Numerical Simulation Of Sub-span Oscillation Of Bundle Conductor Transmission Line

With the rapid growth of electricity transmission capacity in our country, the adoption of bundle conductor transmission lines have become inevitable. Bundle conductor transmission lines have the advantages of high-capacity and low loss. Although UHV is an economical and technically mature approach, the oscillations of bundle conductor transmission lines cause serious damage. Study on wind induced vibration of transmission line has always been a popular issue. Transmission line is a flexible structure with a large span and a small damping. Besides, the large span conductor has characteristic of strong coupling structure and fluid. Transmission conductor will vibrate under wind load excitation, such as vortex-induced vibration, sub-span oscillation, galloping and so on. Previous experimental study of oscillation on transmission line and the numerical simulation of flow around cylinder under low Reynolds number are numerous, but the simulation calculations of elastic cylinder with Reynolds number in sub-critical region are few.The computational fluid dynamics(CFD) is employed in present paper to study the characteristics of transmission conductor with circular section under a uniform inflow.The research work of this paper is mainly focus on the following aspects:Firstly, a user defined function(UDF) based a Newmark-β algorithm was used to realize the numerical calculation of the structural domain. Reasonable computational domain is selected and using ICEM to realize the meshing of computational domain. In order to avoid the deformation of the grid induced by the cylinder movement and the use of moving mesh technique, multi-block grid generation technique is used to deal with the grid. By using moving mesh and dynamic mesh technologies above to realize the boundary update, a numerical calculation method of flow-induced vibration of a rigid cylinder under an elastic support come true. In order to improve the calculation efficiency, the program is written in accordance with the requirements for parallel computation and Fluent parallel computing is taken.Secondly, the effects of time step on the unsteady calculation is studied.Through the trial, reasonable time step is selected to calculate the vortex-induced vibration problem of a single cylinder. The influence of the mass ratio of cylinder and damping ratio on the cylinder amplitude is investigated, and the calculated results and experimental results are analyzed comparatively to validate the reliability of the grid quality and program.Thirdly, fixed cylinders with different spacing ratio between them are simulated at Reynolds number 20000. The related dynamic parameters are obtained at different spacing ratios of the two cylinders, such as drag coefficient, Strouhal number and so on. The vortexes shed from the upstream and downstream cylinders with different space ratios are observed. The results show that there is a critical space ratio at which space the drag and lift coefficients of the two cylinders would change obviously.Fourthly, the vibration type’s characteristics of the downstream elastic cylinder with two-degree-of freedom motion in the wake of an upstream stationary one are investigated. The spacing ratio L/D=2, T/D=1(L means the space between the center of the two cylinders in the horizontal direction,T means the space between the center of the two cylinders in the vertical direction)of the two cylinders is investigated, the vortex-induced vibration and galloping are observed and the numerical results demonstrate good agreement with the experimental results. The condition of the two cylinders in tandem at different space ratios under a uniform flow with different velocities is simulated, the vibration amplitudes of the downstream elastic cylinder with two-degree-of freedom motion versus the space ratio and flow velocity are studied.With the increase of the space ratio, the horizontal amplitude of the downstream cylinder increases and the vertical amplitude shows irregular. With the increase of the velocity of the flow, the horizontal amplitude of the downstream cylinder increases and the vertical amplitude declines in general.Lastly, the condition of the two cylinders both mounted with mass-spring-damping system elastically is investigated. The vibration type’s characteristics of the two cylinders in tandem at different space ratios are investigated. The calculated results are compared with that of the upstream cylinder fixed case. The results show that the horizontal amplitude of the downstream cylinder declines and the vertical amplitude of the downstream cylinder increases in general. Finally, the effects of the natural frequency ratio of the cylinders in two directions on the vibrations of the two cylinders are studied at the space ratio L/D=11 and T/D=0.5. Simply to improve the frequency ratio fy/ fx could decline the vertical amplitudes of both cylinders, but it has little influence on the horizontal amplitude of the two cylinders.