Unravelling the large-scale circulation modes in turbulent Rayleigh-Bénard convection^(a)

Abstract The large-scale circulation (LSC) is the most fundamental turbulent coherent flow structure in Rayleigh-Bénard convection. Further, LSCs provide foundation upon which superstructures, largest observable features convective systems, are formed. In confined cylindrical geometries with diameter-to-height aspect ratios of , LSC dynamics known to be governed by a quasi-two-dimensional, coupled horizontal sloshing and torsional (ST) oscillatory mode. contrast, \gtrsim \sqrt{2}$ cylinders, three-dimensional jump rope vortex (JRV) motion dominates dynamics. Here, we use dynamic mode decomposition (DMD) on direct numerical simulation data liquid metal show that both types modes co-exist = 2$ cylinders but opposite dynamical importance. Furthermore, this analysis, demonstrate ST oscillations originate from tilted elliptical mean superposed symmetric higher-order mode, connected four rolls plane perpendicular tanks.