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Use of an ambiguous language in science generally and

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Unformatted text preview: aid that some theories work so well without work 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. Sweeping 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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