Helical turbulence and puff in transitional sliding Couette flow

Abstract eng:
We performed direct numerical simulations of flows between two concentric cylinders, which flow is driven by a steady sliding motion of the inner cylinder in the axial direction. We parametrically investigated intermittent turbulence in the transitional regime for different radius ratio 77- We found that the reducing Reynolds number (Re) from fully-developed turbulent state gave rise to organized large-scale structures, where localized turbulence and laminar coexisted with some spatial regularities. For 77 = 0.8, a helical pattern of laminar-turbulent structure occurred at Re = 375 and this structure sustained its shape until Re = 337.5. For 17 = 0.5 and 0.1, although the flow became laminar at Re = 375, the laminar patches were observed for 17 = 0.5 at higher Reynolds numbers. The localized turbulence observed for ’7 = 0.1 was intermittent only in the axial direction, which was similar to a turbulent puff in pipe flow.

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