Modeling COVID-19 transmission in aircraft cabin by integrating particle dynamics, dilution effect, and risk assessment
Abstract:Taking airplanes is crucial for many people’s lives, so passengers’ risks of getting Covid-19 are necessary to be considered. To get a more comprehensive view of the risk of taking airplanes with the possible existence of Covid-19 infected passengers, we conducted a project aiming to assess Covid-19 infection risk in aircraft cabins and propose possible measures and modifications that can be implemented to improve the safety of air travel under the pandemic of COVID-19. By developing models that are capable to simulate the fields inside of the cabin and introducing the concept of dilution ratio, the infection risk at different locations inside the aircraft cabin can be estimated. By using the model, several cabin circumstances such as wearing different types of face masks or having different sitting patterns of passengers are considered respectively, and the risk distributions are also found out. Results show that rather than spreading through the entire cabin, the virus-laden bioaerosols exhaled from infectors are restricted to limited zones. As a result, the infection risk to most passengers would be low except to locations in close proximity to the infector. Moreover, the result shows that mechanisms such as wearing face masks, sitting distantly are effective to reduce the infection risk. The study would be helpful to enhance public awareness of self-protection on airplanes and to assist airlines to implement means to protect passengers.
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Additional Project Information
Over the past year, Covid-19 has become a global epidemic. According to the World Health Organization, airborne transmission is a possible mechanism of the spread of Covid-19. Airborne transmission is a path through which the virus spreads through small droplets or small particles produced by human activities. These small droplets or small particles can reach a long distance and keep the virus in the air for a long time. Due to the high occupancy density and long exposure time, airborne transmission in the aircraft cabin is a big concern.
Estimate the Covid-19 infection risk at different locations inside the aircraft cabin and propose possible measures to improve the safety of air travel under the pandemic.
- Developing a mathematical and physical model that can simulate the airflow and particle fields inside the aircraft cabin
In order to start the actual estimation, a model that accurately describes the geometrical situation of the aircraft cabin is needed. A seven rows mockup including airflow inlets, outlets, and passengers will be constructed based on the actual condition of the aircraft. Then the flow field and concentration field for the situation of one infector (pollutant source) will be simulated. After that, a laboratory test should be conducted, and the measurement results will be used to validate the simulation.
2. Developing a method to calculate the infection risk at different locations inside the cabin
This process requires both the field calculated results in step one and equations for infection risk estimation. The traditional Wells-Riley equation is preferred, but cannot be directly applicable to the uneven field inside the aircraft cabin. Modification by proposing a new physical parameter will be necessary for combination with the Wells-Riley equation.
3. Finding possible measures to improve reduce the Covid-19 transmission risk during air travel
In this process, several practical measures including wearing face masks, sitting with vacant seats will be tested to see if they can effectively reduce the infection risk. Suggestions will be made based on quantitative simulation results.
Questions and Answers
1. What was the major objective of your project and what was your plan to achieve it?
Answer: The pandemic raised urgent concerns about whether air travel is safe and by what means can we increase its safety level. Airlines, aircraft manufacturers, and passengers needed answers to how we can prevent or reduce the infection of healthy passengers by unidentified infectors. My project serves to offer potential solutions to this big problem. More specifically, my project uses scientific simulations to understand Covid-19 infection risk in aircraft cabins and propose possible measures and modifications that can be implemented to improve the safety of air travel under the pandemic of COVID-19.
a. Was that goal the result of any specific situation, experience, or problem you encountered?
Answer: I came up with this objective as a result of my personal experience. When the pandemic started last March, my high school announced that all courses would be moved online. On the flight home, I wore clothes that almost covered all of my body, including one surgical mask plus an N95 mask.  Despite these precautions, my family and I felt nervous. In the cabin, passengers are in a crowded, closed environment, and some of them even did not wear masks. Talking to other international students and observing my surroundings, I realized that everybody felt this way. I realized that science might offer us a way to solve this problem. Fortunately, I had an opportunity to meet with my advisor who is an expert on aircraft cabin environment research. Hence, I decided to perform this research under his guidance.
b. Were you trying to solve a problem, answer a question, or test a hypothesis?
