Analysis of Flow Structures and Global Parameters across a Heated Square Cylinder in Forced and Mixed Convection

In the present study, numerical simulations are performed to identify the role of Reynolds number (Re), Richardson number (Ri) and free-stream orientations (alpha) on flow structures, aerodynamic parameters and heat transfer characteristics for the conditions (20 <= Re <= 120, 0 degrees <= alpha <= 90 degrees and 0 <= Ri <= 1.6). Prandtl number (Pr) and cylinder orientation (phi) are kept fixed at 0.71 and 0 degrees. The Oberbeck-Boussinesq approximation is used to account for buoyancy effects. The governing equations of continuity, momentum and energy are discretized on a colocated body-fitted grid by employing a finite difference method. A viscous implicit pressure correction scheme is employed to advance the discrete solution in time. Contour maps of mean/steady drag coefficient and Nusselt number on (alpha-Ri) plane are plotted for 20 <= Re <= 120. From these contour maps, it is possible to identify the ranges of parameters (alpha, Ri) that can yield a relatively high mean/steady heat transfer rate accompanied by relatively low values of mean/steady drag coefficient. For [70 degrees <= alpha <= 90 degrees, 0 <= Ri <= 1.6], such a scenario is possible for any Re is an element of [20, 120]. The Strouhal number is observed to be maximum for Re = 120 at alpha = 45 degrees and Ri = 1.2. Mean or steady coefficient of lift for any free-stream orientation (alpha not equal 0 degrees) is found to be highest at Re = 20 and Ri = 1.6. Sensitivity of (C-D)(Ri = 0.0) to alpha is observed to be minimum for Re = 20 and maximum for Re = 120. Sensitivity of the ratio C-D(Ri,alpha)/C-D(0,alpha) to Re is observed to be lower for unsteady flows than for steady flows, and it decreases with an increase in Re at a fixed value of Ri. Mean Nusselt number (Nu) in the forced flow regime increases significantly with an increase in Re at a fixed alpha. The Nusselt number is observed to be more sensitive to Ri for steady flows than for unsteady flows. The percentage increase in the ratio Nu(Ri,alpha)/Nu(0,alpha) for the entire range of Re is found to be 14.07%, 14.13%, 11.74% and 10.62% at alpha = 30 degrees, 45 degrees, 60 degrees and 90 degrees. At a fixed Ri, the Nusselt number ratio is found to decrease with an increase in Re for the entire range of alpha except for alpha = 90 degrees. It is observed that the rate of heat transfer from the faces of the cylinder increases with an increase in Re for the entire ranges of alpha and Ri.