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Wake modes behind a streamwisely-oscillating cylinder at constant and ramping frequencies.

Hu, Zhanwei and Liu, Jinsheng and Gan, Lian and Xu, Shengjin (2019) 'Wake modes behind a streamwisely-oscillating cylinder at constant and ramping frequencies.', Journal of visualization., 22 (3). pp. 505-527.


studied at Reynolds number Re = 360–460 which are observed by laser-induced fluorescence flow visualization technique. The forcing frequency fe ranges from 0 to 6.85 fs , where fs is the vortex shedding frequency behind a stationary cylinder, and the forcing amplitude A=d ¼ 0:2; 0:5; 1:0, where d is the cylinder diameter. Both time-invariant and linearly ramping fe are investigated. Following our previous modal notation, the following conclusions can be drawn: firstly, three rarely reported modes in numerical studies, C-I, C-II and S-III, are now confirmed in experiments (though with differentiable appearance in their far wake behaviour) at higher A and/or fe ranges and the envelope lines of S modes and C modes, yielded from a vortex circulation model, are shown to be dependent on the peak relative velocity of the free stream to the cylinder surface. So is the occurrence of the S-II mode. Secondly, near the demarcation of A modes and S-I mode, wake mode undergoes constant transition in a stochastic manner at fixed Re, A and fe. Thirdly, a typical hysteretic effect can be observed when the oscillation frequency of the cylinder ramps up and down in a linear way, and the extent of delay is dependent on the ramping rate k. Finally, mode switching during frequency ramping obeys a unidirectional order. During k\0 (ramp-down), when S-I (Type-II) mode switches to A-IV mode, or A-IV to A-III, the flow structure downstream is affected by the upstream and the entire wake flow eventually switched, which is classified as slow switches. In contrast, during k[0 (ramp-up), a clear and abrupt switch can be observed in the wake when A-IV or A-III switch to S-I (Type-II) modes, which are jump switches.

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Publisher statement:© The Author(s) 2019. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (, which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
Date accepted:05 January 2019
Date deposited:25 January 2019
Date of first online publication:25 March 2019
Date first made open access:No date available

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