Numerical investigation of natural convection and thermal uniformity in a rectangular cavity with lattice structures on the hot wall

Efficient thermal management in passive natural convection systems requires enhanced heat transfer and improved thermal uniformity to suppress localized heat accumulation. However, the limitations of natural convection associated with buoyancy-driven hot plumes remain insufficiently addressed. In this study, natural convection in a rectangular cavity with lattice structures installed on the hot wall is investigated to achieve simultaneous mitigation of localized hot spots and overall thermal enhancement. Four lattice topologies — simple cubic (SC), Diamond, body-centered cubic (BCC), and face-centered cubic (FCC) — are examined over porosity and Rayleigh number ranges of ϕ = 0.5 –0.9 and R a = 1 0 4 –10 7 . In the low- R a regime ( R a = 1 0 4 –10 5 ), the equal-weight total performance ψ relative to the bare cubic cavity is governed mainly by flow resistance, yielding a consistent ranking of SC > Diamond > BCC > FCC, with the SC lattice showing up to 10.94% higher performance than the FCC lattice. As R a increases, the performance of the BCC and FCC lattices becomes increasingly sensitive to porosity, leading to a fully reversed ranking at R a = 1 0 7 and ϕ = 0.9 , where the FCC lattice outperforms the SC lattice by up to 8.30%. The ranking reversal is attributed primarily to topology-induced flow modification rather than differences in total heat input. These findings provide practical design guidelines for selecting lattice topologies for passive natural convection systems operating under different Rayleigh number and porosity conditions.