Numerical simulations of the flow and aerosol dispersion in a violent expiratory event: Outcomes of the "2022 International Computational Fluid Dynamics Challenge on violent expiratory events"

This paper presents and discusses the results of the "2022 International Computational Fluid Dynamics Challenge on violent expiratory events" aimed at assessing the ability of different computational codes and turbulence models to reproduce the flow generated by a rapid prototypical exhalation and the dispersion of the aerosol cloud it produces. Given a common flow configuration, a total of seven research teams from different countries have performed a total of eleven numerical simulations of the flow dispersion by solving the Unsteady Reynolds Averaged Navier-Stokes (URANS) or using the Large-Eddy Simulations (LES) or hybrid (URANS-LES) techniques. The results of each team have been compared with each other and assessed against a Direct Numerical Simulation (DNS) of the exact same flow. The DNS results are used as reference solution to determine the deviation of each modeling approach. The dispersion of both evaporative and non-evaporative particle clouds has been considered in twelve simulations using URANS and LES. Most of the models predict reasonably well the shape and the horizontal and vertical ranges of the buoyant thermal cloud generated by the warm exhalation into an initially quiescent colder ambient. However, the vertical turbulent mixing is generally underpredicted, especially by the URANS-based simulations, independently of the specific turbulence model used (and only to a lesser extent by LES). In comparison to DNS, both approaches are found to overpredict the horizontal range covered by the small particle cloud that tends to remain afloat within the thermal cloud well after the flow injection has ceasedThis study was funded by the Spanish Ministerio de Ciencia, Innovación y Universidades through the grants PID2020-113303GB-C21 and RTI2018-100907-A-I00 (MCIU/AEI/FEDER) and by the Generalitat de Catalunya through the grant 2017-SGR-1234. M. Z, V. R. and N. I. acknowledge the Super Computer Center (SCC) «Polytechnic» for providing computational resources. J.W., M.Š. and J.R. would like to thank the valuable insights given by professors Paul Steinmann and Matjaž Hriberšek and the financial support of the Deutsche Forschungsgemeinschaft, Germany under project STE 544/58-2 and the Slovenian Research Agency under project No. P2-0196Postprint (author's final draft

Numerical simulations of particle turbulent dispersion and deposition with implications for the spreading of airborne diseases

