Large Eddy Simulation Study Of Wind Field In Mountainous Canyon Topography

Different from flat terrain,there are many complex phenomena which include air lift,flow separation,terrain acceleration effect,turbulence intermittency,and reattachment when wind flows through mountainous terrain which forming a relatively unique wind environment.The uncertainty of wind field over complex terrain will have a certain impact on the construction of bridges,so it is very important to accurately predict the characteristics of wind field around mountainous terrain.In this paper,CFD numerical simulation method is used to study and analyze the distribution characteristics of wind field in mountainous terrain.The main contents are as follows:(1)Study of the influence of blockage rate on typical mountain wind filed based on Large Eddy Simulation(LES).Taking the two-dimensional hill as the research object,the LES based on vortex method was carried out to study the influence the influence of the blocking rate on the wind field over two-dimensional hill.And the effectiveness of the numerical simulation method and parameters is verified by comparing the LES calculation results of two-dimensional hill with the corresponding wind tunnel test results.The influence of blocking rate on the flow direction,vertical wind profile and wind pressure coefficient of the hill is analyzed,especially for the perspective of time average and transient flow field.The result shows that the LES based on vortex method can effectively simulate the characteristics of the mean and fluctuation wind profiles around two-dimensional hill.With the increase of blocking rate,the separated vortex core on the leeward side of the model is gradually away from the ground and close to the wall,and the vortex shedding frequency is more complex,which leads the changes of the mean and fluctuation wind profiles on the crest and the leeward side of the two-dimensional,and the influence of blocking rate for the wind pressure coefficient is also mainly on the leeward side of the model.(2)The study of wind filed over actual canyon terrain in mountainous areas based on LES.The Reynolds averaging method based on time average was conducted on the actual canyon terrain in a mountainous area to study the influence of the wind direction angle on the wind speed around the actual canyon terrain in a mountainous area.Based on the most unfavorable wind direction angle,the LES based vortex method was conducted on it to analysis the characteristics of the mean and fluctuating wind profile,the terrain acceleration effect and flow fields around the canyon.The results show that the wind direction angle has a great influence on the wind speed ratio in the canyon,and the 0° wind direction angle has the greatest influence on the average and fluctuating wind profiles mainly at the height of z/H near the model wall which does not exceed 1.5.And the terrain acceleration effect of each measuring point near the wall from the position of the mountain gap to the canyon exit is greater than 1,and the maximum can reach 4.82.(3)Numerical Simulation Study on Simplified Canyon Topography.Taking the simplified canyon terrain as the object,the numerical simulation calculation of the simplified terrain under different wind directions is carried out.Based on the most unfavorable wind direction angle,the influences of height difference ratio,mountain radian,canyon spacing and mountain gap position on the terrain wind field were studied.The differences of wind field between simplified terrain and actual terrain are studied with the recommended values of the code.The results show that under different wind directions,the wind speed ratio of each measuring point in the simplified canyon terrain is small;At the most unfavorable wind direction angle of 157.5°,the acceleration area at the entrance of the canyon increases with the height difference ratio and the distance between mountains and hills;When the radian of the mountain range is 0,the terrain acceleration effect of each measuring point is larger than each measuring point in other working condition.When there is a gap in the mountains,the most unfavorable wind direction angle is changed to 22.5°and the area of the wind field acceleration area in the canyon is larger than other wind direction angles.For the mid-span position of the proposed bridge,compared with the code and related study,the terrain acceleration effect of the simplified terrain at the height of z/H=0.07 is basically consistent with the one obtained from the related study.With the increase of height,the terrain acceleration effect coefficients obtained from the actual terrain and the simplified terrain are smaller than those obtained from the specification and related research results.It shows that the terrain acceleration effect should also comprehensively consider the influence of actual factors such as slope,mountain height difference and canyon trend.