In this study, two-dimensional laminar flows past a circular cylinder under isothermal and non-isothermal conditions over a flat-plate were investigated numerically at Re = 200. The gap ratio G / D ranges from 0.5 to 3.0, with G representing the distance between the lower surface of the cylinder and the wall. The effects of G / D on the flow dynamics were explored. For G / D = 0.5 , the vortex shedding of the lower cylinder surface is suppressed and there is a large recirculation region on the wall. For G / D = 1.0 , the recirculation region is small and the lower vortex begins to shed. For G / D ⩾ 1.5 , the flow exhibits similarities to that of an unbounded cylinder. The heat transfer characteristics was evaluated. When the cylinder temperature T c is higher than the air temperature T a , the mean drag coefficient C D ¯ is reduced and the root-mean-square lift coefficient C L ′ is increased. The temperature field is reconstructed using the proper orthogonal decomposition method, which is influenced by the large-scale vortical structures.