Numerical Simulation Study On Large Eddy Of Pulsating Wind Environment Of Bridge Site In Mountainous Area

In order to support the country’s economic work policy,a large number of bridges have been built in the western mountainous region,which greatly strengthens the contact and exchange between remote mountainous regions and the outside world,and is a solid foundation for the revival of the Chinese nation.The mountainous areas in the west are mostly steep with gullies and crisscrosses.When constructing bridges,it is often necessary to span a deep-cut canyon across the mountains.The terrain has large undulations,long crossing routes,and narrow terrain,which are the main reasons for the complicated wind environment in mountainous areas.Conventional numerical simulation usually does not consider the pulsating component of the incoming flow.In order to have a comprehensive understanding of the wind environment at the bridge site,this paper will conduct a numerical simulation study of the mountain wind environment under the average wind and pulsating wind flow.First,a numerical empty wind tunnel is used as the research object.After generating pulsating wind according to the harmonic synthesis method,a UDF program is compiled to add the wind speed time history to different grids at the entrance boundary,and the correctness of the wind field is verified at the inlet.It is found in the computational domain that after the development of the flow field,the pulsating wind characteristics of the wind field basically meet the relevant constraints,which verifies the correctness of the pulsating wind numerical simulation method in this paper.At the same time,through comparison,it is found that the simulation of pulsating wind should use the LES turbulence model rather than the Reynolds average method.Then,an overview of the terrain of a mountain bridge site is introduced,a threedimensional topographic numerical model of the bridge site is established,and a numerical simulation study of the wind environment of the bridge site is conducted under the average wind flow.It is found in the study that the average wind characteristics are very unevenly distributed along the longitudinal direction of the main beam,and it is easier to form high wind angles of attack in mountain and canyon terrain.The wind speed amplification effect at the bridge position is very unevenly distributed along the longitudinal direction of the main beam,and the south wind inflow can form a greater wind speed amplification effect at the bridge location than the north wind inflow.When the inflow direction is along the river,the maximum wind speed amplification factor is 1.21.When the angle between the inflow direction and the course of the river is large and the terrain is steep,the terrain pulsation effect is large,and when the inflow direction is along the river channel,there is a weak terrain pulsation effect.Finally,the numerical simulation of the wind environment in the site of the bridge is carried out under the pulsating wind.Comparing the average wind characteristics of the mean wind incoming flow and the pulsating wind coming down the bridge site area,it is found that the average wind characteristics are basically the same under the two boundary conditions.There are different topographic pulsation effects at the bridge position in different incoming directions.When the incoming direction is the same as the river direction,there are basically no topographic pulsation effects at the bridge position.The power spectrum of the numerical simulation at the bridge position where the pulsating wind comes and flows is more consistent with the Von Karman spectrum.When the incoming wind and the river have a certain angle,especially the north wind,the wind speed fluctuations under both boundary conditions are large.However,when the incoming wind is in the same direction as the river,the wind speed coming from average wind is very stable,and the wind speed coming from the pulsating wind has obvious fluctuations.When the angle between the inflow direction and the channel direction is large and the terrain is steep,the difference of the turbulence intensity at the measurement points near the bridge deck under the two boundary conditions is basically within5%,and the simulation results of the average wind input can be used.When the incoming direction is the same as the river direction,the difference of the turbulence intensity is basically above 90%,and the result of pulsating wind input should be used.