Suppression of vortex shedding from a low-speed rotating cylinder using two counter-rotating smaller cylinders

A pair of counter-rotating smaller control cylinders is known to suppress vortex shedding from a main cylinder MC. However, its effectiveness under the rotation-induced asymmetric flow remains unclear, particularly for Mode I vortex shedding from a rotating MC at low rotation speeds (Formula presented), where αm is the ratio of the peripheral velocity of MC to the crossflow velocity. The stationary control cylinders interfere with the suppression of vortex shedding by the rotation of MC at (Formula presented), resulting in weakened lift generation and drag reduction. Effective suppression of Mode I vortex shedding is achieved once the rotation speeds of control cylinders exceed a critical value, which increases with αm[jls-end-space/]. As the rotation speeds of control cylinders increase, the lift generation of the rotating MC decreases initially and then increases, while the drag decreases continuously. The underlying mechanism is elucidated through analysis of the pressure distribution on MC and variations in mechanical energy within the flow field. Vortex shedding can remain suppressed by maintaining the rotation speed of the upper-side control cylinder while reducing that of the lower-side control cylinder. Furthermore, the deceleration of the lower-side control cylinder improves the lift-drag characteristics of MC by enhancing lift generation and further reducing drag.