On the generation of drift flows in wall-bounded flows transiting to turbulence

TL;DR

This paper investigates how drift flows arise in wall-bounded shear flows during transition to turbulence, revealing that slight mode detuning can generate symmetry-breaking drift flows, aiding understanding of laminar-turbulent pattern formation.

Contribution

It extends Waleffe's approach to show that drift flows are generated by mode detuning at the local scale, providing new insights into laminar-turbulent interface dynamics.

Findings

Drift flows break spanwise symmetry in transitional flows.

Mode detuning leads to the generation of drift flows.

Insights into laminar-turbulent pattern formation.

Abstract

Despite recent progress, laminar-turbulent coexistence in transitional planar wall-bounded shear flows is still not well understood. Contrasting with the processes by which chaotic flow inside turbulent patches is sustained at the local (minimal flow unit) scale, the mechanisms controlling the obliqueness of laminar-turbulent interfaces typically observed all along the coexistence range are still mysterious. An extension of Waleffe's approach [Phys. Fluids 9 (1997) 883--900] is used to show that, already at the local scale, drift flows breaking the problem's spanwise symmetry are generated just by slightly detuning the modes involved in the self-sustainment process. This opens perspectives for theorizing the formation of laminar-turbulent patterns.