| Multi-cylinder system is widely used in marine resources exploration and exploitation.Due to the joint influence of the wake interference between the ocean current and the cylinder,the flow induced vibration of the multi-cylinder system is more complicated than that of the single cylinder.In this paper,a series of model tests of multi-cylinder system were carried out in the circulating flume laboratory to solve the problem of multi-cylinder system induced by flow vibration.Combined with the experimental data,the leakage vortex model of threecylinder series induced by flow vibration was simulated by using the CFD numerical simulation method based on the immersed boundary method,which provides the data basis for further study of the characteristics of multi-cylinder system induced by flow vibration.Firstly,the cylinder spacing ratio(Lx = 2.5D ～ 7.0D)and the flow velocity(U =0.4 ～1.2m/s)were set to conduct a model experiment of a multi-cylinder system in a series of uniform flow with equal spacing distribution.The vibration trajectory,vibration amplitude,cross-flow lift force and acceleration of each cylinder in the multi-cylinder system were measured.The effects of spacing ratio on the vibration amplitude,frequency and lift coefficient of the multi-cylinder system are compared and analyzed,and the response rules of the multicylinder system under different reduction speeds are obtained.Secondly,CFD was used to simulate the fluid induced vibration of a series multi-cylinder system with the cylinder spacing ratio Lx = 3.0D,4.0D and 5.0D.The accuracy of the solver hydro3 d was verified by comparing the experimental data and the results of other researchers.The shedding and development of the vortex in the fluid induced vibration of the series multi-cylinder system was analyzed.The interference process of the tail vortex of the upstream cylinder to the downstream cylinder is analyzed.The results of model test and CFD simulation show that the three cylinders in series have smaller initial velocity and wider vibration range than the two cylinders.At the same spacing ratio,the maximum amplitude of the triple cylinder is larger than that of the double cylinder,and there are several locking regions in the subcritical Reynolds number interval,and the amplitude of the middle cylinder is the largest.At cylindrical spacing ratio Lx <At 4.0D,the vibration amplitude of the middle cylinder and the downstream cylinder presents a step upward trend at a higher flow velocity.In this case,the vibration modes of the middle cylinder and the downstream cylinder are vortex-induced vibration and galloping vibration.At spacing ratio Lx>At 4.0D,the vibration mode of the middle cylinder and the downstream cylinder is vortexinduced vibration and flasticity discontinuity.According to the vorticity cloud map,at this time,the tail vortex of the upstream cylinder has space to develop.Instead of being attached to the middle cylinder,it attracts the boundary layer to separate in advance behind the middle cylinder,which makes the wake of the middle cylinder wider.The wider wake squeezes the trailing vortex of the downstream cylinder from both sides,narrowing it. |
