Numerical and experimental study of motion-induced wake flow and contaminant transport in interior environments
Creators: name: Tao, Yao
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 401204
subject: Computational methods in fluid flow, heat and mass transfer (incl. computational fluid dynamics)

description: This thesis focuses on the characteristics of motion-induced wake flow and their influence on contaminant transport in interior spaces. The motion of objects such as human bodies would generate wake regions that exhibit highly complicated airflow characteristics. Consequently, it affects the air quality by inducing contaminant transport in interior environments such as manufacturing, hospital wards, clean rooms and airline cabin etc., where occupants’ exposure to airborne contaminants are of concern.<br><br>A growing number of Computational Fluid Dynamics (CFD) studies investigated the motion-induced wake dynamics and its integration with particle modelling for air quality assessments. Although CFD with dynamic mesh improves the modelling capability to capture transient effects of motion-induced flow, some characteristics of the dynamic wake induced by the motion that is modelled remain unclear. For example, there are differences in flow field be-tween moving rigid body motion and that of realistic human gait cycles, as well as the heat transfer leading to thermal plumes from the human body during the walking and after stopping. Addressing the airflow disturbances from motion is important for understanding the exposure to airborne contaminants which can be prevalent in indoor environments. On the other hand, flow measurements of moving bodies present significant challenges due to setup, large scales, and their dynamic nature. To date little experimental work has been performed to reproduce and visualise the wake flow induced by a moving object, partly due to the challenges in flow visualisation techniques for capturing dynamic flow fields (as opposed to traditional steady state flows).<br><br>The main body of this thesis is composed of nine chapters:<br><br>In the first two chapters, a research background and a comprehensive literature review are summarised with highlighted research gaps found in the existing literature followed by the research methodology in Chapter 3. Main re-search contributions are demonstrated from Chapters 4 to 8. In Chapter 4, the wake flow generated by the motion of a rigid manikin and its influence on particle re-dispersion from a local source on the ground was investigated by performing CFD simulations of a moving manikin model in a confined room. Chapter 5 presents the determination of discrepancies produced in the wake flow field by a simplified geometry in the form of a cylinder and a man-shaped manikin. Manikin motion with and without swinging limbs and heat transfer from the body were also examined. This part (Chapter 5) identifies the major flow characteristics due to geometry, moving schemes and thermal plume. Subsequently the simulation of particle dispersion from the ﬂoor and its re-dispersion is presented using an anthropomorphic manikin modelled with realistic walking motion and thermal eﬀects under three different walking speeds in Chapter 6. Chapter 7 discusses the wake structures measured from smoke visualisation for three different shaped manikins (slim and larger, standing and walking poses). Qualitative understanding of the gross flow field, captured separation points and vortex shedding phenomena were obtained from the experiments. Chapter 8 presents CFD simulations of airflow induced by the same manikins used in the smoke visualisation, and the CFD modellings were validate using the experimental data by comparing the gross flow field, separation points over the head and vortex structures. All the contributions are concluded and highlighted in Chapter 9.<br><br>In summary, this thesis presents an investigation of the influence of motion-induced flow on contaminant re-dispersion and transport in interior spaces. Experimental measurements were conducted to provide qualitative insight into the wake formation and vortex structures. The research contributes to the following outcomes:<br><br>(a) The experimental and numerical study provided meaningful data for understanding the spatial and temporal characteristics on the wake flow development of different shaped moving manikins. The CFD modelling identified the major discrepancies produced in the wake flow field due to geometry, moving schemes and thermal plume.<br><br>(b) The smoke visualisation technique on moving anthropomorphic manikins reproduced the motion-generated wake and provided a new perspective on visualisation of the dynamic wake structure;<br><br>(c) The CFD modelling revealed details of the flow field and provided reason-ably good agreement with the experimental observations in the wake region, which can help identify the transport of pollutants from and around moving bodies and predict occupant exposure to contaminants;<br><br>The computational and experimental studies presented in this thesis lay a sol-id foundation to the investigation of airﬂow characteristics and vortex structures induced by realistic body motion. Also, they provide a comprehensive understanding of the eﬀects of occupant activity on particle exposure and indoor air quality.<br>