Flow around four cylinders arranged in a square configuration |
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| Institution: | 1. Maritime Research Centre, Nanyang Technological University, 639798 Singapore, Singapore;2. Department of Engineering Mechanics, School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University, Shanghai 200240, China;3. Nanyang Environment and Water Research Institute, School of Civil and Environmental Engineering, Nanyang Technological University, 639798 Singapore, Singapore;1. Institute for Turbulence-Noise-Vibration Interaction and Control, Shenzhen Graduate School, Harbin Institute of Technology, Shenzhen, China;2. Key Lab of Advanced Manufacturing and Technology, Shenzhen Graduate School, Harbin Institute of Technology, Shenzhen, China;1. School of Marine Science and Technology, Northwestern Polytechnical University, Xi''an, Shaanxi, China;2. Department of Civil and Environmental Engineering, University of Houston, Houston, TX, 77204, USA;1. Center for Deepwater Engineering, Dalian University of Technology, Dalian 116024, China;2. State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian 116024, China;3. Department of Computer, Zhejiang Ocean University, Zhoushan 316000, China;4. School of Computing, Engineering and Mathematics, University of Western Sydney, Locked Bag 1797, Penrith, NSW 2751, Australia;5. School of Civil and Resource Engineering, The University of Western Australia, 35 Stirling Highway, WA 6009, Australia |
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| Abstract: | This paper presents an experimental study of the flow around four circular cylinders arranged in a square configuration. The Reynolds number was fixed at Re=8000, the pitch-to-diameter ratio between adjacent cylinders was varied from P/D=2 to 5 and the incidence angle was changed from α=0° (in-line square configuration) to 45° (diamond configuration) at an interval of 7.5°. The flow field was measured using digital Particle Image Velocimetry (PIV) to examine the vortex shedding characteristics of the cylinders, together with direct measurement of fluid dynamic forces (lift and drag) on each cylinder using a piezoelectric load cell. Depending on the pitch ratio, the flow could be broadly classified as shielding regime (P/D≤2), shear layer reattachment regime (2.5≤P/D≤3.5) and vortex impinging regime (P/D≥4). However, this classification is valid only in the case that the cylinder array is arranged nearly in-line with the free stream (α≈0°), because the flow is also sensitive to α. As α increases from 0° to 45°, each cylinder experiences a transition of vortex shedding pattern from a one-frequency mode to a two-frequency mode. The flow interference among the cylinders is complicated, which could be non-synchronous, quasi-periodic or synchronized with a definite phase relationship with other cylinders depending on the combined value of α and P/D. The change in vortex pattern is also reflected by some integral parameters of the flow such as force coefficients, power spectra and Strouhal numbers. |
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| Keywords: | Four cylinders Flow interference Strouhal number Force coefficients Particle Image Velocimetry (PIV) |
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