•Select Specify turbulence variables to enter values or expressions for the Turbulent

kinetic energy k0 (SI unit: m2/s2), and the Turbulent dissipation rate 0

(SI unit: m2/s3).

For recommendations of physically sound values see Inlet Values for the

Turbulence Length Scale and Intensity.

See Also

For the Turbulent Flow, Spalart-Allmaras interface, enter the value 0 for the Undamped turbulent kinematic viscosity (SI unit: m2/s).

Boundary Stress

The Boundary Stress node adds a boundary conditions that represent a very general class of conditions also known as traction boundary conditions.

B O U N D A R Y S E L E C T I O N

From the Selection list, choose the boundaries to apply boundary stress.

B O U N D A R Y C O N D I T I O N

Select a Boundary condition for the boundary stress—General stress (the default),

Normal stress, or Normal stress, normal flow.

• More Open Boundary Conditions for the Turbulent Flow Interfaces

See Also

Normal Stress

If Normal stress f0 (SI unit: N/m2) is selected, enter a value or expression.

• Inlet

See Also

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General Stress

If General stress is selected, enter the components of the Stress F (SI unit: N/m2).The total stress on the boundary is set equal to a given stress F:

– pI + u + u T n = F

using the compressible and the incompressible formulation respectively.

This boundary condition implicitly sets a constraint on the pressure that for 2D flows is

If un n is small, Equation 4-2 states that p n·F.

Normal Stress, Normal Flow

If Normal stress, normal flow is selected, enter the magnitude of the Normal stress f0

(SI unit: N/m2).

In addition to the stress condition set in the Normal Stress condition, this condition also prescribes that there must be no tangential velocities on the boundary:

using the compressible and the incompressible formulation respectively.

This boundary condition also implicitly sets a constraint on the pressure that for 2D flows is

130 | C H A P T E R 4 : S I N G L E - P H A S E F L O W B R A N C H

If un n is small, Equation 4-3 states that p f0.

This boundary condition is not available if the Use memory-efficient form check box is selected (click the Show button () and select Advanced Physics Interface Options>Advanced Settings to display the section) on any

Note

single-phase flow interface Settings page.

M O R E B O U N D A R Y S T R E S S C O N D I T I O N S F O R T H E T U R B U L E N T F L O W

I N T E R F A C E S

Turbulent Boundary Type

Select a Turbulent boundary type to apply to the turbulence variables—Open boundary,

Inlet, or Outlet.

Open Boundary

If Open boundary is selected, then expect parts of the boundary to be an outlet and parts of the boundary to be an inlet. Under Exterior turbulence, enter values for the turbulence variables, which are used on the parts of the boundary where u · n 0, that is, where flow enters the computational domain. These settings are the same as described in More Open Boundary Conditions for the Turbulent Flow Interfaces.

Inlet

Select Inlet when it is expected that the whole boundary is an inlet. Under Exterior turbulence, the same options to specify turbulence variables are available for the Open boundary option is available. The difference is that they, for the Inlet option, apply to the whole boundary. These settings are the same as described in More Open Boundary Conditions for the Turbulent Flow Interfaces.

Outlet

Select Outlet when it is expected that the whole boundary is an outflow. Homogeneous Neumann conditions are applied to the turbulence variables (that is, for k and )

˜ n = 0

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