Schedule 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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