Study On The Mechanism Of Fluid-Induced Coupling Vibration Of Wavy Conical Cylinders In Staggered Arrangement

The proposal of the bladeless wind turbine makes up for the difficulties of installation and maintenance,low land utilization and high cost of traditional blade wind turbines.This paper is based on the wavy conical cylinder proposed by the research group,the vortex wake interference effect,vortex-induced vibration characteristics and "frequency locking" induction mechanism of upstream and downstream wavy conical cylinders at different spacing ratios and staggered angles were mainly explored.Which provides a theoretical basis for the array layout of bladeless wind turbines.First,based on the large eddy simulation,a computational model is established to study the flow characteristics of two wavy conical cylinders in staggered arrangement,and the correctness of the computational model is verified by numerical and experimental results.Then,the fluctuating lift and time-average drag characteristics and wake vortex/wake interference effect of two wavy conical cylinders in staggered arrangement with spacing ratio L/Dm = 4 ～ 9 and staggered angle α = 0 ～ 16° are analyzed emphatically.It is found that the flow structure between the upstream and downstream wavy conical cylinders exhibits different coupling states,namely the shear layer wrapping state,the transition state,the wake impact state,the side impact state and the wake disturbance state.In the side impact state,the vortex shedding formed by the interaction between the upwashing and downwashing flow of the upstream wavy conical cylinder and its side shear incoming flow collides on the side of the downstream wavy conical cylinder,and the vortex shedding interaction with the downstream wavy conical cylinder produces a coupled vortex exciting force,so that the downstream wavy conical cylinder can produce a higher fluctuating lift.For example,when the spacing ratio L/Dm = 5 and the staggered angle α = 8°,the fluctuating lift coefficient of the downstream wavy conical cylinder is up to 21.2 times higher than that of the single straight column.This means that the downstream wavy conical cylinder may induce a more severe vibration response under certain conditions.Furthermore,based on the overset grid and UDF technology,the numerical calculation model of the flow-induced coupled vibration response of two wavy conical cylinders in staggered arrangement is developed,and the correctness of the flow-induced vibration coupled model is verified numerically and experimentally.Finally,numerical studies are carried out on the single and double degrees of freedom vortex-induced vibration characteristics of the downstream wavy conical cylinders of the two wavy conical cylinders in staggered arrangement and its "frequency locking" induction mechanism.At the spacing ratio L/Dm = 4,the staggered angle α = 8 °,the flow between the upstream and downstream wavy conical cylinder shows two coupling modes,one-sided reattachment mode of shear layer and two-sided reattachment mode of shear layer.At the same time,the "2S","P + S" and "2C" vortex shedding modes are observed in different sections behind the downstream wavy conical cylinder.When the downstream wavy conical cylinder is subjected to single degree of freedom vortex induced vibration,the reattachment mode on both sides of the shear layer is the main reason why the downstream wavy conical cylinder has a wider reduced velocity range than the single wavy conical cylinder and still maintains a higher vibration amplitude at high reduced velocity.Its vibration range is widened to Ur = 5 ～ 13,and the maximum amplitude ratio is increased by 32.3%.When the downstream wavy conical cylinder is subjected to two degrees of freedom vortex induced vibration,the two modes also determine the direction of the long axis of the "elliptical" trajectory of the downstream wavy conical cylinder centroid;Under the action of upstream wavy conical cylinder wake,the maximum amplitude of downstream wavy conical cylinder along the flow direction is 29.4 times higher than that of single wavy cone column.This staggered layout can make the wind energy capture structure obtain more wind energy.Combined with experimental verification and numerical simulation,this paper studies the flow characteristics and flow induced vibration response characteristics of wavy conical cylinders in staggered arrangement under different layouts,which provides a theoretical basis for the array layout of bladed wind turbines.