What Is the Two-Layer Approach?

The two-layer approach, first suggested by Rodi [37], is an alternative to the low-Reynolds number approach that allows the K-Epsilon model to be applied in the viscous sublayer. In this approach, the computation is divided into two layers. In the layer adjacent to the wall, the turbulent dissipation rate and the turbulent viscosity are specified as functions of wall distance. The values of specified in the near-wall layer are blended smoothly with the values computed from solving the transport equation far from the wall. The equation for the turbulent kinetic energy is solved in the entire flow. This explicit specification of and is arguably no less empirical than the damping function approach, and the results are often as good or better. In STAR-CCM+, the two-layer formulations will work with either low-Reynolds number type meshes or wall-function type meshes .

Several two-layer formulations have bee proposed, and two have been implemented in STAR-CCM+, one for shear-driven flows and one for buoyancy-driven flows.