Intermittent Patterns in Turbulence Produced by a Conventional Fractal Square Grid and a Spaced Fractal Square Grid

Abstract

Measurements of longitudinal velocity were conducted in an open-circuit suction wind tunnel at the Max-Planck Institute for Dynamics and Self-Organization in Gottingen. A hot wire anemometer was used at various positions within the turbulent flow generated by both a traditional fractal square grid (FSG) and a spaced fractal square grid (SFSG), both possessing similar physical properties. The results indicate the presence of self-similarity. Employing Extended Self Similarity (ESS), we performed a statistical characterization of this intricate turbulent system. We introduce a supplementary methodology suitable for non-homogeneous turbulence, founded on the analysis of the energy transfer hierarchy. The distinctive features of non-homogeneous characteristics within a turbulent field, discerned through nonlocal dynamics, are isolated from those conventionally attributed solely to intermittency. We propose a physical interpretation for the observed scale independence of relative scaling exponents in such non-homogeneous flows, elucidating the compensation effect of energy transfer on the contrast between strong coherent turbulent events and the less intense background turbulence. This approach enables the identification of whether intermittency arises from small scales or is associated with coherent structures.