
(rather than radians) and reading times in user-time (rather than
real-time). The primitive lookup functions and Function1 and Function2
selectors both support specifying a non-standard default unit. For
example, `theta_ = dict.lookup<scalar>("theta", unitDegrees)` will read
an angle in degrees by default. If this is done within a model which
also supports writing then the write call must be modified accordingly
so that the data is also written out in degrees. Overloads of writeEntry
have been created for this purpose. In this case, the angle theta should
be written out with `writeEntry(os, "theta", unitDegrees, theta_)`.
Function1-s and Function2-s behave similarly, but with greater numbers
of dimensions/units arguments as before.
The non-standard user-time unit can be accessed by a `userUnits()`
method that has been added to Time. Use of this user-time unit in the
construction of Function1-s should prevent the need for explicit
user-time conversion in boundary conditions and sub-models and similar.
Some models might contain non-typed stream-based lookups of the form
`dict.lookup("p0") >> p0_` (e.g., in a re-read method), or
`Umean_(dict.lookup("Umean"))` (e.g., in an initialiser list). These
calls cannot facilitate unit conversion and are therefore discouraged.
They should be replaced with
`p0_ = dict.lookup<scalar>("p0", dimPressure)` and
`Umean_(dict.lookup<vector>("Umean", dimVelocity))` and similar whenever
they are found.
Coded functionality now supports basic un-typed substitutions from the
surrounding dictionary. For example:
value 1.2345;
#codeExecute
{
scalar s = $value;
...
};
It also now supports the more functional typed substitutions, such as:
direction (1 0 0);
#codeExecute
{
vector v = $<vector>direction;
...
};
These substitutions are now possible in all code blocks. Blocks with
access to the dictionary (e.g., #codeRead) will do a lookup which will
not require re-compilation if the value is changed. Blocks without
access to the dictionary will have the value directly substituted, and
will require recompilation when the value is changed.
The patch-specific mapper interfaces, fvPatchFieldMapper and
pointPatchFieldMapper, have been removed as they did not do anything.
Patch mapping constructors and functions now take a basic fieldMapper
reference.
An fvPatchFieldMapper.H header has been provided to aid backwards
compatability so that existing custom boundary conditions continue to
compile.
The interface for fvModels has been modified to improve its application
to "proxy" equations. That is, equations that are not straightforward
statements of conservation laws in OpenFOAM's usual convention.
A standard conservation law typically takes the following form:
fvMatrix<scalar> psiEqn
(
fvm::ddt(alpha, rho, psi)
+ <fluxes>
==
<sources>
);
A proxy equation, on the other hand, may be a derivation or
rearrangement of a law like this, and may be linearised in terms of a
different variable.
The pressure equation is the most common example of a proxy equation. It
represents a statement of the conservation of volume or mass, but it is
a rearrangement of the original continuity equation, and it has been
linearised in terms of a different variable; the pressure. Another
example is that in the pre-predictor of a VoF solver the
phase-continuity equation is constructed, but it is linearised in terms
of volume fraction rather than density.
In these situations, fvModels sources are now applied by calling:
fvModels().sourceProxy(<conserved-fields ...>, <equation-field>)
Where <conserved-fields ...> are (alpha, rho, psi), (rho, psi), just
(psi), or are omitted entirely (for volume continuity), and the
<equation-field> is the field associated with the proxy equation. This
produces a source term identical in value to the following call:
fvModels().source(<conserved-fields ...>)
It is only the linearisation in terms of <equation-field> that differs
between these two calls.
This change permits much greater flexibility in the handling of mass and
volume sources than the previous name-based system did. All the relevant
fields are available, dimensions can be used in the logic to determine
what sources are being constructed, and sources relating to a given
conservation law all share the same function.
This commit adds the functionality for injection-type sources in the
compressibleVoF solver. A following commit will add a volume source
model for use in incompressible solvers.
Specific names have been given for expand functions. Unused functions
have been removed, and functions only used locally have been removed
from the namespace. Documentation has been corrected. Default and
alternative value handling has been removed from code template
expansion.
MRF (multiple reference frames) can now be used to simulate SRF (single
reference frame) cases by defining the MRF zone to include all the cells is the
mesh and applying appropriate boundary conditions. The huge advantage of this
is that MRF can easily be added to any solver by the addition of forcing terms
in the momentum equation and absolute velocity to relative flux conversions in
the formulation of the pressure equation rather than having to reformulate the
momentum and pressure system based on the relative velocity as in traditional
SRF. Also most of the OpenFOAM solver applications and all the solver modules
already support MRF.
To enable this generalisation of MRF the transformations necessary on the
velocity boundary conditions in the MRF zone can no longer be handled by the
MRFZone class itself but special adapted fvPatchFields are required. Although
this adds to the case setup it provides much greater flexibility and now complex
inlet/outlet conditions can be applied within the MRF zone, necessary for some
SRF case and which was not possible in the original MRF implementation. Now for
walls rotating within the MRF zone the new 'MRFnoSlip' velocity boundary
conditions must be applied, e.g. in the
tutorials/modules/incompressibleFluid/mixerVessel2DMRF/constant/MRFProperties
case:
boundaryField
{
rotor
{
type MRFnoSlip;
}
stator
{
type noSlip;
}
front
{
type empty;
}
back
{
type empty;
}
}
similarly for SRF cases, e.g. in the
tutorials/modules/incompressibleFluid/mixerSRF case:
boundaryField
{
inlet
{
type fixedValue;
value uniform (0 0 -10);
}
outlet
{
type pressureInletOutletVelocity;
value $internalField;
}
rotor
{
type MRFnoSlip;
}
outerWall
{
type noSlip;
}
cyclic_half0
{
type cyclic;
}
cyclic_half1
{
type cyclic;
}
}
For SRF case all the cells should be selected in the MRFproperties dictionary
which is achieved by simply setting the optional 'selectionMode' entry to all,
e.g.:
SRF
{
selectionMode all;
origin (0 0 0);
axis (0 0 1);
rpm 1000;
}
In the above the rotational speed is set in RPM rather than rad/s simply by
setting the 'rpm' entry rather than 'omega'.
The tutorials/modules/incompressibleFluid/rotor2DSRF case is more complex and
demonstrates a transient SRF simulation of a rotor requiring the free-stream
velocity to rotate around the apparently stationary rotor which is achieved
using the new 'MRFFreestreamVelocity' velocity boundary condition. The
equivalent simulation can be achieved by simply rotating the entire mesh and
keeping the free-stream flow stationary and this is demonstrated in the
tutorials/modules/incompressibleFluid/rotor2DRotating case for comparison.
The special SRFSimpleFoam and SRFPimpleFoam solvers are now redundant and have
been replaced by redirection scripts providing details of the case migration
process.
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.
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.
