Self-Sustained Process at Large Scales in Turbulent Channel Flow

Large-scale motions, important in turbulent shear flows, are frequently attributed to the interaction of structures at smaller scales. Here we show that, in a turbulent channel at Re(T) approximate to 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 L(z) approximate to 1.5h or length shorter than L(x) approximate to 3h which correspond well to the most energetic large scales observed in the turbulent channel.