On the boundary layer development and heat transfer from a sphere at moderate Reynolds numbers

Abstract

Direct and large-eddy numerical simulations have been performed for a heated sphere at Reynolds numbers 200, 300, 500, 750, 1000 and 104, in the context of the development of a spherical wind sensor for Mars atmosphere intended for missions after Rover 2020. A lowdissipation ¿nite element scheme implemented in the multi-physics code Alya has been used to do so. The main heat transfer and aerodynamic parameters are presented, followed by detailed analysis of the wake and boundary layer development and the local heat transfer coe¿cients. Viscous and thermal boundary layer thicknesses decrease with the Reynolds number, the thermal one being thicker than the viscous layer. However, in all cases shape factor is the same in the zone with the favourable pressure gradient. The local Nusselt number is found to be asymmetric in the rear zone of the sphere for the laminar cases and recover its statistical symmetry once the wake transition to turbulent ¿ow. It is also found that the stagnation Nusselt number scales as Re0.47, in fair agreement with previous studies.