Enum DeltaCoeff 

pub enum DeltaCoeff {
    Orthogonal,
    NonOrthogonal,
}

Which face-to-face distance the Laplacian divides by — OpenFOAM’s choice of deltaCoeffs versus nonOrthDeltaCoeffs.

This selects the implicit coefficient only. It says nothing about the explicit deferred correction, which lives in laplacian_corrected and is orthogonal to this choice. Together the two reproduce OpenFOAM’s three snGradSchemes entries:

OpenFOAM snGradSchemes	DeltaCoeff	explicit correction
orthogonal	Orthogonal	none
uncorrected	NonOrthogonal	none
corrected	NonOrthogonal	full (laplacian_corrected)

Why the distinction matters

uncorrected is not “the orthogonal scheme”. It still projects the cell-to-cell vector onto the face normal; it merely drops the explicit term. Treating the two as the same under-estimates every face conductance by 1/cos(theta), theta being the face’s non-orthogonality angle — silently, and with no residual to reveal it. Measured on the GeN-Foam 2D_MSFR neutronics mesh (whose fvSchemes asks for uncorrected), that is 1.7 % on the interior faces and up to 12 % on the boundary patches, worth +580 pcm in k_eff.

Variants

Orthogonal

1/|d| — OpenFOAM’s deltaCoeffs, exact only on an orthogonal mesh.

The default, so that every existing caller keeps its behaviour bit-for-bit.

NonOrthogonal

1/max(n . d, 0.05 |d|) — OpenFOAM’s nonOrthDeltaCoeffs, the projection of the cell-to-cell vector onto the face normal.

On a boundary face OpenFOAM first replaces d = Cf - C_P by its patch-normal component n (n . d) (fvPatch::delta()), which makes the coefficient 1/(n . d) there.

Implementations

impl DeltaCoeff

pub fn interior_delta(self, mesh: &FvMesh, face: usize) -> f64

The distance [m] this scheme divides by on internal face face.

The reciprocal is OpenFOAM’s deltaCoeffs/nonOrthDeltaCoeffs entry for that face. Exposed so a caller that builds its own boundary or face coefficient can divide by exactly the same length the Laplacian does — a Robin condition whose weight uses a different one is silently wrong by 1/cos(theta).

pub fn boundary_delta(self, mesh: &FvMesh, face: usize) -> f64

The distance [m] this scheme divides by on boundary face face (a global face index, patch.start + i).

See Self::interior_delta for why a caller would want this.

Trait Implementations

impl Clone for DeltaCoeff

fn clone(&self) -> Self

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for DeltaCoeff

impl Debug for DeltaCoeff

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for DeltaCoeff

fn default() -> Self

Returns the “default value” for a type.

impl Eq for DeltaCoeff

impl PartialEq for DeltaCoeff

fn eq(&self, other: &Self) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for DeltaCoeff