Forced linear shear flows with rotation: rotating Couette-Poiseuille flow, its stability and astrophysical implications

TL;DR

This paper investigates how forcing and rotation affect the stability of shear flows like Couette and Poiseuille flows, with implications for understanding turbulence in accretion disks and laboratory experiments.

Contribution

It demonstrates that forcing can transform shear flows into Poiseuille flows, which become unstable under rotation, explaining turbulence onset in accretion disks.

Findings

Rotation destabilizes Poiseuille flow at lower Reynolds numbers.

Forcing modifies shear flows into Poiseuille flows in accretion disks.

Flow instability can occur even in Keplerian rotation, leading to turbulence.

Abstract

We explore the effect of forcing on the linear shear flow or plane Couette flow, which is also the background flow in the very small region of the Keplerian accretion disk. We show that depending on the strength of forcing and boundary conditions suitable for the systems under consideration, the background plane shear flow and, hence, accretion disk velocity profile modifies to parabolic flow, which is plane Poiseuille flow or Couette-Poiseuille flow, depending on the frame of reference. In the presence of rotation, plane Poiseuille flow becomes unstable at a smaller Reynolds number under pure vertical as well as threedimensional perturbations. Hence, while rotation stabilizes plane Couette flow, the same destabilizes plane Poiseuille flow faster and forced local accretion disk. Depending on the various factors, when local linear shear flow becomes Poiseuille flow in the shearing box due to the presence of extra force, the flow becomes unstable even for the Keplerian rotation and hence turbulence will pop in there. This helps in resolving a long standing problem of sub-critical transition to turbulence in hydrodynamic accretion disks and laboratory plane Couette flow.