面对面呼吸飞沫传播和防护的流体力学初步分析

针对SARS-CoV-2疫情,围绕病人和戴防飞沫面罩的健康人面对面呼吸状态下飞沫的流动传播问题,利用计算流体力学方法进行了数值模拟。首先采用二维非稳态不可压缩雷诺平均N-S方程描述平均流场,计算区域采用H型结构网格拓扑结构,将多相流的欧拉模型用于描述空气-飞沫流动,湍流脉动采用RNG k-ε湍流模型。计算获得了呼吸飞沫喷射速度、粒径和入口含量对飞沫流动传播的影响规律,分析了水平传播线和垂直传播线的飞沫浓度分布。研究表明:呼吸飞沫喷射速度、入口含量和流动传播速度、浓度分布呈正相关性,粒径主要影响飞沫流动传播的浓度峰值大小;呼吸飞沫跟随空气流动先以水平传播为主,后转变为以垂直扩散为主,扩散过程会形成“猫眼”状飞沫云团;呼吸飞沫在气流作用下侵入到防飞沫面罩内形成旋涡,导致防飞沫面罩的失效,因此,防飞沫面罩必须结合口罩共同使用。

Preliminary fluid dynamics analysis on face-to-face respiratory droplets transmission and protection

For epidemic situation of SARS-CoV-2,computational fluid dynamics method was used to simulate the problem of respiratory droplets transmission in the airflow between the patient and healthy person with anti-droplet face shield.The two dimensional unsteady incompressible Reynolds average N-S equations were solved to obtain the mean flow field.The computational domain was discretized by structural grid technology and H-grid topology.The turbulence fluctuation was described by the RNG k-εturbulence model.The dispersed phase of droplet was treated as continuous fluid by Euler model.The influence of spraying speed,diameter and inlet content of the respiratory droplets on the transmission in the airflow was obtained.The concentration distribution of droplets along the horizontal and vertical transmission line were analyzed.It shows that,the spraying speed and the inlet content are positively correlated with the transmission speed and concentration distribution of the respiratory droplets,while the effect of diameter is mainly reflected in the influence on the peak concentration.The transmission mechanism of respiratory droplets in the airflow is firstly dominated by the convection,and later by the diffusion,which will form a droplets cloud.The anti-droplets face shield can’t protect the respiratory droplet transmission unless the breathing mask is used for physical isolation from droplets,due tu he fact that:the vortex will transport respiratory droplets into the anti-droplets face shield.