There are two main differences between the realizable κ-ε model and the standard κ-ε model:
- In the realizable model, there’s an alternative formulation for turbulent viscosity.
- Modified transport equations for the dissipation rate, ε, are derived directly from the exact equation for the square average of vorticity fluctuations.
The term “realizable” implies that the model satisfies certain mathematical constraints on Reynolds stresses, consistent with the physical phenomena of turbulent flow.
One drawback of the realizable κ-ε model is that its computations produce inaccurate turbulent viscosity when the computational domain contains both rotating and stationary fluid zones simultaneously (such as in cases involving multiple reference frames or rotating sliding meshes).
This issue arises because this model accounts for the effects of rotational averaging when defining turbulent viscosity. However, this problem does not arise in a single moving reference frame.
The equations below represent the transport equations of the realizable κ-ε model:
(6.10)
And
(6.11)
Where,
In the equations above, the descriptions of variables aren’t significantly different from the standard model, although some constants might differ.
Reference: