Baghli, HoudaCheddadi, Abdelkhalek2021-03-102021-03-1020190094-243Xhttps://doi.org/10.1063/1.5138560https://aip.scitation.org/doi/10.1063/1.5138560https://dspace.univ-boumerdes.dz/handle/123456789/6592The numerical Simulation of natural convection within an incompressible Newtonian fluid confined between two isothermal and concentric spheres is carried out. The phenomenon considered is two-dimensional, axisymmetric and permanent, with an annular space ratio of A = 2, filled with air Pr = 0.7, at moderate Rayleigh number Ra between 103 and 106. Simultaneous resolution of the continuity equations, of Navier-Stokes and energy, is carried out by the combination of the implicit method of alternate directions (ADI) with the method of convergence acceleration by successive replacement (SAR), in the Vorticity-Stream function formulation. The isovalues of temperature T and the steam function ψ obtained, as well as the Average Nusselt number, are in a good agreement with previous studies, and gives new Nusselt number correlation Nu = f(Ra)enNatural ConvectionNumericalRayleigh NumberSimulationSpherical annuliOther