A Numerical Simulation Study On The Impact Of Roof Shape On Microclimate In Urban Street Canyon

With the development of the urbanization,the urban environment gradually replaces the natural environment and has formed its own unique microclimate.Because of the differences between building structure,building arrangement and building materials,the temperature in city is higher than the rural.High temperature resulting in more energy demand and reducing residents' comfort.Scholars have a lot of researches on the impacts of building structure on the microenvironment in urban street canyons.However,the research about the influence of the roof shape on the thermal environment is lacked at present.In this paper,taking cold winter and hot summer city Wuhan urban street canyon as an example,the two-dimensional model of Wuhan street canyon is established by the finite element numerical simulation software COMSOL Multiphysics 5.3a,considering two season,four different roof shapes and six building heights.The results mainly about fluid field and temperature,the following aspects are carried out in this paper:(1)Based on the roof structures of the building and the climates in Wuhan,the physical models were established,and systematic micro-environment numerical simulation research is carried out.Based on Wuhan climate and building characteristics,48 two-dimensional street canyon numerical models were constructed with appropriate calculation areas,boundary conditions and parameters.The mathematical-physical model is validated by comparing the results of the wind tunnel experiment.(2)Based on the situations two seasons,considering the H / W values of different urban buildings,the microclimate changes caused by the height changes are analyzed.It is found that there are obvious differences of airflow and temperature distribution in the canyon in winter and summer,the microclimate in the canyon is complex and changeable in summer,the flow structure and temperature distribution in the canyon are greatly affected by the building height.When H / W < 1.12,with the increase of H / W,the temperature in the canyon increased.when H / W > 1.12,with the increase of H / W,the temperature in the canyon decreased.In winter,the microclimate in the canyon is single,with the increase of building height,the flow field structure and air temperature in the canyon are basically unchanged(3)The influence of different roof shapes on urban microenvironment is considered under the important parameter of pedestrian height.It is found that the shape of the building roof will affect the air temperature in the canyon.No matter in winter or summer,the cooling capacity of the round roof is poor,and the temperature in the canyon is high,while the cooling capacity of the down-wedge roof is good,and the temperature in the canyon is low.When H/ W= 1.12,1.24,1.36,1.48,the cooling capacity of the up-wedge roof is weak in summer with high temperature and strong in winter with low temperature.(4)Due to the low temperature in summer and high temperature in winter,with the small temperature difference between winter and summer is conducive to improving residents' comfort,then compared the roof shapes under different heights.It is found that the down-wedge roof is beneficial to heat dissipation in summer and heat preservation in winter;the up-wedge roof has poor heat dissipation in summer and is difficult to preserve heat in winter,which can reduce the roofs of such shape.