Impact of cylinder diameter and spacing on fluid flow, forces, and heat transfer in tandem cylinder configuration

This study numerically investigates the fluid flow, aerodynamic forces, and heat transfer characteristics around a circular cylinder (diameter D) positioned in the wake of another cylinder (diameter d), with varying diameter ratios d/D (= 0.4, 0.6, 0.8, and 1.0) and inter-cylinder spacing ratios L* (= L/D = 1.2 –5.0). Significant effects of d/D and L* are identified on forces, heat transfer, and fluid dynamics at Re_D = 200. For a given L*, time-mean drag, fluctuating lift and drag, and Nusselt number all are generally smaller for larger d/D, with the time-mean drag force even becoming negative for d/D = 1.0. In the reattachment flow regime, the time-mean drag and Nusselt number decrease with increasing L* for smaller d/D = 0.4 and 0.6 but increase for larger d/D = 0.8 and 1.0. In the coshedding flow regime, the Nusselt number and forces increase with L*, regardless of d/D. The critical L* separating the reattachment and coshedding flows increases with increasing d/D from 0.4 to 0.8 before declining from d/D = 0.8 to 1.0. Streamwise velocity fields and local Nusselt number distributions on the cylinder surface are analyzed to explain the observed heat transfer phenomena. Local heat transfer is maximal on the front surface of the cylinder, corresponding to the inflection point on the near-surface velocity profile.