Open AccessHierarchy of coherent structures in turbulent channel flow
Author(s) -
Yutaro Motoori,
Susumu Goto
Publication year - 2020
Publication title -
journal of physics. conference series
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.21
H-Index - 85
eISSN - 1742-6596
pISSN - 1742-6588
DOI - 10.1088/1742-6596/1522/1/012004
Subject(s) - turbulence , vortex , lagrangian coherent structures , scale (ratio) , reynolds number , physics , mechanics , filter (signal processing) , open channel flow , flow (mathematics) , geometry , hierarchy , channel (broadcasting) , statistical physics , mathematics , telecommunications , engineering , quantum mechanics , electrical engineering , economics , market economy
By analyzing a database of fully developed turbulent channel flow at the friction Reynolds number Re τ = 4179, we investigate the sustaining mechanism of a hierarchy of coherent structures in the wall-bounded turbulence. For this purpose, we decompose the turbulent fields into different scales by a band-pass filter. Using the filtered velocity and velocity gradients, we identify the hierarchy of coherent structures to observe that the largest-scale structures at each distance from the wall are composed of quasi-streamwise vortices and low-speed streaks. Since these are similar to well-known coherent structures in the buffer layer, they are likely to be maintained by the self-sustaining process. In contrast, structures smaller than the distance from the wall distribute isotropically. These observations are also confirmed by using a conditional sampling method. Moreover, quantifying the scale-dependent contributions to the vortex stretching and energy transfer, we show that the largest-scale coherent structures are strongly affected by the mean shear, whereas smaller-scale vortices are generated by the energy cascading events. Incidentally, in large-scale ejection regions (i.e. large-scale low-speed streaks), the cascading events are stronger than in large-scale sweep regions.