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The list of models is a very long one indeed it

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Unformatted text preview: me as reflecting the real physical processes. The list of models is a very long one indeed. It starts with the ‘eddy viscosity’ as the simplest version of the ‘solution’ of the ‘problem of closure’, low dimensional representation and ends with most sophisticated versions of LES and similar (so far). Many of these models are based on qualitatively different (and even contradictory) premises/assumptions. Nevertheless, most of the numerous models are in good Nevertheless, agreement with the experimental and numerical evidence. This is not surprising since agreement with limited (by necessity) experimental evidence is not very much significant when one deals with such a highly dimensional system as turbulence. The only exception seems to be the Navier-Stokes equations: Perhaps the biggest fallacy about Perhaps turbulence is that it can be reliably described (statistically) by a system of equations which is far easier to solve than the full timedependent three-dimensional Navier-Stokes equations BRADSHAW 1994 Ambiguity of language. What is ‘scale’ or Ambiguity ‘eddy’ ? What is meant by ‘scale’ is hard to define precisely, CHORIN, 1994 Fully turbulent flows consist of a wide range of scales, which are classified somewhat loosely as either large or small scales. SREENIVASAN AND ANTONIA, 1997 An eddy eludes a precise definition, but it is conceived to be An turbulent motion, localized within a region of size l . POPE, 2000 ...to a large extent we have failed. The key point is that we have not yet agreed on what we mean by an eddy. DAVIDSON, 2004 Ambiguity of language. Ambiguity …there exists a range of eddy (what it is?) sizes which are too (what large to be influenced by viscosity yet too small to `feel' directly the time dependence of the large eddies Another example is when it is said that very large spatial that scales of motion convect very small scales without directly causing significant internal distortion of the small scales, see below see In many cases it is s...
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