Is concentrated vorticity that important?

Abstract

The main purpose of this paper is to bring about a better balance between views of the exaggerated importance of concentrated vorticity, on one hand, and the underestimated role of three kinds of regions other than concentrated vorticity: i — ‘structureless’ background, ii — regions of strong vorticity/strain (self) interaction and strong enstrophy generation, and iii — regions with negative enstrophy production, on the other hand, with the emphasis on the latter. Results of experiments on turbulent grid flow and DNS of decaying turbulent flow in a periodic ‘box’ at the same Reynolds number (Re λ ≈ 75) are used in order to demonstrate that all these regions are strongly non-Gaussian, dynamically significant and possess structure. It is argued that due to the strong nonlocality of turbulence in physical space all the four regions are in continuous interaction and are strongly correlated. Thus the answer to the question posed in the title is that — though important — regions of concentrated vorticity are not as important as is commonly believed.