Suppression of wake-induced vibration in two tandem circular cylinders using bypass channels

Numerical simulations are conducted to investigate the suppression of wake-induced vibration (WIV) of two tandem circular cylinders by bypass channels, where the downstream cylinder is allowed to vibrate transversely while the upstream cylinder remains stationary. The Reynolds number, based on the cylinder diameter (D) and the freestream velocity (U∞), is Re=150, and the center-to-center distance is set to L=2.0D. The thin bypass channels (e.g., T=0.1D) fail to suppress WIV, instead resulting in a 14.5% increase in the maximum vibration amplitude (Amax) compared to the bare cylinders. Here, the lift coefficient of the downstream cylinder, Cld, features a multi-frequency spectrum comprising the fundamental vortex-shedding frequency f0 and its odd harmonics 3f0 and 5f0. This arises from the intricate coupling between the wake of the upstream cylinder and the large-amplitude vibration of the downstream cylinder. For example, the large-amplitude vibration of the downstream cylinder periodically shifts its front stagnation point. However, as T increases further, the alternating vortex shedding is progressively attenuated, leading to a monotonic suppression of WIV. Eventually, at T=0.4D, the proper orthogonal decomposition analysis illustrates that the fluctuating modes in the near wake are eliminated. Therefore, the fluctuation of Cld vanishes entirely and Amax is reduced by more than 99.5%. Linear stability analysis also reveals that the bypass channels reduce the wake shear effect, thereby transforming the original absolute instability into convective instability. This transition is responsible for the suppression of alternating vortex shedding and WIV.