Modi cations and Clari cations for the Implementation of the Spalart-Allmaras Turbulence Model

We present modi cations to the Spalart-Allmaras (S A) turbulence model targeted toward situations of under-resolved grids and unphysical transient states. These modi cations are formulated to be passive to the original model in well resolved ow elds and should produce negligible di erences in most cases. We also comment on the appropriate form of S A for compressible ows and comment on the inclusion of the laminar suppression term for fully turbulent ows. We also present a new analytic solution to S A for law of the wall velocity.