Fluid dynamics and heat transfer in the wake of a sphere

摘要

Direct numerical simulation and large-eddy simulation have been performed for a heated sphere at Reynolds numbers of Re = 1000 and Re = 10(4), respectively. The Prandt1 number for both simulations has been Pr = 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 Re = 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 Re = 1000 with a slope close to x/D-1/2, while at Re = 10(4) it follows a trend close to x/D-1/3.