Study On The Effect Of Wind Environment Over Non-uniform Buildings In Urban Area

Along with the excellent speed of the urbanization in China,heat-island effect,urban high temperature climate,precipitation increasing and fog and haze have been increasingly prominent.Effects of non-uniform buildings is one of the most significant causes for forming urban climate by blocking and disturbing the wind,as well as one of the most important factors for distinguishing urban thermal environment from natural.Accurate calculations of the wind attenuation caused by urban buildings provide supports for researches on heat island effect evaluations,meteorological prediction and optimization of outdoor environment of buildings.However,there is lack of systemic and quantitative studies severely because of complex non-uniformity of real urban buildings.First,on the base of morphological non-uniformity of urban buildings,the study conducted a wide range of interdisciplinary researches and theoretical discussion,and a scheme of parameterization of urban buildings non-uniformity had been set up.The passage ventilation index of non-uniform buildings is presented for the first time,integrating the descriptiveness of building layout by road network,and it effectively describes the flow resistance and buildings layouts.Furthermore,through the precise numerical simulations of effects of simplified buildings layouts on passage flow,formation mechanism of local wind field has been discussed.A simple empirical formula,which can describe the relationship between flux percentage and the width,the length and the pattern angle,is established by a new proposed flux coefficient in passages,acquiring a good validation results.In addition,results show that the formation mechanism of flow in the study passages lies in the superposition of shear flow at the corner caused by blocking effect,and the minimum cross-section is an important factor to determine the passage flow.The Venturi effect may not fit in unconfined passage flow,and the mechanism of blocking effect is the coupling of drag effect and flow around,of which drag is mainly negatively correlated with frontal area.Second,effects of morphological parameters on air flow and drag had been studied by wind tunnel experiments.Results indicate flows in the wind tunnel of all test cases are Re independent,and the measurement of spatial average velocity is to some extent independent of the positions of test points.The impacts of morphological parameters on flow pattern and drag are obviously different.In the same buildings,the distribution trend of surface pressure difference and the local drag coefficient on each module remains the same at different reference velocity.The experiments consider the local drag distribution rule in buildings,as well as the contribution to the drag of whole buildings.Furthermore,a non-intrusive method that measures the overall drag has been set up which is based on the measurement results of surface pressure of several buildings.Fitting a unified distribution law determined from experimental results may actualize measurement of drag in the real buildings.Meanwhile,the distribution of the local drag of several buildings is obvious,and the local drag coefficients decrease sharply from the windward line of buildings.Wind speed and the shape of the local building determine the magnitude of local drag at the first module,while the morphology characteristic of buildings determines the distribution.Finally,this paper analyzes the effect of the shape index and the passage ventilation index on the characteristic of wind flow.It points out that the influences of buildings shape on flow is relatively small,cylinder buildings has the smallest drag coefficient for the smooth diversion effect.Various buildings layouts have much more obvious effect on wind flow than shapes.Furthermore,frontal area index,plane area index,building shape index,passage ventilation index are considered to discuss effects on drag coefficient,and the uniform fitting curves are acquired.A parameterization model to deduce drag coefficient directly from morphology characteristics has been set up on the basis of non-uniform morphological parameterization scheme.In addition,an aerodynamic roughness model is advanced by the morphological parameterization method.The results of this dissertation offer theoretical and technical support to the green building design,eco-city planning,improving urban local thermal environment and accurate evaluating the wind environment within real complicated urban district characterized by non-uniformity.