Study On Characteristics Of Mean Wind Field Of Mountain Range Terrain

China is a mountainous country,with the deepening of economic construction,the number of buildings and structures in mountain environment is also increasing.The existence of mountains will significantly change the characteristics of the wind field,forming a unique mountain wind environment,so sufficient attention must be paied to the impact of hilly terrain wind effects in the structural design process.Existing load code provisions and literature mostly studied on hills without length or two-dimensional terrain of infinite length,but the reality is:most hill has a certain length,so that wind field characteristics will be more complex.Therefore,further research on the the characteristics of mean wind field in mountain range has a great significance on the reference for the wind-resistant design of transmission lines and structures in hilly terrain.In this paper,three key parameters-inlet boundary condition,surface roughness and turbulence model were first studied,with wind tunnel tests which were conducted to demonstrate the validity of the results of numerical simulation.Then,in two wind directions which respectively along and perpendicular to the mountain range,models of isolated mountains,col mountains and canyon mountians with changing length of mountain range,distance between two peaks,gradient of the mountain slope were established to investigate the influence of geomorphological factors on mean wind field.In the last,according to the CFD calculation data,formulas to compute wind pressure topographic modified coefficients on typical location in mountain range terrain for this two wind directions were provided,which could be verified by actual cases of application.Results indicate that:(1)Under the wind direction which along the mountain range,a)Length of mountain range will decrease the wind acceleration effect on mountain top,but it will enhance the wind speed in canyon or col.b)The distance between two peaks has little effect on wind speed on mountain top but mainly affects the wind speed in canyon or col.c)Wind acceleration for mountain top and entrance of canyon or col tends to grow stronger with increasing gradient of the mountain slope.However,the greater mountain slope will also bring greater energy consumption,so the wind deceleration is obvious in the rear space of canyon and col.(2)Under the wind direction which perpendicular to the mountain range,for horizontal mean wind field,a)The effect of the length of the mountain range on the peak and the foot of the mountain is the most significant.b)Velocity of the wind passing the mountain peak is related to the three-dimensional size of the mountain,so it can't simply use mountain slope to describe this problem.For mountains which have same height,horizontal wind velocity on the mountain top will be greater with wider body and lower slope.For vertical wind field,a)The maximum of vertical wind velocity on the upwind side of the mountain is at the location about two-thirds of the mountain height,which value is close to 70%of the incoming wind speed.b)Vertical wind velocity substantially unaffected by changes in the mountains in the space less than 50m above the surface of the mountain;in the space of 50-250m,the speed increase with the increase of the length of the mountain range.In the last part of this paper,the calculation formulas of wind pressure topographic modified coefficient for mountain range terrain can take the influence of length of mountain range,distance between the peaks and slope of the mountain range into account.Length of mountain range is included in the calculation formula for the first time.The formulas can provide reference for the wind-resistant design of transmission lines and structures in mountain range terrain,making up the deficiencies of existing research results.