Numerical experiments of polymer-induced fluctuating states in a parallel channel flow

We investigate the effect of solvent convective nonlinearity, polymer diffusivity, and three-dimensional effects in a parallel channel flow at Re=2000, developing a polymer-induced weak fluctuating state in the absence of external perturbations. In addition to purely polymeric-driven multiscale dynamics developed from the center-mode structure, fluctuations in velocity, polymer concentration, and elongation predominantly develop in planes parallel to the walls in the streamwise and spanwise directions. Fluctuations are strongly amplified by the solvent convective nonlinearity. The rather small polymer diffusion, naturally included in the hybrid Eulerian–Lagrangian approach, allows the formation of sharp concentration gradients, questioning the typical assumption of uniform polymer concentration.