Just in time for summer, incidence rates have fallen and easing of restrictions can be felt everywhere. Many people are taking advantage of this to finally board a plane again and enjoy vacations in distant places. However, the Delta variant has made renewed caution necessary in the COVID-19 pandemic. Maintaining distance and wearing masks therefore remain essential. While the risk of infection outdoors is relatively low, infectious aerosols can easily accumulate indoors and lead to infections. How do these aerosols spread, and how high is the risk of infection in airplanes, supermarkets, classrooms, and similar environments?

Simulation chains instead of individual simulations

Researchers from a total of 15 Fraunhofer institutes and facilities, led by the Fraunhofer Institute for Building Physics IBP, are investigating these questions in the AVATOR project, short for “Anti-Virus-Aerosol: Testing, Operation, Reduction.”
“We simulate and analyze how viruses spread indoors and how indoor air can be effectively cleaned,” says Prof. Dr. Gunnar Grün, Deputy Director of Fraunhofer IBP and overall project coordinator. What makes the project special is that the scientists do not rely on a single simulation method. Instead, the participating institutes create simulations using different methods and levels of detail over long periods of time. This ranges from the immediate near field of an infected person—close to the mouth—to the far field, meaning large rooms.

How many viruses enter the indoor air with different types of masks? How does airflow behave near a person, and to what extent do exhaled viruses spread throughout the room over time? “We create simulations at different scales, which we can combine into a simulation chain depending on the research question,” Grün explains.

For example, Fraunhofer ITWM focuses in near-field simulations on how aerosol concentration changes in the immediate vicinity of an infected person when different masks are worn. Experimental validation data for airflow fields were obtained by expert teams using laser light sheet and schlieren measurement techniques at Fraunhofer EMI. Fraunhofer IBP, in turn, is responsible for large-scale simulations over long periods, such as in aircraft cabins or production halls. To validate the simulations, the research teams compare them with measurement data from IBP’s own aircraft cabin, where indoor airflow patterns are examined.

“In our simulations at Fraunhofer IBP, we consider the entire daily cycle. The simulation therefore cannot be nearly as precise as those from other institutes that focus on just a few minutes. But this is precisely where the great advantage of the simulation chain lies: the simulations complement each other in a meaningful way. Since the transitions between simulations can be linked, the resulting overall picture can be significantly enriched,” says Grün.

Agent-based simulations take movement into account

The situation becomes even more complex when people are not stationary indoors but move around. The Fraunhofer researchers also took this into account in their calculations—using an agent-based tool developed by Fraunhofer Singapore. Who walks where? Whom does a person encounter? Fraunhofer IGD and Fraunhofer EMI provide the corresponding airflow simulations.

What air turbulences are caused by movement? Simulating this for all encounters would exceed available computing capacity. Therefore, Fraunhofer Austria uses machine learning methods to select representative situations, which are then passed on to the airflow simulations. This targeted use of artificial intelligence makes agent-based airflow simulation manageable in the first place. The consortium has already calculated an example of how aerosols spread in a supermarket with moving people. Of course, the model can also be transferred to airplanes, classrooms, and other spaces.

From the simulations, it is possible to derive how aerosols spread in specific rooms. For example, how many viruses does a person inhale on an airplane if an infected person is sitting one row ahead? Using two risk models jointly evaluated by Fraunhofer IFF and Fraunhofer ITEM, the respective infection risk can be assessed and the impact of various protective measures estimated.
“By linking the different models, we can clearly see that simply wearing FFP2 masks in an aircraft cabin reduces exposure by more than 95 percent and thus significantly lowers the risk of infection,” Grün cites as one example. The exact risk naturally depends on various factors, such as the precise distance to the infected person, the number of infectious viruses, and the duration of stay indoors.

Based on the risk assessment data, the project partners derive meaningful hygiene measures and test their effectiveness. Technologies for indoor air purification and the validation of their effectiveness are therefore also a key focus of developments in the AVATOR project.

The AVATOR project was funded by the Fraunhofer-Gesellschaft through its “Anti-Corona” emergency program. The project consortium consists of the following Fraunhofer institutes:

• Fraunhofer Institute for Building Physics IBP
• Fraunhofer Institute for High-Speed Dynamics, Ernst Mach Institute, EMI
• Fraunhofer Institute for Industrial Mathematics ITWM
• Fraunhofer Institute for Chemical Technology ICT
• Fraunhofer Institute for Structural Durability and System Reliability LBF
• Fraunhofer Institute for Applied Polymer Research IAP
• Fraunhofer Institute for Microengineering and Microsystems IMM
• Fraunhofer Institute for Toxicology and Experimental Medicine ITEM
• Fraunhofer Institute for Factory Operation and Automation IFF
• Fraunhofer Institute for Physical Measurement Techniques IPM
• Fraunhofer Institute for Computer Graphics Research IGD
• Fraunhofer Singapore
• Fraunhofer Austria
• Fraunhofer Institute for Manufacturing Technology and Advanced Materials IFAM
• Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB

• Fraunhofer Institute for Building Physics IBP
  Press contact: presse@ibp.fraunhofer.de
• Fraunhofer Institute for High-Speed Dynamics, Ernst Mach Institute, EMI
  Press contact: birgit.bindnagel@emi.fraunhofer.de
• Fraunhofer Institute for Industrial Mathematics ITWM
  Press contact: presse@itwm.fraunhofer.de
• Fraunhofer Institute for Toxicology and Experimental Medicine ITEM
  Press contact: cathrin.nastevska@item.fraunhofer.de
• Fraunhofer Institute for Factory Operation and Automation IFF
  Press contact: rene.maresch@iff.fraunhofer.de
• Fraunhofer Institute for Computer Graphics Research IGD
  Press contact: daniela.welling@igd.fraunhofer.de
• Fraunhofer Singapore
  Press contact: julienne.chan@fraunhofer.sg
• Fraunhofer Austria
  Press contact: elisabeth.guggenberger@fraunhofer.at