Heat transfer modulation and local flow reversal in turbulent vertical convection with rectangular obstacles

This study investigates turbulent vertical convection within a low-aspect ratio cavity equipped with sparsely arranged rectangular obstacles (fins) mounted on vertical sidewalls. The parameters are chosen with Rayleigh number spanning the range of 10 5 ⩽ Ra ⩽ 10 7 and Prandtl number fixed at 0.032. Through two- and three-dimensional direct numerical simulations, we examine the effects of fin length, thermal driving strength, and different roughness configurations on global heat transport and flow topology. The results reveal that appropriately arranged sparse fins can induce more coherent multi-vortex flow structures and significantly enhance heat transfer. This enhancement originates from the topological reorganization of the large-scale circulation (LSC), which facilitates more efficient horizontal thermal transport pathways. The degree of improvement is strongly influenced by the parameter space and geometric configuration. This effect is primarily governed by the inherent geometric arrangement of the fins rather than their symmetry, suggesting a degree of generality and extensibility. Notably, under conditions of relatively low Ra and sufficiently long fins, a novel phenomenon of localized flow reversal is observed in the central region of vertical convection. Fourier mode decomposition of the flow field further highlights a key distinction from traditional Rayleigh-Bénard convection: the competition between the forward LSC driven by the horizontal temperature gradient and the reverse circulation induced by shear and flow separation at fin tips leads to more complex transitional modes. These findings underscore the critical role of roughness design in optimizing LSC coherence and enhancing thermal transport, offering new insight into flow dynamics under broken symmetry conditions.