Shinji Hiejima

Numerical study on the suppression of the vortex-induced vibration of a circular cylinder by acoustic excitation

Abstract In order to investigate the possibility of suppressing flow-induced vibration of structures by applying periodic excitation such as a sound wave to the flow around the structures, numerical simulations of the vortex-induced vibration of a circular cylinder were carried out when a periodic velocity excitation was applied to the flow at two locations on the cylinder surface. A FEM based on the ALE formulation was employed to simulate the vortex-induced vibration, with the time integration being carried out by the predictor-corrector method. The results revealed that the excitation with the transition wave frequency is the most effective in changing the flow characteristics around the cylinder and the characteristics of the vortex-induced vibration. These changes appear to be caused by the promotion of the vortex growth in the early vortex formation behind the cylinder.

Feedback control of vortex shedding around a bluff body by velocity excitation

A feedback control technique of vortex shedding behind a circular cylinder is investigated by means of two-dimensional numerical simulations. Fluid velocity excitation is applied to the separated shear flows at two positions on the cylinder surface with time delay and feedback gain for the fluid velocity at a downstream sensor position. It is shown that the feedback excitation can suppress the vortex shedding considerably, if the time delay of the excitation is varied in accordance with the change of the vortex shedding period and the sensor is located inside the vortex formation region behind the cylinder.

Numerical Study of the Effect of Periodic Velocity Excitation on Aerodynamic Characteristics of an Oscillating Circular Cylinder

A finite element method based on ALE formulation has been adopted in order to examine the effect of periodic velocity excitation on the aerodynamic characteristics of an oscillating circular cylinder. Periodic excitation, which was placed on the cylinder surface, stimulated the separated shear layers around the cylinder, and numerical results showed that some excitation can reduce negative damping, which is caused by unsteady lift force, and thereby stabilize the aerodynamics of the cylinder. Furthermore, the change of lift phase caused by periodic excitation seems to be important in stabilizing the aerodynamics of the cylinder. The simulation also confirmed that periodic excitation can suppress the vortex-induced vibration of the cylinder.