Vortex shedding characteristics and hydrodynamic forces of stationary and elastically mounted side-by-side cylinders fitted with small diameter control rods

Abstract

Vortex shedding behind bluff bodies can induce noise and vibration problems when it engages in a feedback cycle of oscillations with an acoustic or structural mode. Therefore, several passive and active flow control techniques have been developed to suppress vortex shedding behind a single bluff body. However, less attention was given to the case of multiple bluff bodies in cross-flow. Therefore, in this paper, a numerical investigation is performed to study the effect of adding small diameter control rods in the vicinity of two side-by-side cylinders on the vortex shedding characteristics, the hydrodynamic fluid forces, as well as the suppression of vortex-induced vibration. The simulations are conducted at a Reynolds number of Re = 200 and the side-by-side cylinders have a spacing ratio of T∗=2.5. The number of control rods and their angular positions around the main cylinders are varied. Fitting the side-by-side cylinders with control rods has resulted in three different flow regimes compared to the base case with no control rods. These flow regimes depend on the angular positions of the control rods and they are classified as; bistable flow, stable biased flow, and merged wake flow regimes. The stable biased flow regime has resulted in the maximum reduction of the fluctuating lift coefficient of the side-by-side cylinders, especially when the control rods are placed at θ=135° from the flow stagnation point. Increasing the number of control rods around the cylinders has further reduced the fluctuating lift coefficient and produced a more symmetric wake at the rod angles which produce the stable biased flow, and the merged wake flow regimes. The vortex-induced vibration of the side-by-side cylinders is investigated when the control rods are placed at the angular position that results in a stable biased flow regime. It is revealed that fitting the cylinders with control rods at an angular position of θ=135° has resulted in reducing the vibration amplitude over the whole range of the simulated reduced flow velocities, which makes this technique a viable one to control the vortex shedding and the vortex-induced vibration of side-by-side cylinders.