The Rahman-Agarwal-Siikonen (RAS) Turbulence model is a one-equation eddy viscosity model based on closure. The R-transport equation along with the Bradshaw and other empirical relations are used to solve for the turbulent viscosity. A damping function, , is used to represent the kinematic blocking by the wall. To avoid defining a wall distance, a Helmholtz-type elliptic relaxation equation is used for . The model has been validated against a few well-documented flow cases, yielding predictions in good agreement with DNS and experimental data.
The turbulent eddy viscosity is given by
The R-transport equation is