The (intermittency) transition model is a further development based on the - transition model (referred to as the Transition SST model in Ansys Fluent, as described in Transition SST Model). The transition model solves only one transport equation for the turbulence intermittency , and avoids the need for the second equation of the - transition model. The transition model has the following advantages over the - transition model:
It reduces the computational effort (by solving one transport equation instead of two).
It avoids the dependency of the equation on the velocity . This makes the transition model Galilean invariant. It can therefore be applied to surfaces that move relative to the coordinate system for which the velocity field is computed.
The model has provisions for crossflow instability that are not available for the - or the - transition model.
The model formulation is simple and can be fine-tuned based on a small number of user parameters.
Like the - transition model, the transition model is based strictly on local variables. The transition model is also only available in combination with the following turbulence models:
BSL - model
SST - model
Scale-Adaptive Simulation with BSL or SST
Detached Eddy Simulation with BSL or SST
Shielded Detached Eddy Simulation (SDES) with BSL or SST
Stress-Blended Eddy Simulation (SBES) with BSL or SST
Note the following limitations:
The transition 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 model has only been calibrated for classical boundary layer flows. Application to other types of wall-bounded flows is possible, but might require a modification of the underlying correlations.
The transition 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