Design of a novel spillway turbine and optimisation of its intake hydrodynamics

The motivation to expand electricity production from renewable energy sources exists worldwide. A novel, horizontal axis, spillway turbine that attempts to convert high-speed, supercritical flow in steeply sloped channels into electricity is presented in this thesis. The spillway turbine is intended for use in lowhead, low-flow, man-made, concrete-linedchannelssuchaschutes, spillwaysand other similar steeply sloped open-channels. The design of the spillway turbine is inspired by the impulse turbine runner but without a pipe or a nozzle. Thespillwayturbinepresentedinthisthesisconsistsoftherunnerandtheaccelerator channel/wedge that is used to direct the water towards and through the channel blades. The runner design process shows that once the runner is fitted with Pelton-inspired inserts, performance improves both in terms of efficiency and specific speeds. The specific speed and the speed factors calculated confirm that this novel spillway turbine can be categorised as an impulse turbine. The maximum performance efficiency obtained is 43.3 %. The observations made during laboratory testing indicate that the accelerator channel in the final design version could be improved in terms of energy losses inside it if the insight into the hydrodynamics of the flow can be gained. This is the motivation for computational fluid dynamics research into the hydrodynamics of the flow through a contraction. The in-house large-eddy simulation (LES) code Hydro-3D is employed to simulate supercritical flow in a straight-wall, open-channel contraction. The initial channel contraction angle simulated is 6◦, and the ratio of contraction is 2:1, which is the same ratio used in the final accelerator channel design. The LES code solves the filtered Navier-Stokes equations for two-phase flows and uses the level-set method to track the interface between water and air. Overall, a satisfactory agreement of simulated results with experimental data is obtained. Contours of the time-averaged velocities indicate that the flow loses energy and momentum in the contracting channel. The effect of different contraction angles is analysed, and recommendations from numerical simulation research are implemented in the field application prototype of the spillway turbine

Application of CO2 monitoring methods for post occupancy evaluation

The Covid-19 pandemic led to the widespread closure of events. Between April and July 2021, the AIRBODS consortium carried out an Environmental Study as part of the UK government Events Research Programme to assess environmental risk factors for Covid transmission at events. A detailed post-occupancy evaluation of Indoor Air Quality was employed to assess the effectiveness of ventilation systems in operation. CO2 monitors were installed at high spatial resolution throughout the occupied spaces of ten venues around the UK. Data from 55 events was obtained and average and maximum CO2 values were used to classify the spaces in relation to a proposed Air Quality Index. Indoor spaces where ventilation could be improved were rapidly identified and mitigations were tested to reduce the risk of airborne transmission of respiratory diseases

Large-eddy simulation of supercritical free-surface flow in an open-channel contraction

Large-eddy simulations (LES) of supercritical flow in a straight-wall, open-channel contraction of 6° and contraction ratio of 2:1 are performed. The LES code solves the filtered Navier-Stokes equations for two-phase flows (water-air) and employs the level-set method. The simulation was validated by replicating a previously reported experiment. Contours of the time-averaged velocities indicate that the flow loses energy and momentum in the contracting channel. Further, secondary currents in the contraction are redistributing momentum and are responsible for local up-and down-flows. The turbulent kinetic energy reaches very high values at the entrance of the contraction, mainly contributed by the streamwise normal stress. The flow contains coherent turbulence structures which are responsible for carrying low-momentum from the bed and the water surface towards the channel centre. Flow deceleration results in significant turbulence anisotropy in the contracted section. It is shown that mainly pressure drag contributes to the energy loss in the contraction

Measurement of ventilation effectiveness and indoor air quality in toilets at mass gathering events

