Using some kind of mixing-length (MLT) prescription for describing
convection in 1D stellar models, both and a convective velocity
come out of the procedure. These can of course be combined with
some assumptions to give a turbulent pressure. Below I list some
points to bear in mind when doing so:
where is a form factor related to the velocity distribution
function. From Fig.2
we see that this formfactor is not a constant but varies between 1.3
at the transition from convective to radiative energy transport at
z = 0 to 1.9 in the bottom of the simulation. The latter though, might
be a aboundary effect making 1.8 (at z=0.7) the upper limit to
.
So all the dramatic changes in broadness and asymmetry, overshoot
and possible double peakedness all seem to happen close to the top
of the convection zone, - also the only region where ever
gets important.
The
-ratio, peaks with 13% at z=0.1 Mm,
decaying about
three times faster in the overshoot region as compared to the
convective zone. At the bottom of the box the turbulent pressure
only contributes with 0.1% of the total pressure.
It is, though, my experience and impression that 1D turbulent
pressures derived from MLT convective velocities are sensible for
depths greater than about 1-1.5 Mm, but this might depend on the
precise MLT formulation.
Last updated [an error occurred while processing this directive] by: trampedach@pa.msu.edu.