On the origin of wake-induced vibration in two tandem circular cylinders at low Reynolds number |
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| Affiliation: | 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. College of Environmental Science and Engineering, Suzhou University of Science and Technology, Suzhou 215011, P. R. China;2. College of Water Conservancy and Hydropower Engineering, Hohai University, Nanjing 210098, P. R. China;3. College of Environment, Hohai University, Nanjing 210098, P. R. China;1. NUS Graduate School for Integrative Sciences and Engineering, National University of Singapore, 28 Medical Drive, Singapore 117456, Singapore;2. Department of Mechanical Engineering, National University of Singapore, 21 Lower Kent Ridge Road, Singapore 119077, Singapore;1. Institute for Turbulence-Noise-Vibration Interactions and Control, Shenzhen Graduate School, Harbin Institute of Technology, Shenzhen 518055, China;2. Key Lab of Advanced Manufacturing Technology, Shenzhen Graduate School, Harbin Institute of Technology, Shenzhen 518055, China;3. School of Civil and Resource Engineering, The University of Western Australia, Australia |
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| Abstract: | We numerically investigate flow-induced vibrations of circular cylinders arranged in a tandem configuration at low Reynolds number. Results on the coupled force dynamics are presented for an isolated cylinder and a pair of rigid cylinders in a tandem configuration where the downstream cylinder is elastically mounted and free to vibrate transversely. Contrary to turbulent flows at high Reynolds number, low frequency component with respect to shedding frequency is absent in laminar flows. Appearance and disappearance of the vorticity regions due to reverse flow on the aft part of the vibrating cylinder is characterized by a higher harmonic in transverse load, which is nearly three times of the shedding frequency. We next analyze the significance of pressure and viscous forces in the composition of lift and their phase relations with respect to the structural velocity. For both the isolated and tandem vibrating cylinders, the pressure force supplies energy to the moving cylinder, whereas the viscous force dissipates the energy. Close to the excitation frequency ratio of one, the ratio of transverse viscous force to pressure force is found to be maximum. In addition, movement of stagnation point plays a major role on the force dynamics of both configurations. In the case of isolated cylinder, displacement of the stagnation point is nearly in-phase with the velocity. During vortex-body interaction, the phase difference between the transverse pressure force and velocity and the location of stagnation point determines the loads acting on the cylinder. When the transverse pressure force is in-phase with velocity, the stagnation point moves to higher suction region of the cylinder. In the case of the tandem cylinder arrangement, upstream vortex shifts the stagnation point on the downstream cylinder to the low suction region. Thus a larger lift force is observed for the downstream cylinder as compared to the vibrating isolated cylinder. Phase difference between the transverse load and the velocity of the downstream cylinder determines the extent of upstream wake interaction with the downstream cylinder. When the cylinder velocity is in-phase with the transverse pressure load component, interaction of wake vortex with the downstream cylinder is lower compared to other cases considered in this study. We extend our parametric study of tandem cylinders for the longitudinal center-to-center spacing ranging from 4 to 10 diameter. |
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| Keywords: | Wake-induced vibration Tandem arrangement Stagnation point Vortex–body interaction Boundary layer Co-shedding |
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