The k - ω method uses two variables to determine local turbulent dissipation: the turbulent kinetic energy k and the dissipation ω :
The k - ω model provides an improved description of near-wall flows but shows weaknesses in modeling free flows. Its results strongly depend on the choice of ω values in the free flow, leading to high sensitivity to the turbulent length scale Lt.
To address this issue, the SST model (Shear Stress Transport) was developed, combining the advantages of both approaches:
- It uses the k-w model near walls for a more accurate capture of boundary layer flow.
- In free flow, it switches to the k-ε model to leverage its strengths in this region.
- The transition between the models is achieved through blending functions.
Additional improvements in the SST model include:
- A limitation of turbulent viscosity for better prediction of flow separation in adverse pressure gradients.
- A restriction of kinetic energy in the stagnation point region, similar to improved k-ε variants.
- The consideration of shear stress transport, which gives the model its name.