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The Earth is facing huge implications from Anthropogenic Global Warming and peaks in the production of finite fossil fuels. Decision-makers have to choose strategies for combating these dual problems whilst ensuring minimal costs to society and the environment. Unfortunately, renewable technologies in particular have doubt associated with their ability to reduce total life cycle greenhouse gas (GHG) emissions of electricity due to uncertainty in estimates. This thesis analyses historic associated GHG estimates of wind farms, the largest renewables contributor to electricity generation in the UK, to reduce the uncertainty inherent in estimates and better understand critical factors that influence estimation. Through harmonisation of published life cycle GHG emissions estimates, they are reduced by 56% to between 2.9 and 37.3gCO2e/kWh. Average values for onshore and offshore wind power are calculated as 16 and 18.2gCO2e/kWh respectively and exhibit similar characteristics in their life cycle GHG emissions. Ormonde Offshore Wind Farm is analysed using a novel hybrid approach and gives total baseline GHG emissions of 17.5gCO2e/kWh and is the largest wind power installation to be analysed to date. Finally, an estimate of the effect of load variability of wind on thermal plant in the UK system is calculated. It is shown that this effect may reduce the net emissions saving from wind power relative to the whole UK system’s savings when wind power is included.

This work presents a novel technique to measure viscosity in-situ and in real time in engine component interfaces by means of an ultrasonic technique. Viscosity is a key parameter in the characterization of lubrication regime in engine parts because it can be related to friction in the contact, and to the lubricant film thickness. Ultrasound is a non-destructive and non-invasive technique that is based on the reflection of sound from interfaces. The reflection from a solid-air boundary can identify, for instance, the presence of a crack in a material, while reflection from a solid-liquid interface can help detecting the properties of the liquid sample. Reflection of longitudinal waves measures fluid film thickness and chemical composition, while the reflection of ultrasonic shear waves measures the fluid viscosity. The viscosity measurements based on ultrasonic reflection from solid-fluid boundaries are referred to as reflectance viscometry techniques. Common ultrasonic reflectance viscometry methods can only measure the viscosity of Newtonian fluids. This work introduces a novel model to correlate the ultrasonic shear reflection coefficient with the viscosity of non-Newtonian oils by means of the Maxwell model analogy. This algorithm overcomes the limitation of previous models because it is suitable for the analysis of common engine oils, and because it relies only on measurable parameters. However, viscosity measurements are prohibitive at the metal-oil interfaces in auto engines because when the materials in contact have very different acoustic impedances the sound energy is almost totally reflected, and there is very little interaction between the ultrasonic wave and the lubricant. This phenomenon is called acoustic mismatch. When acoustic mismatch occurs, any valuable information about the liquid properties is buried in measurement noise. To prove this, the common reflectance set-up was tested to measure the viscosity of different lubricants (varying from light base oils to greases) using aluminium as solid boundary. More than 99.5% of the ultrasonic energy was reflected for the different oils, and accurate viscosity measurement was not possible because the sensitivity of the ultrasonic measurement at the current state of the art is of ±0.5%. Consequently, the discrimination by viscosity of the oil tested was not possible. In this study a new approach is developed. The sensitivity of the ultrasonic reflectance method is enhanced with a quarter wavelength matching layer material. This material is interleaved between metal and lubricant to increment the ultrasonic measurement sensitivity. This layer is chosen to have thickness and mechanical properties that induce the ultrasonic wave to resonate at the solid-liquid interface, at specific frequencies. In this work, resonance is associated with the destructive interaction between the wave that is incident to the matching layer and the wave that is reflected at the matching layer-oil interface. This solution brings a massive increment in the ultrasonic measurement sensitivity. The matching layer technique was first tested by enhancing the sensitivity of the aluminium-oil set-up that was affected by acoustical mismatch. A thin polyimide layer was used as a matching layer between aluminium and the engine oil. This probe was used as ultrasonic viscometer to validate the sensing technique by comparison with a conventional viscometer