Study On Aerodynamic Performance Of Rectangular Section Under The Effect Of Donwburst

The downburst is a kind of sudden impact airflow produced in thunderstorm weather,which causes a short-term strong wind near the ground after the airflow hits the ground.As an extreme climate that is distributed all over the world,the sudden strong wind load caused by the downburst near the ground is extremely destructive,resulting in a series of damage accidents of transmission line towers,building structures and other engineering structures.At present,there is a few researches on the effect of the sudden wind of the downburst on the bridge structure,considering that the main influence factor of the downburst on the bridge structure is the abrupt horizontal wind speed.The wind load effect of the vertical wind speed on the bridge structure can be ignored.In this paper,the traditional atmospheric boundary layer wind tunnel is improved to simulate the horizontal abrupt wind effect of the downburst wind field in the boundary layer wind tunnel.On this basis,the influence of horizontal abrupt wind effect of downburst flow on the static and aerodynamic performance and vortex vibration performance of bridge structure was studied.The main research work is as follows:(1)The characteristics of downburst flow field were introduced,the similarities and differences in the formation and development of traditional boundary layer wind were compared,and the simulation of downburst flow field and the related research status were reviewed.(2)Based on the large Computational Fluid Dynamics software,Fluent,the two-dimensional impinging jet model and three-dimensional impinging jet model were used to simulate the downburst flow field.It was verified that there is little difference between two-dimensional and three-dimensional downburst flow in horizontal wind speed vertical wind profile near the ground,and three-dimensional downburst flow can be approximately simplified by two-dimensional simulation,which lays a foundation for subsequent two-dimensional analysis.(3)Numerical simulation method was used to simulate the flow field after the inclined plate was used to improve the boundary layer wind tunnel,and the feasibility analysis of the radial wind field of storm flow under the simulation of boundary layer wind tunnel was carried out.According to the numerical simulation results and the actual situation of the boundary layer wind tunnel,a set of downburst test device is designed.The results of boundary layer wind tunnel test show that the horizontal wind speed vertical wind profile formed in a certain range behind the device is in good agreement with the classical field measured results,and the simulation of the horizontal wind field of storm flow in the boundary layer wind tunnel can be realized.(4)The variation of inlet wind speed with time was realized by using UDF programming language in Fluent,and the effect of abrupt wind on the static and aerodynamic performance of rectangular section with aspect ratio of 1:5 was studied.The test model of the rectangular section with aspect ratio of 1:5 was designed,and the effect of the abrupt wind formed by the downburst device on the static aerodynamic performance of the rectangular section was studied.(5)The vortex-induced vibration performance of the rectangular section with aspect ratio of 1:5 under the action of abrupt wind formed by the downburst device was studied by wind tunnel test.The time histories and spectrum curves of wind-induced vibration of the rectangular section under different time-varying wind fields formed by the downburst device were given.The main factors affecting the amplitude of vortex-induced vibration under the condition of abrupt wind field were discussed.