Effect of a single sidewall cooling on Rayleigh-Bénard convection*

Rayleigh-Bénard conveciton is a canonic scenario for studying the thermal convection phenomenon. We explored this probelm with a single sidewall cooling in a rectangular tank. The fluid was heated from the bottom and cooled at the top, and one sidewall had the same temperature as the top cooling; the other sidewalls kept adiabatic conditions. The flow field was characterized using particle image velocimetry at various vertical planes parallel and perpendicular to the cooling sidewall. A canonic RB convection without lateral cooling was also studied to aid insight into the modulation of lateral cooling at Rayleigh-number of Ra = 1.6×10¹⁰ and Prandtl number of Pr = 5.4. Results show that the single sidewall cooling induced flow asymmetry with strong descending motions near the cooling wall, modulating the spatial features of the large-scale circulation (LSC). The asymmetry in the system prevented LSC reversal. It also redistributed thermal diffusion and buoyancy effects, represented by an effective Ra. Flow statistics departed from the canonical case, with reduced impact relatively farther from the sidewall cooling. Velocity spectra showed two scalings, Kolmogorov and Bolgiano types. Inspection of the LSC core motions allowed us to identify a distinct mode with a characteristic timescale on the order of vortex turnover time, which can be associated with different vortex modes. The velovity spectra of the vortex core oscillation along its principal axis showed a -5/3 spectral scaling for the single sidewall cooling, which was dominant closer to the side cooling.