Community contribution from Johan Roenby, DHI

IsoAdvector is a geometric Volume-of-Fluid method for advection of a
sharp interface between two incompressible fluids. It works on both
structured and unstructured meshes with no requirements on cell shapes.
IsoAdvector is as an alternative choice for the interface compression
treatment with the MULES limiter implemented in the interFoam family
of solvers.

The isoAdvector concept and code was developed at DHI and was funded
by a Sapere Aude postdoc grant to Johan Roenby from The Danish Council
for Independent Research | Technology and Production Sciences (Grant-ID:
DFF - 1337-00118B - FTP).
Co-funding is also provided by the GTS grant to DHI from the Danish
Agency for Science, Technology and Innovation.

The ideas behind and performance of the isoAdvector scheme is
documented in:

    Roenby J, Bredmose H, Jasak H. 2016 A computational method for sharp
    interface  advection. R. Soc. open sci. 3: 160405.
    [http://dx.doi.org/10.1098/rsos.160405](http://dx.doi.org/10.1098/rsos.160405)

Videos showing isoAdvector's performance with a number of standard
test cases can be found in this youtube channel:

    https://www.youtube.com/channel/UCt6Idpv4C8TTgz1iUX0prAA

Project contributors:

* Johan Roenby <jro@dhigroup.com> (Inventor and main developer)
* Hrvoje Jasak <hrvoje.jasak@fsb.hr> (Consistent treatment of
  boundary faces including processor boundaries, parallelisation,
  code clean up
* Henrik Bredmose <hbre@dtu.dk> (Assisted in the conceptual
  development)
* Vuko Vukcevic <vuko.vukcevic@fsb.hr> (Code review, profiling,
  porting to foam-extend, bug fixing, testing)
* Tomislav Maric <tomislav@sourceflux.de> (Source file
  rearrangement)
* Andy Heather <a.heather@opencfd.co.uk> (Integration into OpenFOAM
  for v1706 release)

See the integration repository below to see the full set of changes
implemented for release into OpenFOAM v1706

    https://develop.openfoam.com/Community/Integration-isoAdvector

rhoSimpleFoam now instantiates the lower-level fluidThermo which instantiates
either a psiThermo or rhoThermo according to the 'type' specification in
thermophysicalProperties, e.g.

thermoType
{
    type            hePsiThermo;
    mixture         pureMixture;
    transport       sutherland;
    thermo          janaf;
    equationOfState perfectGas;
    specie          specie;
    energy          sensibleInternalEnergy;
}

instantiates a psiThermo for a perfect gas with JANAF thermodynamics, whereas

thermoType
{
    type            heRhoThermo;
    mixture         pureMixture;
    properties      liquid;
    energy          sensibleInternalEnergy;
}

mixture
{
    H2O;
}

instantiates a rhoThermo for water, see new tutorial
compressible/rhoSimpleFoam/squareBendLiq.

In order to support complex equations of state the pressure can no longer be
unlimited and rhoSimpleFoam now limits the pressure rather than the density to
handle start-up more robustly.

For backward compatibility 'rhoMin' and 'rhoMax' can still be used in the SIMPLE
sub-dictionary of fvSolution which are converted into 'pMax' and 'pMin' but it
is better to set either 'pMax' and 'pMin' directly or use the more convenient
'pMinFactor' and 'pMinFactor' from which 'pMax' and 'pMin' are calculated using
the fixed boundary pressure or reference pressure e.g.

SIMPLE
{
    nNonOrthogonalCorrectors 0;

    pMinFactor      0.1;
    pMaxFactor      1.5;

    transonic       yes;
    consistent      yes;

    residualControl
    {
        p               1e-3;
        U               1e-4;
        e               1e-3;
        "(k|epsilon|omega)" 1e-3;
    }
}

Description
    Simple solidification porosity model

    This is a simple approximation to solidification where the solid phase
    is represented as a porous blockage with the drag-coefficient evaluated from

        \f[
            S = - \rho D(T) U
        \f]

    where
    \vartable
        D(T) | User-defined drag-coefficient as function of temperature
    \endvartable

    Note that the latent heat of solidification is not included and the
    temperature is unchanged by the modelled change of phase.

