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Unformatted text preview: aid that some theories work so well without
telling what does this mean.
Use of an ambiguous language in science generally and even more in fields
with profound difficulties such as turbulence brings into existence serious
misconceptions. Sweeping and related.
An underlying assumption of Komogorov theory is that very
large spatial scales of motion convect very small scales without
directly causing significant internal distortion of the small
scales. The assumption usually is considered to be consistent
with, and to imply, statistical independence of small and large
scales, KRAICHNAN 1964 Again problems with ‘scales’. A closely related issue is with the rather popular
assumption that choosing an appropriate ‘local’ system of reference one can get rid
(mostly) of the so called sweeping of SS by the LS. The underlying assumption is that
SS are ‘passive’ and just ‘swept’ by the LS without any participation in the process,
i.e. without any reaction back. This is a major misconception: we have seen that there
is a rich coupling - direct an bidirectional - between SS and LS.
The issue of sweeping is closely related to the comparative aspects of Lagrangian
versus Eulerian descriptions to be addressed in January – March 2008 along with
other issues (such as universality, Re-dependence, strongly anisotropic turbulence...). ‘Statistical scales’ Well defined scales used in turbulence belong to its simplest statistical
characteristics, i.e. they are not some specific scales, but they are
statistically defined quantities, suchas the most popular Kolmogorov
scale η defined via mean dissipation rate of energy. This scale is usually
considered as the smallest spatial relevant scale in turbulence. This,
however, is not obvious, since the instantaneous dissipation ɛ is not
narrow banded around its mean ε, but is distributed with a rather long
tail, so that values as large as, 10²〈ε〉 are not that rare (the maximal
values of ɛ may reach values as high as 104〈ε〉 as in the filed exper...
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- Spring '11
- The Land