Viscoelastic effect on steady wavy roll cells in wall-bounded shear flow

TL;DR

This study investigates how viscoelastic fluids influence steady wavy roll cells in wall-bounded shear flow, revealing suppression of secondary flows and transition to straight roll cells, with implications for drag reduction.

Contribution

It demonstrates the modulation of flow structures by viscoelasticity and explores the underlying mechanisms relevant to drag reduction in wall turbulence.

Findings

Secondary flows are suppressed in viscoelastic flows.

Wavy roll cells become streamwise-independent straight roll cells.

Viscoelastic stress influences energy transport and flow modulation.

Abstract

An alternative step in understanding the flows of near wall drag-reducing turbulence can be examining the flow in a well-organized streamwise vortex with a laminar background. Herein, we studied the flow behaviors of the Giesekus viscoelastic fluid in a rotating plane Couette flow system, which is accompanied by steady roll cell structures. By fixing the Reynolds and rotation numbers at values that provide as steady wavy roll cell, i.e., an array of meandering streamwise vortices, the Weissenberg number was increased up to 2000 (where the relaxation time was normalized by the wall speed and the kinematic viscosity). We observed that, in the viscoelastic flows, the secondary flow (wall-normal and spanwise velocity fluctuations) are suppressed while the streamwise component is maintained, and the wavy roll cells are modulated into streamwise-independent straight roll cells. The kinetic energy transports among the mean shear flow, Reynolds stresses due to the roll cell, and viscoelastic stress are investigated in the non-turbulent background. We further discussed the modulation mechanism and its relevance to the drag reduction phenomenon in the viscoelastic wall turbulence.