Boundary Conditions
The boundary condition parameters for the
Turbulence module apply to
Boundaries in the Flow Analysis Tree. The options also apply to interfaces for which the
Flow module is blanked on one side of the interface, creating a
Boundary.
The boundary conditions appear in the Properties panel when you select a boundary in the Flow Analysis Tree under General Boundaries.
Wall
The
Wall boundary condition for
Turbulence corresponds to a solid boundary. You can select the
Wall boundary condition for
Turbulence for a selected boundary or interface under the
Turbulence module in the Properties panel. The
Wall boundary condition is the default condition for the
Turbulence module when you select a wall for the
Flow module. The effect of wall roughness is modeled using the
Wall Roughness Model. The
Output available with the
Wall boundary condition include
Area,
Normal, and
Y Plus.
• Wall Function
You can select the various Wall Function for turbulence nearwall treatment for a selected Wall under the Turbulence module in the Flow Analysis Tree and implement in the Properties panel. The available wall functions are listed below:
◦ Standard
◦ Nonequilibrium(Kim)
◦ Unified(Shih)
The first Interior Node is placed at a distance from the wall which corresponds to whether a low Reynolds number approach or a high Reynolds number approach is used. Using the low Reynolds number approach (LRN) you place the first Interior node within the viscous sublayer and the outward cell face within the buffer layer. This approach requires a very fine mesh near the wall. Using the high reynolds number approach (HRN) you place the first interior node within the inertial sublayer. This approach requires a coarser mesh near the wall.
• Wall Roughness Model
You can use the
Wall Roughness Model option to make the wall shear a function of wall roughness. You can model the wall finish for the
Turbulence module as smooth or rough:
◦ Smooth
◦ Rough—Defines the desired roughness height.
Specified Pressure Outlet
Use the
Specified Pressure Outlet boundary condition to set the
turbulent kinetic energy and the
turbulent energy dissipation rate at an opening where the flow can exit the domain. You can specify the
Outlet condition and associated parameters for a selected boundary under the
Turbulence module in the Properties panel. The
turbulent kinetic energy and the
turbulent energy dissipation rate of the fluid exiting the
Outlet are based on the internal (upwind)
turbulent kinetic energy and the
turbulent energy dissipation rate. The
turbulent kinetic energy and the
turbulent energy dissipation rate of any fluid reentering the domain are based on the
turbulent kinetic energy and the
turbulent energy dissipation rate that you specify for this boundary. The specified
turbulent kinetic energy and the
turbulent energy dissipation rate at the
Outlet can influence the internal
turbulent kinetic energy and the
turbulent energy dissipation rate by diffusion. Typically this effect is insignificant unless the outflow is very small or the
conductivity is very high (low Péclet number). The
Output available with the
Outlet boundary condition include
Area and
Normal.

Outlet is the default boundary condition for the Turbulence module when you select Specified Pressure Outlet or Resistor Capacitor boundary condition for the Flow module.

Specified Values
You can use
Specified Values as a
Turbulence boundary condition when the
turbulent kinetic energy and the
turbulent energy dissipation rate at a boundary are known or the default value is acceptable. You can specify the
Specified Values boundary option for a selected
Boundary under the
Turbulence module in the Properties panel.
Specified Values is the default boundary condition for the
Turbulence module when you select
Specified Velocity,
Specified Volumetric Flux,
Specified Total Pressure, or
Specified Pressure Inlet for the
Flow module. The
turbulent kinetic energy and the
turbulent energy dissipation rate of any fluid exiting the domain is based on the internal (upwind)
turbulent kinetic energy and the
turbulent energy dissipation rate. The
turbulent kinetic energy and the
turbulent energy dissipation rate of any fluid entering the domain are based on the
turbulent kinetic energy and the
turbulent energy dissipation rate that you specify for this boundary. The specified
turbulent kinetic energy and the
turbulent energy dissipation rate at an outlet can influence the internal
turbulent kinetic energy and the
turbulent energy dissipation rate by diffusion. Typically this effect is insignificant unless the outflow is very small or the conductivity is very high (low Péclet number).
Symmetry
The
Symmetry boundary condition for the
Turbulence module is input under the
Turbulence module in the Properties panel. Symmetry for the
Turbulence module means that there is no flux or gradient of the
turbulent kinetic energy at the boundary.
Symmetry is the default boundary condition for the
Turbulence module when you select a
Symmetry boundary condition for the
Flow module. A
Symmetry boundary condition for the
Turbulence module usually corresponds to a physical symmetry in the model, but is not necessary if the effects of this boundary condition are acceptable.
Output
The integrated quantities available as output from the
Turbulence module for the boundaries are shown in
output variables.
Interface Conditions
The
Interface attributes options and
Output for the
Turbulence module are the same as the
Boundary attributes, if the interface separates a solid and fluid. If the interface separates two solids or two fluid volumes, the Interface treatment defaults to the standard treatment for the interface between two internal cells.
The
Interface attributes for the
Turbulence module are the same as the attributes for the boundary condition if one side of the
Interface is
Blanked for flow. If the
Flow module is
Active on both sides of an interface, then the interface can only be assigned as a
Default Interface.
The Porosity is set in the Common module.