and by applying a temperature and pressure variation to the samples analysed. The results showed that the ultrasonic viscometer is as precise as a conventional viscometer when Newtonian oils are tested, while for Non-Newtonian oils the measurement is frequency dependent. In particular, it was noticed that at high ultrasonic frequency only the viscosity of the base of the oil was measured. The ultrasonic viscometer was used to validate the mathematical model based on the Maxwell analogy for the correlation of the ultrasonic response with the liquid viscosity. At a second stage, this technique was implemented in a journal bearing. The ultrasonic viscometer was mounted in the shaft to obtain the first viscosity measurement along the circumference of a journal bearing at different rotational speeds and loads. The ultrasonic viscometer identified the different viscosity regions that are present in the journal bearing: the inlet, the regions characterized by the rise in temperature at the contact and the maximum loaded region were the minimum film thickness occurs. The results were compared with the analytical isoviscous solution of the Reynolds equation to confirm that the shape of the angular position-viscosity curves was correct. Finally, the method was preliminarily tested on a coated shell bearing to show that the coating presents in bearing, like iron-oxide or babbit, is a good matching layer for the newly developed ultrasonic viscometer technique. This means that ultrasonic transducers, with sizes as small as a pencil tip, have the potential to be mounted as viscometers in real steel bearings where the coating layer in contact with the fluid acts as a matching layer. Overall, the results obtained showed that this technique provides robust and precise viscosity measurements for in-situ applications in engine bearings.

The climate change due to emissions from the combustion of fossil fuel to meet the ever increasing energy demands of the growing world population has roused the attention of governments and individuals to protect the environment. The formulated policies to protect the environment have aroused interest in wind turbines as an alternative source of energy. The suitability of the vertical axis wind turbines (VAWTs) in harnessing energy from the wind in the built areas have been shown, but there still exists a large knowledge gaps in the aerodynamics and performance of the VAWT especially in the design and selection of an appropriate blade chord. This thesis studied the influence of the blade chord on the aerodynamics and performance of vertical axis wind turbines through experimental and computational fluid dynamics methods. Two VAWT configurations of blade chords 0.04m (AR = 15) and 0.03m (AR = 20) with corresponding solidities of 0.34 and 0.26 were used for the investigations. The performance and the flow fields of the two configurations were measured experimentally through the use of performance measurement method and Particle Image Velocimentry (PIV) measurement techniques. All the experimental tests were conducted in a low-speed open suction wind tunnel and the results are presented. Computational fluid dynamics modelling based on the Unsteady Reynolds Average Navier-stokes (URANS) was employed to simulate the two configurations at the same wind tunnel test conditions to complement the revelations from the experimental tests. The developed CFD models after a parametric study that enabled the selection of the model’s features were validated against experimental data by comparing both forces and the flow physics. Vorticity of the CFD flow visualisation and blade forces provided an additional and penetrating insight into the aerodynamics and performance of the VAWTs by linking flow physics, and performance to the aerodynamics. The VAWT flow physics, aerodynamics and performances have been shown to depend on the Reynolds numbers that ranges from 1.27x103 to 1.1x105, the blade chord (solidity), the azimuth angle blade stall is initiated and the dynamic stall associated with the flow fields around the blade. At 6m/s test condition, the C = 0.04m VAWT attained peak CP = 0.165 at λ = 4, while the C = 0.03m VAWT performed in the negative region at all the λ. The better performance attained by the C = 0.04m VAWT over the C = 0.03m VAWT was repeated at all other wind speeds tested in the experiments and also in the computational fluid dynamics investigations. The C = 0.04m VAWT attained a higher peak CP = 0.326 at 8m/s at λ = 3.75 indicating increased performance with increases in Reynolds numbers. This trend was equally seen with the C = 0.03m VAWT in the experiments and also the computational fluid dynamics results. The VAWT with σ = 0.34 performed better than σ = 0.26 VAWT in all the conditions tested due to its higher Reynolds numbers and solidity differences that influence the nature of the dynamic stall phenomenon associated with the flow fields around the blades.

