Nonmodal elastic instability and elastic waves in weakly perturbed channel flow

Abstract

Adding tiny amounts of long polymer chains to a fluid dramatically alters its behavior. In this work, we show that channel flows of such viscoelastic fluids at vanishingly small Reynolds numbers are highly sensitive to weak disturbances, even though they are linearly stable. We thus show experimentally that a weak disturbance elicits strong fluctuations with a continuous spectrum in three different regimes and elastic waves far from the excitation location through a non-modal bifurcation.