This study numerically investigates the two-dimensional natural convection in a square enclosure with different arrays of two inner cylinders at Rayleigh numbers of 10(3) <= Ra <= 10(6). A simulation was carried out based on the immersed boundary method to obtain an accurate solution. The results were compared with those of two inner circular cylinders with different vertical locations from a previous study. Detailed analysis results are presented for the distribution of the flow and thermal fields and the time- and surface-averaged Nusselt numbers. The flow and thermal fields eventually reach steady or unsteady states, depending on the variation in the distance between the cylinders. (C) 2017 Elsevier Ltd. All rights reserved.