(526f) Nested Travelling Wave Underlying Elastoinertial Turbulence

Polymeric additives are commonly used in pipeline transport of liquids such as crude oil transport, water heating and cooling systems, and airplane tank filling to reduce turbulent drag. However, there is a limit beyond which turbulent drag cannot be reduced through polymeric additives, because the presence of polymer beyond a certain concentration in the turbulent flow promotes velocity fluctuations instead of suppressing them. Elastoinertial turbulence is a chaotic flow state resulting from the interplay between inertia and viscoelasticity, and it plays a critical role in promoting velocity fluctuations during turbulent drag reduction and hence limits the drag reduction due to polymeric additives. We use, Spectral Proper Orthogonal Decomposition (SPOD), a modal decomposition technique and investigate the dynamics of elastoinertial turbulence. We discover that the chaotic dynamics of elastoinertial turbulence is predominantly made of a collection of nested traveling waves. The structure of the most dominant traveling mode exhibits shift-reflect symmetry similar to the viscoelasticity-modified Tollmien–Schlichting (TS) wave, where the velocity fluctuation in the traveling mode is characterized by the formation of large-scale regular structures spanning the channel and the polymeric stress field is characterized by the formation of thin, inclined sheets of high polymeric stress localized at the critical layers near the channel walls. The formation of thin inclined sheets of high polymeric stress at the critical layer of each structure act like “wall” for next-faster traveling structure and hence leads to the emergence of a nested family of traveling waves.