
For flows using one of the

models, one of the

models, or the RSM, the converged solutions or (for unsteady calculations) the solutions after a sufficiently long time has elapsed should be independent of the initial values for
and
(or
and
). For better convergence, however, it is beneficial to use a reasonable initial guess for
and
(or
and
).
In general, it is recommended that you start from a fullydeveloped state of turbulence. When you use the enhanced wall treatment for the  models or the RSM, it is critically important to specify fullydeveloped turbulence fields. Guidelines are provided below.
You should specify an initial guess for so that the resulting eddy viscosity ( ) is sufficiently large in comparison to the molecular viscosity. In fullydeveloped turbulence, the turbulent viscosity is roughly two orders of magnitude larger than the molecular viscosity. From this, you can compute .
(12.151) 
where is the turbulent viscosity ratio which can be prescribed at the inlet and then used for the domain initialization.
Note that, for the RSM, Reynolds stresses are initialized automatically using Equations 12.141 and 12.142.