The divergence of a property $$Q$$ describes the net rate at which it changes as a function of space, represented using the notation:

$\div Q$

If $$Q$$ is a vector quantity, this equates to

$\div \vec{Q} = \frac{\partial Q_x}{\partial x} + \frac{\partial Q_y}{\partial y} + \frac{\partial Q_z}{\partial z}$

## Usage🔗

Divergence schemes are specified in the fvSchemes file under the divSchemes sub-dictionary using the general syntax:

divSchemes
{
default         none;
div(Q)          Gauss <interpolation scheme>;
}


A typical use is for convection schemes, which transport a property, $$Q$$ under the influence of a velocity field $$\phi$$, specified using:

divSchemes
{
default         none;
div(phi,Q)      Gauss <interpolation scheme>;
}


The phi keyword is typically used to represent the flux (flow) across cell faces, i.e.

• volumetric flux: $$\phi = \u_f \dprod \vec{S}_f$$
• mass flux: $$\phi = \rho_f \left( \u_f \dprod \vec{S}_f \right)$$

## Options🔗

### NVD/TVD convection schemes🔗

Many of the convection schemes available in OpenFOAM are based on the TVD and NVD [PROVIDE REF] For further information, see the page invalid item schemes-divergence-nvdtvd

## Special cases🔗

Several options are available for convection schemes for certain flow cases, including for steady state, bounded scalar transport and limited schemes.

For steady state cases the bounded form can be applied:

divSchemes
{
default         none;
div(phi,Q)      bounded Gauss <interpolation scheme>;
}


This adds a linearised, implicit source contribution to the transport equation of the form

$\ddt{\u} + \div (\u \otimes \u ) - \color{red}{( \div \u ) \u} = \div ( \Gamma \grad \u ) + S_u$

i.e. it removes a component proportional to the continuity error. This acts as a convergence aid to tend towards a bounded solution as the calculation proceeds. At convergence, this term becomes zero and does not contribute to the final solution.

### Bounded scalars🔗

The limited<interpolation scheme> options bound scalar field values to user-specified limits, e.g. for the Van Leer scheme

limitedVanLeer -1 3


Many fields require bounding between 0 and 1, for which the following syntax is used:

<interpolation scheme>01


### V schemes🔗

A set of schemes for vector fields where the limiter is applied in the direction of greatest change.

## Example🔗

See this example to see the relative performance of the schemes.

## Further information🔗

See the Implementation details “implementation details” to see how the schemes are coded.