Numerical and experimental study of motion-induced wake flow and contaminant transport in interior environments

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. 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). The main body of this thesis is composed of nine chapters: 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. 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: (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. (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; (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; 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

Modelling heat transfer and respiration of occupants in indoor climate

Although the terms "Human Thermal Comfort" and "Indoor Air Quality (IAQ)" can be highly subjective, they still dictate the indoor climate design (HVAC design) of a building. In order to evaluate human thermal comfort and IAQ, one of three main tools are used, a) direct questioning the subjects about their thermal and air quality sensation (voting, sampling etc.), b) measuring the human thermal comfort by recording the physical parameters such as relative humidity, air and radiation temperature, air velocities and concentration gradients of pollutants or c) by using numerical simulations either including or excluding detailed thermo-physiological models. The application of the first two approaches can only take place in post commissioning and/or testing phases of the building. Use of numerical techniques can however be employed at any stage of the building design. With the rapid development in computational hard- and software technology, the costs involved in numerical studies has reduced compared to detailed tests. Employing numerical modelling to investigate human thermal comfort and IAQ however demand thorough verification and validation studies. Such studies are used to understand the limitations and application of numerical modelling of human thermal comfort and IAQ in indoor climates. This PhD research is an endeavour to verify, validate and apply, numerical simulation for modelling heat transfer and respiration of occupants in indoor climates. Along with the investigations concerning convective and radiation heat transfer between the occupants and their surroundings, the work focuses on detailed respiration modelling of sedentary human occupants. The objectives of the work have been to: verify the convective and radiation numerical models; validate them for buoyancy-driven flows due to human occupants in indoor climates; and apply these validated models for investigating human thermal comfort and IAQ in a real classroom for which field study data was available. On the basis of the detailed verification, validation and application studies, the findings are summarized as a set of guidelines for simulating human thermal comfort and IAQ in indoor climates. This PhD research involves the use of detailed human body geometries and postures. Modelling radiation and investigating the effect of geometrical posture has shown that the effective radiation area varies significantly with posture. The simulation results have shown that by using an effective radiation area factor of 0.725, estimated previously (Fanger, 1972) for a standing person, can lead to an underestimation of effective radiation area by 13% for the postures considered. Numerical modelling of convective heat transfer and respiration processes for sedentary manikins have shown that the SST turbulence model (Menter, 1994) with appropriate resolution of near wall region can simulate the local air velocity, temperature and heat transfer coefficients to a level of detail required for prediction of thermal comfort and IAQ. The present PhD work has shown that in a convection dominated environment, the detailed seated manikins give rise to an asymmetrical thermal plume as compared to the thermal plumes generated by simplified manikins or point sources. Validated simulation results obtained during the present PhD work have shown that simplified manikins can be used without significant limitations while investigating IAQ of complete indoor spaces. The use of simplified manikins however does not seem appropriate when simulating detailed respiration effects in the immediate vicinity of seated humans because of the underestimation in the amount of re-inhaled CO2 and pollutants from the surroundings. Furthermore, the results have shown that due to the simplification in geometrical form of the nostrils, the CO2 concentration is much higher near the face region (direct jet along the nostrils) as compared to a detailed geometry (sideways jet). Simulating the complete respiration cycle has shown that a pause between exhalation and inhalation has a significant effect on the amount of re-inhaled CO2. Previous results have shown the amount of re-inhaled CO2 to range between 10 - 19%. The present study has shown that by considering the pause, this amount of re-inhaled CO2 falls down to values lower than 1%. A comparison between the simplified and detailed geometry has shown that a simplified geometry can cause an underestimation in the amount of re-inhaled CO2 by more than 37% as compared to a detailed geometry. The major contribution to knowledge delivered by this PhD work is the provision of a validated seated computational thermal manikin. This PhD work follows a structured verification and validation approach for conducting CFD simulations to predict human thermal comfort and indoor air quality. The work demonstrates the application of the validated model to a classroom case with multiple occupancy and compares the measured results with the simulation results. The comparison of CFD results with measured data advocates the use of CFD and visualizes the importance of modelling thermal manikins in indoor HVAC design rather than designing the HVAC by considering empty spaces as the occupancy has a strong influence on the indoor air flow. This PhD work enables the indoor climate researchers and building designers to employ simplified thermal manikin to correctly predict the mean flow characteristics in indoor surroundings. The present work clearly demonstrates the limitation of the PIV measurement technique, the importance of using detailed CFD manikin geometry when investigating the phenomena of respiration in detail and the effect of thermal plume around the seated manikin. This computational thermal manikin used in this work is valid for a seated adult female geometry