There is currently an increasing desire for local small-scale sustainable energy generation. This has lead to increased interest in the concept of the vertical axis wind turbine (VAWT), which is potentially well-suited to operation within the built environment. This study investigates the performance and flow physics of a small-scale VAWT using experimental and computational methods. The experiments utilise the University’s low-speed open-section wind tunnel. The design and use of a variety of existing and newly developed methods and apparatus is detailed, this includes the development of an entire VAWT-testing rig and associated measurement equipment. Also included, is a new method for the experimental determination of the power performance. A full performance curve is shown to be determined using a short test taking a few minutes. The near-blade flow physics of the rotating blades were interrogated using particle image velocimetry (PIV) as part of a measurement campaign which goes beyond the existing literature in both the range of measurements taken and the subsequent analysis which is presented. Details of the effect of changes in azimuthal position, tip speed ratio and fixing angle on the flow physics are presented. Comparable CFD simulations are first validated against the PIV measurements before they are used to provide additional information for the performance analysis. A new methodology for determining flowfield-corrected lift and drag polars from a CFD solution allows detailed examination of the performance-impact of the changes in the aerodynamic forces with azimuthal position and tip speed ratio.

Increasing growth of wind turbine systems suggests a more systematic research around their design, operation and maintenance is needed. These systems operate under challenging enviromental conditions and failure of some of their parts, for the time being, is frequent, although undesirable. Wind turbine gearboxes, more particularly, seem to be so problematic that some wind turbine designs avoid including them. Structural health monitoring and condition monitoring of wind turbines appear to be necessary in order to determine the condition and lifespan of the wind turbine components and the drivetrain respectively. In this way reparative actions could be taken whenever needed resulting in reduction of maintenance costs. This thesis focuses on the condition monitoring of wind turbine gearboxes, taking into account the varying loads that they endure. Currently, the vibration-based damage detection methods used in real life wind turbine condition monitoring systems are based on conventional methods that generally fail to detect damage at its early stage under the operational conditions observed in wind turbines. Load and speed variations of the drivetrain that are observed commonly in wind turbines influence the vibration signals and can possibly affect potential damage features. This shows a demand for effective methods for early damage detection. Developments in the area of advanced signal processing should be examined and applied in damage detection of wind turbine gearboxes. Methods from time-frequency analysis, time-scale analysis, pattern recognition, multivariate statistics and econometrics are examined in this study in a condition monitoring context. One important part of the work presented is the development of a simple gearbox model interfaced with realistic wind loading, a model feature that appears to be novel. Other interesting aspects of this thesis are related to the use of the empirical mode decomposition method for time-frequency analysis. The use of Teager-Kaiser energy operator as an alternative technique to Hilbert transform for the estimation of the instantaneous characteristics of the decomposed signals is one of these aspects. The study showed that for some cases and under certain conditions this operator could help to improve the time-frequency analysis. Another aspect is the observation of the change of the number of the intrinsic mode functions produced, for the different load and damage cases, during the decomposition process. This observation was connected theoretically with what is known as the mode mixing problem of the empirical mode decomposition method. For the feature discrimination part of this work, the simplest novelty detection method, outlier analysis, was used in a slightly different manner than in previous studies and the results obtained were compared with a novel adaptive thresholding technique, the 3D phase-space thresholding method. The previously described approaches were applied on the simulated gearbox data but also on real wind turbine gearbox data. Finally, cointegration analysis was proposed as a potential method for removing the effects of the gearbox load variations. This is a novel concept for the condition monitoring of wind turbine gearboxes. An approach which makes it possible to use data from just a single sensor in order to perform cointegration analysis was developed and the process for applying multiscale cointegration using either wavelets or the empirical mode decomposition method was discussed. This final part of the work is an initial step towards applying cointegration to condition monitoring data.

