Splitting of localized disturbances in viscoelastic channel flow

Abstract

We examine the response of an inertialess viscoelastic channel flow to localized perturbations. We thus performed an experiment in which we perturbed the flow using a localized velocity pulse and probed the perturbed fluid packet downstream from the perturbation location. While for low Weissenberg numbers the perturbed fluid reaches the measurement location as a single velocity pulse, for sufficiently high Weissenberg numbers and perturbation strengths, a random number of pulses arrive at the measurement location. The average number of pulses observed increases with the Weissenberg number. This observation constitutes a transition to a novel elastic pulse-splitting regime. Our results suggest a possible new direction for studying the elastic instability of viscoelastic channel flows at high elasticity through the growth of localized perturbations.

Purely elastic turbulence in pressure-driven channel flows

“…Sudden relaminarization events are key characteristics of the transition scenario in linearly stable Newtonian parallel shear flows ( 29 ), indicative of a fractal laminar–turbulent boundary ( 30 ), finite turbulent lifetimes ( 31 ), and localized flow structures ( 32 ). Our observations, supported by further evidence below and by recent experimental reports of sudden splitting of localized structures in elastic pressure-driven channel flows ( 33 ), suggest a similar transition scenario for linearly stable purely elastic flows.…”

Perspectives on viscoelastic flow instabilities and elastic turbulence

“…Given these three features, and given the apparent agreement with the predictions of [520], the authors propose that such waves are indeed elastic waves. Moreover, they note that they observed these waves exclusively in random flows: either in chaotic flows above the non-normal mode bifurcation and further in ET in a straight channel with and without strong perturbations [198,200,201] or only above the transition to ET in a flow past an obstacle or between two obstacles hindering a channel flow [83,522]. In addition, the elastic waves were not found in flow geometries with curvilinear streamlines including ET.…”