Simulation And Evaluation On Thermal Radiation Intensity’s Influence On Pedestrian-Level Thermal Comfort Around Elevated Buildings

In the process of urbanization,densely-packed buildings in big cities block the wind flows between buildings,which results in wind velocities that are too low to take away the environmental heat at the pedestrian-level.This phenomenon intensifies the urban heat island(UHI)and causes oppressive outdoor thermal environment for pedestrians,which undermines livability in the cities.Building’s elevation design has been proved to be able to effectively amplify the wind velocity and the turbulence intensity in the surrounding area.However,most studies have focused on the influence of a single elevated building,with and without the surrounding buildings.There is a lack of research on the scenarios that involve multiple elevated buildings in the same building arrays and their effects on the pedestrian-level wind and thermal environment.In addition,the existing studies on the wind environment of buildings only consider the influence of the single factor of wind,and there are few coupled quantitative researches on the influence of thermal radiation intensity on the pedestrian-level wind and thermal environment around the buildings,which make it difficult to systematically analyze the influence of the building’s elevation design on pedestrian’s thermal comfort.This study aims to investigate the influence of thermal radiation intensity on pedestrian thermal comfort around building arrays with different building’s elevation strategies,and to apply the research results to engineering applications.The specific research contents,methods and results are as follows:(1)Through the observation and perception of the effect of elevated buildings on the pedestrian-level thermal environment and pedestrian thermal comfort in practical engineering,the research questions of this paper are put forward.By conducting the literature review,the research status regarding the influence of wind and thermal environment around elevated buildings on the thermal comfort of pedestrians is clarified,and the research content and the technical route of this study are determined.(2)Two wind tunnel experiments of isothermal and non-isothermal flows around ideal building arrays severally were selected to validate the prediction accuracy and validity of the turbulence model and the numerical method employed in this paper.The results show that the correlation coefficient between Computational Fluid Dynamics(CFD)simulation and the isothermal wind tunnel experiment is 0.83,and the predicted temperature field results are in good agreement with the non-isothermal experimental results.Therefore,the Reynolds-Averaged Naiver-Stokes(RANS)method with RNG k-ε model,the numerical method,and the boundary conditions used in this study are validated.(3)The sizes of buildings in this study are determined according to the geometry used in the wind tunnel experiment and the data from field measurement,then three different ideal building arrays with multiple elevated buildings are proposed,including Type 1(no elevated),Type 2(Ntype)and Type 3(M-type).The geographical location and meteorological parameters are set as in Shanghai,a typical city of hot summer and cold winter regions.The wind velocity ratio,the turbulence intensity,the vortices,the wind gust,the physiological equivalent temperature(PET),the mean wind velocity change ratio,the temperature,the convective heat transfer coefficient and other indexes are used to analyze and discuss the simulation results.The results show that building’s elevation design can amplify the wind velocity and the turbulence intensity in and around the underneath the elevated building space at pedestrian-level height,and provide a thermally comfortable resting space for residents.Besides,after considering the influence of thermal radiation,the wind velocity field around a single elevated building is significantly different than that without considering the thermal radiation,especially at the pedestrian-level where the mean wind velocity change ratio is 30%.(4)An office building with a podium in the hot summer and cold winter area was selected as the engineering renovation object,and the research results were used to improve the local pedestrian-level wind and thermal environment as well as pedestrian thermal comfort around the building.By comparing between the wind velocity fields,the turbulence intensity fields,the temperature fields and the distributions of thermal comfort conditions of the building with and without windward elevated buildings,the results show that the building’s elevation design can improve the vortex distribution on the leeward side of the office building,reduce the turbulence intensity of the windward side of the office building,and improve pedestrian thermal comfort around the building.In this study,numerical simulation was used to quantitatively explore the influence of elevated buildings on the pedestrian-level wind and thermal environment as well as pedestrian thermal comfort in complex building arrays under the condition of thermal radiation,and the theoretical research outcomes were applied to the practical reconstruction projects.The conclusions have practical significance for the planning and reconstruction projects of ecological cities.