Study On Vortex-Induced Vibration And Bionic Flow Control Of Slender Cylinder

The flow around a cylinder has always been the focus of the flow around a blunt body.At the same time,the circular section,as a simple section,is often used in various engineering structures.With the reduction of material weight,the improvement of strength and the lengthening and maximization of engineering structures,the slenderness ratio of cylindrical structures gradually is increasing.The influence of wind loads is increasingly prominent,and vortex-induced vibration is extremely prone to occur.Typical slender cylinders,such as stay cable,suspender,street lamp on bridge and signal columns,often have large-amplitude vortexinduced vibration.Long-term large-amplitude vortex-induced vibration is easy to cause structural fatigue damage and seriously affect the structural safety and service life.Therefore,it is of great significance to study the characteristics of vortex-induced vibration and how to suppress or even eliminate the vortex-induced vibration of cylinder.Based on the phenomenon of vortex-induced vibration of lamp column with weld on sea crossing bridge,this paper deeply analyzed the characteristics and mechanism of vortex-induced vibration of cylinder with weld.The giant cactus,in South America,can stand in the desert with strong wind all year round,and its unique aerodynamic shape plays a vital role.Therefore,based on the shape of the cactus,this paper proposed a bionic cylinder model which was used for the vortex-induced vibration control of the cylinder,and explores the flow field control effect,influencing factors and mechanism of the bionic cylinder.The main research contents of this paper include:(1)Taking the lamp column with weld as the research object,the phenomenon of vortexinduced vibration of the lamp column with weld was reproduced through the wind tunnel test of segmental model and aeroelastic model,and the influence of weld position on the vortexinduced vibration of the cylinder and its mechanism were studied.Firstly,the segmental model test of vibration and pressure measurement of cylinder with weld was carried out,and the vortex-induced vibration response of cylinder was obtained when the weld was located at different position on the cylinder surface.It was found that the weld on the cylinder surface could not only completely suppress the vortex-induced vibration,but also enhance the vortex-induced vibration.Secondly,according to the peak value of vortex-induced vibration response,the weld angle was divided into five intervals(Ⅰ～Ⅴ).According to the cylinder vortex-induced vibration characteristics of different weld intervals,the action mechanism of weld affecting cylinder vortex-induced vibration was analyzed through the pressure time history of each measuring point on the cylinder surface.Finally,the aeroelastic model of variable section light pole,which satisfied the requirement of similarity ratio,was designed and manufactured through welding several thin-walled hollow aluminum tubes and covering foam tubes and flexible PVC film.The vortex-induced vibration of the light pole was reproduced,and the influence of weld position on vortex-induced vibration was researched.The vortex shedding frequency along the height of light pole and time-frequency characteristics of vortex-induced vibration were analyzed by Fourier transform and wavelet analysis.Subsequently,the vortex-induced vibration lock-in characteristics of a variable section light pole was proposed.(2)The static flow around a cylinder and vortex-induced vibration responses of the cylinder with weld were calculated by CFD numerical simulation.Based on the segmental model wind tunnel test,the two-dimensional numerical simulation of the cylinder with weld was carried out.The comparison between the numerical calculation results and the experimental results verified the correctness of the numerical calculation.Then,the static aerodynamic coefficient,surface pressure distribution and wake characteristics of the cylinder with weld were analyzed,and the mechanism of the weld affecting the cylinder was revealed.Finally,the vortex-induced vibration response of the cylinder with weld was calculated,and the vortex vibration characteristics of the cylinder with weld were studied.(3)Based on the aerodynamic shape of giant cactus,a bionic cylinder model was proposed,and the flow control effect of bionic cylinder was explored through CFD numerical simulation.Firstly,the bionic cylinder parameters of the serrate structure height ratio and angle were studied.By comparing the aerodynamic coefficients and flow field changes of the bionic cylinder,it was found that the bionic shape had the effect of reducing drag and pulsating lift.Secondly,the influence of the number of serrate structure was explored.The mechanism of serrate structure was studied through flow field analysis.Finally,the bionic cylinder was applied to vortex vibration control,and the vortex-induced vibration of the bionic cylinder was numerically simulated.It was found that the bionic aerodynamic shape could reduce the vortex vibration response of the cylinder.