Numerical Investigation On Wake-induced Vibration Of Two Cylinders In Tandem Arrangement

Wake-induced vibration appear widely in various engineering fields,such as high-rise buildings,large-span bridge cables,platform columns,submarine pipelines,and transmission pipelines,etc.The cylinder structure with elastic support is submerged in the wake of the other structure,causing the surface of downstream structure is subjected to fluid forces at both the inline and transverse direction.The fluid forces lead the structure to oscillate,and the flow field around it will change as well.The structure may vibrate or resonate under the periodic fluid forces,resulting in local fatigue damage or overall damage.Therefore,wake-induced vibration is a practical subject with potential significances in engineering fields.The wake-induced vibration of two cylinders in tandem arrangement has been numerically investigated by using semi-implicit Characteristics-Based Split(CBS)finite element algorithm.The wake-induced vibration of unequal diameter two tandem circular cylinders,unequal diameter upstream square cylinder-downstream circular one,and two square cylinders in tandem arrangement are analyzed,and the structure dynamic response is revealed according to the analysis of the characteristic of the flow field,which can provide reference for engineering design.The main research work of this paper is organized as follows:(1)The Wake-induced vibrations of a 2-DOF circular cylinder which is placed behind a stationary circular cylinder with different diameters are numerically investigated.The influence of diameter ratio(d/D)and reduced velocity(Ur)on the wake-induced vibration dynamic response of the downstream cylinder are analyzed.The dynamic response characteristics of the downstream cylinder is revealed and the evolution of the flow is explored.Numerical results demonstrate that the mutual interference between the two cylinders will change from the vortex interference to the wake one with the increasing of the d/D.The change of d/D and Ur has a great influence on the amplitude of the downstream cylinder in the transverse direction,while has small influence in the inline direction.When d/D=1.0,the motion orbit of the downstream cylinder is complicated and irregular.The wake interference becomes strong as the diameter ratio increases from 1 to 1.5,and the main X-Y trajectory of the downstream cylinder is "8" and "double 8" shape.Meanwhile,the wake vortex pattern mainly presents two modes: 2S and P+S at d/D=1.0.As d/D increases to 1.5,the wake vortex pattern will show 2S,P+S and 2P.(2)The wake-induced vibrations of a 2-DOF circular cylinder which is placed behind a stationary square cylinder with different size ratios(d/D)are numerically investigated.The influence of size ratio(d/D)and reduced velocity(Ur)on the wake-induced vibration dynamic response of the downstream cylinder were analyzed.The dynamic response of the downstream cylinder is revealed and the evolution of the flow is explored.Numerical results demonstrate that the mutual interference between the two cylinders will change from the vortex interference to the wake one with the increasing of the d/D.The change of d/D and Ur has a great influence on the amplitude of the downstream cylinder in the transverse direction,while has small influence in the inline direction.The frequency characteristics of the wake-induced vibration also have a large change compared with the flow-induced vibration.When d/D=1.0,the motion orbit of the downstream cylinder is complicated and irregular.The wake interference becomes strong as the diameter ratio increases from 1 to 1.5,and the main X-Y trajectory of the downstream cylinder is "8" and "double 8" shape.Meanwhile,the wake vortex pattern mainly presents two modes: 2S and P+S at d/D=1.0.As the d/D increases to 1.5,the wake vortex pattern will show 2S,P+S and 2P.(3)The wake-induced vibrations of a 2-DOF square cylinder which is placed behind a stationary square cylinder are numerically investigated.The influence of two key parameters,such as Reynolds number(Re)and reduced velocity,on the dynamic response characteristics of the downstream square cylinder are analyzed,and the internal mechanism of the wake-induced vibration is revealed.The results show that the Ur and Re have little effect on the amplitude of the single square cylinder,while have a great influence on the amplitude of the downstream square one.As Re increases,the mutual interference effect will change from the vortex interference to the wake one.Meanwhile,the motion trajectories of the single cylinder resemble “8” shape.However,the trajectory of the downstream square cylinder is more complicated.Under different Ur and Re,the wake pattren of the two-cylinder system exhibits 2S,2P,P+S,2T and steady mode.