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Quasi-Periodic Oscillating Flows in a Channel with a Suddenly Expanded Section

Department of Aeronautics and Astronautics, Tokyo Metropolitan University, Hino 191-0065, Japan
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Symmetry 2019, 11(11), 1403; https://doi.org/10.3390/sym11111403
Received: 15 October 2019 / Revised: 7 November 2019 / Accepted: 10 November 2019 / Published: 13 November 2019
(This article belongs to the Special Issue Symmetry in Fluid Flow)
In this study, two-dimensional numerical simulation was carried out for an oscillatory flow between parallel flat plates having a suddenly expanded section. Governing equations were discretized with the second-order accuracy by a finite volume method on an unequal interval mesh system resolving finer near walls and corners to obtain the characteristics of the oscillatory flow accurately. Amplitude spectrums of a velocity component were obtained to investigate the periodic characteristics of the oscillatory flow. At low Reynolds numbers, the flow is periodic because the spectrum mostly consists of harmonic components, and then at high Reynolds numbers, it transits to a quasi-periodic flow mixed with non-harmonic components. In conjunction with the periodic oscillation of a main flow, separation vortices that are not uniform in size are generated from the corner of a sudden contraction part and pass through a downstream region coming into contact with the wall. The number of the vortices decreases rapidly after they are generated, but the vortices are generated again in the downstream region. In order to specify where aperiodicity is generated, the turbulent kinetic energy is introduced, and it is decomposed into the harmonic and non-harmonic components. The peaks of the non-harmonic component are generated in the region of the expanded section. View Full-Text
Keywords: two-dimensional flow; instability; transition; separation; amplitude spectrum; turbulent kinetic energy two-dimensional flow; instability; transition; separation; amplitude spectrum; turbulent kinetic energy
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Masuda, T.; Tagawa, T. Quasi-Periodic Oscillating Flows in a Channel with a Suddenly Expanded Section. Symmetry 2019, 11, 1403.

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