Relaminarization of spanwise-rotating viscoelastic plane Couette flow via a transition sequence from a drag-reduced inertial to a drag-enhanced elasto-inertial turbulent flow

Direct numerical simulation of spanwise-rotation-driven flow transitions in viscoelastic plane Couette flow from a drag-reduced inertial to a drag-enhanced elasto-inertial turbulent flow state followed by full relaminarization is reported for the first time. Specifically, this novel flow transition begins with a drag-reduced inertial turbulent flow state at a low rotation number 0 <= Ro <= 0.1, and then transitions to a rotation/polymer-additive-driven drag-enhanced inertial turbulent regime, 0.1 <= Ro <= 0.3. In turn, the flow transitions to a drag-enhanced elasto-inertial turbulent state, 0.3 <= Ro <= 0.9, and eventually relaminarizes at Ro = 1. In addition, two novel rotation-dependent drag enhancement mechanisms are proposed and substantiated. (1) The formation of large-scale roll cells results in enhanced convective momentum transport along with significant polymer elongation and stress generated in the extensionally dominated flow between adjacent roll cells at Ro <= 0.2. (2) Coriolis-force-generated turbulent vortices cause strong incoherent transport and homogenization of significant polymer stress in the bulk via their vortical circulations at Ro = 0.5-0.9.