Answer: The crucial problem I aim to solve in this project is the concern of the safety of air travel under the pandemic of COVID-19.
2. What were the major tasks you had to perform in order to complete your project?
There were three major tasks that I performed to complete my research project.
The first task was to accurately simulate the non-uniform airflow field and the pollutant concentration field inside the aircraft cabin, which has a complicated geometrical structure and boundary conditions including temperature and ventilation rate.
Based on the fields calculated from the previous task, the second task was to introduce a new term, the dilution ratio, to show how much the pollutant is diluted at a certain location compared to the source. The introduction of dilution ratio makes it possible to calculate the infection risk at different locations under different circumstances.
The third task was to combine the dilution ratio with the traditional risk assessment model, which in the past could be only applied in an environment with uniform concentration fields. This innovative model was then used to quantitatively assess the infection risks inside the aircraft cabin under different conditions and with varied locations of infection sources. Furthermore, suggestions on lowering the infection risk were proposed based on the modeling results.
a. For teams, describe what each member worked on.
Answer: Not applicable
3. What is new or novel about your project?
Answer: The novel aspect of my project is its approach. I developed a model that is innovative in that it shows a deep and realistic understanding of the fields inside the complex space of the aircraft cabin. Previous models overly simplified the field inside the aircraft cabin to be uniform, making it impossible to distinguish the infection risk level when sitting close to an infector or away from him/her. In my model, the airfields inside are treated as non-uniform which is closer to reality. Moreover, the approach I used is new: it uses a clear physical parameter (dilution ratio) to provide non-uniform information for calculating the infection risks at different locations in the aircraft cabin.
a. Is there some aspect of your project's objective, or how you achieved it that you haven't done before?
Answer: I started my entire project from scratch, learning new knowledge in the process. Before doing this project I self-studied ventilation in a room at the beginning of my sophomore year. The composition of the aircraft ventilation system and how it works were totally new to me. Hence, it took me several months to study and understand this field better, especially when I learned the fundamentals of fluid mechanics and the mechanisms of droplets or aerosol transmission in the air.
b. Is your project's objective, or the way you implemented it, different from anything you have seen?
Answer: My project differed from the past research that I reviewed in that it used a more complex distribution model that better resembled reality, whereas the previous models used an overly simplified uniform distribution model. Therefore my project was able to make quantitative assessments of infection risk under non-uniform distribution inside the aircraft cabin possible.
c. If you believe your work to be unique in some way, what research have you done to confirm that it is?
Answer: To test the uniqueness of my project’s approach, I conducted a literature search on Google Scholar by using such keywords as “aircraft cabin”, “infection risk.” Through my literature review, I found that past research did not consider this problem to such a sophisticated extent, possibly because there had been no situations like Covid-19 to encourage such in-depth research. Ultimately, my simulation results about the fluid field and pollutant concentration field are consistent with the testing results from the aircraft cabin mockup. The accuracy of my simulations was proved to be promising.
4. What was the most challenging part of completing your project?
Answer: The most challenging part of completing this project was how to combine existing scientific knowledge with a new approach. As a high school student, most of the knowledge needed was new to me, so I had to grasp it within a short time. Meanwhile, there were also knowledge gaps that I needed to fill. For example, the traditional risk assessment model (Wells-Riley equation) is only applicable to a space whose air is uniformly mixed. This is clearly not the case in an aircraft cabin so I had to develop a new approach. Through this rigorous training, I gained a much better understanding of scientific research and truly enjoyed this process.
a. What problems did you encounter, and how did you overcome them?
There were challenges in each of the three tasks I conducted.
