Small-scale dynamics of elasto-inertial and elastic turbulence: Role and resolution of large polymer stress sheets*

Polymer additives in liquid flows may trigger chaos in a variety of flows at various Reynolds numbers (Re). Under favorable conditions, polymers fully sustain flow perturbations in elastic turbulence (ET) when Re << 1. Elasto-inertial turbulence (EIT) is the general category of flows affected by polymer-driven perturbations at inertial Reynolds numbers. In some range of subcritical Reynolds numbers, polymer dynamics may drive chaos like ET, whereas, in some upper range of subcritical $Re$ and in a range of supercritical Re, EIT may coexist and interact with inertial instabilities and coherent structures with direct consequences to drag and heat transfer. In numerical simulations, a universal structure of ET and EIT is the thin sheet of large polymer stress, large polymer stress sheet (LPSS). It is surmised that sheet-to-sheet and/or sheet-to-wall interactions are at the center of chaos generation in ET and EIT. We conduct a systematic spectral analysis of fluctuations of polymer stress and flow variables for various flow configurations to discover the relation between Re, viscoelastic parameters, and polymer conformation tensor diffusion, characterized by a Peclet number Pe. Our study highlights the strong dependence of the LPSS’ thickness and intensity with Pe, which in turn has significant impact on the small and large scale dynamics of the flow. One of the flows isolates the sheet-to-sheet interactions, and the energy fluctuations they cause.