Boundary layer of elastic turbulence

TL;DR

This paper provides an analytical and numerical study of the boundary layer in elastic turbulence of dilute polymer solutions at high Weissenberg numbers, revealing how polymer conformation statistics and flow fluctuations are related.

Contribution

It introduces a theoretical framework for understanding the near-wall boundary layer in elastic turbulence, including polymer conformation and flow fluctuation estimates.

Findings

Polymer conformation is highly nonuniform near the wall.

The ratio of mean flow to flow fluctuations depends on polymer properties.

Asymptotic analysis captures qualitative features of elastic turbulence.

Abstract

We investigate theoretically the near-wall region in elastic turbulence of a dilute polymer solution in the limit of large Weissenberg number. As it was established experimentally, elastic turbulence possesses a boundary layer where the fluid velocity field can be approximated by a steady shear flow with relatively small fluctuations on the top of it. Assuming that at the bottom of the boundary layer the dissolved polymers can be considered as passive objects, we examine analytically and numerically statistics of the polymer conformation, which is highly nonuniform in the wall-normal direction. Next, imposing the condition that the passive regime terminates at the border of the boundary layer, we obtain an estimate for the ratio of the mean flow to the magnitude of flow fluctuations. This ratio is determined by the polymer concentration, the radius of gyration of polymers and their length in the fully extended state. The results of our asymptotic analysis reproduce the qualitative features of elastic turbulence at finite Weissenberg numbers.