Flow-Induced vibration and heat transfer enhancement in tandem cylinders: Effects of cylinder shape, corner radii, and spacing ratio

Abstract

In this work, flow-induced vibration (FIV) of two heated cylinders in the tandem arrangement is numerically investigated at a Reynolds number of 150. The effect of the spacing ratio (L/D) and the corner radius (r*) is investigated by changing L/D from 2 to 4 and r* from 0 to 1, where 0 corresponds to the square cross-section and 1 to the circular cross-section. The cylinders are oriented to maintain a constant angle of attack of 45° and are allowed to vibrate in the transverse direction only. The one degree of freedom (1-DOF) motion of the cylinders is studied with varying reduced velocities (Ur = 2–10). The mass ratio (m*) of the cylinder is taken as 10, while the damping is neglected to obtain the maximum vibrational amplitude. The findings suggest that the maximum vibrational amplitude (A/D) occurs for square-shaped cylinders, while the least occurs for circular shapes. It was found that the lock-in for a single cylinder occurred at Ur = 6, irrespective of the corner radius. For tandem cylinders with L/D = 2, the lock-in region occurred at Ur = 6–8 for circular cylinders and at Ur = 8–10 for square cylinders. However, lock-in occurred at Ur = 6–8 for both square and circular tandem cylinders at L/D = 4. The vorticity patterns observed in this study include 2S, C(2S), 2P, and P + S. The flow topology, the response behavior of the cylinders, and local (Nul) and average (Nuavg) Nusselt numbers were affected by various parameters, including the corner radius, spacing ratio, reduced velocity, and the average drag coefficient. For the single cylinder, changing the shape from square to circular resulted in a 40.4% and 4.71% decrease in the maximum A/D and Nuavg, respectively. Considering the twin square cylinders in tandem with L/D = 2, the upstream and downstream cylinders experienced 3.86% and 58.0% higher A/D as compared to the single cylinder. However, increasing L/D to 4 from 2 decreased the maximum A/D for upstream and downstream square cylinders by 5.41% and 3.07%, respectively. Compared to the square cylinders at L/D = 4, the circular cylinders resulted in a 28.6% and 35.1% decrease in maximum A/D for upstream and downstream cylinders, respectively, whereas at the same time experienced 33.1% and 32.0% higher Nuavg, respectively. In conclusion, the circular cylinders in tandem arrangement give higher rates of heat transfer while experiencing lower vibration as compared to square and filleted cylinders.