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• DNS and LES of the flow and heat transfer past a sphere are performed. • Local and average Nusselt number are determined. • Viscous and thermal boundary layer are analysed. • Wake behaviour and its characteristics are studied for moderate Reynolds numbers. Direct numerical simulation and large-eddy simulation have been performed for a heated sphere at Reynolds numbers of R e = 1000 and R e = 10 4 , respectively. The Prandtl number for both simulations has been P r = 0.7. Measurements of the local and average Nusselt number are performed and compared with literature available experimental results. Average and front stagnation point Nusselt numbers increase with the Reynolds number, while the minimum value moves towards the sphere apex as the flow enters the sub-critical regime. Differences in both viscous and thermal boundary layers are observed, while the shape factor at Reynolds number R e = 10 4 behaves similarly to that observed in circular cylinders at comparable Reynolds numbers. It is shown that as the Reynolds number increases, the increase in turbulent kinetic energy promotes the entrainment of irrotational flow thus enhancing the temperature mixing in the zone. The near wake, between 5 ≤ x / D ≤ 15, spreads at a faster rate at R e = 1000 with a slope close to x / D 1/2, while at R e = 10 4 it follows a trend close to x / D 1/3. [ABSTRACT FROM AUTHOR]

Direct numerical simulations of the flow and forced convective heat transfer around a sphere at Reynolds numbers between R e = 500 and R e = 1000 are performed. We investigate the effects of the Prandtl number (P r) on the forced convective heat transfer from a sphere for various fluids having P r = 0. 01 , 0. 1 , 0. 7. At the larger Prandtl number, the convective transport due to the vortex shedding process dominates over the diffusive transport. As the Prandtl number decreases, diffusive effects become important. Moreover, the thermal boundary layer increases with decrements of the Prandtl number, which results in a reduction in the local and mean non-dimensional heat transfer coefficient. It is seen that at R e = 500 and R e = 750 , the vortex shedding process is asymmetric, which results not only in a non-zero lift coefficient, but in an asymmetric temperature field in the wake of the sphere at P r ≥ 0. 1. The dual asymmetry in the flow and the convective heat transfer is smooth out when the Prandtl number reaches P r = 0. 01 as the heat diffusion dominates and asymmetries in the vortex formation zone are no longer relevant in the heat transport. The descend in Prandtl number also produces an attenuation of the temperature fluctuations and thereby, in the turbulent heat transfer. As a direct consequence, two factors emerge at P r = 0. 01 : (1) a lower decay ratio of the temperature in the wake centreline, and (2) a larger wake spread compared to higher Prandtl numbers. [ABSTRACT FROM AUTHOR]