The recent COVID-19 pandemic necessitates an increased need for understanding the airflow patterns and its role in containing and spreading of airborne contaminants in an enclosed environment.  Airflow is the primary carrier of moisture, airborne contaminants, and heat.  The study of room or building airflow patterns is rich in the literature; however, there is a lack of understanding of the air circulation behaviors inside the cabin of a bus.  Social distancing policies may not be sufficient on public transportation modes, since HVAC systems are likely to redistribute the air and airborne virus throughout the entire cabin, risking the health of both drivers and passengers. Thus, this present study employs numerical techniques and it aims to understand air circulation patterns inside the cabins of different bus configurations and conditions.  The numerical simulations will be compared qualitatively with the smoke experiments and point measurements.  Three different bus configurations including two rural transit buses and one city transit bus will be modeled. Large amount of effort is spent on profiling the interior geometries of the buses including driver and passengers’ seats, windows, supply air diffusers/slots, exhaust grilles, stairs, driver’s dashboard, and storage area.  The supply air diffusers/slots and exhaust grilles are included in the numerical study.   Numerical three-dimensional flow visualizations including air circulation patterns as well as velocity, temperature, and relative humidity distributions inside the bus will be presented.  The present work utilizes the computational fluid dynamics software ANSYS Fluent to simulate the airflow numerically.  Non-reactive species (passive scalars) mixing model including heat transfer will be employed to simulate the air circulation and thermal behavior.  Two-equation k-epsilon turbulence model is used to simulate airflow turbulence.  Empirical-based inlet and outlet boundary conditions will be discussed and specified accordingly.  Some of the metrics that are adopted in the present study include air speed, temperature, and relative humidity. Furthermore, these different simulations are implemented under different vehicle conditions, e.g. stationary, in motion, with passengers windows open and shut, and with heating, ventilating, and air conditioning (HVAC) in cooling operations. Moreover, these simulations are conducted on different vehicles, with different sizes and with different HVAC configurations. Results of this numerical study could be significantly valuable and directly lead to improved protection of passengers and drivers on public transportation modes against all forms of air-borne viruses both locally as well as across the entire globe.  Recommendations for mitigating spreading of airborne contaminants will be provided based on a better understanding of the airflow patterns inside the cabin of the bus. 


Impact of Transit Bus Configurations and Vehicle Conditions on Interior Air Circulation Patterns: Numerical Study

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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