Vortex-Induced Vibration of a Circular Cylinder With Fairings
- Shengping Liang (aSchool of Naval Architecture, Shanghai Jiao Tong University) | Jiasong Wang (aSchool of Naval Architecture, Shanghai Jiao Tong University) | Zhongming Hu (aSchool of Naval Architecture, Shanghai Jiao Tong University)
- Document ID
- International Society of Offshore and Polar Engineers
- The 28th International Ocean and Polar Engineering Conference, 10-15 June, Sapporo, Japan
- Publication Date
- Document Type
- Conference Paper
- 2018. International Society of Offshore and Polar Engineers
- Vortex-induced vibration, harmonics, Wind tunnel experiments, fairing
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- 45 since 2007
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The research about response of a circular cylinder with fairings has been performed to control VIV previously, but not comprehensively. In the present study, the vibration of a circular cylinder with different fairings(θ=120°, 1050, 900, 750, 600, 450, θ is the character angle of fairings) was investigated experimentally in a wind tunnel. It was found that all the response here shows the typical VIV phenomenon, where the excitation was limited in a discrete range of velocities. The vortex shedding frequency also demonstrates the typical frequency lock-in. The attachment of fairings would lead to the expansion of initial branch. When the character angle is large, the amplitude is slightly smaller than that of circular cylinders. With the further decrease of character angle, the amplitude rises up again till θ=600. FFT spectrums of velocity downstream show the coexistence of natural frequency component and higher harmonics, which is related to vortex shedding modes. The fairings would induce frequent presence of high harmonics.
Bluff bodies have been ubiquitous in practice, especially in ocean engineering. When the flow passes the structure, alternate vortices could shed with an oscillating force exerted on the body. Under certain circumstances when the vortex shedding frequency is close to the natural frequency of the structure, severe vibrations may be induced. This solid fluid interaction is called vortex-induced vibration(VIV)(Blevins, 1990).
Severe catastrophic events could be caused due to VIV, which makes the suppression of VIV remarkably essential in practice. There are two kinds of suppression strategies, the active and the passive. The latter one can well control the vortex shedding by attaching different devices. It has been widely utilized for its efficiency and convenience of installments. These passive devices include splitter plates, fairings, strakes and so on. Based on the suppression mechanism, these auxiliary structures have been sorted into three types: (1) devices to interfere the spanwise correlation, such as strakes, bumps and the wavy surfaces; (2) devices to impair the generation of shear layers, such as rods and porous shrouds; (3) devices to obstruct the communications of shear layers, such as splitter plates and fairings(Zdravkovich, 1981).
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