Gamma Transition Models

The Gamma transition model and the SA Gamma transition model are one-equation, correlation-based transition models that provide a truly local approach for the onset of transition in a turbulent boundary layer.

The Gamma transition model [381] is a simplified version of the Gamma ReTheta Transition Model and can be coupled with the SST K-Omega turbulence model. It avoids the transport equation for the transition momentum thickness Reynolds number and solves for turbulence intermittency only. Like the Gamma ReTheta model, it uses transition onset criteria in terms of the momentum thickness Reynolds number, but computes them algebraically using local variables. Furthermore, the complex formulations of the experimental correlations are simplified and the definition of the free-stream edge is omitted.

Like the Gamma ReTheta model, the Gamma transition model incorporates an optional correlation for cross-flow instabilities. However, for the Gamma Transition model, the correlation is implemented as a modification of the transition trigger function given by Eqn. (1502), which activates the production term for the transported intermittency.

The SA Gamma transition model [386] is an extension of the Gamma transition model to combine it with the Spalart-Allmaras (SA) turbulence model, including crossflow modifications and roughness induced transition effects.