© 2021Flow structure is an essential aspect for the intensity of natural convective heat transfer in enclosures. Improvements in the enclosure geometry affecting the flow structure can increase the natural convective heat transfer performance. As the dome shaped walls can change the flow direction in a way to improve the flow circulations and natural convection, the present work numerically investigates laminar flow and natural convective heat transfer of air in dome shaped enclosures with three different dome inclinations. The dome shape can be designed for such enclosures by either filleting the corners of a rectangular cavity or replacing one of the adiabatic walls of a square cavity with a dome shaped wall. Therefore, the impact of dome shape utilization is analyzed from these two perspectives by separately considering the rectangular and square enclosures as reference cases. To broaden the investigation for various circumstances, three different Rayleigh numbers and four different cavity inclination angles are considered. Furthermore, the non-dimensional entropy generation rates are computed for each enclosure to evaluate their performance in terms of second law of thermodynamics. The results show that the dome shape wall significantly changes the flow structure by providing a smoother circulation, which facilitates more intensified convection currents by directing the hot fluid to the colder region of the enclosure, hence, establishing a more effective natural convective heat transfer. The computed results reveal that the mean Nusselt number can be augmented up to 22.5 and 25.0% by the utilization of dome shaped enclosure compared to the equivalent rectangular and square enclosures, respectively. The impact of the dome is dependent on the cavity inclination and generally decreases as Ra increases. Besides, the dome shaped enclosure codified by D45 gives the lowest entropy generation value.