Vortex-induced vibration of a collinear array of bottom fixed flexible cylinders

Abstract

An experimental study of vortex-induced vibrations of a collinear array of 10 identical flexible cylinders was conducted between 140<Re<450. The experiments were performed in a water tunnel using 0.13 mass-damping and 1% blockage ratio. Each cylinder response, for tested Reynolds number range, was determined tracking the cylinder free-end by means of a particle tracking velocimetry technique. Free-end displacements, free-end orbits, phase angle between cylinders as well as each cylinder frequency were obtained with data post-processing. The natural frequencies of one of the cylinders, in still water and still air, were measured as a reference throughout the lock-in region. The results show that the maximum displacement in the cross-flow direction for the first cylinder in the array is 28% higher compared to when it is isolated. Synchronization is reached from cylinder 2 throughout cylinder 8 for 340<Re<450. Under these conditions the cylinders have a CCW rotation and the cylinder frequency matches very accurately the cylinder natural frequency in still water. Moreover, the phase angle with respect to cylinder 2 shows a gradual delay as the Reynolds number is increased. The phase angle and the cylinder response are correlated with the vortex wake behavior and with the number of coherent vortices in the gaps between cylinders, respectively.