Transverse flow-induced vibrations of a sphere in the proximity of a free surface: A numerical study

Chizfahm, Amir; Joshi, Vaibhav; Jaiman, Rajeev K.

doi:10.1016/j.jfluidstructs.2021.103224

Cited by 13 publications

(10 citation statements)

References 38 publications

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“…Recently, Chizfahm, Joshi & Jaiman (2021) numerically investigated the transverse FIV of an elastically mounted sphere in the vicinity of a FS at , 0 and 1 over the reduced velocity range . The response amplitude decreased as decreased from to , but it increased as further decreased to 0.25, consistent with the findings of Sareen et al.…”

Section: Introductionsupporting

confidence: 74%

Vortex-induced vibration of a sphere close to or piercing a free surface

2021

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Vortex-induced vibration (VIV) of an elastically mounted sphere placed close to or piercing a free surface (FS) was investigated numerically. The submergence depth ( $h$ ) was systematically varied between $1$ and $-$ 0.75 sphere diameters ( $D$ ) and the response simulated over the reduced velocity range $U^*\in [3.5,14]$ . The incompressible flow was coupled with the sphere motion modelled by a spring–mass–damper system, treating the free-surface boundary as a slip wall. In line with the previous experimental findings, as the submergence depth was decreased from $h^* = h/D =1$ , the maximum response amplitude of the fully submerged sphere decreased; however, as the sphere pierced the FS, the amplitude increased until $h^* = -0.375$ , and then decreased beyond that point. The fluctuating components of the lift and drag coefficients also followed the same pattern. The variation of the near-wake vortex dynamics over this submergence range was examined in detail to understand the effects of $h^*$ on the VIV response. It was found that $h^* = 1$ is a critical submergence depth, beyond which, as $h^*$ is decreased, the vortical structures in the wake vary significantly. For a fully submerged sphere, the influence of the stress-free condition on the VIV response was dominant over the kinematic constraint preventing flow through the surface. For piercing sphere cases, two previously unseen vortical recirculations were formed behind the sphere near times of maximal displacement, enhancing the VIV response. These were strongest at $h^* = -0.375$ , and much weaker for small submergence depths, explaining the observed response-amplitude variation.

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Section: Introductionsupporting

confidence: 74%

Vortex-induced vibration of a sphere close to or piercing a free surface

2021

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“…For 0 < h * < 1, downstream vortex loops were connected to the FS, as expected. The shape of the vortex loops were also modified, by stretching and twisting, as also observed by [2]. For the sphere placed close to the FS, the near wake becomes more affected.…”

Section: Response Of a Fully-submerged Spherementioning

confidence: 58%

“…These findings strongly resemble those of Sareen et al [15], although the Reynolds number of their study varied in the range 5 000 ≤ Re ≤ 30 000, while Re was fixed at 2 000 in the present study. Chizfahm et al [2] also reported that A * was small at h * = 0 compared with the value observed for h * = 1. The sphere response was highly periodic over both mode I and II regimes, even when it was in the vicinity of the FS (see figure 3 cient increased through the synchronisation regime from its preoscillatory value, as has been previously found for a bluff body undergoing VIV [1,4,11,13].…”

Section: Response Of a Fully-submerged Spherementioning

confidence: 82%

“…On the other hand, when the sphere pierced the FS, the response amplitude first increased and then decreased, as h * decreased. Chizfahm et al [2] examined numerically the effect of a FS on the VIV response of a sphere for three different submergence depths, h * = −0.25, 0, and 1, and reported similar observations to [15]. To the authors' knowledge, only these three studies have examined the influence of a free-surface on the VIV response of a sphere.…”

Section: Introductionmentioning

confidence: 85%

“…Interestingly, this amplitude was even higher than that for a fully submerged sphere. Recently, Chizfahm et al [2] also reported a large response amplitude at h * = −0.25. The vibration signal was highly periodic in the synchronisation regime for −5/8 ≤ h * ≤ −3/8, and slightly less so for −3/8 < h * < 0, as shown in 5(b).…”

Section: Response Of a Semi-submerged Spherementioning

confidence: 93%

See 2 more Smart Citations

Vortex-Induced Vibration of a Sphere Close to or Piercing a Free Surface

Rajamuni¹,

Thompson²,

Hourigan³

2020

Australasian Fluid Mechanics Conference (AFMC)

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Vortex-induced vibration (VIV) of an elastically mounted sphere placed in proximity to or piercing a free-surface (FS) was investigated numerically. The effect of the free-surface was examined over the reduced velocity range 3.5 ≤ U * ≤ 14, by systematically varying the submergence depth (h) between 1 and −5/8 sphere diameters (D). The fully-coupled fluid-structure system was solved assuming the flow is incompressible and treating the free-surface boundary as a non-deformable free-slip surface. In-line with previous experimental findings, the maximum sphere response amplitude was found to be sensitive to the submergence depth, and indeed the influence of submergence depth variation was stronger for the piercing-sphere cases, with the maximum response for h * = −3/8. The varying near-wake vortex dynamics was examined in detail to understand the effect of h * on the VIV response of the sphere. For piercingsphere cases, two previously unseen vortical recirculation bubbles were formed behind the sphere near times of maximum displacement, enhancing the VIV response. These were strongest at h * = −3/8, and much weaker for small submergence depths, explaining the observed response amplitude variation.

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