Structure of elastoinertial turbulence in pipe flow

Addition of a tiny amount of high molecular weight polymeric chains dramatically suppresses inertial turbulence and hence reduces frictional drag. Therefore, they are widely used to reduce energy loss during the transport of liquids and have also been envisioned for use for flood remediation and other environmental applications. Elastoinertial turbulence (EIT) is a self-sustaining chaotic state resulting from the interplay between inertia and elasticity in the flow of dilute polymeric solutions, and its emergence is believed to limit the achievable drag reduction in turbulence flow using polymer additives. In this talk, I will discuss the dynamics of elastoinertial turbulence in axisymmetric pipe flow of a FENE-P fluid. Using a viscoelastic variant of spectral proper orthogonal decomposition (VESPOD) that incorporates both kinetic and stored elastic energy, we discover that the dynamics of EIT in pipe flow is dominated by several distinct families of traveling waves. The stress fluctuations of each wave are localized around the critical layer position where the wavespeed and mean velocity coincide. Similar to the channel flow case we have previously studied, the waves with higher speed have stresses that are "nested" within the region between the critical layers of the lower speed wave. These observations illustrate the origin of the "sheetlike" structure that is widely observed in computations of stress fields for EIT.