    Example of the solidification model specification:
    \verbatim
        type            solidification;

        solidificationCoeffs
        {
            // Solidify between 330K and 330.5K
            D table
            (
                (330.0     10000) // Solid below 330K
                (330.5     0)     // Liquid above 330.5K
            );

            // Solidification porosity is isotropic
            // use the global coordinate system
            coordinateSystem
            {
                type    cartesian;
                origin  (0 0 0);
                coordinateRotation
                {
                    type    axesRotation;
                    e1      (1 0 0);
                    e2      (0 1 0);
                }
            }
        }
    \endverbatim

Avoids slight phase-fraction unboundedness at entertainment BCs and improved
robustness.

Additionally the phase-fractions in the multi-phase (rather than two-phase)
solvers are adjusted to avoid the slow growth of inconsistency ("drift") caused
by solving for all of the phase-fractions rather than deriving one from the
others.

Renamed the original volRegion -> volFieldValue to clarify the purpose
of this class to process vol fields on a volRegion.

Reference:
    Poletto, R., Craft, T., and Revell, A.,
    "A New Divergence Free Synthetic Eddy Method for the
    Reproduction of Inlet Flow Conditions for LES",
    Flow Turbulence Combust (2013) 91:519-539

to simplify writing common functionObjects and avoid unnecessary code duplication

splitMeshRegions: handle flipping of faces for surface fields

subsetMesh: subset dimensionedFields

decomposePar: use run-time selection of decomposition constraints. Used to
    keep cells on particular processors. See the decomposeParDict in

$FOAM_UTILITIES/parallel/decomposePar:
  - preserveBaffles: keep baffle faces on same processor
  - preserveFaceZones: keep faceZones owner and neighbour on same processor
  - preservePatches: keep owner and neighbour on same processor. Note: not
    suitable for cyclicAMI since these are not coupled on the patch level
  - singleProcessorFaceSets: keep complete faceSet on a single processor
  - refinementHistory: keep cells originating from a single cell on the
    same processor.

decomposePar: clean up decomposition of refinement data from snappyHexMesh

reconstructPar: reconstruct refinement data (refineHexMesh, snappyHexMesh)

reconstructParMesh: reconstruct refinement data (refineHexMesh, snappyHexMesh)

redistributePar:
  - corrected mapping surfaceFields
  - adding processor patches in order consistent with decomposePar

argList: check that slaves are running same version as master

fvMeshSubset: move to dynamicMesh library

fvMeshDistribute:
  - support for mapping dimensionedFields
  - corrected mapping of surfaceFields

parallel routines: allow parallel running on single processor

Field: support for
  - distributed mapping
  - mapping with flipping

mapDistribute: support for flipping

AMIInterpolation: avoid constructing localPoints

This condition creates a zero-dimensional model of an enclosed volume of
gas upstream of the inlet. The pressure that the boundary condition
exerts on the inlet boundary is dependent on the thermodynamic state of
the upstream volume.  The upstream plenum density and temperature are
time-stepped along with the rest of the simulation, and momentum is
neglected. The plenum is supplied with a user specified mass flow and
temperature.

The result is a boundary condition which blends between a pressure inlet
condition condition and a fixed mass flow. The smaller the plenum
volume, the quicker the pressure responds to a deviation from the supply
mass flow, and the closer the model approximates a fixed mass flow. As
the plenum size increases, the model becomes more similar to a specified
pressure.

The expansion from the plenum to the inlet boundary is controlled by an
area ratio and a discharge coefficient. The area ratio can be used to
represent further acceleration between a sub-grid blockage such as fins.
The discharge coefficient represents a fractional deviation from an
ideal expansion process.

