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CHALLENGE PRESENTATION

The COVID-19 pandemic has evidenced the need for a better understanding of the flow physics behind the airborne transmission of infectious diseases. To understand the The COVID-19 pandemic has evidenced the need for a better understanding of the flow physics behind the airborne transmission of infectious diseases. To understand the transmission of pathogens via the aerosols spewed into the air by a person who sneezes, coughs, talks or sings, it is crucial to elucidate the dynamics of the exhaled air through the mouth and nose and the dispersion processes of the resulting aerosol cloud. The capacity of the infectious particles to remain afloat strongly depends on the exhalation conditions and their size.

The aim of this challenge is to assess the validity of using a  computationally affordable turbulence model to reproduce both the hydrodynamics of a prototypical rapid exhalation mimicking a mild cough (stage I) and the dispersion of the aerosol cloud in an idealized environment (stage II). Existing DNS will be used as a benchmark for this assessment.

Simulations can be performed using any of the turbulence modelling techniques available (RANS, LES, hybrid techniques…) and any numerical or discretization scheme for simulating fluid flows (finite element, finite volume, spectral methods, Lattice-Boltzmann…). The dispersion of the aerosol can be simulated with Lagrangian or Eulerian approaches.

SPECIFIC GOALS

This challenge is aimed at answering two questions, each one belonging to a stage. Each team may choose to provide answers for both or just one question. However since the transmission of airborne diseases depends on the dispersion of pathogen-laden particles, we strongly encourage the teams to address both stages.

  1. STAGE 1: determine the ability of each combination of numerical method and turbulence modelling used for the simulation to reproduce predictions of DNS of the unsteady hydrodynamics of an idealized exhalation event characterized by the rapid but limited in time injection of warm air into an initially quiescent ambient. 
  2. STAGE 2: estimate the impact of the particle size and evaporation on the dispersion of the aerosol cloud generated by the STAGE 1 exhalation event and compare the results with the predictions obtained combining DNS of the flow with a one-way coupling Lagrangian tracking scheme.

DNS of the flow and of the dispersion of the aerosol are reported, respectively, in Fabregat et al. (2021a) and Fabregat et al. (2021b).

DELIVERABLES

  1. To exchange the data files, we will use a dedicated Google Drive folder. Upon acceptance, a unique link for file sharing will be sent to each team. Accepted files must be either ASCII and vtk to facilitate post-processing in Paraview. (http://www.paraview.org). Please make sure that you can use Google Drive and export your results in any of the file formats readable with Paraview before considering participating in this challenge. The list of readable file formats can be found at https://www.paraview.org/Wiki/ParaView/Users_Guide/List_of_readers.
  2. All submitted data must be stored in ASCII files (except maybe Paraview files).
    1. STAGE 1: files must include the temporal evolution of spatially averaged quantities and Paraview vtk files with the instantaneous distribution of velocities, temperature and turbulence quantities in certain planes at different instants of time.
    2. STAGE 2: files must include the particle cloud information at several times.
  • More information will be provided in the Instructions document. 
  1. Details about the code, mesh, spatial and temporal discretization, turbulence and numerical models will also be required.
  2. Each team’s results will be anonymously kept and presented.

IMPORTANT DATES

  • October 1 2021: Challenge Announcement.
  • October 15 2021: Challenge starts.
  • May 1 2022: Deadline for results submission.
  • June 27 2022: Virtual workshop. All teams are expected to participate and present and discuss their results and conclusions.
  • Fall 2022: Paper submission. The outcomes of the challenge will be presented in a single paper led by the organizers and co-authored by all challenge participants. The maximum number of co-authors per contribution will be limited to two.

ORGANIZERS AND CONTACT

TheThe Challenge is jointly organized by University Rovira i Virgili (Tarragona, Spain) (Jordi Pallares, Alexandre Fabregat and Salvatore Cito) and Università degli Studi di Udine (Udine, Italy) (Cristian Marchioli). Please address your questions to coughcfdchallenge@gmail.com

PARTICIPATION

To participate in the 2022 International CFD Challenge on Violent Expiratory Events, please send an email with your name and affiliation to coughcfdchallenge@gmail.com before October 15 2021. After being enrolled, each team will be granted access to the Google Drive account and will receive the instructions to participate in the Challenge.

REFERENCES

  • Fabregat, A., Gisbert, F., Vernet, A., Dutta, S., Mittal, K., & Pallarès, J. (2021a). Direct numerical simulation of the turbulent flow generated during a violent expiratory event. Physics of Fluids, 33(3), 035122.
  • Fabregat, A., Gisbert, F., Vernet, A., Ferré, J. A., Mittal, K., Dutta, S., & Pallarès, J. (2021b). Direct numerical simulation of turbulent dispersion of evaporative aerosol clouds produced by an intense expiratory event. Physics of Fluids, 33(3), 033329.

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