Aquesta tesi doctoral examina la dinàmica de partícules en fluxos turbulents mitjançant simulacions numèriques, enfocant-se en dos escenaris clau: els fluxos generats per l'exhalació i els impulsats per flotabilitat en espais tancats. Inicialment, s'avaluen diferents mètodes numèrics per predir la dispersió de partícules en tos suau, destacant que les simulacions totalment resoltes superen els models Unsteady Reynolds Averaged Navier-Stokes en la captura de la dispersió vertical. Posteriorment, s'examina la dispersió de partícules després d'exhalació mitjançant el "Reto de Dinámica de Fluidos Computacional Internacional de 2022". Es detecta una subestimació constant en la mescla vertical, particularment en models basats en equacions de Navier-Stokes no estacionàries. L'estudi es centra també en la fase post-exhalació, explorant la dinàmica de partícules patògenes en corrents d'aire de fons. A més, s'investiga el transport d'aerosols en fluxos turbulents en espais tancats, revelant una distribució homogènia de partícules amb el temps. Finalment, es considera la dispersió i deposició de partícules sòlides en suspensió en una caixa cúbica amb parets escalfades, correlacionant resultats amb experiments i solucions analítiques. Aquesta recerca destaca la importància de la modelització precisa en la resposta a emergències i la reducció de la transmissió de malalties per l'aire, contribuint a la comprensió d'aquests fenòmens crítics mitjançant comparacions amb dades experimentals i models teòrics.Esta tesis doctoral aborda el movimiento de partículas en flujos turbulentos mediante simulaciones numéricas en dos contextos clave: flujos de partículas generados por la exhalación y flujos turbulentos en espacios cerrados impulsados por flotación. Primero, se evalúan diferentes enfoques numéricos para predecir la dispersión de partículas durante la tos inicial. Se encuentra que el modelo de Navier-Stokes no estacionario con un modelo de turbulencia k-epsilon captura aspectos importantes pero subestima la dispersión vertical en comparación con simulaciones más detalladas. Luego, se participa en el "Desafío Internacional de Dinámica de Fluidos Computacionales de Eventos de Exhalación Violenta de 2022" para evaluar modelos de dispersión de partículas post-exhalación. Se detecta una subestimación constante de la mezcla vertical en modelos basados en Navier-Stokes no estacionarios. La investigación explora la dinámica de partículas y patógenos en corrientes de aire posteriores a la turbulencia. También investiga el transporte de aerosoles en flujos turbulentos en espacios cerrados, observando una distribución uniforme de partículas de diferentes tamaños con el tiempo. Además, se examina la dispersión y deposición de partículas en una caja cúbica con paredes calentadas de manera diferencial, relacionando los resultados con experimentos y soluciones analíticas, aportando valiosos conocimientos sobre la transferencia de calor y la deposición de partículas. En resumen, este estudio integral de la dinámica de partículas resalta la importancia de la modelización precisa en la respuesta a emergencias y la reducción de la transmisión de enfermedades transmitidas por el aire.This doctoral thesis thoroughly investigates particle movement in turbulent flows through numerical simulations. It focuses on two scenarios: particle-laden jet flows triggered by expiratory events and buoyancy-driven turbulent flows in enclosed spaces. The research begins by evaluating numerical methodologies for predicting particle dispersion during the initial phase of a cough. The Unsteady Reynolds Averaged Navier-Stokes model captures essential features but underestimates vertical dispersion compared to fully resolved simulations. Participation in the "2022 International Computational Fluid Dynamics Challenge on Violent Expiratory Events" reveals consistent underestimation of vertical mixing in various models, particularly in Unsteady Reynolds Averaged Navier-Stokes. The study also examines the second stage of expiratory events, where pathogen-particle dynamics depend on background air currents after turbulent energy dissipation. Additionally, it explores aerosol transport in buoyancy-driven turbulent flows within enclosed spaces, showing homogeneous particle distribution over time. The work extends to dispersion and deposition of airborne solid particles in a cubical cavity with differentially heated walls, offering valuable insights into heat transfer and particle deposition. In summary, this research contributes to our understanding of particle dispersion and deposition dynamics, vital for emergency response and mitigating airborne disease transmission, by comparing simulations with experimental data and theoretical models

Numerical simulations of the flow and aerosol dispersion in a violent expiratory event

This paper presents and discusses the results of the “2022 International Computational Fluid Dynamics Challenge on violent expiratory events” aimed at assessing the ability of different computational codes and turbulence models to reproduce the flow generated by a rapid prototypical exhalation and the dispersion of the aerosol cloud it produces. Given a common flow configuration, a total of 7 research teams from different countries have performed a total of 11 numerical simulations of the flow dispersion by solving the Unsteady Reynolds Averaged Navier–Stokes (URANS) or using the Large-Eddy Simulations (LES) or hybrid (URANS-LES) techniques. The results of each team have been compared with each other and assessed against a Direct Numerical Simulation (DNS) of the exact same flow. The DNS results are used as reference solution to determine the deviation of each modeling approach. The dispersion of both evaporative and non-evaporative particle clouds has been considered in 12 simulations using URANS and LES. Most of the models predict reasonably well the shape and the horizontal and vertical ranges of the buoyant thermal cloud generated by the warm exhalation into an initially quiescent colder ambient. However, the vertical turbulent mixing is generally underpredicted, especially by the URANS-based simulations, independently of the specific turbulence model used (and only to a lesser extent by LES). In comparison to DNS, both approaches are found to overpredict the horizontal range covered by the small particle cloud that tends to remain afloat within the thermal cloud well after the flow injection has ceased