Theoretical Study On Thermal Environment And Ventilation Optimization Strategy Of Xi'an Railway

As the most effective and convenient urban transportation system,the subway has developed rapidly in recent years,and the thermal environment of its internal platform and rail section has attracted more and more attention.Metro is relatively closed in underground space,and because of the heat generated by train operation,there will be significant adverse changes in the thermal environment in the track section after perennial operation.Therefore,ventilation system must be set up to maintain the stability of the thermal environment in the section.Metro operation time is longer than other buildings.The ventilation and air-conditioning systems of subway platform and rail section need to pay special attention to energy-saving control.Therefore,it is of practical significance to select an energy-saving and effective ventilation scheme for rail-line section.In order to explore more effective energy-saving technical scheme of ventilation system in metro section and to achieve the control of thermal environment in metro section with lower energy consumption,this paper takes the track section between a subway station under construction and its upper station in Xi'an as the research object,simulates and analyses the airflow velocity field and temperature field in the section during train operation with CFD software,and summarizes the above results.The movement law of airflow in the process,and according to the comparison of different working conditions,provide reference suggestions for optimizing ventilation design and management.Finally,according to the law of air flow and heat balance analysis,a definite optimization scheme of VAV ventilation is determined,and its effectiveness is verified.The main work of this paper is as follows: 1)The analysis of heat balance in Metro section: firstly,the heat relationship in metro section is analyzed;secondly,the heat sources and main heat dissipation modes in the section are determined separately and the heat generation of each heat source is estimated;finally,the relationship between ventilation and heat dissipation is clarified,which provides direction for the next ventilation simulation research and provides a way for ventilation simulation.The calculation of air volume provides a theoretical basis.2)Establishment of CFD model for Metro section: A simplified physical model for calculation is established according to the construction drawings of the research object,and meshing is carried out.Appropriate mathematical model and boundary conditions are selected to set up effective contrastive working conditions.3)Analysis of airflow field in track section when a single vehicle is running: Firstly,according to the simulation results,the airflow velocity field and temperature field of each air inlet and outlet section in the study section are analyzed when a train is running;then,the airflow velocity of each air inlet and outlet in different working conditions,i.e.different vehicle speed and air well arrangement,is compared and analyzed;and then,the airflow movement rules in the process are summarized.The key time point at which the flow field changes obviously is put forward,and the concept scheme of VAV ventilation is put forward with the critical time point as the control point.4)Proposal of optimization scheme of ventilation system: According to the flow field analysis in the section,summarize the law of airflow movement in the section during train operation and the flow field condition in the metro section studied in this paper.According to the comparative analysis of the flow field under different working conditions in the previous chapter,provide reference suggestions for the optimization of ventilation design and management,and from the layout of shield doors,platform space optimization,piston tuyere distribution.The detailed optimization strategies for variable air volume ventilation are explored in the aspects of setting and variable air volume ventilation,and then the specific ventilation volume in the concept scheme of variable air volume ventilation is calculated to put forward the specific variable air volume ventilation scheme.Finally,the CFD model after adopting the variable air volume ventilation scheme is established again to verify that the scheme meets the ventilation requirements.