Module fv_options 

Layer 3 — optional source terms attached to finite-volume equations, OpenFOAM’s fvOptions (Foundation fvModels) mechanism. Optional source terms added to finite-volume equations — OpenFOAM’s fvOptions mechanism.

What this is for

A solver assembles a fixed equation — momentum, energy, a transported scalar. Real cases then need extra terms in it that the solver itself knows nothing about: a heat source in one region, a porous drag in another, a phase-change latent heat, a momentum sink representing a fan. Editing the solver for each is unworkable, so OpenFOAM lets a case attach source terms to named equations from the outside. That is fvOptions.

The pattern is the same everywhere it appears:

solve( ddt(rho, U) + div(phi, U) - laplacian(mu, U) == fvModels.source(rho, U) );

The solver names the equation; the case decides what, if anything, is added to it.

A note on the name

What ESI OpenFOAM (openfoam.com) calls fvOptions, the OpenFOAM Foundation (openfoam.org) split into fvModels — terms that add sources to an equation — and fvConstraints — terms that constrain a solution, such as fixing a value in a cell set. This port follows the Foundation split, because the vendored reference tree is the Foundation one, but the module is named fv_options because that is the name most users will search for. FvModel is the source half; constraints are not yet ported.

Why this lives in outram-foam-basic-lib

It operates directly on FvMatrix, and every solver crate needs it — the multiphase, turbulence and application layers all assemble equations that a case may want to add to. Putting it in a solver crate would make it unavailable to the others. This mirrors OpenFOAM’s own dependency position, where fvOptions/fvModels sits directly on finiteVolume.

Sign convention, and the trap in it

Sources are added to the right-hand side, i.e. the equation reads ddt(...) + div(...) == source. A positive scalar source therefore increases the solved quantity.

Internally an FvMatrix stores the system as A·φ = b, so a right-hand side contribution goes into source, while an implicit contribution proportional to φ goes onto the diagonal with the opposite sign. That asymmetry is the classic way to get a source term backwards, so FvModel never asks a caller to place terms by hand: add_source_scalar and add_source_vector do the placement, and the individual models express themselves as an explicit part and an implicit coefficient.

Cell selection

Every model applies over a CellSelection — the whole mesh, or a named subset. This is upstream’s cellSetOption/fvCellZone. Selections hold their cell list behind an Arc, per the workspace rule against lifetime parameters, so sharing one selection between several models is free.

Structs

EquationField

Which equation a source term is being applied to.

FvModels

A collection of source terms, applied together to an equation.

SemiImplicitSource

A constant source term with an explicit and an implicit part.

SolidificationMelting

Solidification and melting of a pure or eutectic material.

SolidificationMeltingCoefficients

Material and numerical coefficients of the melting model.

SolidificationPorosity

Simple solidification as a porous blockage — upstream porosityModels::solidification.

SourceContribution

The explicit and implicit halves of a source term, per cell.

TemperatureTable

A monotone-in-temperature lookup table with linear interpolation and end-clamping.

VofSolidificationMelting

Solidification and melting of the condensed phase of a VoF simulation.

Enums

CellSelection

The set of cells a source term acts on.

FvModel

One optional source term.

MomentumEquationForm

Which momentum equation the drag is being added to.