The transported variable in the Spalart-Allmaras model,
, is
identical to the turbulent kinematic viscosity except in the near-wall
(viscous-affected) region. The transport equation for
is

(12.3-1)

where
is the production of turbulent viscosity and
is the
destruction of turbulent viscosity that occurs in the near-wall region due
to wall blocking and viscous damping.
and
are
constants and
is the molecular kinematic viscosity.
is
a user-defined source term. Note that since the turbulence kinetic energy
is not calculated in the Spalart-Allmaras model, the last term in Equation
12.2-5
is ignored when estimating the Reynolds stresses.