The large-scale circulation and temperature oscillation in turbulent thermal convection in a flattened cylindrical cell of aspect ratio 2.

This article presents an experimental investigation of the large-scale circulation (LSC) and temperature oscillations in turbulent Rayleigh–Bénard convection (RBC) within a flattened cylindrical cell of aspect ratio Γ = 2, at Prandtl number Pr ≈ 5.7 and Rayleigh number Ra ranging from 8.0 × 10^7 to 6.5 × 10^8. The study finds that the LSC consistently forms a dominant single-roll structure with orientation confined to a narrower azimuthal range than in cells with smaller aspect ratios (Γ = 1 or 1/2), and that its azimuthal motion exhibits superdiffusive behavior rather than normal diffusion. Temperature oscillations occur ubiquitously at the mid-height plane with characteristic frequencies f₀ and 2f₀, differing from previously reported oscillations in Γ = 1 cells; these are attributed to a unique periodic vortex center ("jump rope") motion in the Γ = 2 cell. Additionally, both the strength and orientation of the LSC show prominent oscillations linked to this vortex center motion, highlighting the significant influence of cell geometry on flow dynamics and thermal oscillations in RBC.