Poiseuille flow-induced vibration of two tandem cylinders with different diameters in a confined channel

Poiseuille flow-induced vibration of two tandem cylinders with different diameters in a confined channel flow is numerically examined by the lattice Boltzmann method. We explore how the Reynolds number (Re), cylinder distance (S/d), and cylinder blockage ratio (β) affect the drag force, the phase angle, and fluid velocity on the motion of tandem cylinders. The cylinders rest at the channel centerline (CR mode), oscillate near one side of the wall (OSL mode), and vibrate around the channel centerline (OCL modes) are discovered. It is interesting to find that when the upstream cylinder is larger than the downstream cylinder with a small distance, two cylinders can be considered as a single entity that keeps the significant oscillations even under low fluid inertia, then the vibration mode is changed with increasing Re and S/d. Sidewall amplifies shear layer interactions, enabling significant vibrations at low Reynolds numbers. As the diameter ratio of the upstream cylinder to the downstream cylinder increases, the Reynolds number corresponding to the formation of the OCL mode continuously decreases. Thus, by controlling the cylinder blockage ratio and distance, the OCL mode can be achieved at low fluid inertia. This study offers potential use in enhancing the fluid and mass transfer in a confined channel.