Vortex-induced vibration of a transversely rotating sphere

Abstract

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 : 18563To link to this article : DOI : URL :Any correspondence concerning this service should be sent to the repository administrator: staff-oatao@listes-diff.inp-toulouse.fr AbstractVortex-induced vibration (VIV) of a sphere is one of the most basic fluid-structure interaction problems. Since such vibrations can lead to fatal structural failures, numerous studies have focused on suppressing such flow-induced vibrations. In this study, for the first time, the effect of an imposed transverse rotation on the dynamics of the VIV of an elastically mounted sphere has been investigated. It was observed that the non-dimensional vibration amplitude for a rotating sphere (A * = √ 2y rms /D, where y rms is the root mean square of the displacement in the transverse direction and D = sphere diameter) exhibits a bell-shaped evolution as a function of reduced velocity, similar to the classic VIV response of a non-rotating sphere. The sphere is found to oscillate freely up to a rotation ratio α (ratio of the equatorial velocity of the sphere to the free-stream velocity) close to 0.5. For lower rotation ratios (α ≤ 0.3), the response looks similar to the non-rotating case but with slightly smaller vibration amplitude. For higher α values, the amplitude was found to decrease significantly with the rotation up to α = 0.5. The amplitude dropped drastically after it reached the peak amplitude. This is unlike the VIV response of a rotating circular cylinder where the vibration amplitude increases up to three times the maximum vibration amplitude in the nonrotating case due to a novel asymmetric wake pattern (see [1]).

Vortex dynamics and vibration modes of a tethered sphere

“…Thus, it can be assumed that the sphere undergoes a very small amount of rotation when it is also subjected to torsion. Our previous study (Rajamuni et al 2018b) and the study of Sareen et al (2018a) investigated the VIV response of an elastically mounted sphere under a forced rotation. Both of these studies found that the effect of rotation is negligible on the VIV response of the sphere, for small rotation rates.…”

“…In addition, mode II also appears sensitive to disturbances and other factors. For example, the experimental study of Sareen et al (2018a) and the computational study of Rajamuni et al (2018b) found that the mode II response weakens if even weak rotation (in the transverse direction) is imposed on the sphere. In particular, they observed a considerable reduction in the maximum oscillation amplitude and a narrowing of the synchronization regime.…”

“…The FIV response was strongly dependent on Reynolds number for higher reduced velocities (U * > 13); at Re = 300, the sphere showed two small-amplitude vibration regions, whilst at Re = 800, it showed intermittent bursts (mode IV). Rajamuni, Thompson & Hourigan (2016 and Sareen et al (2018a) studied the effect of transverse rotation on the VIV of a sphere computationally and experimentally, respectively. They found that the response amplitude decreased and the synchronization regime narrowed as the rotation rate increased.…”

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

“…Interestingly, the amplitude of mode II was observed to be about twice that of mode I. In contrast to these experimental observations at high Reynolds numbers, the transition between modes I and II was obscure in the amplitude response at low Reynolds numbers (Behara, Borazjani & Sotiropoulos 2011; Behara & Sotiropoulos 2016; Rajamuni, Thompson & Hourigan 2018 a , b ). The recent study of Rajamuni, Thompson & Hourigan (2020 b ) numerically investigated vibration modes of a tethered sphere, and found that the effect of Reynolds number on the modes I and II regimes was significant over the Reynolds number range , although it was found to be insignificant beyond that range for in the experimental studies of Govardhan & Williamson (2005).…”

“…This solver with a similar computational set-up was used for the computational study of Rajamuni, Thompson & Hourigan (2016) and Rajamuni et al. (2018 b ) to examine the effect of transverse rotation on the FIV of a sphere. In addition, Rajamuni et al.…”