How do infectious aerosols spread in supermarkets, airplanes, and other indoor areas where large numbers of people congregate? Researchers from 15 Fraunhofer institutes and institutions are investigating this in the »AVATOR« project. The Fraunhofer Institute for Industrial Mathematics ITWM is on board and is developing a multi-scale simulator for this purpose, which can be used to calculate aerosol dispersion indoors.
Just in time for the summer, incidence rates have gone down, and restrictions are being eased everywhere. Many people are taking advantage of this to finally get back in the air and enjoy a holiday in other climes. But the Delta variant is forcing renewed caution in the coronavirus pandemic. Social distancing and wearing a mask are there-fore still the order of the day. While the risk of infection is quite low outdoors, infec-tious aerosols can easily accumulate indoors and lead to infection. How do these aero-sols spread, and how high is the risk of infection in airplanes, supermarkets, classrooms and the like?
A total of 15 Fraunhofer institutes and institutions are involved in the AVATOR project, short for Anti-Virus Aerosol: Test, Operation, Reduction. The researchers at the Fraunhofer ITWM are also contributing their knowledge: »We are developing a dynamic multiscale simulator that calculates aerosol dispersion in indoor spaces. Among other things, we consider means of transport, such as the aircraft, as scenarios,« says Dr. Christian Leithäuser of the department »Transport Processes«. The methodology of the multi-scale simulator is based on the institute's own grid-free simulation software MESHFREE, which can be used to model dynamic flow scenarios. The experience in the field of modelling and simulation of filters also proves to be particularly helpful, says Dr. Ralf Kirsch, team leader »Filtration and Separation« of the department »Flow and Material Simulation«.
Fraunhofer ITWM scientists are working on the project across departments and, thanks to the multi-scale approach, are also able to incorporate fine details into long-term observations – for example, the type of individual protective equipment.
AVATOR is characterised, among other things, by the effective cooperation of several Fraunhofer institutes. The special feature: the researchers do not work with a single simulation method, but create simulations at the participating institutes using different procedures and levels of detail over long periods of time. »We create simulations of different scales, which we can combine into a simulation chain depending on the problem at hand«, specifies Prof. Dr. Gunnar Grün, deputy head of the Fraunhofer Institute for Building Physics IBP and overall project manager. To validate the simulations, teams of experts compare them with measurement data from the aircraft cabin at Fraunhofer IBP. Here, the occurring room air flows can be optimally investigated and simulations can be meaningfully linked.
The situation becomes even more complex when people move around in a room rather than just stand still. The Fraunhofer researchers also included this aspect in their simula-tions by using an agent tool developed by Fraunhofer Singapore. Who walks in which direction? Who does the person come into contact with in the process? Fraunhofer IGD and Fraunhofer EMI, on the other hand, are responsible for simulating the correspond-ing indoor airflows.
To what extent does turbulence occur as a result of the movement? There is simply not enough computing capacity to simulate all the contacts made. Fraunhofer Austria therefore uses machine learning methods to select representative situations, which are then transferred to the airflow simulation. This targeted use of artificial intelligence is what makes agent-based flow simulation possible in the first place. The consortium has already simulated how aerosols spread in a supermarket with different people moving around. Of course, the model can also be applied to airplanes, classrooms and other rooms.
From the simulations, the researchers can predict how the aerosols spread in specific rooms. For example, how many viruses does a person breathe in on an airplane when an infected person sits one row in front? Two risk models jointly evaluated by Fraunho-fer IFF and Fraunhofer ITEM can be implemented to assess the respective risk of infec-tion and the effectiveness of various protective measures.
Grün cites one of the results as an example: »By linking the different models, we can see very clearly that wearing an FFP2 mask in an aircraft cabin is sufficient to reduce exposure by more than 95 per-cent, and thus also the risk of infection.« The exact risk depends, of course, on a num-ber of factors: for example, the precise distance away from the infected person, the quantity of infectious viruses and the duration of stay in the room. From the risk assess-ment data, the project participants can derive useful hygiene measures and study their effectiveness. Indoor air purification techniques, as well as the evaluation of their effec-tiveness, are therefore a further focus of developments in the AVATOR project.
The AVATOR project was financed with funds from the Fraunhofer-Gesellschaft’s »Anti-Corona« emergency program. The project consortium is made up of the following Fraunhofer institutes:
Video: AVATOR Simulation Scenario Aircraft. © Fraunhofer IBP / Fraunhofer ITWM
The scenario considered in the video is based on the aircraft cabin found in the Fraunhofer IBP flight laboratory. Air and aerosol dispersion within a cabin section are simulated. The grid-free flow solver MESHFREE from Fraunhofer ITWM is used for the simulation. The air flow is significantly influenced by the air conditioning and by the rise of warm breathing air.
When we exhale and speak, droplets and aerosols of various sizes are emitted. Larger droplets (red) sink downwards. Smaller droplets (yellow, green, blue) first rise upwards, because body heat creates a buoyant flow. In indoor spaces, aerosols do not simply disappear, but spread throughout the room over time. A suitable ventilation or filter concept reduces the aerosol concentration. Different types of protective mouth-and-nose cover prevent dispersion to varying degrees. In the video: Simulations in comparison – a particle-filtering mask (FFP2/N95), a medical face mask (surgical mask), a face visor (Faceshield) and completely without protection.
Video: Simulation of aerosol dispersion with different types of protection. © Fraunhofer ITWM
Fraunhofer Institute for Industrial Mathematics ITWM