Corrected the handling of reverse-flow and forced-flow.

src/finiteVolume/fields/fvPatchFields/derived/fan/fanFvPatchFields.C

@@ -29,19 +29,18 @@ License
 #include "volFields.H"
 #include "surfaceFields.H"
 
-// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+// * * * * * * * * * * * * * * Static Data Members * * * * * * * * * * * * * //
 
 namespace Foam
 {
-
-// * * * * * * * * * * * * * * Static Data Members * * * * * * * * * * * * * //
-
     makePatchTypeField(fvPatchScalarField, fanFvPatchScalarField);
+}
 
+// * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
 
 //- Specialisation of the jump-condition for the pressure
 template<>
-void fanFvPatchField<scalar>::updateCoeffs()
+void Foam::fanFvPatchField<Foam::scalar>::updateCoeffs()
 {
     if (updated())
     {
@@ -58,27 +57,33 @@ void fanFvPatchField<scalar>::updateCoeffs()
         const fvsPatchField<scalar>& phip =
             patch().patchField<surfaceScalarField, scalar>(phi);
 
-        scalarField Un =
+        scalarField Un = max
+        (
             scalarField::subField(phip, size()/2)
-           /scalarField::subField(patch().magSf(), size()/2);
+           /scalarField::subField(patch().magSf(), size()/2),
+            0.0
+        );
 
         if (phi.dimensions() == dimDensity*dimVelocity*dimArea)
         {
-            Un /= patch().lookupPatchField<volScalarField, scalar>("rho");
+            Un /=
+                scalarField::subField
+                (
+                    patch().lookupPatchField<volScalarField, scalar>("rho"),
+                    size()/2
+                );
         }
 
         for(label i=1; i<f_.size(); i++)
         {
             jump_ += f_[i]*pow(Un, i);
         }
+
+        jump_ = max(jump_, 0.0);
     }
 
     jumpCyclicFvPatchField<scalar>::updateCoeffs();
 }
 
 
-// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
-
-} // End namespace Foam
-
 // ************************************************************************* //