Resonant Vibrations of Bluff Bodies Cause Multivortex Shedding and High Frequency Forces

Dahl, Jason; Hover, Franz S.; Triantafyllou, Michael S.; Dong, Shen; Karniadakis, G. E.

doi:10.1103/physrevlett.99.144503

Cited by 149 publications

(122 citation statements)

References 16 publications

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“…The alternate vortex shedding observed at the peak of the first branch causes the cylinder to vibrate in the transverse direction at f x /2; this can be seen in figure 10(a), as the cylinder appears to follow a figure-of-eight trajectory. The figure-of-eight pattern appears to be characteristic of VIV, and has been observed in a number of studies of multi-DOF cylinders (Dahl et al 2007;Sanchis et al 2008;Blevins & Coughran 2009;Horowitz & Williamson 2010). This pattern becomes more pronounced as the reduced velocity and A y /D increase ( figure 10b-h); at U r /f * = 2.3 the pattern is strongly asymmetrical about the line x/D = 0, but becomes increasing symmetrical as U r /f * increases.…”

Section: Cylinder Trajectoriessupporting

confidence: 62%

Streamwise vortex-induced vibrations of cylinders with one and two degrees of freedom

Cagney

Balabani

2014

J. Fluid Mech.

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Measurements are presented of the structural response and wake of a two-degree-offreedom (2-DOF) pivoted cylinder undergoing streamwise vortex-induced vibrations (VIV), which were carried out using particle-image velocimetry (PIV). The results are compared with those of previous studies performed in the same experimental facility examining a cylinder free to move only in the streamwise direction (1-DOF). The aim of this study is to examine to what extent the results of previous work on streamwise-only VIV can be extrapolated to the more practical, multi-DOF case. The response regimes measured for the 1-and 2-DOF cases are similar, containing two response branches separated by a low-amplitude region. The first branch is characterised by negligible transverse motion and the appearance of both alternate and symmetric vortex shedding. The two wake modes compete in an unsteady manner; however, the competition does not appear to have a significant effect on either the streamwise or transverse motion. Comparison of the phase-averaged vorticity fields acquired in the second response branch also indicates that the additional DOF does not alter the vortex-shedding process. However, the additional DOF affects the cylinder-wake system in other ways; for the 1-DOF case the second branch can appear in three different forms (each associated with a different wake mode), while for the 2-DOF case the second branch only exists in one form, and does not exhibit hysteresis. The cylinder follows a figure-of-eight trajectory throughout the lock-in range. The phase angle between the streamwise and transverse motion decreases linearly with reduced velocity. This work highlights the similarities and differences between the fluid-structure interaction and wake dynamics associated with 1-and 2-DOF cylinders throughout the streamwise response regime, which has not received attention to date.

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Section: Cylinder Trajectoriessupporting

confidence: 62%

Streamwise vortex-induced vibrations of cylinders with one and two degrees of freedom

Cagney

Balabani

2014

J. Fluid Mech.

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“…Therefore, an orientation more favourable to positive energy transfer also exists at large inclination angle. The selection of the counter-clockwise orientation for body excitation is expected to be driven by similar mechanisms to those previously described in the normal incidence case, under parallel vortex shedding (closer proximity of the cylinder and the recently shed vortices, specific phasing between body motion and vortex suction forces [16,46]). The inclined body results show that the link between energy transfer and orbit orientation persists over a range of wake configurations, i.e.…”

Section: (A) Structural Responsesmentioning

confidence: 73%

Vortex-induced vibrations of a flexible cylinder at large inclination angle

Bourguet

Triantafyllou

2015

Phil. Trans. R. Soc. A.

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The free vibrations of a flexible circular cylinder inclined at 80° within a uniform current are investigated by means of direct numerical simulation, at Reynolds number 500 based on the body diameter and inflow velocity. In spite of the large inclination angle, the cylinder exhibits regular in-line and cross-flow vibrations excited by the flow through the lock-in mechanism, i.e. synchronization of body motion and vortex formation. A profound reconfiguration of the wake is observed compared with the stationary body case. The vortex-induced vibrations are found to occur under parallel, but also oblique vortex shedding where the spanwise wavenumbers of the wake and structural response coincide. The shedding angle and frequency increase with the spanwise wavenumber. The cylinder vibrations and fluid forces present a persistent spanwise asymmetry which relates to the asymmetry of the local current relative to the body axis, owing to its in-line bending. In particular, the asymmetrical trend of flow–body energy transfer results in a monotonic orientation of the structural waves. Clockwise and counter-clockwise figure eight orbits of the body alternate along the span, but the latter are found to be more favourable to structure excitation. Additional simulations at normal incidence highlight a dramatic deviation from the independence principle, which states that the system behaviour is essentially driven by the normal component of the inflow velocity.

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“…2S, P + S) that have commonly been reported in previous VIV studies of a non-rotating cylinder (e.g. Williamson & Roshko 1988;Blackburn & Henderson 1999;Mittal & Kumar 2003;Jauvtis & Williamson 2004;Dahl et al 2007). However, they also identified a n ovel T +S w ake p attern c omposed o f a t riplet o f v ortices and a single vortex shed per oscillation cycle, which was attributable to the largest amplitude response.…”

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confidence: 88%

Experimental investigation of flow-induced vibration of a rotating circular cylinder

et al. 2017

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OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. This is an author-deposited version published in : http://oatao.univ-toulouse.fr/ Eprints ID : 18605 While flow-induced vibration of bluff bodies has been extensively studied over the last half-century, only limited attention has been given to flow-induced vibration of elastically mounted rotating cylinders. Since recent low-Reynolds-number numerical work suggests that rotation can enhance or suppress the natural oscillatory response, the former could find applications in energy harvesting and the latter in vibration control. The present experimental investigation characterises the dynamic response and wake structure of a rotating circular cylinder undergoing vortex-induced vibration at a low mass ratio (m * = 5.78) over the reduced velocity range leading to strong oscillations. The experiments were conducted in a free-surface water channel with the cylinder vertically mounted and attached to a motor that provided constant rotation. Springs and an air-bearing system allow the cylinder to undertake low-damped transverse oscillations. Under cylinder rotation, the normalised frequency response was found to be comparable to that of a freely vibrating non-rotating cylinder. At reduced velocities consistent with the upper branch of a non-rotating transversely oscillating cylinder, the maximum oscillation amplitude increased with non-dimensional rotation rate up to α ≈ 2. Beyond this, there was a sharp decrease in amplitude. Notably, this critical value corresponds approximately to the rotation rate at which vortex shedding ceases for a non-oscillating rotating cylinder. Remarkably, at α = 2 there was approximately an 80 % increase in the peak amplitude response compared to that of a non-rotating cylinder. The observed amplitude response measured over the Reynolds-number range of (1100 Re 6300) is significantly different from numerical predictions and other experimental results recorded at significantly lower Reynolds numbers.

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Resonant Vibrations of Bluff Bodies Cause Multivortex Shedding and High Frequency Forces

Cited by 149 publications

References 16 publications

Streamwise vortex-induced vibrations of cylinders with one and two degrees of freedom

Streamwise vortex-induced vibrations of cylinders with one and two degrees of freedom

Vortex-induced vibrations of a flexible cylinder at large inclination angle

Experimental investigation of flow-induced vibration of a rotating circular cylinder

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