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12.20.3 Reynolds Stress Model

The specification of turbulent boundary conditions for the RSM is the same as for the other turbulence models for all boundaries except at boundaries where flow enters the domain. Additional input methods are available for these boundaries and are described here.

When you choose to use the RSM, the default inlet boundary condition inputs required are identical to those required when the $k$- $\epsilon$ model is active. You can input the turbulence quantities using any of the turbulence specification methods described in Section  7.2.2. FLUENT then uses the specified turbulence quantities to derive the Reynolds stresses at the inlet from the assumption of isotropy of turbulence:

$\displaystyle \overline{u_{i}^{'2}}$ $\textstyle =$ $\displaystyle \frac{2}{3}k \;\;\;\;\;\;\;\;\;\;\;\;\;\; (i=1,2,3)$ (12.20-1)
$\displaystyle \overline{u'_{i} u'_{j}}$ $\textstyle =$ $\displaystyle 0.0$ (12.20-2)

where $\overline{u_{i}^{'2}}$ is the normal Reynolds stress component in each direction. The boundary condition for $\epsilon$ is determined in the same manner as for the $k$- $\epsilon$ turbulence models (see Section  7.2.2). To use this method, you will select K or Turbulence Intensity as the Reynolds-Stress Specification Method in the appropriate boundary condition panel.

Alternately, you can directly specify the Reynolds stresses by selecting Reynolds-Stress Components as the Reynolds-Stress Specification Method in the boundary condition panel. When this option is enabled, you should input the Reynolds stresses directly.

You can set the Reynolds stresses by using constant values, profile functions of coordinates (see Section  7.26), or user-defined functions (see the separate UDF Manual).

Figure 12.20.1: Specifying Inlet Boundary Conditions for the Reynolds Stresses

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