Determination Of Urban Ground Roughness Height Based On Test And Numerical Calculation

With the continuous acceleration of the urbanization construction process in China,the height and shape of buildings are also becoming more and more diversified,which generates complex urban topography.The complex urban topography will greatly change the roughness of the urban ground and have a significant impact on the urban wind environment.In view of the shortcomings of the current research on the ground roughness height（z₀）,it is necessary to further improve the research method for the determination of the ground roughness length,so as to save time and resources.In this thesis,taking the urban landform of downtown Kowloon,Hong Kong as an example,wind tunnel tests and numerical calculations are carried out for the z₀ values under different upstream fetch lengths,and finally the two methods are compared and analyzed to determine the values under this landform.The main work contents are as follows:（1）A wind tunnel test was performed on a landform model of the central area of Kowloon,Hong Kong,to investigate the evolution pattern of the urban surface wind profile under the upstream fetch lengths of 250m,500m,750m and 1000m.And the ground roughness height in this area is determined according to the evolution of the wind profile.The average wind speed profile and the turbulent intensity profile was also examined under those different upstream fetch lengths.（2）Using the GIS system to obtain the real topographic images in Kowloon,Hong Kong with regard to the upstream fetch length in question,and using Agisoft Metashape to reconstruct the 3D models of the landform,and finally use two different morphometric methods to analyze the ground roughness lengths z₀.These two different morphometric methods were compared and analyzed,and a more suitable method was determined.（3）The experimental results are compared with the numerical calculation results to verify the accuracy of the numerical calculation.The source of the error is analyzed,and the main influencing factors of the error are determine,and the length of the minimum upstream wind area for the urban exposure to fully develop the upstream wind profile is discussed.