Influence of counter-rotating von Karman flow on cylindrical Rayleigh-Benard convection

TL;DR

This study explores how counter-rotating flow in a cylindrical Rayleigh-Benard system affects flow transitions, revealing bifurcation types and complex dynamics influenced by rotation and temperature gradients.

Contribution

It provides a detailed bifurcation analysis of flow states in a combined Rayleigh-Benard/von Karman setup with counter-rotation, including phase portraits and spectral evolution.

Findings

Symmetry-breaking transition occurs at finite Rayleigh number for Re>0.

Different bifurcation types (pitchfork, Hopf) depend on Re value.

Complex bifurcation scenarios including SNIPER and global bifurcations are identified.

Abstract

The axisymmetric flow in an aspect-ratio-one cylinder whose upper and lower bounding disks are maintained at different temperatures and rotate at equal and opposite velocities is investigated. In this combined Rayleigh-Benard/von Karman problem, the imposed temperature gradient is measured by the Rayleigh number Ra and the angular velocity by the Reynolds number Re. Although fluid motion is present as soon as Re is non-zero, a symmetry-breaking transition analogous to the onset of convection takes place at a finite Rayleigh number higher than that for Re=0. For Re<95, the transition is a pitchfork bifurcation to a pair of steady states, while for Re>95, it is a Hopf bifurcation to a limit cycle. The steady states and limit cycle are connected via a pair of SNIPER bifurcations except very near the Takens-Bogdanov codimension-two point, where the scenario includes global bifurcations. Detailed phase portraits and bifurcation diagrams are presented, as well as the evolution of the leading part of the spectrum, over the parameter ranges 0<Re<120 and 0<Ra<30,000.