Mass gathering events were closed in 2020 to reduce the spread of SARS-CoV-2. These events included music concerts, theatre shows, and sports matches. It is known, however, that the long-range aerosol transmission of pathogens, such as SARS-CoV-2, can be reduced with sufficient ventilation indoors. This paper examines the risk of reopening these mass gathering events by measuring the CO2 concentration, as a proxy for ventilation effectiveness, at 58 events, with a specific focus on small enclosed spaces with short occupancy. Toilets (sanitary accommodation) are spaces that are densely and continuously occupied for short durations throughout the events, such as during theatre intervals or half-time at sports events. The results showed that the average air quality in toilets was good at most events. There were, however, considerable peaks in CO2 concentration of up to 3431 ppm in toilets at times when occupancy was presumed high, indicating that the risk of exposure to exhaled breath, which may contain virus-laden aerosols, is higher in toilets than elsewhere in the venue (although occupancy duration will be much lower). Recommendations are provided to encourage building designers and operators to be mindful of the ventilation strategies used in toilets given their occupancy and size

Findings and Guidance for Airborne Infection Resilience

This guidance provides insights into airborne infection risks and proposes mitigation measures to improve airborne infection resilience of indoor and semi-outdoor spaces. In some poorly-ventilated and/or highly occupied spaces, the provision of increased ventilation performance can be the key to reducing airborne infection risk down to 'acceptable' (although currently undefined) levels.This is a complex area of study with many areas of uncertainty that form the basis of ongoing research. That said, the AIRBODS programme, in the context of the global research efforts associated with the COVID-19 pandemic, has generated a sound basis for improving airborne infection resilience. Key aspects of the guide with its many recommendations include:• Experiments carried out in a test chamber showing how screens can improve or, even, worsen airborne infection risk.• Field studies undertaken as part of the Events Research Programme which underpinned the opening up of the UK hospitality sector in summer of 2021. Good practice advice is provided on how to drive high resolution CO2 and microbiological studies and then appropriately interpret results.• Analytical models were developed to understand how infection risk, using a mass balance approach with many different parameters, might be mitigated in some circumstances when compared to reference spaces. These models were then developed into a 'full building' tool which can be downloaded as part of this guidance.• Computational fluid dynamics (CFD) models were developed to provide insights into the physics of droplets or aerosols at microscale. Following completion of a test chamber validation exercise, models were developed to investigate breathing or coughing mannequins at single human moving towards audience or crowd scale.Local ventilation effectiveness and associated airborne infection risk aspects of some real spaces may significantly differ from assumed 'fully-mixed' equivalent spaces. This, along with a number of other issues, will form part of ongoing research activities.• Focus groups were also used to provide some wider context and support some of our recommendations.AIRBODS has produced a repository of data and modelling methods with the mindset of enabling building professionals to inform their design and operation decisions towards improving airborne infection resilience in their buildings

AIRBODS: Findings and guidance for airborne infection resilience

This guidance provides insights into airborne infection risks and proposes mitigation measures to improve airborne infection resilience of indoor and semi-outdoor spaces. In some poorly-ventilated and/or highly occupied spaces, the provision of increased ventilation performance can be the key to reducing airborne infection risk down to 'acceptable' (although currently undefined) levels.This is a complex area of study with many areas of uncertainty that form the basis of ongoing research. That said, the AIRBODS programme, in the context of the global research efforts associated with the COVID-19 pandemic, has generated a sound basis for improving airborne infection resilience. Key aspects of the guide with its many recommendations include:•Experiments carried out in a test chamber showing how screens can improve or, even, worsen airborne infection risk.•Field studies undertaken as part of the Events Research Programme which underpinned the opening up of the UK hospitality sector in summer of 2021. Good practice advice is provided on how to drive high resolution CO2 and microbiological studies and then appropriately interpret results.• Analytical models were developed to understand how infection risk, using a mass balance approach with many different parameters, might be mitigated in some circumstances when compared to reference spaces. These models were then developed into a 'full building' tool which can be downloaded as part of this guidance.• Computational fluid dynamics (CFD) models were developed to provide insights into the physics of droplets or aerosols at microscale.Following completion of a test chamber validation exercise, models were developed to investigate breathing or coughing mannequins at single human moving towards audience or crowd scale. Local ventilation effectiveness and associated airborne infection risk aspects of some real spaces may significantly differ from assumed 'fully-mixed' equivalent spaces. This, along with a number of other issues, will form part of ongoing research activities.• Focus groups were also used to provide some wider context and support some of our recommendations.AIRBODS has produced a repository of data and modelling methods with the mindset of enabling building professionals to inform their design and operation decisions towards improving airborne infection resilience in their buildings

