Experimental investigation of the flow-induced vibration of a curved cylinder in convex and concave configurations

Abstract

Experiments have been conducted to investigate the two-degree-of-freedom vortex-induced vibration (VIV) response of a rigid section of a curved circular cylinder with low mass-damping ratio. Two curved configurations, a concave and a convex, were tested regarding the direction of the flow, in addition to a straight cylinder that served as reference. Amplitude and frequency responses are presented versus reduced velocity for a Reynolds number range between 750 and 15 000. Results for the curved cylinders with concave and convex configurations revealed significantly lower vibration amplitudes when compared to the typical VIV response of a straight cylinder. However, the concave cylinder showed relatively higher amplitudes than the convex cylinder which were sustained beyond the typical synchronisation region. We believe this distinct behaviour between the convex and the concave configurations is related to the wake interference taking place in the lower half of the curvature due to perturbations generated in the horizontal section when it is positioned upstream. Particle-image velocimetry (PIV) measurements of the separated flow along the cylinder highlight the effect of curvature on vortex formation and excitation revealing a complex fluid–structure interaction mechanism

The influence of higher harmonic flow forces on the response of a curved circular cylinder undergoing vortex-induced vibration

“…4(b)), the wake can be divided into two regions: in the lower part of the cylinder, no vortex shedding was observed but in the upper part of the cylinder, where the cylinder was mainly perpendicular to the oncoming flow, vortex shedding was observed with mainly vertical vortex columns. These observations are in agreement with the numerical results of Miliou et al [24] and the experimental results of Assi et al [21] for stationary curved cylinders.…”

“…This difference in the response will be addressed in Section 5 by looking at the flow forces acting on the cylinder. The decrease in the amplitude of oscillations for the curved cylinder (both orientations) compared to the vertical cylinder is in agreement with the experimental results of Assi et al [21]. However, a direct quantitative comparison cannot be made since the set-up used in their work had a pendulum-like motion in two directions and also the cylinder had a horizontal extension, while the set-up used here had pure transitional motion with no extension in either end.…”

“…Vortex dislocations were observed for the convex orientation at mid-span of the curved cylinder as a consequence of different shedding frequencies at the lower and upper parts of the cylinder. Assi et al [21] conducted a series of tests on a curved cylinder, placed in flow and free to oscillate in two perpendicular directions. Their set-up had a horizontal extension attached to the lower end of the curved cylinder, similar to the cylinder used by de Vecchi et al [19].…”

Wake behind a concave curved cylinder

“…Since VIV is out of the scope of the present study, interested readers are directed to Refs. [12][13][14] and the relevant references therein.…”

Experimental investigation on in-plane/out-of-plane vortex-induced vibrations of curved cylinder in parallel and perpendicular flows

“…For freely oscillating curved cylinders, Assi et al [16] investigated the 2-DOF VIV of a low mass and damping cylinder in both convex and concave configurations with R/D = 10 and in the Re range of 750-15000. They found that, in comparison with a vertical cylinder VIV, both out-of-plane (cross-flow) and in-plane (in-line) maximum amplitudes of curved cylinders are reduced due to the curvature effect.…”