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The present study investigates the effects of a circular cylinder on the three-dimensional characteristics of free convective heat transfer. The circular cylinder is mounted horizontally on a heated vertical plate and is categorized as high aspect ratio obstacle, which means the height of cylinder is comparable to its diameter. The obtained results are provided for the laminar flow regime. In addition, during numerical study the governing differential equations are solved around the Grashof number equals to 3 108. In order to illustrated the regions of high gradients of temperature, the flow temperature is shown in terms of non-dimensional contours and diagrams. At the near junction region in upstream of cylinder, by description of heat transfer coefficients represented to the temperature gradients at intended points, the effects of cylinder emplacement on the heat transfer rate is surveyed. As expected, the value of the buoyancy-induced heat transfer coefficient increases at the cylinder junction in the upstream side. The maximum value of heat transfer coefficient is seen at the symmetry plane of study domain, which is corresponded to the location of horseshoe vortex system core. Finally, by deviation calculating between numerical and experimental results also by analysis of the experimental method uncertainty the validity and reliability of numerical and experimental approaches are proved

In recent years, there are more efforts on natural convection heat transfer from a horizontal cylinder, because of its practical applications. However, unconfined cylinder is well studied; the effect of introducing end-walls on the heat transfer rate of cylinder is considerably less investigated (Clifford and Kimber in J Heat Transfer 136:112502 (2014) [1].

The present study numerically describes the nature of the arising boundary layer along an isothermal vertical plate, on which is mounted a bluff body. The investigation parameter is the cross-section shape of the bluff body, which includes a square, circular, and prismatic cylinders. To entirely embedded cylinder in the incoming boundary layer, the simulations include short cylinders with an aspect ratio fixed to unity. The cylinder location related to the leading edge of the plate is identified by considering laminar Grashof number, which experimentally is investigated in parallel work. Besides this, the experimental study of a square cylinder, confirms the reliability and accuracy of numerical simulation. As a result, by providing steady-state simulation, the presence of a complex vortex structure is proved. Besides, the effects of the cross-section shape of the cylinder on the dynamics characteristics of the vortex system include vorticity strength, size, and position are categorized. Finally, the significant effects of formed juncture flow on the three-dimensional thermal characteristics of arising free convective boundary layers along with the heated vertical plate are emphasized by a description of heat transfer coefficients. In particular, the importance of the frontal bluntness of cylinder in the field of thermal management is claimed, where the maximum value of the heat transfer coefficient for circular, prismatic, and square cylinders, respectively appears at the angular coordinates of 0 , 45 , and 90 degrees, which correspond with the location of cylinder edges.