surface gradient
Hi,
in the openFoam programmer's guide on P40 there is an explanation for the surface normal gradient: surfaceScalarField gradnq=fvc::snGrad(q); which gives (grad(q))_f*n_f. I want to calculate only grad(q)_f , it should be something like: surfaceVectorField gradq=????????(q); Maybe someone has an useful idea, thanks, M. 
Hi Martin,
Isn't that simply fvc::grad()? Or am I missing the point of your question? 
Hi Gijs,
Thanks for your reply, fvc::grad is using the Gauss integral theory to calculate the gradient at the cell center – so it's not what I was seeking for. As I can see now, the gradient at the face center will not be calculated within the snGrad calculation. The surface normal Gradient (for an orthogonal mesh) will be calculated directly by g[faceI]=(v[neighbour[faceI]]v[owner[faceI]])/d (This can be seen in src/finiteVolume/finiteVolume/snGradSchemes/snGradScheme.C on line 142.) The calculation applies to internal Faces. For fully understanding I would like to know how the snGrad is calculated on boundary Faces. Maybe you (or someone else) can tell me where I can find the calculation for snGrad on the boundary faces. Thanks, Martin. 
Hi Martin,
Right, I see :). I am not entirely sure, but from the discussion here I gather that $WM_PROJECT_DIR/applications/utilities/postProcessing/wall/wallGradU.C contains some hints. In particular, this might be interesting: Code:
forAll(wallGradU.boundaryField(), patchi) 
Hi Gijs,
I think in your example snGrad() will also be used as a member function of the boundary field (patchfield). I think I have found the calculation in src/finiteVolume/fields/fvPatchFields/fvPatchField/fvPatchField.C in line 180: // Return gradient at boundary template<class Type> Foam::tmp<Foam::Field<Type> > Foam::fvPatchField<Type>::snGrad() const { return (*this  patchInternalField())*patch_.deltaCoeffs(); } Now I will try to find out if there is a nonorthogonal mesh correction of the surface normal gradient on the boundary. M. 

Hi Alicja,
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Hi Gijs!
Thx for your Answer! I have a further question about fvc:: (alpha). I use the most simple discretisation scheme, 'Gauss linear'. I took a look at interFoam solver. I want to know, how is the curvature calculated. I have this to discretise: See interfaceProperties.C To calculate : firstly i calculate fvc::grad(alpha). So i 've run debug modus and i was in this class, gaussGrad.C firstly at line 134 and then at line 55. You see at the line 113 multiplikation with . Which term is the correct one, (1) or (2)? (1) fvc::grad(alpha) http://www.cfdonline.com/Forums/vbL...e3de52d31.gif or (2) fvc::grad(alpha) http://www.cfdonline.com/Forums/vbL...0d74d68e1.gif ? I think the term (1) is the correct one. Perhaps later when i build the matrix or equation system i do multiply with . See fvMatrix.C at the line 1448. But i'm not sure. Greetings, Alicja 
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the first one is true but not with dot product(.) . because it's for divergence not grad. 
snGradient
hi
i need the formulation of crrected snGradien scheme for laplacian(Q) can help me? 
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