Docs

Set gradient to zero boundary condition type

The set gradient to zero boundary condition type prescribes the gradient of a field on a boundary to 0. Typical use cases are:

  • Outlets (of pipes etc.)

    The gradient for the velocity field or transported quantities (such as turbulent kinetic energy or dissipation rate) are often set to 0.

  • Adiabatic walls

    The temperature gradient is set to 0 on walls that do not conduct heat (adiabatic walls)

  • Walls

    The pressure gradient is often set to 0.

Since the zero gradient boundary condition implicitly contains all required values (the gradient is set to 0), no values must be set.

Zero gradient boundary condition for OPENFOAM®

Zero gradient boundary condition for OPENFOAM® simulations

An example of a zero gradient boundary condition for OPENFOAM® simulations where the velocity gradient is set to zero.

In the input file, the depicted boundary condition will look similar to the following:

wall
{
    type            zeroGradient;
}

Mathematically, the boundary condition can be formulated as

\[\frac{\partial \vec{U}}{\partial \vec{x}}\bigg|_{\Gamma} = 0\]

where \(\Gamma\) represents the boundary.