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.

Overview

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

Basic boundary conditions

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

Turbulent flow boundary conditions

• RAS boundary conditions

Thermophysical boundary conditions

• Thermophysical boundary conditions

Wall-functions

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

Wall-functions

• wall functions

Thermal wall-functions for incompressible flow

• Incompressible turbulence wall functions

Thermal wall-functions for compressible flow

• Compressible turbulence wall functions

Typical usage for pressure-velocity systems

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