ENH: snGradSchemes: new scheme relaxedSnGrad

Surface gradient scheme with under-/over-relaxed
full or limited explicit non-orthogonal correction.

A minimal example by using system/fvSchemes:

  snGradSchemes
  {
      snGrad(<term>)       relaxed;
  }

and by using system/fvSolution:

  relaxationFactors
  {
      fields
      {
          snGrad(<term>)   <relaxation factor>;
      }
  }

src/finiteVolume/Make/files

@@ -456,6 +456,7 @@ $(snGradSchemes)/orthogonalSnGrad/orthogonalSnGrads.C
 $(snGradSchemes)/quadraticFitSnGrad/quadraticFitSnGrads.C
 $(snGradSchemes)/linearFitSnGrad/linearFitSnGrads.C
 $(snGradSchemes)/skewCorrectedSnGrad/skewCorrectedSnGrads.C
+$(snGradSchemes)/relaxedSnGrad/relaxedSnGrads.C
 
 convectionSchemes = finiteVolume/convectionSchemes
 $(convectionSchemes)/convectionScheme/convectionSchemes.C

src/finiteVolume/finiteVolume/snGradSchemes/relaxedSnGrad/relaxedSnGrad.C

@@ -0,0 +1,78 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | www.openfoam.com
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+    Copyright (C) 2021 OpenCFD Ltd.
+-------------------------------------------------------------------------------
+License
+    This file is part of OpenFOAM.
+
+    OpenFOAM is free software: you can redistribute it and/or modify it
+    under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
+    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+    for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
+
+\*---------------------------------------------------------------------------*/
+
+#include "fv.H"
+#include "relaxedSnGrad.H"
+#include "volFields.H"
+#include "surfaceFields.H"
+
+// * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
+
+template<class Type>
+Foam::tmp<Foam::GeometricField<Type, Foam::fvsPatchField, Foam::surfaceMesh>>
+Foam::fv::relaxedSnGrad<Type>::correction
+(
+    const GeometricField<Type, fvPatchField, volMesh>& vf
+) const
+{
+    typedef GeometricField<Type, fvsPatchField, surfaceMesh> SurfFieldType;
+
+    // Calculate explicit correction field
+    tmp<SurfFieldType> tcorrection = correctedScheme_().correction(vf);
+
+    // Retrieve relaxation factor value
+    const word fieldName(vf.name());
+    const word oldFieldName(fieldName + "_0");
+    const scalar relax =
+        vf.mesh().fieldRelaxationFactor("snGrad("+fieldName+")");
+
+    // Return explicit correction field if
+    // previous-time step correction is unavailable
+    const objectRegistry& obr = vf.db();
+    if (!obr.foundObject<SurfFieldType>(oldFieldName))
+    {
+        SurfFieldType* oldCorrection =
+            new SurfFieldType(oldFieldName, tcorrection());
+        oldCorrection->store();
+    }
+
+    // Return under/over-relaxed explicit correction field
+    tmp<SurfFieldType> trelaxedCorrection(new SurfFieldType(tcorrection()));
+
+    SurfFieldType& oldCorrection =
+        obr.lookupObjectRef<SurfFieldType>(oldFieldName);
+
+    trelaxedCorrection.ref() *= relax;
+    trelaxedCorrection.ref() += (scalar(1) - relax)*oldCorrection;
+
+    oldCorrection = tcorrection;
+
+    return trelaxedCorrection;
+}
+
+
+// ************************************************************************* //

src/finiteVolume/finiteVolume/snGradSchemes/relaxedSnGrad/relaxedSnGrad.H

@@ -0,0 +1,166 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | www.openfoam.com
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+    Copyright (C) 2021 OpenCFD Ltd.
+-------------------------------------------------------------------------------
+License
+    This file is part of OpenFOAM.
+
+    OpenFOAM is free software: you can redistribute it and/or modify it
+    under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
+    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+    for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
+
+Class
+    Foam::fv::relaxedSnGrad
+
+Group
+    grpFvSnGradSchemes
+
+Description
+    Surface gradient scheme with under-/over-relaxed
+    full or limited explicit non-orthogonal correction.
+
+Usage
+    Minimal example by using \c system/fvSchemes:
+    \verbatim
+    snGradSchemes
+    {
+        snGrad(<term>)       relaxed;
+    }
+    \endverbatim
+
+    and by using \c system/fvSolution:
+    \verbatim
+    relaxationFactors
+    {
+        fields
+        {
+            snGrad(<term>)   <relaxation factor>;
+        }
+    }
+    \endverbatim
+
+
+SourceFiles
+    relaxedSnGrad.C
+
+\*---------------------------------------------------------------------------*/
+
+#ifndef relaxedSnGrad_H
+#define relaxedSnGrad_H
+
+#include "correctedSnGrad.H"
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+namespace Foam
+{
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+namespace fv
+{
+
+/*---------------------------------------------------------------------------*\
+                        Class relaxedSnGrad Declaration
+\*---------------------------------------------------------------------------*/
+
+template<class Type>
+class relaxedSnGrad
+:
+    public snGradScheme<Type>
+{
+    // Private Data
+
+        //- Type of correction scheme
+        tmp<snGradScheme<Type>> correctedScheme_;
+
+
+    // Private Member Functions
+
+        //- No copy assignment
+        void operator=(const relaxedSnGrad&) = delete;
+
+
+public:
+
+    //- Runtime type information
+    TypeName("relaxed");
+
+
+    // Constructors
+
+        //- Construct from mesh
+        relaxedSnGrad(const fvMesh& mesh)
+        :
+            snGradScheme<Type>(mesh),
+            correctedScheme_(new correctedSnGrad<Type>(this->mesh()))
+        {}
+
+        //- Construct from mesh and data stream
+        relaxedSnGrad(const fvMesh& mesh, Istream& schemeData)
+        :
+            snGradScheme<Type>(mesh),
+            correctedScheme_(new correctedSnGrad<Type>(this->mesh()))
+        {}
+
+
+    //- Destructor
+    virtual ~relaxedSnGrad() = default;
+
+
+    // Member Functions
+
+        //- Return the interpolation weighting factors for the given field
+        virtual tmp<surfaceScalarField> deltaCoeffs
+        (
+            const GeometricField<Type, fvPatchField, volMesh>&
+        ) const
+        {
+            return this->mesh().nonOrthDeltaCoeffs();
+        }
+
+        //- Return true if this scheme uses an explicit correction
+        virtual bool corrected() const noexcept
+        {
+            return true;
+        }
+
+        //- Return the explicit correction to the relaxedSnGrad
+        //- for the given field using the gradients of the field components
+        virtual tmp<GeometricField<Type, fvsPatchField, surfaceMesh>>
+        correction(const GeometricField<Type, fvPatchField, volMesh>&) const;
+};
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+} // End namespace fv
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+} // End namespace Foam
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+#ifdef NoRepository
+    #include "relaxedSnGrad.C"
+#endif
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+#endif
+
+// ************************************************************************* //

src/finiteVolume/finiteVolume/snGradSchemes/relaxedSnGrad/relaxedSnGrads.C

@@ -0,0 +1,35 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | www.openfoam.com
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+    Copyright (C) 2021 OpenCFD Ltd.
+-------------------------------------------------------------------------------
+License
+    This file is part of OpenFOAM.
+
+    OpenFOAM is free software: you can redistribute it and/or modify it
+    under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
+    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+    for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
+
+\*---------------------------------------------------------------------------*/
+
+#include "relaxedSnGrad.H"
+#include "fvMesh.H"
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+makeSnGradScheme(relaxedSnGrad)
+
+// ************************************************************************* //