This condition is useful for simulating unsteady internal flow problems
for which both a mass flow boundary is unrealistic, and a pressure
boundary is susceptible to flow reversal. It was developed for use in
simulating confined combustion.

tutorials/compressible/rhoPimpleFoam/laminar/helmholtzResonance:
    helmholtz resonance tutorial case for plenum pressure boundary

This development was contributed by Will Bainbridge

Also added the new prghTotalHydrostaticPressure p_rgh BC which uses the
hydrostatic pressure field as the reference state for the far-field
which provides much more accurate entrainment is large open domains
typical of many fire simulations.

The hydrostatic field solution is controlled by the optional entries in
the fvSolution.PIMPLE dictionary, e.g.

    hydrostaticInitialization yes;
    nHydrostaticCorrectors 5;

and the solver must also be specified for the hydrostatic p_rgh field
ph_rgh e.g.

    ph_rgh
    {
        $p_rgh;
    }

Suitable boundary conditions for ph_rgh cannot always be derived from
those for p_rgh and so the ph_rgh is read to provide them.

To avoid accuracy issues with IO, restart and post-processing the p_rgh
and ph_rgh the option to specify a suitable reference pressure is
provided via the optional pRef file in the constant directory, e.g.

    dimensions      [1 -1 -2 0 0 0 0];
    value           101325;

which is used in the relationship between p_rgh and p:

    p = p_rgh + rho*gh + pRef;

Note that if pRef is specified all pressure BC specifications in the
p_rgh and ph_rgh files are relative to the reference to avoid round-off
errors.

For examples of suitable BCs for p_rgh and ph_rgh for a range of
fireFoam cases please study the tutorials in
tutorials/combustion/fireFoam/les which have all been updated.

Henry G. Weller
CFD Direct Ltd.

e.g. (fvc::interpolate(HbyA) & mesh.Sf()) -> fvc::flux(HbyA)

This removes the need to create an intermediate face-vector field when
computing fluxes which is more efficient, reduces the peak storage and
improved cache coherency in addition to providing a simpler and cleaner
API.

    Wall-velocity condition to be used in conjunction with the single rotating
    frame (SRF) model (see: FOAM::SRFModel)

    The condition applies the appropriate rotation transformation in time and
    space to determine the local SRF velocity of the wall.

        \f[
            U_p = - U_{p,srf}
        \f]

    where
    \vartable
        U_p     = patch velocity [m/s]
        U_{p,srf} = SRF velocity
    \endvartable

    The normal component of \f$ U_p \f$ is removed to ensure 0 wall-flux even
    if the wall patch faces are irregular.

    \heading Patch usage

    Example of the boundary condition specification:
    \verbatim
    myPatch
    {
        type            SRFWallVelocity;
        value           uniform (0 0 0);    // Initial value
    }
    \endverbatim

To be used instead of zeroGradientFvPatchField for temporary fields for
which zero-gradient extrapolation is use to evaluate the boundary field
but avoiding fields derived from temporary field using field algebra
inheriting the zeroGradient boundary condition by the reuse of the
temporary field storage.

zeroGradientFvPatchField should not be used as the default patch field
for any temporary fields and should be avoided for non-temporary fields
except where it is clearly appropriate;
extrapolatedCalculatedFvPatchField and calculatedFvPatchField are
generally more suitable defaults depending on the manner in which the
boundary values are specified or evaluated.

The entire OpenFOAM-dev code-base has been updated following the above
recommendations.

Henry G. Weller
CFD Direct

The boundary conditions of HbyA are now constrained by the new "constrainHbyA"
function which applies the velocity boundary values for patches for which the
velocity cannot be modified by assignment and pressure extrapolation is
not specified via the new
"fixedFluxExtrapolatedPressureFvPatchScalarField".

The new function "constrainPressure" sets the pressure gradient
appropriately for "fixedFluxPressureFvPatchScalarField" and
"fixedFluxExtrapolatedPressureFvPatchScalarField" boundary conditions to
ensure the evaluated flux corresponds to the known velocity values at
the boundary.

