Numerical investigation of flow and heat transfer characteristics in buoyancy-driven convection around cylinder arrays within an enclosure

This study examines the flow and heat transfer characteristics of buoyancy-driven convection around cylindrical arrays within an enclosure, employing a monolithic immersed boundary projection method. The effects of Rayleigh numbers, volume fraction, and cylinder count on flow regimes and heat transfer are systematically analyzed, identifying three distinct regimes: steady, periodic unsteady, and chaotic unsteady. Transitions between these regimes are strongly influenced by interactions among the parameters, with odd-count cylinder configurations promoting flow instability and broadening the range of periodic flow. Flow and temperature field analyses reveal that the flow regime is governed by the available space for fluid motion (determined by cylinder count and volume fraction) and thermal driving forces (determined by Rayleigh numbers). Time- and surface-averaged Nusselt numbers demonstrate heat transfer enhancement with increasing Rayleigh numbers and decreasing cylinder counts. At lower Rayleigh numbers, a linear increase in Nusselt numbers with total surface area is observed, while at higher Rayleigh numbers, the increase exhibits a gradually decreasing slope, providing insight for optimizing thermal performance. These findings underscore the critical roles of Rayleigh numbers, volume fraction, and cylinder count in influencing heat transfer characteristics in buoyancy-driven convection systems.