Self-sustaining cycle of purely elastic turbulence

Abstract

Direct numerical simulation of purely elastic turbulence (ET) in the Taylor-Couette flow of dilute polymer solutions is used to identify the dominant flow structures, namely, unsteady diwhirls that almost span the entire gap and axially and azimuthally elastic waves that occupy the inner rotating cylinder region to midgap. In accord with experiment, the azimuthal wave speed increases monotonically with enhanced Wi and it travels nearly 50 times faster than the axial waves. The interaction of elastic waves with unsteady diwhirls leads to stochastic or chaotic cycles of polymer stretch and relaxation and commensurate fluctuations in elastic stresses over a broad range of spatiotemporal frequency that produce turbulent kinetic energy and sustain turbulent dynamics. To this end, the self-sustaining cycle of ET is elucidated. Overall, this study paves the way for mechanistic understanding of this inertia less turbulence in curvilinear flows.