The "fixedFluxPressureFvPatchScalarField" boundary condition operates
exactly as before, ensuring the correct flux at fixed-flux boundaries by
compensating for the body forces (gravity in particular) with the
pressure gradient.

The new "fixedFluxExtrapolatedPressureFvPatchScalarField" boundary
condition may be used for cases with or without body-forces to set the
pressure gradient to compensate not only for the body-force but also the
extrapolated "HbyA" which provides a second-order boundary condition for
pressure.  This is useful for a range a problems including impinging
flow, extrapolated inlet conditions with body-forces or for highly
viscous flows, pressure-induced separation etc.  To test this boundary
condition at walls in the motorBike tutorial case set

    lowerWall
    {
        type            fixedFluxExtrapolatedPressure;
    }

    motorBikeGroup
    {
        type            fixedFluxExtrapolatedPressure;
    }

Currently the new extrapolated pressure boundary condition is supported
for all incompressible and sub-sonic compressible solvers except those
providing implicit and tensorial porosity support.  The approach will be
extended to cover these solvers and options in the future.

Note: the extrapolated pressure boundary condition is experimental and
requires further testing to assess the range of applicability,
stability, accuracy etc.

Henry G. Weller
CFD Direct Ltd.

noSlip is equivalent to fixedValue with a value of (0 0 0) but is
simpler to specify e.g.

     upperWall
     {
         type            noSlip;
     }

For example the sinusoidal motion of the floating object in the
potentialFreeSurfaceFoam/oscillatingBox tutorial is now specified thus

    floatingObject
    {
        type            fixedNormalInletOutletVelocity;

        fixTangentialInflow false;

        normalVelocity
        {
            type            uniformFixedValue;
            uniformValue    sine;
            uniformValueCoeffs
            {
                frequency 1;
                amplitude table
                (
                    (   0     0)
                    (  10 0.025)
                    (1000 0.025)
                );
                scale     (0 1 0);
                level     (0 0 0);
            }
        }

        value           uniform (0 0 0);
    }

rather than using

    floatingObject
    {
        type            fixedNormalInletOutletVelocity;

        fixTangentialInflow false;

        normalVelocity
        {
            type            oscillatingFixedValue;
            refValue        uniform (0 1 0);
            offset          (0 -1 0);
            amplitude       table
            (
                (   0     0)
                (  10 0.025)
                (1000 0.025)
            );
            frequency       constant 1;
        }

        value           uniform (0 0 0);
    }

fvOptions are transferred to the database on construction using
fv::options::New which returns a reference.  The same function can be
use for construction and lookup so that fvOptions are now entirely
demand-driven.

The abstract base-classes for fvOptions now reside in the finiteVolume
library simplifying compilation and linkage.  The concrete
implementations of fvOptions are still in the single monolithic
fvOptions library but in the future this will be separated into smaller
libraries based on application area which may be linked at run-time in
the same manner as functionObjects.

Updated objects
- corrected Peclet number for compressible cases
- propagated log flag and resultName across objects

New function objects
- new fluxSummary:
  - calculates positive, negative, absolute and net flux across face
    zones
- new runTimeControl
  - abort the calculation when a user-defined metric is achieved.
    Available options include:
    - average value remains unchanged wrt a given threshold
    - equation initial residual exceeds a threshold - useful to abort
      diverging cases
    - equation max iterations exceeds a threshold - useful to abort
      diverging cases
    - min/max of a function object value
    - min time step exceeds a threshold - useful to abort diverging
      cases
- new valueAverage:
  - average singular values from other function objects, e.g. Cd, Cl and
    Cm from the forceCoeffs function object

This is useful when applying an experimentally obtained profile as an
inlet condition:

