Dispersion of Droplets in Environmental Transmission and Intervention Studies
01 Jan 2021
A*STAR’s Institute of High Performance Computing (IHPC) has built upon existing fluid dynamic capabilities and developed a droplet dispersion/spread model. It is to understand the flight trajectories of airborne droplets, from emission to deposition
on a human subject at a distance when coughing, singing, or talking, as well as aerodynamics, droplets physics and their interactions. Droplet dispersion is not a solitary factor when it comes to the transmission of viruses. The spread of droplets
is much dependent on environmental conditions such as wind speed, humidity levels and ambient air temperature.
- Time dependent air flow rate (expulsion force and fluid volume)
- Droplet size distribution
- Cough angle
- Mouth opening area (expulsion force)
- Normal breathing
- Evaporation (heat transfer)
- Non-volatile particle (incorporated with physics of evaporation)
- Biological effect (e.g. viral load in the droplet)
The Science Behind
A fundamental part of being able to derive accurate insight is to simulate and visualise the droplets’ transport and dispersion process and its evolution in a physically consistent manner. Droplet dynamics are generally governed by drag force between
air and droplet, inertial force, and gravity force. Evaporation plays an important role in determining the droplet behaviour, as the droplet shrinks in the evaporation process. It could change the competing effects of drag, inertial and gravity forces
exerted on the droplet and subsequently determining the droplet fate, i.e., settling to the ground or lingering in the air. More details can be referred to the scientific publications, which include:
- Dispersion of Evaporating Cough Droplets in Tropical Outdoor Environment (Feature Article, Physics of Fluids, 32, 113301)
- Airborne Dispersion of Droplets during Coughing: A Physical Model of Viral Transmission (Accepted by Scientific Report)
Together with A*STAR’s Institute of Materials Research and Engineering (IMRE), the team has been working with public sector agencies, event providers and organisers, and various organisations to review and implement measures for the re-opening of
economic activities and community events. These include addressing factors that contribute to virus spread, such as crowd sizes, distancing between people, and confined spaces with poor ventilation. The team also worked with the A*STAR’s biomedical
research institutes and the National Centre of Infectious Disease (NCID) to better understand COVID-19 cough droplet transmission’s infectivity. The computational modelling studies are conducted via a national supercomputer facility, supported
by the National Supercomputing Centre, Singapore (NSCC).
The science-based study to investigate and implement measures have allowed events to take place safely. More details can be referred to the links below:Science behind why masks help prevent COVID-19 spread Advanced computational modelling of airborne droplets dispersion in tropical environments Ever wondered how droplets spread in a train cabin?