Numerical investigation of fluid flow and heat transfer from two cylinders with different diameter in tandem arrangement

In this study, the flow over two finite-length cylinders positioned in tandem and the heat transfer from the cylinders were numerically investigated. The cylinder diameter ratio and the gap ratio between the cylinders are varied as d/D=0.5, 0.75, 1 and L/D=1.5, 2, 3, 5, respectively. These analyzes were performed under the laminar regime conditions for the Reynolds number of 300, and the cylinder surfaces were assumed isothermal. Additionally, the length-to-diameter ratio of the downstream cylinder was fixed at 4. As a result of the analysis, irregular and complex vortex structures were observed behind the cylinders. As can be seen from the vorticity images and the temperature distributions, it can be stated that the temperature gradient on the rear surface of the downstream cylinder increases due to the vortex shedding that forms behind the cylinder at the relevant altitude. The highest local time averaged Nusselt number values were obtained at around the leading edge of the upstream cylinder, while the highest local time averaged Nusselt number value was also obtained at the leading edge of the downstream cylinder for d/D=0.75 and 1. However, in the case of d/D=0.5, the maximum local Nusselt number value was obtained at an elevation close to the downstream cylinder base due to distinctive flow behavior observed in the gap between the cylinders. The highest Nu_D,yan value was obtained in the case of d/D=0.75, L/D=5 as 6.691 due to the decreasing shielding effect of the upstream cylinder. The highest Nu_d,yan value was achieved in the case of d/D=1, L/D=2 as 8.324. Furthermore, the highest C_d and C_D (drag coefficient) values were obtained in the cases of d/D=0.5, L/D=3 and d/D=0.5, L/D=5 as 0.924 and 0.544, respectively.