Conjugate flow and heat transfer has been investigated in an unbaffled pilot-scale stirred tank reactor with a plain jacket. The vessel volume was 25 litres with a nominal capacity of 20 litres. Experiments and three-dimensional CFD simulations have been conducted on this vessel. The experiments involved heating, boiling, and cooling of methanol as well as water. The heat transfer medium in the jacket was an oil mixture called ‘DW-Therm’. The CFD simulations of some aspects of these experiments have been broken down into jacket-only and process-only simulations, followed by a fully conjugate simulation. The link between flow patterns, pressure drop and heat transfer in conventional jackets of stirred tank reactors has been analysed. The experiments and CFD simulations have been performed using a range of DW-Therm inlet temperatures. The CFD results were compared with experimental data of temperature measurements and with the use of engineering correlations found in the literature to predict heat transfer coefficients from the experimental data. The simulations produced values of total heat transferred by the jacket within 10% of the experimental results. The simulations of boiling inside the vessel approximated a constant process temperature which was used to investigate the jacket-only phenomena. The process-only and the conjugate simulations simulated heating of water inside the vessel. Mathematical analysis as well as and industrially and academically used correlations from the literature were used to estimate heat transfer coefficients for boiling and external heat loss. These correlations for overall heat transfer coefficients overlook maldistribution of heat transfer coefficients in jackets that use a liquid heat transfer medium. This is industrially important because it provides new information to consider when maintaining highly temperature-dependent processes, in which adequate heat transfer to or from the process is required. This could be for a variety of reasons, from maintenance of product quality to preventing runaway reactions.

In the present work, for the first time, an experimental and theoretical study of the heat transfer characteristics of a bubble type three-phase direct contact condenser has been carried out. The experiments were conducted using a Perspex column of 70 cm in total height and 4 cm inner diameter, as a direct contact condenser. The active column height throughout the experiments was 48 cm. Pentane vapour at three different initial temperatures (40℃, 43.5℃ and 47.5℃), was used as the dispersed phase while tap water at a constant temperature (19℃) was used as the continuous phase. Seven different dispersed phase mass flow rates and five different continuous phase mass flow rates were tested. The experiments considered the transient temperature distribution along the direct contact condenser, the steady-state temperature distribution, the volumetric heat transfer coefficient, the heat transfer rate per unit volume and the holdup ratio. Also, the efficiency and capital cost of the direct contact condenser were estimated, and the heat transfer of the three-phase direct contact condenser during flooding was studied. Theoretical models describing the direct contact condenser were developed. These models included the transient temperature distribution, the steady-state temperature distribution and the volumetric heat transfer coefficient. These models implicitly involved new derivations for the surface heat transfer coefficient, the two-phase bubble size, the relative velocity of two-phase bubbles, the drag coefficient and the added mass of the two-phase bubble. All expressions were derived analytically except for the transient temperature distribution along the condenser which was found numerically, using MATLAB. The results showed that the mass flow rate ratio has a significant effect on the heat transfer characteristics of the condenser, while the initial temperature of the dispersed phase has only a slight effect. The models developed were fitted the experimental data well.

