Vorticity production through rotation, shear and baroclinicity
by
Fabio Del Sordo(NORDITA)
→
Europe/Stockholm
122:026
122:026
Description
In the absence of rotation and shear, and under the assumption of
constant temperature or specific entropy, purely potential forcing
by localized expansion waves is known to produce irrotational flows
that have no vorticity.
Here we study the production of vorticity under idealized conditions
when there is rotation, shear, or baroclinicity, to address the problem
of vorticity generation in the interstellar medium in a systematic fashion.
We use three-dimensional periodic box numerical simulations to
investigate the various effects in isolation.
We find that for slow rotation, vorticity production
in an isothermal gas is small in the sense that the ratio
of the root-mean-square values of vorticity and velocity
is small compared with the wavenumber of the energy carrying motions.
For Coriolis numbers above a certain level, vorticity production saturates at a
value where the aforementioned ratio becomes comparable with the
wavenumber of the energy carrying motions.
Shear also raises the vorticity production, but no saturation is found.
When the assumption of isothermality is dropped, there is significant
vorticity production by the baroclinic term once the turbulence becomes
supersonic.
In galaxies, shear and rotation are estimated to be insufficient to
produce significant amounts of vorticity, leaving therefore only the
baroclinic term as the most favorable candidate.
We also demonstrate vorticity production visually as a result of colliding shock
fronts.
