Experiment Study On Axial Flow Induced Vibration Of Cylinder Cluster Using Fiber Bragg Grating Sensors

It is of great significance to study axial flow induced vibration of slender cylinders in engineering such as heat exchangers and nuclear engineering.The experiments is carried out in a water tunnel.Fiber Bragg grating(FBG)sensors were proposed to measure the the vibration amplitude of cylinder.In order to validate the measurements of the FBG sensors,the vibration amplitude of the cylinder which was vibrating one-dimentionally was measured using a laser vibrometer.The results show a perfect linear correlation between strain and vibration amplitude.With the correlation between strain and vibration amplitude,FBG sensors were used to study the vibration amplitude,displacement and natural frequency of the flexible cylinder in three cylinders configuration and five cylinders configuration.The effects of turbulence and gap ratio between flexible cylinder and rigid one on the flow induced vibration of flexible cylinder were studied as well.For the case of one flexible cylinder,the vibration amplitude of the rigid cylinder is negligibly small compared with that of flexible cylinder,and it can be considered that the rigid cylinder has no vibration in axial flow.In three cylinders configuration,vibraion in the direcion where the rigid cylinders located is smaller than that in another direction.However,the vibration in two directions are the same in five cylinders configuration.In both cases,the effects of gap ratio and turbulence intensity on the vibration are qualitatively similar.Changing gap ratio or turbulence intensity do not affect the vibration frequency of the flexible cylinder.When the gap ratio increases,the vibration amplitude of flexible cylinder decreases and finally approaches vibration in one flexible cylinder configuration.The larger gap ratio is,the slower amplitude decreases.Vibration amplitude of flexible cylinder increases with increasing turbulence intensity.The effect of turbulence intensity on vibration amplitude is not obvious at low non-dimensional velocity,and the effect of turbulence on vibration amplitude in lager gap ratio case is stronger than that in small gap ratio case.