Authors:
Steven R. Allmaras, Research Engineer, Department of Aeronautics and Astronautics, MIT
Forrester T. Johnson, Senior Technical Fellow, Boeing Commercial Airplanes (retired)
Philippe R. Spalart, Senior Technical Fellow, Boeing Commercial Airplanes

We present modifications to the Spalart-Allmaras (S-A) turbulence model targeted
toward situations of under-resolved grids and unphysical transient states.
These modifications are formulated to be passive to the original model in well
resolved flowfields and should produce negligible differences in most cases.
They are motivated primarily by numerical issues near the interface between
turbulent and irrotational regions. We also comment on the appropriate form of
S-A for compressible flows, the inclusion of the laminar suppression term for
fully turbulent flows, and the use of maximum value limiters on the turbulence
solution.  We also present a new analytic solution to S-A for law of the wall
velocity.