Flow control around a circular cylinder by internal acoustic excitation

Fujisawa, Nobuyuki; Takeda, Gentaro

doi:10.1016/s0889-9746(03)00043-4

Cited by 76 publications

(38 citation statements)

References 14 publications

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“…The velocity distributions in Figs. 2 and 3 can be said to be similar that obtained by Fujisawa and Takeda [29]. It is clear that v=U values for all Re are very small away from the cylinder boundary as seen in Fig.…”

Section: Resultssupporting

confidence: 77%

PIV measurements on the passive control of flow past a circular cylinder

Oruç

Akıllı

Şahi̇n

2016

Experimental Thermal and Fluid Science

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Section: Resultssupporting

confidence: 77%

PIV measurements on the passive control of flow past a circular cylinder

Oruç

Akıllı

Şahi̇n

2016

Experimental Thermal and Fluid Science

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“…However, the magnitude of fluctuating velocity is increased near the cylinder surface, which may be due to the variation of separation points over the cylinder surface by the influence of rotational oscillation. It is to be mentioned that the forcing frequency of the circular cylinder at Sf=1 agrees with the effective frequency range of the shear-layer synchronization (Hsiao andShyu 1991, Fujisawa andTakeda 2003). Therefore, the turbulent structure of the shear layer can be synchronized with the cylinder oscillation, which weakens the shear-layer interaction in the downstream of the cylinder.…”

Section: Resultssupporting

confidence: 53%

A study on drag reduction of a rotationally oscillating circular cylinder at low Reynolds number

Fujisawa

Ugata

Suzuki

2005

J Vis

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The flow field around a rotationally oscillating circular cylinder in a uniform flow is studied by using a particle image velocimetry to understand the mechanism of drag reduction and the corresponding suppression of vortex shedding in the cylinder wake at low Reynolds number. Experiments are conducted on the flow around the circular cylinder under rotational oscillation at forcing Strouhal number 1, rotational amplitude 2 and Reynolds number 2,000. It is found from the flow measurement by PIV that the width of the wake is narrowed and the velocity fluctuations are reduced by the rotational oscillation of the cylinder, which results in the drag reduction rate of 30%. The mechanism of drag reduction is studied by phase-averaged PIV measurement, which indicates the formation of periodic small-scale vortices from both sides of the cylinder. It is found from the cross-correlation measurement between the velocity fluctuations that the large-scale structure of vortex shedding is almost removed in the cylinder wake, when the small-scale vortices are generated at the unstable frequency of shear layer by the influence of rotational oscillation.

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“…However, it is well known that the introduction of such devices along the long slender structure modifies the structural configuration and increases the drag forces, apart from their high costs in manufacturing, installation, and maintenance. Alternatively, active flow controls by introducing, for instance, a surface suction and blowing [8], an acoustic actuation [15,21], and a neighboring rotational cylinder [14,20,24] have also been explored with the aim of delaying, interrupting, or intervening in the vortex formation process in the wake. Nevertheless, due to the frequent changes and uncertainties in ocean environments, it might be impractical to accurately predict the space-time-varying vortex formations and implement the active flow control methods in real time for deep-water structures.…”

Section: Introductionmentioning

confidence: 99%

Two-dimensional vortex-induced vibration suppression through the cylinder transverse linear/nonlinear velocity feedback

Srinil

2017

Acta Mech

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Suppressing vortex-induced vibration (VIV) has recently attracted numerous researchers due to its practical significance in many engineering applications. Most of the previous studies have focused on a passive or active flow control. A structurally active control approach to mitigate a two-dimensional, nonlinear coupled, cross-flow/in-line VIV has not been well studied. This paper presents a reduced-order fluid-structure dynamic model and combined analytical-numerical solutions for the efficient suppression of two-dimensional VIV of a flexibly mounted circular cylinder in uniform flows. The theoretical model is based on the use of coupled Duffing-Rayleigh oscillators with three variables describing the cylinder cross-flow/in-line displacements and the strength of the fluid vortex circulation in the cylinder wake. These equations of fluid-structure motions contain geometric and hydrodynamic nonlinearities. Closed-loop linear and nonlinear velocity feedback controllers are implemented in the transverse direction governing the larger cross-flow response than the associated in-line counterpart. Approximated analytical expressions are derived by using the harmonic balance to explicitly capture the system nonlinear dynamic features and the effects of key dimensionless parameters. Parametric investigations are carried out to evaluate the linear versus nonlinear controller performance in terms of the maximum response suppression capability and the power requirement in a wide range of reduced flow velocities, mass ratios, and control gains. Over the main lock-in resonance region with coupled cross-flow/inline responses, the linear controller is found to be more efficient in suppressing the two-dimensional VIV by also modifying the system frequencies and phase relationships. Nevertheless, based on the power comparison, the nonlinear control is superior to the linear control for very small targeted controlled amplitudes of a very low-mass cylinder. These active control strategies may be further applied to the multimode VIV suppression of a long flexible cylinder with multi degrees of freedom.

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Flow control around a circular cylinder by internal acoustic excitation

Cited by 76 publications

References 14 publications

PIV measurements on the passive control of flow past a circular cylinder

PIV measurements on the passive control of flow past a circular cylinder

A study on drag reduction of a rotationally oscillating circular cylinder at low Reynolds number

Two-dimensional vortex-induced vibration suppression through the cylinder transverse linear/nonlinear velocity feedback

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