A novel transition route to elastically dominated turbulence in viscoelastic Taylor-Couette flow

A novel transition sequence to elastically dominated turbulence (EDT) in Taylor-Couette flow of dilute polymeric solutions at elasticity number El = Wi/Re = 0.15 that signifies the ratio of elastic to inertial forces, has been elucidated via direct numerical simulation. Specifically, as the Reynolds number (Re) and Weissenberg number (Wi) are progressively increased, the primary instability causes a flow transition from an azimuthal Taylor-Couette flow (AZI) to a flow composed of rotating standing wave (RSW), which in turn transitions to disordered oscillations (DO) followed by an intriguing modulated traveling wave (MTW) flow pattern and eventually to EDT (AZI-* RSW-* DO-* MTW-* EDT). The MTW pattern is found to be a spiral mode superimposed on a RSW-like mode. The experimentally observed transition hysteresis is examined by detailed examination of the different flow patterns obtained as the flow transitions from MTW-* EDT and the reverse transition, namely from EDT-* MTW. Furthermore, distinct flow regions have been identified in the EDT state, namely, an elasticity-dominated outer-wall region in which the polymeric stress shares the same patterns with the radial velocity and an inertia-dominated inner-wall region in which no similarity between these two patterns is observed. Detailed examination of turbulent statistics demonstrates that the intense merging and splitting events of the large-scale vortices adjacent the outer-wall regions give rise to large, highly localized and fluctuating polymeric stresses. Moreover, in the EDT flow state the elastic production of turbulent kinetic energy is mostly derived from interactions of fluctuating elastic shear stresses and shear strain fluctuations.