The Scale-Adaptive Simulation (SAS) is an improved URANS formulation, which allows the
resolution of the turbulent spectrum in unstable flow conditions. Figure 4.6: Resolved Structures for Cylinder in Cross Flow (top: URANS; bottom: SST-SAS) shows isosurfaces where 
for a cylinder in cross flow (
), calculated using the SST model (URANS) and the SST-SAS model. The URANS
simulation produces only the large-scale unsteadiness, whereas the SST-SAS model adjusts to the
already resolved scales in a dynamic way and allows the development of a turbulent spectrum in
the detached regions.
The SAS concept is based on the introduction of the von Kármán length-scale into the turbulence scale equation. The information provided by the von Kármán length-scale allows SAS models to dynamically adjust to resolved structures in a URANS simulation, which results in an LES-like behavior in unsteady regions of the flow field. At the same time, the model provides standard RANS capabilities in stable flow regions.
For information about the synthetic turbulence generation on inlets, refer to Inlet Boundary Conditions for Scale Resolving Simulations.