Feb 8, 2000
Turbulence and Fossil Turbulence in Natural Fluids
Carl Gibson, (UCSD)
Turbulence is defined as an eddy-like state of fluid motion where the inertial-
vortex forces of the eddies are larger than any of the other forces which tend to
damp the eddies out. Turbulence always begins at the Kolmogorov scale when a
universal critical Reynolds number implied by Kolmogorov's 1941 universal
similarity hypotheses is exceeded, and cascades to larger and larger scales by a
non-linear, self-similar cascade process,
extracting energy through inertial-vortex forces from the irrotational (and
therefore non-turbulent) external
flow. In natural fluids, turbulence is constrained at the largest scale
by buoyancy and Coriolis forces (as in the ocean and atmosphere), self-
gravitational forces
(as in the primordial fluids of cosmology and astrophysics), and by magnetic
forces in some plasma flows. The turbulent kinetic energy is converted to a
unique class of non-propagating internal wave motions termed "fossil vorticity
turbulence" for the case of buoyancy forces, and scars of the irreversible mixing
processes persist as fossils of the previous turbulence in a variety of
hydrophysical fields, reflecting the wide variety of forces that constrain
turbulence. Fossil turbulence is defined as a fluctuation in some hydrophysical
field of the fluid caused by
turbulence that persists after
the flow ceases to be turbulent at the scale of the fluctuation. Fossil
turbulence and fossil non-turbulence remnants (footprints, scars) preserve
information about the
hydrodynamic state of the fluid existing at the time when they were formed, and
this information may be extracted using fossil turbulence theory. Previous
hydrodynamic
information may be difficult or impossible to recover in the absence of such
hydropaleontology. Further information is available at:
Carl H. Gibson HomePage. A titled
list of articles is given at:
C. H. Gibson astro-ph
articles. The ones most important to this talk are:
astro-ph/9904230, astro-ph/9904237, astro-ph/9904283, astro-ph/9904260
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