Oscillation-buoyancy interplay over a heated sphere by numerical simulation

This study numerically investigates buoyancy-driven convection and heat transfer around a heated sphere subjected to prescribed vertical oscillations. A low-Mach-number compressible CFD framework, combined with a sharp-interface immersed boundary method on hierarchical Cartesian grids, is employed to resolve the phase-dependent thermal boundary layer and plume dynamics at Rayleigh number R a D = 1.567 × 10 7 based on sphere diameter indicating buoyancy relative to viscous and thermal diffusion. Four cases are examined by varying the Richardson number Ri from ∞ (stationary natural convection) to 0 (zero gravity; vibration-dominated convection). When the forcing frequency is comparable to the intrinsic plume time scale, the plume remains coherent and the cycle-averaged Nusselt number is close to the stationary value, while the upper-cap angular non-uniformity is alleviated. At higher forcing frequency, oscillation disrupts plume development, thickens the upper thermal boundary layer, and reduces both local and global heat transfer. In the absence of gravity, oscillatory shear produces nearly symmetric convection but yields the lowest mean Nusselt number. These results provide a frequency-based framework to interpret oscillation–buoyancy coupling and to tune the trade-off between heat-transfer magnitude and angular uniformity.