wallDist: Added nRequired option to the wallDist dict

src/finiteVolume/fvMesh/wallDist/patchDistMethods/Poisson/PoissonPatchDistMethod.H

@@ -58,6 +58,10 @@ Description
         wallDist
         {
             method Poisson;
+
+            // Optional entry enabling the calculation
+            // of the normal-to-wall field
+            nRequired false;
         }
     \endverbatim
     Also the solver specification for yPsi is required in fvSolution, e.g.

src/finiteVolume/fvMesh/wallDist/patchDistMethods/advectionDiffusion/advectionDiffusionPatchDistMethod.C

@@ -99,7 +99,10 @@ bool Foam::patchDistMethods::advectionDiffusion::correct
         (
             "ny",
             mesh_.time().timeName(),
-            mesh_
+            mesh_,
+            IOobject::NO_READ,
+            IOobject::NO_WRITE,
+            false
         ),
         mesh_,
         dimensionedVector("ny", dimless, vector::zero),

src/finiteVolume/fvMesh/wallDist/patchDistMethods/advectionDiffusion/advectionDiffusionPatchDistMethod.H

@@ -58,6 +58,10 @@ Description
         {
             method advectionDiffusion;
 
+            // Optional entry enabling the calculation
+            // of the normal-to-wall field
+            nRequired false;
+
             advectionDiffusionCoeffs
             {
                 method    Poisson;

src/finiteVolume/fvMesh/wallDist/patchDistMethods/meshWave/meshWavePatchDistMethod.H

@@ -39,6 +39,10 @@ Description
         wallDist
         {
             method meshWave;
+
+            // Optional entry enabling the calculation
+            // of the normal-to-wall field
+            nRequired false;
         }
     \endverbatim
 

src/finiteVolume/fvMesh/wallDist/wallDist/wallDist.C

@@ -34,6 +34,37 @@ namespace Foam
 }
 
 
+// * * * * * * * * * * * * * Private Member Functions  * * * * * * * * * * * //
+
+void Foam::wallDist::constructn() const
+{
+    n_ = tmp<volVectorField>
+    (
+        new volVectorField
+        (
+            IOobject
+            (
+                "nWall",
+                mesh().time().timeName(),
+                mesh()
+            ),
+            mesh(),
+            dimensionedVector("nWall", dimless, vector::zero),
+            patchDistMethod::patchTypes<vector>(mesh(), pdm_->patchIDs())
+        )
+    );
+
+    const labelHashSet& patchIDs = pdm_->patchIDs();
+    const fvPatchList& patches = mesh().boundary();
+
+    forAllConstIter(labelHashSet, patchIDs, iter)
+    {
+        label patchi = iter.key();
+        n_().boundaryField()[patchi] == patches[patchi].nf();
+    }
+}
+
+
 // * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
 
 Foam::wallDist::wallDist(const fvMesh& mesh)
@@ -60,33 +91,16 @@ Foam::wallDist::wallDist(const fvMesh& mesh)
         dimensionedScalar("yWall", dimLength, SMALL),
         patchDistMethod::patchTypes<scalar>(mesh, pdm_->patchIDs())
     ),
-    n_(NULL)
-{
-    // Temporarily always construct n
-    // until the demand-driven interface is complete
-    n_ = tmp<volVectorField>
+    nRequired_
     (
-        new volVectorField
-        (
-            IOobject
-            (
-                "nWall",
-                mesh.time().timeName(),
-                mesh
-            ),
-            mesh,
-            dimensionedVector("nWall", dimless, vector::zero),
-            patchDistMethod::patchTypes<vector>(mesh, pdm_->patchIDs())
-        )
-    );
-
-    const labelHashSet& patchIDs = pdm_->patchIDs();
-    const fvPatchList& patches = mesh.boundary();
-
-    forAllConstIter(labelHashSet, patchIDs, iter)
+        static_cast<const fvSchemes&>(mesh).subDict("wallDist")
+       .lookupOrDefault<Switch>("nRequired", false)
+    ),
+    n_(volVectorField::null())
+{
+    if (nRequired_)
     {
-        label patchi = iter.key();
-        n_().boundaryField()[patchi] == patches[patchi].nf();
+        constructn();
     }
 
     movePoints();
@@ -101,6 +115,24 @@ Foam::wallDist::~wallDist()
 
 // * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
 
+const Foam::volVectorField& Foam::wallDist::n() const
+{
+    if (isNull(n_()))
+    {
+        WarningIn("Foam::wallDist::n()")
+            << "n requested but 'nRequired' not specified in the wallDist "
+               "dictionary" << nl
+            << "    Recalculating y and n fields." << endl;
+
+        nRequired_ = true;
+        constructn();
+        pdm_->correct(y_, n_());
+    }
+
+    return n_();
+}
+
+
 bool Foam::wallDist::movePoints()
 {
     if (pdm_->movePoints())

src/finiteVolume/fvMesh/wallDist/wallDist/wallDist.H

@@ -26,7 +26,24 @@ Class
 
 Description
     Interface to run-time selectable methods to calculate the distance-to-wall
-    field.
+    and normal-to-wall fields.
+
+    Example of the wallDist specification in fvSchemes:
+    \verbatim
+        wallDist
+        {
+            method meshWave;
+
+            // Optional entry enabling the calculation
+            // of the normal-to-wall field
+            nRequired false;
+        }
+    \endverbatim
+
+SeeAlso
+    Foam::patchDistMethod::meshWave
+    Foam::patchDistMethod::Poisson
+    Foam::patchDistMethod::advectionDiffusion
 
 SourceFiles
     wallDist.C
@@ -57,17 +74,23 @@ class wallDist
     // Private data
 
         //- Run-time selected method to generate the distance-to-wall field
-        autoPtr<patchDistMethod> pdm_;
+        mutable autoPtr<patchDistMethod> pdm_;
 
         //- Distance-to-wall field
-        volScalarField y_;
+        mutable volScalarField y_;
 
-        //- Distance-to-wall field
-        tmp<volVectorField> n_;
+        //- Flag to indicate if the distance-to-wall field is required
+        mutable bool nRequired_;
+
+        //- Normal-to-wall field
+        mutable tmp<volVectorField> n_;
 
 
     // Private Member Functions
 
+        //- Construct the normal-to-wall field as required
+        void constructn() const;
+
         //- Disallow default bitwise copy construct
         wallDist(const wallDist&);
 
@@ -100,10 +123,7 @@ public:
         }
 
         //- Return reference to cached normal-to-wall field
-        const volVectorField& n() const
-        {
-            return n_();
-        }
+        const volVectorField& n() const;
 
         //- Update the y-field when the mesh moves
         virtual bool movePoints();