Analysis On Transmission Characteristics Of Virus Droplet In Urban Rail

In recent years,the COVID-19 pandemic has caused immeasurable damage to all of humanity.Respiratory diseases such as COVID-19 mainly rely on droplets to spread diseases,and the internal environment of urban rail vehicles is complex,densely populated and highly mobile,which provides favorable conditions for the spread of diseases.To this end,the study of the transmission characteristics of virus droplets in urban rail vehicles has certain reference significance for the healthy operation of urban rail vehicles.In the present thesis,the characteristics and kinetic parameters of virus droplet are investigated,and the corresponding processing is carried out.A numerical model of evaporation and diffusion of virus droplet in a B type subway car was established.The influence of passenger factors on virus droplet diffusion was studied.The influence of vehicle environment on droplet propagation was compared and analyzed.A simulation model of the protective effect of masks was established,and the influence of wearing masks or not on passengers was compared.The results indicate that:(1)the movement distance of droplets with a particle size of 200 microns exhaled by coughing was no more than 1.1 meters;For the quality of suspended droplets in the carriage,within a period of time after the infected person coughs,the droplets exhaled by the infected person near the air supply outlet deposit a lot and decrease rapidly,while the droplets exhaled by the infected person near the air return outlet cannot deposit and are at a high level,but the subsequent time is mainly determined by the ventilation effect;Infected people will aggravate the spread of droplets near the air supply outlet and make the large-scale spread last longer,while it is just the opposite near the air return outlet.(2)When the passenger density in the carriage is at a low level,the change of passenger density will have a great impact on the mass of suspended droplets in the carriage;The mass of droplet deposition on the human body surface increases exponentially with the seat density in the carriage,and the mass of discharged droplets decreases exponentially with the seat density.(3)Under the condition of different speaking time of infected persons,the peak concentration of droplets in the spherical monitoring area increases sharply when the speaking time increases from 10 seconds to 20 seconds.For the cross-section of standing and sitting breathing areas,the duration of large-scale diffusion of droplets increases in logarithmic function with the speaking time.(4)The total mass of suspended droplets in the carriage is positively correlated with temperature,but the effect is not significant.The average change proportion of the total mass of suspended droplets in the carriage under different temperatures is less than 5%;The total mass of suspended droplets in the carriage is negatively correlated with humidity,but in the low humidity carriage environment,due to the interaction between droplet deposition and discharge,the total mass of suspended droplets in the carriage finally increases by only about 3%,while the increase of humidity in the carriage promotes a large number of droplet deposition,resulting in a 30%decrease in the total mass of droplets in the carriage.(5)Opening the subway door for 10 seconds can effectively reduce the suspended mass of droplets in the carriage,but opening the door makes the droplets spread to the whole computing domain,and has a more significant impact on the breathing area of the seated and standing person.(6)After the infected person wears the mask,it can effectively inhibit the spread of droplets,so that the time lag for each monitoring object to start inhaling droplets is 1-5 seconds,but the droplets will form particle aggregates near the infected person’s mouth,resulting in a reduction of less than 95% in the amount of droplets inhaled by passengers close to the infected person.