and a quantity called 
, which is defined as the specific dissipation rate, that is, the dissipation rate per unit turbulent kinetic energy (
).
The K-Omega model is a two-equation model that is an alternative to the K-Epsilon model. The transport equations solved are for the turbulent kinetic energy and a quantity called , which is defined as the specific dissipation rate, that is, the dissipation rate per unit turbulent kinetic energy ().
The book by D.C. Wilcox [43] is the most comprehensive reference on the K-Omega model, discussing the origin of the model, comparing it to other models, and presenting the latest version of the model. As the originator of the K-Omega model, Wilcox touts the superiority of his model over the K-Omega model, and the superiority of the Omega transport equation over other scale equations.
One reported advantage of the K-Omega model over the K-Epsilon model is its improved performance for boundary layers under adverse pressure gradients. Perhaps the most significant advantage, however, is that it may be applied throughout the boundary layer, including the viscous-dominated region, without further modification. Furthermore, the standard K-Omega model can be used in this mode without requiring the computation of wall distance.
The biggest disadvantage of the K-Omega model, in its original form, is that boundary layer computations are very sensitive to the values of 
in the free stream. This translates into extreme sensitivity to inlet boundary conditions for internal flows, a problem that does not exist for the K-Epsilon models. The versions of the model included in STAR-CCM+ have been modified in an attempt to address this shortcoming.
There are three versions of the K-Omega model in STAR-CCM+: