This section presents the standard, RNG, and realizable $k$- $epsilon$ models. All three models have similar forms, with transport equations for $k$ and $epsilon$. The major differences in the models are as follows:
the method of calculating turbulent viscosity
the turbulent Prandtl numbers governing the turbulent diffusion of $k$ and $epsilon$
the generation and destruction terms in the $epsilon$ equation
The transport equations, methods of calculating turbulent viscosity, and model constants are presented separately for each model. The features that are essentially common to all models follow, including turbulent production, generation due to buoyancy, accounting for the effects of compressibility, and modeling heat and mass transfer.