Force Analysis And Numerical Study Of Subway Particles In Underground Tunnel Under Power Supply Of Catenary

As a special pollutant in subway environment,subway particles have higher concentration level and more complex element composition,which is more toxic to human body.Therefore,it is of great significance to study the subway particle.The underground tunnel is chose as main research range and subway particle is selected as main object.This article is aimed at the shortcomings existing in present research of subway particles.At first,from the perspective of theoretical research,based on existing literature and experimental results,dust sources and generating rates of subway particles are analysed and determined.The balance equation of mass concentration is established,Element composition of subway particle is listed and the density value is distinguished according to particle sizes.Based on theory of gas-solid two-phase flow,the force condition of particle is analyzed and verified.Finally,from the perspective of numerical study,the simulation results of subway PM10 under different train speed in different running status by utilizing DPM model.Diffusion status and concentration distribution of subway particle is discussed.At the mean time,particle trajectories and concentration distributions around the air conditioning under different train speed is compared.Through the study of this paper,the main conclusions are drawn as follows:1?The underground tunnel environment is mainly influenced by internal source,namely,the wear particles,which include braking,wheel-rail and pantograph-catenary wear particles.There are three phases in the course of a running train in a tunnel,that is,phase of uniform speed,earlier phase of braking and later phase of braking.Meanwhile,The dust source combination and the dust intensity are different at every phase.2?The densities of subway particles vary with particle size.For subway PM10,PM2.5 and PM1,the mean density is 4.043g/cm3,3.766 g/cm3 and 2.562 g/cm3.Force condition of the particles cannot be generalized.For subway PM1,only Brownian force and drag force are considered.For subway PM2.5,Brownian force,dragforce and gravity should be considered.For subway PM10,all the major forces,including Brownian force,dragforce,gravity and Saffman force can't be ignored.3?The wear particles of different internal dust sources have different diffusion forms and concentration values.Pantograph-catenary wear particles diffuse at the upper part of tunnel in the form of belt and elliptical lump.Concentration value of the particles reduce gradually with decrease of vehicle speed in zone around the train and behind the train..Wheel-rail and the brake wear particles diffuse at the lower part of the tunnel in the form of strip.The mixing concentration value increases gradually with the decrease of vehicle speed in above zones.4?Under different running phases,every section of underground tunnel has different particle concentration characteristics.At the phase of uniform speed,peak concentration value is relatively high at every section.And the particles mainly suspended in tunnel behind the train.At the earlier phase of braking,peak concentration value is close at every section.And particles suspended evenly around the train and in the tunnel.At the later phase of braking,peak concentration value is dispersing at every section.And the particles mainly suspended and deposited around the train.5?Under different running phases,there are different concentration distributions near the train air conditioning units.At the phase of uniform speed or at the later phase of braking,there is no concentration distribution at left side or right side of the train air conditioning.Thus,particles almost have no influence on the air quality in carriage.At the earlier phase of braking,there is a low concentration area adhered to the left side or right side of the air conditioning wall.which has a range from 7.32×10-9kg/m3 to 2.32 ×10-8kg/m3.Therefore,particles have influence on the air quality in carriage.6?Particles of different internal dust sources have different installation locations for filter equipment.By discussing particle trajectories under different running phases,it can be found that filtration equipment should be installed at the bottom zone or back of the final carriage,if wheel-rail wear particle and braking wear particle is moved.What's more,corresponding filtration device should be set up in the upper zone of tunnel space,if pantograph-cetenary wear particle is moved.