The performance of small, H-Darrieus vertical axis wind turbines has been investigated numerically and experimentally with particular attention paid to turbine performance at low tip speed ratios (low Reynolds number) and to turbine self-starting. Comprehensive wind tunnel measurements have been performed to provide accurate aerofoil data at low Reynolds numbers and high angles of attack; a unique requirement for vertical axis wind turbine (VAWT) starting studies. Two-dimensional CFD models and blade element momentum (BEM) models were created and assessed to provide new insight into turbine performance for different wind conditions and into different turbine geometries in order to guide the design of the experimental investigation. The experimental and numerical studies have demonstrated that design parameters including turbine solidity, blade profile, blade pitch angle and blade surface roughness have strong influences on turbine performance and turbine self-starting capability. Although other authors have conducted numerical studies of the effect of these parameters, this work represents the first experimental validation for turbine performance at low tip speed ratios. In contrast to some previous studies it is shown that there is no advantage to be gained from the use of cambered blades and that symmetrical blades set at small negative incidence provide the best design solution. It is also shown that increasing the turbine’s solidity can significantly improve self-starting capability and that for a given solidity, increasing the rotor radius with a corresponding increase of blade chord improves performance further. However, these starting performance gains are achieved at the expense of a small loss of peak power output. In addition, bio-inspired blades with tubercle leading edges are demonstrated to be able to significantly improve the turbine self-starting capability by introducing a more gradual stall characteristic. These results are the only reported measurements of the effect of tubercle leading edges on vertical axis wind turbines. Finally, a novel, real-time on-board pressure measurement system was developed and employed to examine the instantaneous blade pressure distribution and its variation when the turbine is rotating. The complex flow physics including dynamic stall, laminar separation and flow curvature were successfully recorded and provide unique, unsteady data to increase our knowledge and understanding of the transient aerodynamics of the H-Darrieus wind turbine. The experimental results were also compared with the available CFD and BEM predictions. It is demonstrated that BEM based approaches are highly sensitive to the quality of the aerofoil data that is provided as input to the model. This thesis provides validation of previous work on the question of whether H-Darrieus wind turbines can start without external assistance and in the light of this research a set of revised design rules are proposed to achieve self-starting turbines.

Wind turbines (WTs) are a proven source of clean energy with wind power energy harvesting technologies supplying about 3% of global electricity consumption in 2014. However there is an increasing demand on maintenance and operational improvements since turbines have been plagued with downtime problems ofmajor components e.g. gearboxes, which in particular are known to have a higher downtime per failure than other WT subassemblies. This is as a result of two reasons. First, WT gearboxes have historically suffered from early failures due to the underestimation of operational load conditions. Second, WT gearboxes have very complex repair procedures needing heavy lifting equipment such as external cranes for repair and replacement. This downtime results in revenue loss for the customer. Hence, for a company like Vestas Wind Systems AlS, who designs, manufactures and services WTs dealing with the gearbox downtime issue is of great importance. This thesis focuses on the gearbox challenge specific to Vestas organisational context based on a research journey undertaken by the author whilst embedded in Vestas as an employee. It focuses on the 2MW fleet of gearboxes serviced by Vesias globally. Furthermore, the thesis addresses two dimensions of the industrial problem - (i) investigating the gearbox problem, i.e. the issue with reliability and maintainability, and identifying solutions for improving these, and (ii) improvement of Vestas internal processes which contribute to delivering maintenance and repair solutions for gearboxes e.g. the capturing and reusing of maintenance and repair data for failure and reliability analysis. These two strands of the research equip decision makers within Vestas with tools and techniques for making decisions concerning the maintenance and repair challenges. Hence, enabling the company to improve performance of the gearboxes and extending the life of gearboxes. The main outcomes of this thesis are the development of new and novel in-service decision-making models (and tools) which are currently adding 'value to Vestas. First, a preventive maintenance optimisation model was developed by applying state of the art approaches used in industries like aerospace and marine, to historical gearbox in-service data from Vestas operational WTs. This model estimates the optimal interval for preventive replacements, repair and inspections of gearboxes. The benefit to Vestas is that the model helps WT managers to make timely decisions regarding planning and scheduling maintenance, which can reduce the downtime considerably and avoid consequential failures, hence resulting in cost savings for the company. Second, a novel extreme vibration model was developed using the automated condition monitoring data from operational gearboxes. This model can help in detecting failures on the high speed and intermediate speed stages of the gearbox as early as one month in advance. The model was recently developed and validated and is soon to be implemented in the organisation but it is expected to help avoid consequential failures and reduce downtime due to the ability to plan and schedule maintenance early as soon as a fault is detected. Third, a decision support framework (with an accompanying tool) for repair cost estimation, gearbox damage classification and feedback of repair data to design, was developed using a soft systems approach. In addition, a data repository has been created which contains repair statistics that is used for analysis purposes for guiding repair decisions and of the design of new gearboxes. The developed models, framework and tools are now being used across the organisation by engineers and service personnel, and by Vestas external repair providers, which has led to savings for Vestas in the order of hundreds of thousands of Euros yearly.