Stiehl Bernhard, Shrestha Rajendra, Schroeder Steven, Delgado Juanpablo, Bazzi Alexander, Reyes Jonathan, Kinzel Michael, Ahmed Kareem
AIP Adv. 2022 Jul 7;12(7):075210. doi: 10.1063/5.0102078. eCollection 2022 Jul.
The present paper investigates droplet and aerosol emission from the human respiratory function by numerical and experimental methods, which is analyzed at the worst-case scenario, a violent sneeze without a face covering. The research findings develop the understanding of airborne disease transmission relevant to COVID-19, its recent variants, and other airborne pathogens. A human sneeze is studied using a multiphase Computational Fluid Dynamics (CFD) model using detached eddy simulation coupled to the emission of droplets that break up, evaporate, and disperse. The model provides one of the first experimental benchmarks of CFD predictions of a human sneeze event. The experiments optically capture aerosols and droplets and are processed to provide spatiotemporal data to validate the CFD model. Under the context of large random uncertainty, the studies indicate the reasonable correlation of CFD prediction with experimental measurements using velocity profiles and exposure levels, indicating that the model captures the salient details relevant to pathogen dispersion. Second, the CFD model was extended to study the effect of relative humidity with respect to the Wells curve, providing additional insight into the complexities of evaporation and sedimentation characteristics in the context of turbulent and elevated humidity conditions associated with the sneeze. The CFD results indicated correlation with the Wells curve with additional insight into features, leading to non-conservative aspects associated with increased suspension time. These factors are found to be associated with the combination of evaporation and fluid-structure-induced suspension. This effect is studied for various ambient air humidity levels and peaks for lower humidity levels, indicating that the Wells curve may need a buffer in dry climates. Specifically, we find that the increased risk in dry climates may be up to 50% higher than would be predicted using the underlying assumptions in Wells' model.
本文通过数值和实验方法研究了人类呼吸功能产生的飞沫和气溶胶排放情况，分析了最糟糕的情况，即不戴口罩的剧烈打喷嚏。研究结果加深了对与新冠病毒、其近期变种以及其他空气传播病原体相关的空气传播疾病传播的理解。使用多相计算流体动力学（CFD）模型对人类打喷嚏进行了研究，该模型采用分离涡模拟并结合了飞沫的破碎、蒸发和扩散排放。该模型为人类打喷嚏事件的CFD预测提供了首批实验基准之一。实验通过光学手段捕获气溶胶和飞沫，并进行处理以提供时空数据来验证CFD模型。在存在较大随机不确定性的情况下，研究表明CFD预测与使用速度剖面和暴露水平的实验测量结果具有合理的相关性，这表明该模型捕捉到了与病原体扩散相关的显著细节。其次，扩展了CFD模型以研究相对湿度对韦尔斯曲线的影响，从而在与打喷嚏相关的湍流和高湿度条件下，对蒸发和沉降特性的复杂性有了更多了解。CFD结果表明与韦尔斯曲线相关，并对其特征有了更多见解，从而揭示了与悬浮时间增加相关的非保守方面。发现这些因素与蒸发和流固诱导悬浮的组合有关。针对各种环境空气湿度水平对这种效应进行了研究，发现较低湿度水平时效应达到峰值，这表明在干燥气候下韦尔斯曲线可能需要一个缓冲。具体而言，我们发现干燥气候下增加的风险可能比使用韦尔斯模型的基本假设预测的高出50%。
