CEA, DAM, DIF, 91297, Arpajon, France.
FLUIDIAN, 95000, Cergy, France.
Sci Rep. 2022 Mar 7;12(1):4025. doi: 10.1038/s41598-022-08067-6.
Computational fluid dynamics (CFD) modelling and 3D simulations of the air flow and dispersion of droplets or drops in semi-confined ventilated spaces have found topical applications with the unfortunate development of the Covid-19 pandemic. As an illustration of this scenario, we have considered the specific situation of a railroad coach containing a seated passenger infected with the SARS-CoV-2 virus (and not wearing a face mask) who, by breathing and coughing, releases droplets and drops that contain the virus and that present aerodynamic diameters between 1 and 1000 µm. The air flow is generated by the ventilation in the rail coach. While essentially 3D, the flow is directed from the bottom to the top of the carriage and comprises large to small eddies visualised by means of streamlines. The space and time distribution of the droplets and drops is computed using both an Eulerian model and a Lagrangian model. The results of the two modelling approaches are fully consistent and clearly illustrate the different behaviours of the drops, which fall down close to the infected passenger, and the droplets, which are carried along with the air flow and invade a large portion of the rail coach. This outcome is physically sound and demonstrates the relevance of CFD for simulating the transport and dispersion of droplets and drops with any diameter in enclosed ventilated spaces. As coughing produces drops and breathing produces droplets, both modes of transmission of the SARS-CoV-2 virus in human secretions have been accounted for in our 3D numerical study. Beyond the specific, practical application of the rail coach, this study offers a much broader scope by demonstrating the feasibility and usefulness of 3D numerical simulations based on CFD. As a matter of fact, the same computational approach that has been implemented in our study can be applied to a huge variety of ventilated indoor environments such as restaurants, performance halls, classrooms and open-plan offices in order to evaluate if their occupation could be critical with respect to the transmission of the SARS-CoV-2 virus or to other airborne respiratory infectious agents, thereby enabling relevant recommendations to be made.
计算流体动力学 (CFD) 模型和半封闭通风空间中液滴或液滴的空气流动和扩散的 3D 模拟，随着新冠疫情的不幸发展，找到了热门应用。作为这种情况的一个例子，我们考虑了一个特定的情况，即在一个有座位的乘客感染了 SARS-CoV-2 病毒的火车车厢内（未戴口罩），他通过呼吸和咳嗽释放含有病毒的液滴和液滴，这些液滴和液滴的空气动力学直径在 1 到 1000 微米之间。空气流动是由火车车厢内的通风产生的。虽然本质上是 3D 的，但流动是从车厢底部到顶部的，由流线显示的大到小的漩涡组成。使用欧拉模型和拉格朗日模型计算液滴和液滴的空间和时间分布。两种建模方法的结果完全一致，清楚地说明了两种液滴的不同行为，其中靠近感染乘客的液滴下降，而与空气流一起携带的液滴则侵入火车车厢的大部分区域。这一结果是合理的，证明了 CFD 在模拟封闭通风空间中任何直径的液滴和液滴的传输和扩散方面的相关性。由于咳嗽会产生液滴，而呼吸会产生飞沫，因此我们在 3D 数值研究中考虑了 SARS-CoV-2 病毒在人体分泌物中的这两种传播模式。除了火车车厢的具体实际应用之外，本研究通过展示基于 CFD 的 3D 数值模拟的可行性和有用性，提供了更广泛的范围。事实上，我们的研究中所实施的相同计算方法可以应用于各种通风的室内环境，如餐馆、表演厅、教室和开放式办公室，以评估它们的使用是否会对 SARS-CoV-2 病毒或其他空气传播的呼吸道传染病原体的传播构成风险，从而能够提出相关建议。
