Stream-wise and cross-flow vortex induced vibrations of single tapered circular cylinders: An experimental study

• The vortex-excited stream-wise and cross-flow vibrations of tapered cylinders are investigated.
• Results from in-water towing-tank experiments in a uniform flow are reported.
• The lock-in range in tapered cylinders is wider than that in their equivalent uniform cylinder.
• The response of the strongly tapered cylinder is dominated by the larger end of the cylinder.
• Upside-downing the tapered cylinder has not very significant effects on the cross-flow vibrations.

Tapered circular cylinders are employed in a variety of ocean engineering applications. While being geometrically simple, this configuration creates a complex flow pattern in the near wake of the structure. Most previous experimental studies on tapered circular cylinders were dealing with stationary cylinders to explore the wake flow field and vortex shedding patterns past the cylinder. Few studies paid attentions to the vortex induced vibration of the tapered cylinders. This paper reports some results from in-water towing-tank experiments on the vortex-excited vibrations of tapered circular cylinders in a uniform flow. Cylinders with different mean diameters (28 and 78 mm), mass ratios (6.1 and 2.27) and tapers (5–20), along with their equivalent uniform cylinders, have been examined. The single degree of freedom vibrating system has a low mass-damping parameter (m*ξ = 0.0084–0.0279). The Reynolds number, based on mean diameter of the cylinders, ranges from 1400 to 70,200. The reduced velocities vary from 1.5 to 22. Effects of variations in the taper and mass ratios on the lock-in range, the reduced response amplitude, the reduced velocity for the peak vibration response and other stream-wise and cross-flow VIV parameters are reported and discussed.