Comprehensive optimization of air quality in high speed rail cabins using CFD
Creators: name: Yang, Lin
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 401204
subject: Computational methods in fluid flow, heat and mass transfer (incl. computational fluid dynamics)

description: In recent years, High-speed rails (HSR) have been rapidly developed in many counties due to convenience and high efficiency. A growing number of people choose High-speed train (HST) for long-distance travel. The good air quality in train cabin relates to the HVAC performance, which can optimize passengers' comfort zones, efficiently control the gas/particle contaminants transportation inside a cabin. Thus, in-cabin air quality is of great interest to many researchers. The air quality is affected by many factors such as ventilation scheme, cabin geometry, contaminant property, train operation condition, and ambient environment. The focus of this project is to comprehensively and effectively assess the air quality in HST cabins and propose corresponding optimization strategies.<br><br>Computational Fluid Dynamics (CFD) has been proven as a cost-efficient approach to analyze and optimize air quality of indoor environments. However, the holistic optimization of air quality in HST cabin is still absent in existing literature due to the extreme complexity of the impact factors, which are dependent on unknown relationships. The HST cabin environment is influenced by many factors, ranging from cabin interior to exterior. Considering the interior, diffuser design is key to the ventilation performance, which can induce the overall ventilation flow pattern in a train cabin. Additionally, passengers' activities from the interior cabin can also influence the air quality, such as coughing droplets from passenger which are the main source of contaminants transportation. On the other hand, train operation conditions and ambient environment are the main exterior impact factors for air quality. High-pressure waves are induced in two situations: when crossing another HST and when passing through a tunnel. Though these two situations always happen during HST operation, the study on the impact of the induced pressure waves on HST interior air quality is rare. Besides, considering HSTs are significantly exposed to solar radiation, the change of interior air quality due to solar radiation cannot be neglected. In order to optimize the air quality in HST, it is necessary to consider various objectives such as thermal comfort, containment control, and energy consumption. Therefore, an integrated optimization approach is expected.<br><br>The main body of this thesis was composed of nine chapters. In the first two chapters, research background was introduced, and literature was summarized with research gaps identified. Research methodology was explained in Chapter 3. Then, the main research contributions were demonstrated from Chapters 4 to 8. Specifically, Chapter 4 and 5 discussed two impact factors with regard to the HST interior. In Chapter 4, four types of popularly-used diffusers were studied and compared regarding their ventilation performance and contaminate control. Chapter 5 investigated the transient coughing process released from passengers. This was the main source of particle contaminants in a densely occupied train cabin. For the HST exterior, the induced pressure fluctuation and solar radiation effects were presented in Chapter 6 and Chapter 7 respectively. The change of interior air quality when two HSTs passing by each other and when the HST passing through a tunnel were analyzed in Chapter 6. Chapter 7 demonstrated the influence of solar radiation on the HST cabin environment. Simulation under different setups including various daytime durations and with curtain applied situations were studied. As all the above-mentioned interior and exterior impact factors were found having a strong influence on the air quality in HST cabin, a multi-objective optimization algorithm was introduced in Chapter 8 to find the suitable ventilation solution based on user requirement. All the findings presented in chapters 4 to 8 were concluded and highlighted in Chapter 9, followed by a list of all the published work during the PhD candidature period.<br><br>In summary, this thesis presents an investigation of the HST interior air quality. This research contributed to the following outcomes: (a) A comprehensive understanding of the different type of diffuser effect on HST cabin ventilation performance, thermal comfort and containment dispersion processes; (b) A preciously cough-jet model to represent the transport and distribution of cough-generated airborne contaminants under the cabin environment; (c) A systematic CFD model of the interior air response to the induced pressure waves during the period of two HSTs passing by each other and the HST passing through a tunnel; (d) A quantizable approach to assessing the solar radiation effect on thermal comfort in a HST cabin; (e) An efficient approach to managing the multi-objective optimization in HST cabin ventilation system. The computational studies presented in this thesis lay a solid foundation for air quality optimization and health risk assessments in HST cabin environment, which can be also applied in other densely occupied spaces such as metro, bus, and airline.  Meanwhile, the outcomes of this study can be a supplement to the current industry standards.