Flow topology transition via global bifurcation in turbulent Rayleigh-Benard convection

We present experimental observation of a spontaneous symmetry breaking induced transition in turbulent Rayleigh-Benard convection. The experiment was carried out in a vertical annulus convection cell with the aspect ratio Γ=H/(2R_o)=1.87 and the radius ratio γ=R_i/R_o=0.88. Here H=100.0 mm is the height of the cell, R_i=84.5 mm and R_o=96.0 mm are the radius of the inner and outer sidewalls, respectively. Simultaneous measurements of the heat transport, i.e., the Nusselt number, and the topology of the LSF were performed. It is found that the heat transport shows a sharp transition with the increase of the Rayleigh number Ra in the range of 6.0×10⁷≤ Ra ≤ 1.3×10⁹ and at fixed Prandtl number Pr=5.4. Analysis of the LSF structure suggests that the transition is resulted from a global bifurcation of its pattern from a high-symmetry quadruple structure (QS) to a low-symmetry dipole structure (DS). In the transition zone spanned about half a decade in Ra, the system switches stochastically between the two metastable QS and DS states [1].[1]Xie, Ding and Xia, Phys. Rev. Lett. 120, 214501 (2018)