The effect of end conditions on the flow-induced vibration of circular cylinders in tandem arrangements

Abstract

The current paper reports the results of in-water experiments to study the effect of end conditions on cross flow induced vibration (FIV) of a pair of circular cylinders in a tandem arrangement. The upstream cylinder remains fixed but the downstream cylinder is elastically mounted. The single degree of freedom vibrating system has a low mass-damping parameter (m*ζ= 0.012, to 0.013). The Reynolds number ranges from 3.5 × 103 to 4 × 104. Various spacing ratios (S/D= 2, 3, 4, 5 and 6) are examined. The upper end of the oscillating cylinder is the free water surface, but the lower one remains either with or without an endplate.Based on the experimental results it is concluded that the response category, say wake induced vibration (WIV), vortex induced vibration (VIV) or transition, does not change by the presence or absence of the endplate. With the WIV category, the oscillation amplitude (A*) is predominantly higher in the absence of an endplate and the maximum amplitude (A*max) may increase as much as 100%. The maximum lift force coefficient may increase as much as 25%. In the absence of the endplate, the lift force signals contain a perceptible 3rd sub-harmonic at both low and high reduced velocities. With the VIV type of response, the maximum amplitude is less significantly affected by the end conditions.