A numerical investigation is performed for heat transfer phenomena occurring in enclosures with different aspect ratios, emissivities and Rayleigh numbers. Interaction of surface radiation and turbulent natural convection of differentially heated enclosures with different positions of heat source and sink has been assessed systematically. The mass, momentum and energy equations have been solved in two-dimensional cartesian coordinates. The turbulence has been modeled using k − ε model. The simulations have been performed on rectangular enclosures with different aspect ratios (0.5, 1, 1.5 and 2) filled with air having Prandtl number 0.7. Surface to Surface radiation model has been incorporated to study the effect of surface radiation on the heat transfer characteristics. The results have been presented in terms of Nusselt number, isotherms and streamlines for various cases. It is concluded that the results can provide insight when designing enclosures for complex engineering applications involving turbulent conditions. © 2021, Indian Academy of Sciences.