On a self-sustained process at large scale in the turbulent channel flow

TL;DR

This study demonstrates that large-scale motions in turbulent channel flow can self-sustain independently of smaller-scale structures, challenging traditional views on their interaction and dependence.

Contribution

It reveals a self-sustained mechanism for large-scale motions in turbulent flows that operates even when smaller scales are suppressed.

Findings

Large-scale motions can self-sustain without small-scale interactions.

Self-sustenance occurs in large enough computational domains.

Smaller-scale structures are not necessary for large-scale turbulence maintenance.

Abstract

Large-scale motions, important in turbulent shear flows, are frequently attributed to the interaction of structures at smaller scale. Here we show that, in a turbulent channel at Re_{\tau} \approx 550, large-scale motions can self-sustain even when smaller-scale structures populating the near-wall and logarithmic regions are artificially quenched. This large-scale self-sustained mechanism is not active in periodic boxes of width smaller than Lz ~ 1.5h or length shorter than Lx ~ 3h which correspond well to the most energetic large scales observed in the turbulent channel.