  Elasto-inertial turbulence is a new state of turbulence found in flows with
polymer additives . The dynamics of turbulence generated and controlled by such
additives is investigated from the perspective of the coupling between polymer
dynamics and flow structures. Direct numerical simulations of channel flow with
Reynolds numbers ranging from 1000 to 6000 (based on the bulk and the channel
height) are used to study the formation and dynamics of elastic instabilities
and their effects on the flow. The resulting mechanism of interactions between
polymer dynamics and the flow helps resolve a long-standing controversy in the
understanding of polymer drag reduction and explains the phenomenon of early
turbulence, or onset of turbulence at lower Reynolds numbers than for Newtonian
flows, previously observed in polymeric flows. Polymers also point out an
interesting analogy with the forward and backward energy cascade in
two-dimensional turbulence.
