Mixed heat transfer from a square cylinder near the wall

This study investigates the effect of flow and heat transfer on a square cylinder placed near a planar wall. The square cylinder is assumed to be within the boundary layer of the planar wall. Five different wall-to-cylinder gap ratios are considered, i.e., G/D = 0.2, 0.6, 1.2, 2, and 3. The Reynolds number based on the cylinder width is fixed at Re = 150. In this study, a two-dimensional analysis is performed for mixed convection under the influence of aiding and opposing buoyancy on the cylinder (−1≤Ri ≤ 1). The unsteady governing continuity, momentum, and energy equations are solved with the fully implicit fractional-step method using a computer code written in FORTRAN. The numerical results have been presented in terms of the flow characteristics, such as the mean drag and rms lift coefficients, and heat transfer characteristics, such as local and mean Nusselt number variations. For qualitative assessment, the flow field and temperature distributions have also been acquired to interpret and understand the underlying physical mechanism because the flow and temperature patterns change simultaneously. In the case of pure forced convection, the heat transfer rate in G/D = 0.2 case was about half that of the G/D = 3 case. This significant change in the heat transfer rate was caused by a large velocity difference between the top and front surfaces of the cylinder when the cylinder was within the boundary layer of the plane wall. Additionally, for Ri > 0, the effect of the G/D ratio on the mean drag coefficient and the mean Nu number decreased.