Study On Aerodynamic Characteristics Of Parallel Cables

With the application of emerging composite materials and the improvement of bridge construction technology,modern bridges are developing towards lighter and larger spans.the length of stay cables has also increased and its arrangment form presents a diversification characteristics.the downstream cable is disturbed by the wake of the upstream cable,which is prone to wind-induced vibration problems that seriously affecting the driving comfort and even threatening the safety of the bridge.The flow characteristics of parallel cables and the problem of wake galloping always been the research hotspots of bridge wind engineering.Parallel cable wind-induced vibration problem is essentially a bluff body flow problem.In this thesis,the numerical simulation method was used to study the flow characteristics of single and double cables with low Reynolds number.Then the wind tunnel test was used to study the aerodynamic characteristics of the cable with low Reynolds number to high Reynolds number.The experimental results have been compared with the numerical simulation results.Based on the experimental results,the instability region of the wake galloping of the downstream cable was predicted.The main work and achievements of this thesis are as follows:1.The wind-induced vibration type and vibration reduction measures of the cable were expounded.The research status of the parallel cable flow were reviewed,and the research methods and research ideas of this thesis were proposed.2.The governing equations in fluid mechanics and the numerical simulation methods of turbulence were introduced.The large eddy Simulation and the sub-grid scale model used in this thesis are introduced.3.The numerical simulation results of single cable are compared with previous experiments or numerical simulation results,and the correctness of mesh division and parameter setting in numerical simulation in this thesis is proved.4.The numerical simulation of the parallel cable was carried out under low Reynolds number.It was found that a large range of backflow area is formed between the two cables when the wind angle is small.As the angle increases,a gap flow with fast speed will appear between the cables.This makes the flow characteristics of the parallel cables at different angles produce a big difference.5.The correctness of the numerical simulation is verified by the wind tunnel test.The aerostatic coefficients is studied with high Reynolds number.Based on the single degree of freedom classic galloping instability theory,it was predicted that the downstream cable is most prone to galloping instability when the wind angle near 8°.