Effects of inclination angle on Rayleigh–Bénard convection under non-Oberbeck–Boussinesq approximation in air

This study employs direct numerical simulations to explore the combined effects of inclination angles (ϕ) and non-Oberbeck–Boussinesq (NOB) conditions on heat transfer and flow patterns in inclined Rayleigh–Bénard convection (RBC). The simulations, conducted in air, classify flow behavior into seven regimes based on roll number and flow state. Heat-transport efficiency is found to be higher in the single-roll state. The study investigates the influence of NOB and inclination on top-bottom symmetry in a fluid-filled cavity, with systematic analysis revealing complex non-monotonic behaviors of the Nusselt number (Nu) and Reynolds number (Re) under different conditions. The effects of ϕ on heat transfer are significant in the modest to moderate range of Rayleigh numbers, becoming less pronounced as these values increase. The study finds that power-law scalings of Nu and Re are sensitive to the inclination angle and robust against NOB effects for ϕ≥40^∘. Moreover, in NOB scenarios, the distributions of the local thermal boundary layers (BLs) along the hot and cold walls exhibit a lack of antisymmetry. As a result, there is an obvious deviation between the hot and cold global thermal BLs, which is further influenced by the inclination angle.