Study Of Basic Wind Field On Typical Mountaious Based On Large Eddy Simulation

In China,a large proportion of land areas are mountain terrains.Different from the flat terrain,affected by the undulating terrain,airflow through the mountainous terrain will form a complex wind field distribution,such as acceleration effect,backflow,impact and other phenomena.That makes it more difficult to accurately predict the wind speed near the surface of the mountain.In order to accurately predict the wind field characteristics of mountainous terrain,based on the large eddy simulation(LES)under vorticity generation method,this paper studies the wind field distribution characteristics of typical mountainous terrain,and analyzes its distribution characteristics from the flow field mechanism.The main research work and achievements are as follows:(1)Study on three dimensional effects of typical mountain wind field by LES.Based on the large eddy simulation of the vortex synthesis method,the basic wind field parameters of the two-dimensional symmetrical ridge and the three-dimensional symmetrical hill with the same slope are compared and analyzed,and the flow field characteristics are analyzed.The results show that: the large eddy simulation method based on vortex method can effectively simulate the average wind and turbulence characteristics of two-dimensional symmetrical ridge and three-dimensional symmetrical hill;the variation law of average wind and fluctuating wind of two-dimensional symmetric ridge and three-dimensional symmetrical hill is similar under the same slope,but the generation and end of flow separation in threedimensional symmetrical hill are earlier than that in two-dimensional symmetrical hill in leeward side Symmetrical ridge According to the flow field analysis,the two models have complex vortex shedding and reattachment phenomenon on the leeward side,and the vortex shedding frequency on the leeward side of the three-dimensional symmetrical hill is more complex;the terrain acceleration effect change rule of the two types of terrain at different locations is similar,and the three-dimensional terrain is relatively large,and Canada and ISO specifications are relatively safe on the windward side and the mountain top,while the leeward side is recommended Refer to Japanese specifications.(2)Large eddy simulation of wind field over 3D hilly terrain with different slopes.Taking3 D hill as the object,the large eddy simulation(LES)method based on spatial average is used to simulate the unsteady flow around the 3D hill,The effectiveness of the method is verified by comparison with literature tests,On this basis,the wind field characteristics of four different slopes(15 °,21.8 °,30 ° and 45 °)are compared and analyzed in detail,and the influence of slope on the average wind field and turbulence structure is studied,the terrain acceleration effect of different slopes is compared with the norms of different countries,And the flow field was analyzed.The results show that: the LES method can effectively simulate the characteristics of average wind and fluctuating wind in different slopes of hills;and their change laws are similar,the difference is that in the near wall area of the mountain top and within a certain height range of the backwind surface and tailings area,with the increase of the slope,the average wind profile of the flow direction of the steep slope increases,The gentle slope is opposite,the greater the attenuation of turbulence,the average wind pressure coefficient increases on the windward side and decreases on the leeward side.with the increase of the slope,when the slope is less than 30°,the fluctuating wind pressure coefficient increases on the windward and leeward sides,and the slope is greater than 30° is opposite,At the top of the mountain,the change trend is not obvious,in the area near the windward surface,the terrain acceleration effect gradually decreases,and gradually increases at the top of the mountain.the terrain acceleration effect of 45° is the largest on the leeward surface;According to the flow field analysis,with the increase of the slope the size of the trapped vortex on the windward surface increases,the separation bubble on the leeward surface is closer to the mountain wall and downstream,and the secondary circulation is also more obvious.As the slope increases,the energy is more concentrated in the near-wall area,and the vortex trajectory is more stable.(3)Study on the effect of distance on wind field over two parallel mountains by large simulation.Taking three-dimensional hills as the research object,the large eddy simulation was carried on two hills in parallel with different spacings in the turbulent boundary layer wind field.The basic parameters of the wind field obtained by the numerical simulation were compared with those of the single-hill wind field to study the characteristics of topographical wind field characteristics of two hills in parallel.The results show that the interference effect of the parallel double mountains has no obvious influence on the flow direction wind profile and the average wind pressure coefficient,but mainly concentrated on the average wind speed,turbulence profile and wind pressure coefficient distribution of the inner canyon zone along the span of the hill.And the interference effect of the mountains on both sides of the basic parameters of the wind field measured in the hills and valleys is negligible when the distance between the two hills in parallel is grater than 2H.For the terrain acceleration effect,the terrain acceleration effect that develops along the flow direction is less affected by the interference effect of the double mountains.In the middle of the hills and valleys,the interference effect of double mountains is the greatest,and the terrain acceleration effect in the near-wall area is obviously reduced,and the maximum distance that the double mountain interference effect exists is between 2H ～ 3H.For the aspect of flow filed,affected by the influence of interference effect of two hills in parallel,the size of the trapped-vortex located at the foot of the hill in windward was changed.On the leeward,the separated vortex gradually move away from the hill wall with the influence of both sides hill.And the vortices on the inner side of the canyon are mainly small-scale vortices.The vortex trajectory of the leeward surface has a certain deviation with time,and gradually returns to stability with the increase of the distance between the two mountains.