Is the log-law a first principle result from Lie-group symmetry analysis?

https://arxiv.org/abs/1412.3069

Essence of this Comment: Since the statistical equations in turbulence are unclosed, so are their
symmetries. Hence, when performing any invariant analysis on such an unclosed system of equations, it will predominately result into a non-unique set of invariant solutions involving arbitrary
functions for which from the outset it is not clear how to specify them. 
The closure problem of turbulence cannot be circumvented, or “somewhat bypassed” in the sense of Oberlack , by just employing the method of Lie-group invariant analysis alone, since the arbitrariness in the results just gets shifted from one function to another. Hence, without modelling these unclosed equations, an a priori prediction from Lie-group theory alone as how turbulence scales is and will not be possible. Only a posteriori, by anticipating what to expect from numerical or experimental data, the adequate invariant scalings can be generated through an iterative trial-and-error process as recently shown again in https://doi.org/10.13140/RG.2.2.27341.69608. But again, note that these are only approximate phenomenological solutions or possibly guessed candidate solutions, and not first principle solutions of the Navier-Stokes equations, as misleadingly claimed by Oberlack for nearly two decades now, as here in 2000, or in 2014, or just recently again in 2018.

Popular posts from this blog

Symmetries and turbulence modeling

On the optimal systems of subalgebras for the equations of hydrodynamic stability analysis of smooth shear flows and their group-invariant solutions