Department of Mechanical Engineering, Texas Tech University, Lubbock, TX, USA.
Department of Mechanical, Aerospace & Biomedical Engineering, UT Space Institute, University of Tennessee, Knoxville, TN, USA.
Sci Total Environ. 2022 Jul 20;831:154856. doi: 10.1016/j.scitotenv.2022.154856. Epub 2022 Mar 30.
Face shield is a common personal protection equipment for pandemic. In the present work, three-dimensional computational fluid dynamic (CFD) method is used to simulate a cough jet from an emitter who wears a face shield. A realistic manikin model with a simplified mouth cavity is employed. A large eddy simulation with a dynamic structure subgrid scale model is applied to model the turbulence. An Eulerian-Lagrangian approach is adopted to model the two-phase flows, with which the droplets are represented by a cloud of particles. The droplet breakup, evaporation, dispersion, drag force, and wall impingement are considered in this model. An inlet velocity profile that is based on a variable mouth opening area is considered. Special attentions have been put the vortex structure and droplet re-distribution induced by the face shield. It is found that the multiple vortices are formed when the cough jet impinges on the face shield. Some droplets move backward and others move downward after the impinging. It is also found that a small modification of the face shield significantly modifies the flow field and droplet distribution. We conclude that face shield significantly reduces the risk factor in the front of the emitter, meanwhile the risk factor in the back of the emitter increases. When the receiver standing in front of the emitter is shorter than the emitter, the risk is still very high. More attentions should be paid on the design of the face field, clothes cleaning and floor cleaning of the emitters with face shields. Based on the predicted droplet trajectory, a conceptual model for droplet flux is proposed for the scenario with the face shield.
面罩是一种常见的个人防护设备，用于应对大流行疾病。在本工作中，采用三维计算流体动力学（CFD）方法模拟了戴面罩的发射者咳嗽产生的射流。使用了带有简化口腔的逼真人体模型。应用大涡模拟与动态结构亚网格尺度模型来模拟湍流。采用欧拉-拉格朗日方法来模拟两相流，其中液滴用粒子云来表示。该模型考虑了液滴的破裂、蒸发、扩散、阻力和壁面撞击。采用了基于可变口面积的入口速度分布。特别关注了面罩引起的涡流结构和液滴再分布。结果发现，当咳嗽射流撞击面罩时，会形成多个涡流。一些液滴向后移动，另一些向下移动。还发现，面罩的小修改显著改变了流场和液滴分布。我们得出结论，面罩显著降低了发射者前方的风险因素，但同时也增加了发射者后方的风险因素。当站在发射者前面的接收者比发射者矮时，风险仍然很高。对面罩使用者的面罩设计、衣物清洁和地板清洁应给予更多关注。基于预测的液滴轨迹，提出了一种带有面罩场景下的液滴通量概念模型。
