Dynamics of Flow and Heat Transfer Around Two Circular Cylinders of Different Diameters in Tandem Subjected to Forced Convection

Two-dimensional numerical simulations for heated and unheated flows over two circular cylinders of different diameters in tandem are conducted. The study is conducted for Re = 150 and temperature ratio 1 ≤ (T* = Ts/T∞) ≤ 2.3. The study is limited to spacing ratios in the range 2 ≤ L/Dd ≤ 8 and diameter ratios 0.5 ≤ Du/Dd ≤ 2. The effect of heating on the flow is captured by modelling the thermophysical properties of the fluid fitted as polynomial functions of temperature. The flow features are visualized by plotting the streamlines and velocity magnitude contours. These flow patterns are also discussed based on the reattachment and co-shedding regimes which are classification found in literature. The effect of varying geometrical parameters on the flow in terms of change of regime is discussed. Furthermore, the drag coefficient (Cd) on both upstream and downstream cylinders is presented as a function of spacing and diameter ratios. Additionally the average surface heat transfer coefficient (h) is presented for the interval of spacing and diameter ratios stated. Results show that the presence of an upstream cylinder led to reduction of Cd on the downstream cylinder to a value lower than that of single cylinder for all cases studied. Heating both cylinders causes Cd on both cylinders to become less sensitive to a change in L/Dd, and increasing Du/Dd is found to decrease h on both upstream and downstream cylinders.