The problem of the natural convection in a twodimensional
octagonal enclosure is investigated numerically. A
circular hot solid cylinder is placed at the center of the enclosure
while all the eight walls of the enclosure is kept at a cold isothermal
temperature. The cylinder moves by an equal amount (R/2 and R) in
the horizontal, vertical and diagonal directions. The development
mathematical model is governed by the coupled equations of
continuity, momentum and energy and is solved by using the finite
volume method. The computations are carried out for wide ranges of
the governing parameters such as Rayleigh number (Ra) and internal
circular cylinder location (?).The results explained that the cylinder
location has a significant effect on the flow and thermal fields in the
octagonal enclosure. Also, it is found that the average Nusselt
number of the internal hot cylinder (NuC) is greater than the overall
average Nusselt number for various orientation locations.