ENH: Digital-Filter Based Synthetic Turbulence Generation Method for LES/DES Inflows

    Velocity boundary condition generating synthetic turbulence-alike
    time-series for LES and DES turbulent flow computations.

    To this end, two synthetic turbulence generators can be chosen:
    - Digital-filter method-based generator (DFM)

    \verbatim
    Klein, M., Sadiki, A., and Janicka, J.
        A digital filter based generation of inflow data for spatially
        developing direct numerical or large eddy simulations,
        Journal of Computational Physics (2003) 186(2):652-665.
        doi:10.1016/S0021-9991(03)00090-1
    \endverbatim

    - Forward-stepwise method-based generator (FSM)

    \verbatim
    Xie, Z.-T., and Castro, I.
        Efficient generation of inflow conditions for large eddy simulation of
        street-scale flows, Flow, Turbulence and Combustion (2008) 81(3):449-470
        doi:10.1007/s10494-008-9151-5
    \endverbatim

    In DFM or FSM, a random number set (mostly white noise), and a group
    of target statistics (mostly mean flow, Reynolds stress tensor profiles and
    length-scale sets) are fused into a new number set (stochastic time-series,
    yet consisting of the statistics) by a chain of mathematical operations
    whose characteristics are designated by the target statistics, so that the
    realised statistics of the new sets could match the target.

    Random number sets ---->-|
                             |
                         DFM or FSM ---> New stochastic time-series consisting
                             |           turbulence statistics
    Turbulence statistics ->-|

    The main difference between DFM and FSM is that the latter replaces the
    streamwise convolution summation in DFM by a simpler and a quantitatively
    justified equivalent procedure in order to reduce computational costs.
    Accordingly, the latter potentially brings resource advantages for
    computations involving relatively large length-scale sets and small
    time-steps.

src/finiteVolume/Make/files

@@ -200,6 +200,7 @@ $(derivedFvPatchFields)/translatingWallVelocity/translatingWallVelocityFvPatchVe
 $(derivedFvPatchFields)/turbulentDFSEMInlet/turbulentDFSEMInletFvPatchVectorField.C
 $(derivedFvPatchFields)/turbulentDFSEMInlet/eddy/eddy.C
 $(derivedFvPatchFields)/turbulentDFSEMInlet/eddy/eddyIO.C
+$(derivedFvPatchFields)/turbulentDigitalFilterInlet/turbulentDigitalFilterInletFvPatchVectorField.C
 $(derivedFvPatchFields)/turbulentInlet/turbulentInletFvPatchFields.C
 $(derivedFvPatchFields)/turbulentIntensityKineticEnergyInlet/turbulentIntensityKineticEnergyInletFvPatchScalarField.C
 $(derivedFvPatchFields)/uniformDensityHydrostaticPressure/uniformDensityHydrostaticPressureFvPatchScalarField.C

src/finiteVolume/fields/fvPatchFields/derived/turbulentDigitalFilterInlet/turbulentDigitalFilterInletFvPatchVectorFieldTemplates.C

+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | Copyright (C) 2016 - 2019 OpenCFD Ltd.
+     \\/     M anipulation  | 
+-------------------------------------------------------------------------------
+                              Copyright (C) 2015 OpenFOAM Foundation
+-------------------------------------------------------------------------------
+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 "pointToPointPlanarInterpolation.H"
+#include "Time.H"
+#include "IFstream.H"
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+template<class Type>
+Foam::tmp<Foam::Field<Type>>
+Foam::turbulentDigitalFilterInletFvPatchVectorField::interpolateOrRead
+(
+    const word& fieldName,
+    const dictionary& dict,
+    bool& interpolateField
+) const
+{
+    if (dict.found(fieldName))
+    {
+        tmp<Field<Type>> tFld
+        (
+            new Field<Type>
+            (
+                fieldName,
+                dict,
+                this->patch().size()
+            )
+        );
+
+        interpolateField = false;
+        return tFld;
+    }
+    else
+    {
+        interpolateField = true;
+        return interpolateBoundaryData<Type>(fieldName);
+    }
+}
+
+
+template<class Type>
+Foam::tmp<Foam::Field<Type>>
+Foam::turbulentDigitalFilterInletFvPatchVectorField::interpolateBoundaryData
+(
+    const word& fieldName
+) const
+{
+    const word& patchName = this->patch().name();
+
+    fileName valsFile
+    (
+        fileHandler().filePath
+        (
+            fileName
+            (
+                this->db().time().path()
+               /this->db().time().caseConstant()
+               /"boundaryData"
+               /patchName
+               /"0"
+               /fieldName
+            )
+        )
+    );
+
+    autoPtr<ISstream> isPtr
+    (
+        fileHandler().NewIFstream
+        (
+            valsFile
+        )
+    );
+
+    Field<Type> vals(isPtr());
+
+    Info<< "Turbulent DFM/FSM patch " << patchName
+        << ": Interpolating field " << fieldName
+        << " from " << valsFile << endl;
+
+    return patchMapper().interpolate(vals);
+}
+
+
+template<class Form, class Type>
+Form Foam::turbulentDigitalFilterInletFvPatchVectorField::generateRandomSet
+(
+    const label len
+)
+{
+    Form randomSet(len);
+
+    std::generate
+    (
+        randomSet.begin(),
+        randomSet.end(),
+        [&]{return rndGen_.GaussNormal<Type>();}
+    );
+
+    return randomSet;
+}
+
+// ************************************************************************* //