Numerical Simulation Study On The Law Of Droplet Transport And Propagation

Since the 21st century,there have been multiple outbreaks of respiratory infectious diseases worldwide.At the end of 2019,the global outbreak of the COVID has severely affected people’s normal work and life.Droplet is one of the important transmission routes of respiratory infectious diseases.Understanding the law of droplet transmission and migration has important theoretical and practical significance for preventing infection.Based on extensive literature review,this paper selects computational fluid dynamics numerical simulation methods to investigate the movement and propagation of droplets generated by coughing in open spaces that can maintain a certain social distance and typical closed spaces such as buses.First of all,using the conversation between patients and healthy people in an open space as a model,the effect of air humidity of 20%-80%on droplet evaporation and the effect of environmental wind speeds of 1-4m/s on the movement of droplets when the patient coughs is studied.The results show that when droplets enter the air from the mouth with a relative humidity of 100%,the greater the difference in humidity between the two environments,the faster the droplet evaporation rate,and the larger the initial particle size of the droplet,the longer the evaporation time.When the ambient wind speed is low,the large particle size droplets will quickly settle under the influence of inertia and gravity,and the small particle size droplets will float with the airflow;.Secondly,taking the air-conditioned bus with the return air outlet in the middle of the roof as the object,the evaporation,sedimentation and diffusion of droplets produced by coughing when the air velocity is 0.25-2m/s and the passengers are in the front,middle and rear of the car compartment are studied.The results show that the amount of suspended droplets in the vehicle decreases with the increase of wind speed.When the wind speed is greater than lm/s,the decrease rate is almost unchanged;The amount of droplets deposited on the ground reaches the minimum when the wind speed is 1m/s;The droplet on the roof of the vehicle reaches a high percentage at lm/s.Considering comprehensively,the recommended air inlet speed of the carriage is lm/s under the conditions of this model.When the patient is in the front of the vehicle,the droplets mainly settle on the vehicle wall,followed by the ground.When the patient is in the middle and rear of the car,the droplets mainly settle on people and seats,followed by the ground.When the patient is in the back of the compartment,the droplet has a large impact area.Finally,the air distribution of the air-conditioned bus was changed.Taking the air return outlets located in the front of the car roof and under the seats on both sides of the car body as the object,the influence of 0.25-2m/s supply air speed on the movement of cough droplets was studied,and the three air distribution forms were compared.The results show that for the models with the air return vent in the front of the car roof and the lower part of the car body in this study,the recommended air inlet speeds of the car are 0.5m/s and lm/s,respectively.Among the three models,the air-conditioning bus model with the return air outlet located in the middle of the roof has a better control effect on droplets when the air inlet speed is 1m/s.