Flow-induced Vibrations Of Two Cylinders Of Different Natural Frequencies And Wind Tunnel Documentation

As we know,combinations of multiple cylindrical structures appear widely in various engineering fields,and the researching for flow around cylinders have never been given up.Among the researches,flow-induced vibration of two tandem cylinders have a same condition of identical natural frequency for both cylinders,but the two cylinders may not always have same natural frequency in our real life.This paper presents an experimental investigation on characteristics of flow-induced vibrations of two circular cylinders with different natural frequencies in tandem arrangement principally;and the documentation of wind tunnel.Both cylinders are allowed to vibrate in the cross-flow direction only.Six different natural frequency ratios fn* = 0.6,0.8,1.0,1.2,1.4 and 1.6 are considered,where fn* = fn,u/fn,d,fn,u and fn,d are the natural frequencies of the upstream and downstream cylinders respectively.The spacing ratio L/D(where L is the spacing between the two cylinder centers and D is the diameter)is varied as 1.5,2.0 and 2.5.Simultaneous measurements of cylinder vibration and frequency responses and vortex shedding frequency are conducted using laser vibrometer and hotwire respectively.The results indicate that the different natural frequencies of the cylinders may suppress both VE(vortex excitation)and galloping vibration of the cylinders at different velocity range,with the vibration response characteristics and their connections with oscillation frequency being elucidated.How the different natural frequencies of upstream and downstream cylinders affect the vortex shedding frequency in the downstream cylinder wake has also been illustrated.