The full gradient of a property \( Q \) at a face can can be interpolated from the cell-based gradient. The surface-normal contribution is then represented by:
\[ \snGrad Q = \vec{n} \dprod \left( \grad Q \right)_f \]
where \( \vec{n} \) is the face unit normal. The stencil for the gradient calculation at the face, \( f \), between cells P and N is described by the following figure: where the vector \( \vec{d} \) joins the two cell centres. A variety of schemes are available that differ in their application based on the angle, \( \theta \), between the \( \vec{d} \) and \( \vec{n} \) vectors, representing the degree of non-orthogonality.
Surface-normal gradient schemes are specified in the fvSchemes file under the snGradSchemes
sub-dictionary using the syntax:
Source code:
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