Transition in the asymptotic suction boundary layer over a heated plate

TL;DR

This paper investigates how adding a temperature gradient affects the transition to turbulence in the asymptotic suction boundary layer, revealing complex interactions between thermal convection and shear flow.

Contribution

It extends the bypass transition scenario to thermal boundary layers, analyzing the influence of temperature gradients on flow stability and bifurcations.

Findings

Laminar state becomes unstable via subcritical bifurcation

Critical Rayleigh number depends on Prandtl number

Identification of localized states and turbulent transients

Abstract

The asymptotic suction boundary layer (ASBL) is a parallel shear flow that becomes turbulent in a bypass transition in parameter regions where the laminar profile is stable. We here add a temperature gradient perpendicular to the plate and explore the interaction between convection and shear in determining the transition. We find that the laminar state becomes unstable in a subcritical bifurcation and that the critical Rayleigh number and wavenumber depend strongly on the Prandtl number. We also track several secondary bifurcations and identify states that are localized in two directions, showing different symmetries. In the subcritical regime, transient turbulent states which are connected to exact coherent states and follow the same transition scenario as found in linearly stable shear flows are identified and analyzed. The study extends the bypass transition scenario from shear flows to thermal boundary layers and highlights the intricate interactions between thermal and shear forces.