Numerical Simulation Research On Flow Structure Optimization In Subway Cabin

With the rapid increase of China’s urbanization,in order to alleviate the pressure of ground transportation,subway as a kind of “green traffic” with the advantages of efficiency,low energy consumption and less pollution,has gradually spread to more central cities.More and more people travel by subway,and the thermal comfort and indoor air quality are an important issue that cannot be ignored in subway cabin.The reasonable airflow organization is a necessary condition to ensure passengers’ thermal comfort and air quality.Therefore,computational fluid dynamics analysis(CFD)is widely used in the research and optimization the airflow in the cabin.For the long-narrow confined space with high heat flux density,the simulation results which computational domain is partial cabin is difficult to accurately describe the true internal flow structure.In principle,using the entire cabin as the computational domain can make the result more consistent with the actual situation in the cabin,but the number of grids is large and the calculation is time consuming.However,the previous studies have limitations.In order to reduce the cost of numerical calculation,most researchers use 1/2,1/4 or even 1/8 cabin as the numerical model,and analyze the simulation results with temperature field and velocity field.Therefore,the computational domain selection of the appropriate mathematical-physical model have a great influence on the accuracy of the simulation results of the airflow in the cabin.Moreover,basis on the accuracy of the simulation results,it is of great practical significance to optimized computational domain to save computer resources and calculating time cost.In this study,the turbulence model of the flow structure in the cabin and theoretically analyzes the internal flow field vortex structure.In this research,the whole subway cabin as the numerical model is calculated by CFD,and the airflow in the subway cabin is simulated under different inlet conditions.Then,the simulation results are compared and analyzed temperature field,velocity field,flow field vortex structure and PMV-PPD index,and the optimized ventilationis obtained.The results show that 0° and 126° are the most unfavorable supply angle of the cabin,and the recommended values of supply angle are 60° and 90°.The supply air can generate many vortex structures along the length of the subway cabin.Under a certain supply angle,due to the large momentum of air jet the discrete vortex structure on the top of the cabin is small and distributed compactly.The supply angle affects the formation of the vortex structure,and the vortex structure generated at the working area of the cabin under 0° supply angle condition.Based on the optimal supply angles,this research simulated the airflow of subway cabin with different computational domains,and the simulation results are compared and analyzed from temperature,velocity.The results show that the calculation domain has influence on the airflow in the cabin.The smaller the calculation domain,the greater the deviation of the simulation results from the actual airflow.The calculation domain of the nearest 3/4 cabin can reduce the computer configuration and save the calculation time under the condition of satisfying the accuracy of the simulation results.This research provides theoretical method guidance for airflow organization simulation in a long narrow and confined space.In the study of the influence of the supply angles and the computational domain size on the airflow,this research make a longitudinal comparison analysis of the simulation results of the two cabin models(the difference is the distribution form of passengers in the cabin).The results show that the distribution form of passengers has a certain influence on the accuracy of the airflow organization simulation results in the cabin.