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This is a pure terminology question. The term "turbulence" ("turbulent" etc.) appears in many phrases from an ordinary technical description to apparent parables. In my limited knowledge, turbulence is a state of flow or a regime of flow.

  • How wrong is the usage of "there are turbulences" etc. (like "there is a pink elephant" - nice and localized)?

  • Is an attribute "to be turbulent" strictly dichotomic or is there any graduation? I am aware of the concept of transition and fully developed turbulence. Again, I aim for the terminology.

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'When I use a word,' Humpty Dumpty said, in rather a scornful tone, 'it means just what I choose it to mean — neither more nor less.'

When the pilot tells the passengers 'We are about to experience extreme turbulence' he uses the word in a semi-technical way, as does the passenger who says, 'we had a lot of turbulence on our trip.'

A flow can certainly be more turbulent or less turbulent, in the sense of spatial extent, or temporal preponderance, or relative intensity, but it is difficult to combine these various possibilities into a single measure. One measure that is used is intermittency. This is the fraction of time for which the flow at a given point meets some criterion for 'being turbulent'. It is used in the vicinity of a transition point, where intermittency changes from zero upstream to unity downstream. It forms part of some numerical algorithms for predicting turbulent flows, but there is no such reliable algorithm because they are all based on some fundamentally unreliable concept.

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