Reverse transition of a turbulent spiral Poiseuille flow at Ta=1500

Direct numerical simulations of a turbulent spiral Poiseuille flow (SPF) in a narrow-gap geometry at low Taylor number have been performed to analyse the reverse transition dynamics. The presently investigated SPF results from a Taylor–Couette arrangement with a rotating inner cylinder and a stationary outer one, subject to a time-constant axial pressure gradient. Keeping fixed the Taylor number and reducing the axial Reynolds number, several flow regimes have been obtained until a complete laminarization occurred. In agreement with previous experimental evidence, it has been found that the laminar state is achieved at a Reynolds number significantly smaller than the corresponding non-rotating value. Moreover, the route to turbulence suppression has been shown to differ in the two cases, as confirmed by the increased Reynolds number friction coefficient envelope. The differences occurring in the reverse transition process between SPF and plain Poiseuille flow are attributed to a modification of the isotropy of the Reynolds stress tensor, caused by an alteration of the velocity pressure-strain redistribution mechanisms.