Time resolved measurements of vortex-induced vibrations of a tethered sphere in uniform flow

Hout, R. van; Krakovich, A.; Gottlieb, O.

doi:10.1063/1.3466660

Cited by 35 publications

(33 citation statements)

References 20 publications

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“…The forcing caused by vortex shedding also remains at close to the natural frequency. This vibration response is very similar to the bifurcation region III reported by van Hout et al (2010) for a heavy tethered sphere. They also observed less periodic, intermittent large oscillation amplitudes in the transverse direction for higher U * values of U * 15.…”

Section: Methodssupporting

confidence: 72%

Vortex-induced vibration of a rotating sphere

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. Vortex-induced vibration (VIV) of a sphere represents one of the most generic fundamental fluid-structure interaction problems. Since vortex-induced vibration can lead to structural failure, numerous studies have focused on understanding the underlying principles of VIV and its suppression. This paper reports on an experimental investigation of the effect of imposed axial rotation on the dynamics of vortex-induced vibration of a sphere that is free to oscillate in the cross-flow direction, by employing simultaneous displacement and force measurements. The VIV response was investigated over a wide range of reduced velocities (i.e. velocity normalised by the natural frequency of the system): 3 U * 18, corresponding to a Reynolds number range of 5000 < Re < 30 000, while the rotation ratio, defined as the ratio between the sphere surface and inflow speeds, α = |ω|D/(2U), was varied in increments over the range of 0 α 7.5. It is found that the vibration amplitude exhibits a typical inverted bell-shaped variation with reduced velocity, similar to the classic VIV response for a non-rotating sphere but without the higher reduced velocity response tail. The vibration amplitude decreases monotonically and gradually as the imposed transverse rotation rate is increased up to α = 6, beyond which the body vibration is significantly reduced. The synchronisation regime, defined as the reduced velocity range where large vibrations close to the natural frequency are observed, also becomes narrower as α is increased, with the peak saturation amplitude observed at progressively lower reduced velocities. In addition, for small rotation rates, the peak amplitude decreases almost linearly with α. The imposed rotation not only reduces vibration amplitudes, but also makes the body vibrations less periodic. The frequency spectra revealed the occurrence of a broadband spectrum with an increase in the imposed rotation rate. Recurrence analysis of the structural vibration response demonstrated a transition from periodic to chaotic in a modified recurrence map complementing the appearance of broadband spectra at the onset of bifurcation. Despite considerable changes in flow structure, the vortex phase (φ vortex ), defined as the phase between the vortex force and the body displacement, follows the same pattern as for the non-rotating case, with the φ vortex increasing gradually from low values in Mode I of the sphere vibration to almost 180• as the system undergoes a continuous transition to Mode II of the sphere vibration at higher reduced velocity. The total phase (φ total ), defined as the phase between the transverse lift force and the body displacement, only increases from low values after the peak amplitude † Email address for correspondence: jisheng.zhao@monash.edu response in Mode II has been reached. It reaches its maximum value (∼165• ) close to the transition from the Mode II upper plateau t...

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Section: Methodssupporting

confidence: 72%

Vortex-induced vibration of a rotating sphere

et al. 2017

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“…The present experiments were performed in a closed loop, square water channel facility consisting of a centrifugal pump, magnetic flow meter and an inlet section composed of a honeycomb and contraction section (9:1) (see also Van Hout et al, 2010). The 2-m long test section had an internal cross sectional area of 50 Â 50 mm 2 and was made of glass to ensure optical access from all sides ( Fig.…”

Section: Experimental Set-up and Methodologymentioning

confidence: 99%

“…Karanfilian and Kotas, 1978;Wakabe and Balachandar, 2007) and g is the gravitational constant. Data processing to extract the sphere dynamics were similar for both data sets and included determination of the sphere's centroid position by iteratively fitting a circle to the sphere's perimeter using Matlab's image processing toolbox (see Van Hout et al, 2010). The inaccuracy of the sphere's center position was estimated to be less than 1.2% of the sphere's diameter.…”

Section: Tablementioning

confidence: 99%

“…They showed that a tethered sphere in uniform water flow experienced large amplitude transverse oscillations with peak to peak amplitudes comparable to the sphere's diameter. Since then few papers have been published (Govardhan and Williamson, 2005;Jauvtis et al, 2001;Lee et al, 2008aLee et al, , 2008bVan Hout et al, 2010) providing some insight into the complex, inherently three-dimensional, coupled flow-structure behavior. These studies have identified multiple oscillation modes with increasing reduced velocity, U n ¼ U/f N D where f N is the natural frequency of the pendulum in the immersed fluid.…”

mentioning

confidence: 98%

“…In addition, the transverse vortex force exerted by the hairpin vortices on the sphere was quantified in analogy with wing trailing vortices. More recently, Van Hout et al (2010) presented detailed time-resolved PIV measurements of VIV of a 'heavy' tethered sphere (m n ¼7.87) in a uniform water flow. These measurements resolved both the sphere motion as well as the associated wake flow in a horizontal plane positioned at the sphere's center.…”

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confidence: 99%

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