Carbon Dioxide Monitoring in Refuse Collection Vehicle Cabins to Reduce the Risk of SARS-CoV-2 Airborne Transmission

During the COVID-19 pandemic, essential workers such as waste collection crews continued to provide services in the UK, but due to their small size, maintaining social distancing inside waste collection vehicle cabins is impossible. Ventilation in cabins of 11 vehicles operating in London was assessed by measuring air supply flow rates and carbon dioxide (CO2) in the driver’s cabin, a proxy for exhaled breath. The indoor CO2 indicated that air quality in the cabins was mostly good throughout a working day. However, short episodes of high CO2 levels above 1500 ppm did occur, mainly at the beginning of a shift when driving towards the start of their collection routes. This data indicated that the ventilation systems on the vehicles were primarily recirculating air and the fresh air supply made up only 10-20 % of the total airflow. Following recommendations to partly open windows during shifts and to maintain ventilation systems, a second monitoring campaign was carried out, finding on average, an improvement in ventilation on board the vehicles

Application of CO2 monitoring methods for post occupancy evaluation

The Covid-19 pandemic led to the widespread closure of events. Between April and July 2021, the AIRBODS consortium carried out an Environmental Study as part of the UK government Events Research Programme to assess environmental risk factors for Covid transmission at events. A detailed post-occupancy evaluation of Indoor Air Quality was employed to assess the effectiveness of ventilation systems in operation. CO2 monitors were installed at high spatial resolution throughout the occupied spaces of ten venues around the UK. Data from 55 events was obtained and average and maximum CO2 values were used to classify the spaces in relation to a proposed Air Quality Index. Indoor spaces where ventilation could be improved were rapidly identified and mitigations were tested to reduce the risk of airborne transmission of respiratory diseases

Post-Occupancy study of indoor air quality in university laboratories during the pandemic

This post-occupancy study aims to assess the indoor air quality (IAQ) and ventilation performance in workshops and laboratories of a UK university during the COVID-19 pandemic. Supply airflow rates and CO2 were monitored as a proxy for evaluating ventilation performance. Additionally, particulate matter (PM10) was monitored to address the occupant's concerns about dust. Monitoring showed that maximum CO2 values recorded are mostly below 1000 ppm, with weekly averages below 520 ppm. This was expected as the supply airflow rates were significantly larger than recommended 10 l/s per occupant. Despite the large flow rates, PM10 levels in some laboratories were above the threshold value of 50 [g/m3] supporting the poor IAQ claims of the occupants. The study indicated the room air re-circulation and indoor activities as the likely reasons for the elevated PM10 levels and some practical operational solutions were suggested for IAQ concerns

Application of CO2 monitoring methods for post- occupancy evaluation of ventilation effectiveness to mitigate airborne disease transmission at events

The Covid-19 pandemic led to the widespread closure of events. Between April and July 2021, the AIRBODS consortium carried out an Environmental Study as part of the UK government Events Research Programme to assess environmental risk factors for Covid transmission at events. A detailed post-occupancy evaluation of Indoor Air Quality was employed to assess the effectiveness of ventilation systems in operation. CO2 monitors were installed at high spatial resolution throughout the occupied spaces of ten venues around the UK. Data from 55 events was obtained and average and maximum CO2 values were used to classify the spaces in relation to a proposed Air Quality Index. Indoor spaces where ventilation could be improved were rapidly identified and mitigations were tested to reduce the risk of airborne transmission of respiratory diseases