For Task 1: I needed to make sure the simulation was consistent with the field conditions and basic physics. I spent several weeks figuring out how to model the thermal plume from humans and how to set the correct boundary conditions.
For Task 2: I came up with a new concept called the dilution factor, based also on the physics of and the insight into the non-uniform nature of the cabin environment. This was key to solving the risk assessment in a non-uniform environment like an aircraft cabin.
For Task 3: I needed to suggest rational ways for passengers to reduce the likelihood of infection. For instance, I could not increase the ventilation rate of the ventilation system. I could not ask people to breathe slower. However, I could suggest them to wear facial masks and demonstrate how beneficial it was to both themselves and others.
b. What did you learn from overcoming these problems?
Answer: Through solving the above challenges, I learned how to conduct rigorous scientific research to solve pressing problems. First, grasping solid scientific knowledge and research skills was crucial. I also learned that existing knowledge might not be sufficient to solve novel problems, so I had to learn to develop new knowledge and fill in the gaps in the existing research. I realized that a successful researcher should always be ready to face new challenges and find ways to solve them.
5. If you were going to do this project again, are there any things you would you do differently the next time?
For the most part, I would do the project the same, because I learned a lot along my research path. I began with an initial study on relevant topics such as fluid dynamics, computational fluid dynamics (CFD) simulations, and aircraft ventilation systems. After getting familiar with basic knowledge, I started my project and ultimately got useful results. Later I analyzed my entire research process and felt what I did was actually a good way of mastering the skills of scientific research.
One area I would improve on is that I would pay more attention to the organization and planning of my research, especially its challenging points. Since this my first formal science research project, I sometimes underestimated the difficulty of the project which caused mistakes. If I can do this project again, I would make sure to understand the functions in Fluent better, especially for their applied range before starting to simulate the fields. By doing so I wouldn’t have gotten an inaccurate result in the beginning, and have to spend a lot of time seeking ways to modify it.
6. Did working on this project give you any ideas for other projects?
This project gave me a lot of useful ideas for other projects. My first idea was to determine the boundary conditions for some special air vents such as gaspers in airplanes. I believe this topic is important because solving it will provide us with a more precise model and a better understanding of aerodynamics inside the aircraft cabin. Such a model would make it possible for follow-up research on improving the performance and functions of gaspers, giving passengers a better flight travel experience. I came up with this research idea when I was setting the boundary conditions for my cabin model. The actual gasper structures inside the aircraft are different from our simplifications, which are merely circular outlets. Because of this, I wondered whether we had oversimplified our model. Besides, since the interactions between airflow and outlet walls contain impulses that are partly based on probability, our simplified function, which uses the idea of mean, might neglect some circumstances caused by chance. Therefore, we can have a more precise model.
The second project I thought of is the investigation of how particles interact with airflow. A better understanding of this problem will not only help us gain a better sense of the movement of particles but also understand the fate of virus-laden particles, which will allow us to better control the spread of infectious diseases in enclosed spaces and improve public safety accordingly. This problem arose when I was using the Lagrange method to calculate the flow field and see how particles are moving. I realized that many forces act on a single particle, which makes particles very complicated. Due to this complicated situation, I want to look for a simplification of or a more general solution for particle interactions with airflow.
7. How did COVID-19 affect the completion of your project?
COVID-19 prevented me from doing the field test on the aircraft cabin mockup in my supervisor’s laboratory. After I worked on computer simulations from March to October last year, I planned to do a field test in the aircraft cabin mockup to verify the simulation results. I had prepared the lab skills that I need to conduct the tests. However, COVID-19 started to spread weeks before the day of the scheduled experiment, so I was not able to go to the university to do the field test. It was a pity, but I kept in close communication with my supervisor and his team. Later I received the experimental results and used them to verify my simulation model. By doing so, I ultimately made sure that my simulations were accurate and consistent with the field test results. Hence I found an improvisation that helped me get around the complications caused by COVID-19.