Elastic Pseudoturbulence in Polymer Solutions

We study the effects of polymer additives on pseudoturbulence induced by a swarm of bubbles rising in a quiescent fluid. We find that, even in the absence of background shear, beyond a critical polymer concentration, the energy spectra of velocity fluctuations in bubble-induced turbulence decay more steeply with respect to the wave number k. This new scaling is significantly steeper than the classical k^{-3} scaling observed for bubbles in Newtonian fluids; it is independent of the gas volume fraction in the inertial limit and occurs within the length scales between the bubble wake length and the bubble diameter. Furthermore, we provide quantitative evidence that the presence of polymers enhances the coherence of the flow, as revealed by Lagrangian stretching statistics, highlighting the significant role of polymer additives in modifying the characteristics of pseudoturbulence. Our findings demonstrate that viscoelastic effects can modulate turbulence even in shear-free environments, offering a new perspective on the role of elastic stresses in complex multiphase flows.