Wind-Tunnel Study On Boundary Layer Flow Over Complex Topography

The heterogeneous underlying surface caused by topographic relief is extremely common in nature and its influence on the airflow of the atmospheric boundary layer has great research value and practical significance.The undulating topography of the mountains are generally composed of multiple hills with random distribution of location and size,while the current research on the heterogeneous underlying surface caused by topographic relief mainly focuses on the simplified isolated hill or multiple hills with uniform and regular arrangement,which is quite different from the actual topography.In a few cases of researched actual topography,the research work is usually carried out only for specific real landform cases,and it is difficult to extract relevant topographic parameters to quantitatively analyze the boundary layer flow affected by topography.In this thesis,the 3D printing technology is used to manufacture complex topography models that multiple hills are randomly arranged.Then,the boundary layer flow over these complex topography models is simulated and the flow field information of the leeward of these models is measured in the wind tunnel.Finally,the effect of topography factors including the random location of hills,the number of hills,and the standard deviation of hills height on the flow field within the boundary layer is studied.On this basis,the flow mean wind speed profile is nonlinear fitted to obtain the parameters reflecting the properties of underlying surface,and the effect of topography factors on these parameters is discussed.The main conclusions of this thesis are as follows:1.On the leeward of hills,the effect of hills on flow field including mean wind speed and turbulence statistics is mainly distributed below z/H=2.2.The effect of the change of topography factors on the flow field of the leeward of hills is mainly reflected below z/H=1.2.The effect of the change of random location of hills on the flow field is very little.The effect of the change of the number of hills on the flow field is great.The change of standard deviation of hills height is able to aggravate the fluctuation of flow field.3.The mean flow speed profile on the leeward of hills follows different regularities of distribution in the near-ground region and high-altitude region,respectively.The near-ground part is fitted with the exponential function to obtain the index ?,while the high-altitude part is fitted with the logarithmic function to obtain the friction wind velocity u*,aerodynamic roughness length z0,and zero plane displacement height d.4.In the near-ground part,z/H ?0.4,the value of ? hardly changes with the change of incoming wind speed.The change of random location of hills does not significantly change the value of ?,the change of the number of hills has significant effect on the value of ?,and the change of the standard deviation of hills height is able to aggravate the fluctuation of ?.In the high-altitude part,z/H?0.4,u*increases with the increase of incoming wind speed,while z0 and d decrease with the increase of incoming wind speed.The effect of the change the random location of hills on u*,z0,and d can be neglected,u*,z0,and d increase with the increase of the number of hills,and the change of standard deviation of hills height is able to aggravate the fluctuation of u*,z0,and d.