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In this study the coexistence of laminar and turbulent states in a drag-reduced pipe flow is being numerically examined. The drag reduction is enforced by applying a spanwise-forcing technique. The study is carried out with direct numerical simulations of the incompressible Navier-Stokes equations, under the costant mass flow rate condition (CFR).
Owing to the drag reduction technique, the usual relationship between Rebulk and Retau is changed, and we observe the regime of localized turbulence well above the usual range 1800 < Rebulk < 2200. The typical structures of this regime are present, but they appear to assume a different scaling and a peculiar edge dynamics. We estimate that a localized regime might be observed up to Rebulk of the order of 6000-7000.