The Realizable k-ε Turbulence Model
The Realizable k-ε turbulence model (Ref. 14) is an extension to the standard k-ε model with built-in realizability conditions,
(3-87)
The transport equation for the turbulent kinetic energy is the same as for the standard k-ε model, Equation 3-77, while Equation 3-88 is solved for the turbulent dissipation rate,
(3-88)
where,
(3-89)
The turbulent viscosity is given by Equation 3-76, but Cμ is not constant for the realizable k-ε model,
(3-90)
with,
(3-91)
and,
(3-92)
Sij and Ωij are the mean strain- and rotation-rate tensors respectively. The default constants for the Realizable k-ε model are,
(3-93)
Model Properties
Compared to the standard k-ε model, the realizable k-ε model yields better predictions for certain flows. One example is the round jet, for which the standard k-ε model overestimates the spreading rate. In general, since the realizability conditions in Equation 3-87 are approached asymptotically, the turbulence characteristics are more consistent than for the standard k-ε model. The realizable k-ε model uses wall functions and has the same default initial conditions and scalings as the standard k-ε model (see Wall Functions, Initial Values and Scaling for Time-Dependent Simulations).