    Example of the boundary condition specification:
    \verbatim
    myPatch
    {
        type            fixedProfile;
        profile    csvFile;

        profileCoeffs
        {
            nHeaderLine         0;          // Number of header lines
            refColumn           0;          // Reference column index
            componentColumns    (1 2 3);    // Component column indices
            separator           ",";        // Optional (defaults to ",")
            mergeSeparators     no;         // Merge multiple separators
            fileName            "Uprofile.csv";  // name of csv data file
            outOfBounds         clamp;      // Optional out-of-bounds handling
            interpolationScheme linear;     // Optional interpolation scheme
        }
        direction        (0 1 0);
        origin           0;
    }
    \endverbatim

or a simple polynomial profile:

    Example setting a parabolic inlet profile for the PitzDaily case:
    \verbatim
    inlet
    {
        type            fixedProfile;

        profile         polynomial
        (
            ((1 0 0)        (0 0 0))
            ((-6200 0 0)    (2 0 0))
        );
        direction       (0 1 0);
        origin          0.0127;
    }
    \endverbatim

Based on code provided by Hassan Kassem:
http://www.openfoam.org/mantisbt/view.php?id=1922

- user provides two planes and pressure drop across these
- bc assume potential flow and works out inlet velocity that would cause
an equivalent pressure drop

- user provides two planes and pressure drop across these
- bc assume potential flow and works out inlet velocity that would cause
an equivalent pressure drop

- redistributePar to have almost (complete) functionality of decomposePar+reconstructPar
- low-level distributed Field mapping
- support for mapping surfaceFields (including flipping faces)
- support for decomposing/reconstructing refinement data

- redistributePar to have almost (complete) functionality of decomposePar+reconstructPar
- low-level distributed Field mapping
- support for mapping surfaceFields (including flipping faces)
- support for decomposing/reconstructing refinement data

Resolves some stability issues with the outlet of multiphase problems.

cellCoBlended: New surfaceInterpolation scheme based on CoBlended using the cell-based Courant number

    This scheme is equivalent to the CoBlended scheme except that the Courant
    number is evaluated for cells using the same approach as use in the
    finite-volume solvers and then interpolated to the faces rather than being
    estimated directly at the faces based on the flux.  This is a more
    consistent method for evaluating the Courant number but suffers from the
    need to interpolate which introduces a degree of freedom.  However, the
    interpolation scheme for "Co" is run-time selected and may be specified in
    "interpolationSchemes" and "localMax" might be most appropriate.

    Example of the cellCoBlended scheme specification using LUST for Courant
    numbers less than 1 and linearUpwind for Courant numbers greater than 10:
    \verbatim
    divSchemes
    {
        .
        .
        div(phi,U)  Gauss cellCoBlended 1 LUST grad(U) 10 linearUpwind grad(U);
        .
        .
    }

    interpolationSchemes
    {
        .
        .
        interpolate(Co) localMax;
        .
        .
    }
    \endverbatim

Now the specification of the LTS time scheme is simply:

ddtSchemes
{
    default         localEuler;
}

advectionDiffusionPatchDistMethod: Calculation of approximate distance to nearest patch for all cells
and boundary by solving the Eikonal equation in advection form with diffusion smoothing.

wallDist/patchDistMethods/Poisson: New method for fast calculation of an approximate wall-distance field
by solving Poisson's equation

Currently these vectors are generated at the same time as the wall-distance field
by the same run-time selected algorithm.  This will be changed so that the wall-reflection
vectors are only generated and stored if required.

When using models which require the wallDist e.g. kOmegaSST it will
request the method to be used from the wallDist sub-dictionary in
fvSchemes e.g.

wallDist
{
    method meshWave;
}

specifies the mesh-wave method as hard-coded in previous OpenFOAM versions.

In preparation for run-time selectable methods

    The standard/previous general symmetry type is now named symmetry
    both in class and lookup name for consistency.  The rigorous
    symmetryPlane type is needed for moving-mesh cases in which the
    motion it constrained by one or two planes.