The Spalart-Allmaras model [621] is a one-equation model that solves a modeled transport equation for the kinematic eddy (turbulent) viscosity. The Spalart-Allmaras model was designed specifically for aerospace applications involving wall-bounded flows and has been shown to give good results for boundary layers subjected to adverse pressure gradients. It is also gaining popularity in turbomachinery applications.

In its original form, the Spalart-Allmaras model is effectively a low-Reynolds number model, requiring the viscosity-affected region of the boundary layer to be properly resolved ( meshes). In Ansys Fluent, the Spalart-Allmaras model has been extended with a -insensitive wall treatment, which allows the application of the model independent of the near-wall resolution. The formulation blends automatically from a viscous sublayer formulation to a logarithmic formulation based on . On intermediate grids, , the formulation maintains its integrity and provides consistent wall shear stress and heat transfer coefficients. While the sensitivity is removed, it still should be ensured that the boundary layer is resolved with a minimum resolution of 10-15 cells.

The Spalart-Allmaras model was developed for aerodynamic flows. It is not calibrated for general industrial flows, and does produce relatively larger errors for some free shear flows, especially plane and round jet flows. In addition, it cannot be relied on to predict the decay of homogeneous, isotropic turbulence.