The Transition SST model (also known as the 
-
model) is based on the coupling of the SST 
transport equations with two other transport equations, one for the
intermittency and one for the transition onset criteria, in terms of momentum-thickness Reynolds
number. An ANSYS empirical correlation (Langtry and Menter) has been developed to cover standard
bypass transition as well as flows in low freestream turbulence environments.
In addition, a very powerful option has been included to allow you to enter your own user-defined empirical correlation, which can then be used to control the transition onset momentum thickness Reynolds number equation.
Note the following limitations:
The Transition SST model is only applicable to wall-bounded flows. Like all other engineering transition models, the model is not applicable to transition in free shear flows. The model will predict free shear flows as fully turbulent.
The Transition SST model is not Galilean invariant and should therefore not be applied to surfaces that move relative to the coordinate system for which the velocity field is computed; for such cases the Intermittency Transition model should be used instead.
The Transition SST model is designed for flows with a defined nonzero freestream velocity (that is, the classical boundary layer situation). It is not suitable for fully developed pipe / channel flows where no freestream is present. For the same reason, it is also not suitable for wall jet flows. For such scenarios, the Intermittency Transition model should be used instead. Note, however, that it might be necessary to adjust the Intermittency Transition model for such flows by modifying the underlying correlations.
The Transition SST model has not been calibrated in combination with other physical effects that affect the source terms of the turbulence model, such as:
buoyancy
multiphase turbulence
To learn how to set up the Transition SST model, see Setting Up the Transition SST Model (in the User's Guide).