Study On The Flow Field Characteristics Of The π Shape Bridge Based On CFD Technology

As the main form of modern long-span bridges,the wind-induced vibration needs to be considered in the design stage of the cable-stayed bridge.Because of the simple modeling,clear force and convenient construction,the π section has gradually become the main section form of modern cable-stayed bridges.However,the semi open cross-section form is seriously passivated,and the separation and reattachment in the surface flow are more obvious and complex than the fully enclosed box girder,which seriously weakens the wind resistance of this kind of bridge section.Both the flutter performance and the vortex vibration performance of the π section is significantly lower than that of the fully enclosed box girder.The air nozzle,stabilizing plate,spoiler and guide plate are the main measures to improve the aerodynamic performance of the π section,but it still rely on the wind tunnel test to determine the right size and combination scheme,which cost large amount of time.and force.Thus,the mechanism of wind induced vibration of π section needs to be studied urgently.Based on Fluent software,numerical simulation is carried out for different sections.The measuring points are set around the section for the time history of wind speed and wind pressure coefficient.The flow field trace around the section is extracted through post-processing software Tecplot.The parameters such as maximum swirl scale,turbulence integral scale and surface partial pressure coefficient are obtained to describe the characteristics of flow field.On this basis,the wind attack angle effect and Reynolds number effect of the flow field characteristics of the π section are investigated.The influence of the different air nozzle size,the position of the stable plate and the opening rate of the stable plate on the flow field characteristics of the π beam is also studied.The study shows that the wind angle of attack has a great influence on the flow field characteristics of the π beam.When the angle of attack is positive,the maximum scale and the average scale of the vortex are larger,resulting in the decrease of aerodynamic performance of the section.In the low Reynolds number range,the flow field is independent of Reynolds number.When the turbulence integral scale is higher than 0.3 or less than 0.1,the aerodynamic performance of the section is improved.The wind nozzle and the lower stability plate can effectively reduce the vortex size of the flow field.The flow field characteristics of the π section is better when angle of the upper edge of the wind nozzle is at 41~43 degrees.and the lower edge of the wind nozzle is at 20~24 degree.The best angle of the wind nozzle is 60~65 degrees.The wind tunnel test proves that the flutter stability and vortex vibration stability of the π beam are good when the angle of the upper edge of the wind nozzle is 42.3 degrees,and the angle of the lower edge is 20.2 degrees,and the central stabilizing plate is set under the section.