Phenomenology

There is no definition of what is phenomenology of turbulent flows. In a broad sense, it can be defined by a statement of impotence: it is almost everything except the direct experimental results (numerical, laboratory and field) and/or results (a very small set indeed), which can be obtained from the first principles, e.g., NSE. Phenomenology of turbulence involves use of dimensional analysis, a variety of scaling arguments, symmetries, invariant properties and various assumptions, some of which are of unknown validity and obscured physical and mathematical justification (if any). Thus in the broad sense phenomenology of turbulence includes also most of the semi-empirical approaches and turbulence modelling¹. Doing all this requires insight into the basic physics of turbulence, hard experimentation and painful efforts of interpretation. The latter may be quite problematic, especially in models having enough free parameters² to guarantee the right results not necessarily for the right reasons.