4.8.1. Overview

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