Laboratory fume hood performance

ABSTRACT Introduction Laboratory fume hoods are mechanical devices used to extract harmful vapours from indoor workplaces in order to prevent human exposure thereto. Laboratory fume hoods are considered an engineering control in the hierarchy of control and are ubiquitous in the modern laboratory. Protection offered by the fume hood depends on whether it is performing according to its original design. This performance needs to be maintained for as long as the fume hood is in use. Gaining a better understanding of this performance and the limitations of the fume hood are essential in ensuring constant operator protection. No performance or measurement standard to which fume hoods need to comply exists in South Africa. The Occupational Health and Safety Act, 1993 (Act no. 85 of 1993) requires engineering controls to be evaluated every 24 months. The Act does not stipulate how such evaluations need to be conducted. The Forensic Science Laboratory (FSL) of the South African Police Service has 49 fume hoods installed in its facility in Silverton, Pretoria. The FSL set a performance standard for its fume hoods at 0.51 m.s-1 ± 20% average across the face of the fume hood. The FSL selected the ANSI/ASHRAE 110 test method to evaluate the performance of its fume hoods against this standard. v Objectives The first objective of the study was to measure face velocities of fume hoods as installed in a forensic science laboratory and calculate the averages, and to determine whether these comply with the set standard. The second objective was to measure face velocities of fume hoods as installed in a forensic science laboratory and calculate the average in order to determine their performance over time. The third study objective was to observe laboratory fume hoods as installed in a forensic science laboratory to see whether fans were operational each month for 11 months (i.e. down time). Methods 10 Observations and 10 tests were carried out on each fume hood. Observations related to whether fume hood fans were functioning or not. Testing was a measure of performance and required the actual measurement of face velocities. A calibrated thermal anemometer was used to take velocity measurements. Measurements taken represent standard velocities. Fume hood faces were divided into imaginary grids not exceeding 30 cm x 30 cm. Velocity measurements were taken at the centre points of these grids. The arithmetic means were calculated for these measurements. The mean of the test means was then vi calculated for every fume hood. This, so that a comparison could be made between the mean and the set standard. Observations indicated that at the onset of the study 14% of fume hoods were not operational. By the end of the study 27% were not operational. A decline of 13% over the study period. At one point during the study 47% of the fume hoods were not functioning. Results 82% of the fume hood population performed outside the standard. 12% underperformed at less than 0.41 m.s-1 while 70% overperformed at velocities exceeding 0.61 m.s-1. ANOVA and regression analyses revealed that performance of the fume hoods over time remained fairly constant (e.g. regression analyses p-value = 0.8538). Discussion and conclusion Fume hood operability and performance results indicate the need for urgent investigation into the correct use of this resource within the FSL. Results are less than satisfactory with the health of laboratory personnel being potentially compromised. Comprehensive procurement, installation, operating and testing procedures need to be compiled, or if available, reviewed and implemented. Further study into the performance of the fume hoods may also be necessary using additional performance indicators

Internet of medical things – integrated, ultrasound-based respiration monitoring system for incubators

The study's aim was to develop a non-contact, ultrasound (US) based respiration rate and respiratory signal monitor suitable for babies in incubators. Respiration rate indicates average number of breaths per minute and is higher in young children than adults. It is an important indicator of health deterioration in critically ill patients. The current incubators do not have an integrated respiration monitor due to complexities in its adaptation. Monitoring respiratory signal assists in diagnosing respiration rated problems such as central Apnoea that can affect infants. US sensors are suitable for integration into incubators as US is a harmless and cost-effective technology. US beam is focused on the chest or abdomen. Chest or abdomen movements, caused by respiration process, result in variations in their distance to the US transceiver located at a distance of about 0.5 m. These variations are recorded by measuring the time of flight from transmitting the signal and its reflection from the monitored surface. Measurement of this delay over a time interval enables a respiration signal to be produced from which respiration rate and pauses in breathing are determined. To assess the accuracy of the developed device, a platform with a moving surface was devised. The magnitude and frequency of its surface movement were accurately controlled by its signal generator. The US sensor was mounted above this surface at a distance of 0.5 m. This US signal was wirelessly transmitted to a microprocessor board to digitise. The recorded signal that simulated a respiratory signal was subsequently stored and displayed on a computer or an LCD screen. The results showed that US could be used to measure respiration rate accurately. To cater for possible movement of the infant in the incubator, four US sensors were adapted. These monitored the movements from different angles. An algorithm to interpret the output from the four US sensors was devised and evaluated. The algorithm interpreted which US sensor best detected the chest movements. An IoMT system was devised that incorporated NodeMcu to capture signals from the US sensor. The detected data were transmitted to the ThingSpeak channel and processed in real-time by ThingSpeak’s add-on Matlab© feature. The data were processed on the cloud and then the results were displayed in real-time on a computer screen. The respiration rate and respiration signal could be observed remotely on portable devices e.g. mobile phones and tablets. These features allow caretakers to have access to the data at any time and be alerted to respiratory complications. A method to interpret the recorded US signals to determine respiration patterns, e.g. intermittent pauses, were implemented by utilising Matlab© and ThingSpeak Server. The method successfully detected respiratory pauses by identifying lack of chest movements. The approach can be useful in diagnosing central apnoea. In central apnoea, respiratory pauses are accompanied by cessation of chest or abdominal movements. The devised system will require clinical trials and integration into an incubator by conforming to the medical devices directives. The study demonstrated the integration of IoMT-US for measuring respiration rate and respiratory signal. The US produced respiration rate readings compared well with the actual signal generator's settings of the platform that simulated chest movements

Aeronautical engineering: A cumulative index to a continuing bibliography

This bibliography is a cumulative index to the abstracts contained in NASA SP-7037 (197) through NASA SP-7037 (208) of Aeronautical Engineering: A Continuing Bibliography. NASA SP-7037 and its supplements have been compiled through the cooperative efforts of the American Institute of Aeronautics and Astronautics (AIAA) and the National Aeronautics and Space Administration (NASA). This cumulative index includes subject, personal author, corporate source, foreign technology, contract, report number, and accession number indexes