For the -based RSM, can be modeled by the generalized gradient-diffusion model of Daly and Harlow  [132]:

(4–227)

However, this equation can result in numerical instabilities, so it has been simplified in Ansys Fluent to use a scalar turbulent diffusivity as follows  [371]:

(4–228)

The turbulent viscosity, , is computed using Equation 4–259 for the -based RSM.

Lien and Leschziner  [371] derived a value of by applying the generalized gradient-diffusion model, Equation 4–227, to the case of a planar homogeneous shear flow. Note that this value of is different from that in the standard and realizable - models, in which .

For the -based Reynolds stress models, Equation 4–228 is also used to model the turbulent diffusive transport, and the turbulent viscosity is calculated from Equation 4–74.

The stress-omega model sets to a value of 2.0, whereas the stress-BSL model blends the value between the inner region (=2.0) and outer region (=1.0) using the blending function from Equation 4–107:

(4–229)