Boundary Conditions

Boundary Conditions are required to 'close' the simulation problem. Careful attention should be applied to their selection so as to create a well-posed system of equations, which can be solved numerically.

The set of available Boundary Conditions comprise of basic, turbulent and thermophysical types.

- Constraint boundary Conditions
- Inlet boundary Conditions
- Outlet boundary Conditions
- Generic boundary Conditions
- Coupled boundary Conditions
- Wall boundary Conditions

Wall-functions in OpenFOAM are modelled as boundary conditions, applied to the viscosity for momentum, and thermal diffusivity for energy.

Wall-functions

Thermal wall-functions for incompressible flow

Thermal wall-functions for compressible flow

The choice as to the most appropriate set of boundary conditions is dictated by the type of flow problem. In many cases, multiple possible selections exist; the following tables offer suggestions for subsonic flow.

subsonic inlet (flow specified):

Variable | Symbol | Type |
---|---|---|

`pressure` | p | zeroGradient |

`velocity` | U | fixedValue |

`transported` property | - | fixedValue |

`derived` property | - | calculated or zeroGradient |

subsonic outlet:

Variable | Symbol | Type |
---|---|---|

`pressure` | p | fixedValue |

`velocity` | U | inletOutlet or pressureInletOutletVelocity |

`transported` property | - | inletOutlet |

`derived` property | - | calculated or zeroGradient |

wall (impermeable, non-slip):

Variable | Symbol | Type |
---|---|---|

`pressure` | p | zeroGradient |

`velocity` | U | fixedValue |

`transported` property | - | fixedValue |

`derived` property | - | calculated or zeroGradient |

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