DOI: 10.1615/TSFP10
Temporal and spatial intermittencies within channel flow turbulence near transition
要約
Direct numerical simulations of a pressure driven turbulent flow are performed in a large rectangular channel. Extreme and moderate drag regimes within turbulence that have earlier been found to exist temporally in minimal channels at transitional Reynolds numbers have been observed both spatially and temporally in full-size turbulent flows. These intermittent regimes, namely, "hyperactive", "active" and "hibernating" turbulence, display very different structural and statistical features. Using conditional sampling, we identify these intermittent intervals and present the differences between them in terms of simple quantities like mean velocity, all shear stress and flow structures. By conditionally sampling of the low wall shear stress events in particular, we show that the local mean velocity in large domains occasionally approaches that of one family of the exact coherent states that are characteristic of very low drag in Newtonian minimal channel flows.