functionObjects::fluidMaxDeltaT: New functionObject to set the maximum Courant number and time-step

at Function1s of time.

Underlying this new functionObject is a generalisation of the handling of the
maximum time-step in the modular solvers to allow complex user-specification of
the maximum time-step used in a simulation, not just the time-dependency
provided by fluidMaxDeltaT but functions of anything in the simulation by
creating a specialised functionObject in which the maxDeltaT function is
defined.

The chemical and combustion time-scale functionObjects adjustTimeStepToChemistry
and adjustTimeStepToCombustion have been updated and simplified using the above
mechanism.

applications/modules/fluidSolver/functionObjects/fluidMaxDeltaT/fluidMaxDeltaT.C

@@ -0,0 +1,113 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     | Website:  https://openfoam.org
+    \\  /    A nd           | Copyright (C) 2023 OpenFOAM Foundation
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+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 "fluidMaxDeltaT.H"
+#include "fluidSolver.H"
+#include "addToRunTimeSelectionTable.H"
+
+// * * * * * * * * * * * * * * Static Data Members * * * * * * * * * * * * * //
+
+namespace Foam
+{
+namespace functionObjects
+{
+    defineTypeNameAndDebug(fluidMaxDeltaT, 0);
+
+    addToRunTimeSelectionTable
+    (
+        functionObject,
+        fluidMaxDeltaT,
+        dictionary
+    );
+}
+}
+
+
+// * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
+
+Foam::functionObjects::fluidMaxDeltaT::fluidMaxDeltaT
+(
+    const word& name,
+    const Time& runTime,
+    const dictionary& dict
+)
+:
+    fvMeshFunctionObject(name, runTime, dict)
+{
+    read(dict);
+}
+
+
+// * * * * * * * * * * * * * * * * Destructor  * * * * * * * * * * * * * * * //
+
+Foam::functionObjects::fluidMaxDeltaT::~fluidMaxDeltaT()
+{}
+
+
+// * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
+
+bool Foam::functionObjects::fluidMaxDeltaT::read(const dictionary& dict)
+{
+    fvMeshFunctionObject::read(dict);
+
+    maxCoPtr_ = Function1<scalar>::New("maxCo", dict);
+    maxDeltaTPtr_ = Function1<scalar>::New("maxDeltaT", dict);
+
+    return true;
+}
+
+
+bool Foam::functionObjects::fluidMaxDeltaT::execute()
+{
+    return true;
+}
+
+
+bool Foam::functionObjects::fluidMaxDeltaT::write()
+{
+    return true;
+}
+
+
+Foam::scalar Foam::functionObjects::fluidMaxDeltaT::maxDeltaT() const
+{
+    scalar deltaT =
+        time_.userTimeToTime(maxDeltaTPtr_().value(time_.userTimeValue()));
+
+    const scalar CoNum =
+        mesh_.lookupObject<solvers::fluidSolver>(solver::typeName).CoNum;
+
+    if (CoNum > small)
+    {
+        const scalar maxCo = maxCoPtr_().value(time_.userTimeValue());
+
+        deltaT = min(deltaT, maxCo/CoNum*time_.deltaTValue());
+    }
+
+    return deltaT;
+}
+
+
+// ************************************************************************* //