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Numerical Investigation on Vortex-Induced Rotations of A Triangular Cylinder Using An Immersed Boundary Method 被引量:3
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作者 WANG Hua-kun YAN Yu-hao +2 位作者 CHEN Can-ming JI Chun-ning ZHAI Qiu 《China Ocean Engineering》 SCIE EI CSCD 2019年第6期723-733,共11页
A numerical study of vortex-induced rotations(VIRs) of an equivalent triangular cylinder, which is free to rotate in the azimuthal direction in a uniform flow, is presented. Based on an immersed boundary method, the n... A numerical study of vortex-induced rotations(VIRs) of an equivalent triangular cylinder, which is free to rotate in the azimuthal direction in a uniform flow, is presented. Based on an immersed boundary method, the numerical model is established, and is verified through the benchmark problem of flow past a freely rotating rectangular body.The computation is performed for a fixed reduced mass of m~*=2.0 and the structural stiffness and damping ratio are set to zero. The effects of Reynolds number(Re=25-180) on the characteristics of VIR are studied. It is found that the dynamic response of the triangular cylinder exhibits four distinct modes with increasing Re: a rest position,periodic rotational oscillation, random rotation and autorotation. For the rotational oscillation mode, the cylinder undergoes a periodic vibration around an equilibrium position with one side facing the incoming flow. Since the rotation effect, the outset of vortex shedding from cylinder shifts to a much lower Reynolds number. Further increase in Re leads to 2 P and P+S vortex shedding modes besides the typical 2 S pattern. Our simulation results also elucidate that the free rotation significantly changes the drag and lift forces. Inspired by these facts, the effect of free rotation on flow-induced vibration of a triangular cylinder in the in-line and transverse directions is investigated. The results show that when the translational vibration is coupled with rotation, the triangular cylinder presents a galloping response instead of vortex-induced vibration(VIV). 展开更多
关键词 vortex-induced rotation triangular cylinder dynamic response vortex shedding mode immersed boundary method
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Numerical simulation of flow past twin near-wall circular cylinders in tandem arrangement at low Reynolds number 被引量:2
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作者 Guo-qiang Tang Chuan-qi Chen +1 位作者 Ming Zhao Lin Lu 《Water Science and Engineering》 EI CAS CSCD 2015年第4期315-325,共11页
Fluid flow past twin circular cylinders in a tandem arrangement placed near a plane wall was investigated by means of numerical simulations. The two-dimensional Navier-Stokes equations were solved with a three-step fi... Fluid flow past twin circular cylinders in a tandem arrangement placed near a plane wall was investigated by means of numerical simulations. The two-dimensional Navier-Stokes equations were solved with a three-step finite element method at a relatively low Reynolds number of Re -- 200 for various dimensionless ratios of 0.25 ≤ G/D ≤2.0 and 1.0 ≤ L/D ≤ 4.0, where D is the cylinder diameter, L is the center-to-center distance between the two cylinders, and G is the gap between the lowest surface of the twin cylinders and the plane wall. The influences of G/D and L/D on the hydrodynamic force coefficients, Strouhal numbers, and vortex shedding modes were examined. Three different vortex shedding modes of the near wake were identified according to the numerical results. It was found that the hydrodynamic force coefficients and vortex shedding modes are quite different with respect to various combinations of G/D and L/D. For very small values of G/D, the vortex shedding is completely suppressed, resulting in the root mean square (RMS) values of drag and lift coefficients of both cylinders and the Strouhal number for the downstream cylinder being almost zero. The mean drag coefficient of the upstream cylinder is larger than that of the downstream cylinder for the same combination of G/D and L/D. It is also observed that change in the vortex shedding modes leads to a significant increase in the RMS values of drag and lift coefficients. 展开更多
关键词 Navier-Stokes equations Finite element method Circular cylinder vortex shedding mode Hydrodynamic force coefficient
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Rotational Oscillation Effect on Flow Characteristics of a Circular Cylinder at Low Reynolds Number
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作者 Alice Rosa da Silva Aristeu da Silveira-Neto Antonio Marcos Goncalves de Lima 《World Journal of Mechanics》 2015年第10期195-209,共15页
Two dimensional numerical simulations of flow around a rotationally oscillating circular cylinder were performed at Re = 1000. A wide range of forcing frequencies, fr, and three values of oscillation amplitudes, A, ar... Two dimensional numerical simulations of flow around a rotationally oscillating circular cylinder were performed at Re = 1000. A wide range of forcing frequencies, fr, and three values of oscillation amplitudes, A, are considered. Different vortex shedding modes are observed for a fixed A at several values of fr, as well as for a fixed fr at different values of A. The 2C mode of vortex shedding was obtained in the present study. It is important to point out that this mode has not been observed by other investigators for rotationally oscillating case. Also, it is verified that this mechanism has great influence on the drag coefficient for high frequency values. Furthermore, the lift and pressure coefficients and the power spectra density are also analyzed. 展开更多
关键词 Rotationally Oscillating Cylinder vortex shedding modes Drag Coefficient
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Vortex shedding in the flow around two side-by-side circular cylinders of different diameters 被引量:2
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作者 邱翔 毕贞晓 +1 位作者 罗剑平 刘宇陆 《Journal of Hydrodynamics》 SCIE EI CSCD 2017年第3期470-478,共9页
In this paper,the 3-D turbulent flow around two side-by-side circular cylinders of different diameters,at sub-critical Reynolds number(Re=3 900),is numerically simulated by the large eddy simulation(LES).The spaci... In this paper,the 3-D turbulent flow around two side-by-side circular cylinders of different diameters,at sub-critical Reynolds number(Re=3 900),is numerically simulated by the large eddy simulation(LES).The spacing ratios(T/D)between the two cylinders are considered in four cases(T/D=1.2,1.5,1.8 and 2.7)to study the vortex shedding and turbulent properties in the flow field.The main results are focused on the drag and lift coefficients,the vortex shedding frequency,the coherent structure,and the scale properties.It is shown that when T/D is equal to 1.2,the vortex shedding of the main cylinder is strongly suppressed by the small cylinder,the drag and lift coefficients of the main cylinder are smaller than those in other three cases.While T/D is equal to 1.5,the vortex shedding of the main cylinder can be improved,the drag and lift coefficients of the main cylinder are larger than those in other three cases.The empirical mode decomposition(EMD)method is applied to decompose the velocity signals traced by the LES.It is shown that there is a linear relationship between the mean period and the mode in the semi-log coordinates.The vortex shedding period of the main cylinder is consistent with the period of the restructured coherent structures quantitatively. 展开更多
关键词 Large eddy simulation(LES) drag and lift coefficients vortex shedding frequency empirical mode decomposition(EMD)
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