Thousands of load calculations for wind turbine design have been calculated by manufactures, consultants and certification bodies. These have been done as required to develop and validate specific designs. However, there has not been a general systematic study of trends in loads related to key wind turbine design parameters and external operating conditions. The aim of this thesis is parameterise and quantify trends of extreme and fatigue loads based on systematic modifications of wind turbine characteristics. This thesis is in two main parts. The first part provides an overview of loads calculation methods, flow modelling and approach adopted also considering scaling rules, comparing scaling with similarity and the scaling evident in from commercial world turbines data. The second part presents and evaluates loading trends for extreme and fatigue loads related to systematic alterations of key wind turbine parameters. Three chapters of results investigate the load impacts of blade structural properties, rotor solidity and up-scaling respectively. The chapter on blade structural properties demonstrates that the self-weight of blades is a major component influencing loads of the blade root and hub. The chapter on rotor solidity shows that significant load reduction can result for blade root, shaft and yaw bearing in reducing the solidity of rotor. However, the aerodynamic damping reduces with reducing solidity, which is crucial for tower base fore-aft loads; therefore the reducing rotor solidity has an adverse impact on the tower base fore-aft loads. The chapter on up-scale demonstrates that up-scaling with similarity method can give good prediction of loads with an error of ±10% and ±15% for extreme and fatigue loads of large wind turbines (up to 10MW) at the mean wind speed within power production range. Additional, the chapter of up-scaling showed that the up-scaled wind turbines reduce the sensitivity to turbulence with the size of rotor.

This thesis leads to a framework for micrositing, the process through which the specific location for mounting micro wind turbines in urban environments is determined. It can be used as a guidance on how to model an area of interest, find the optimum location for micro wind turbines installation and calculate the annual energy production, commenting on the accuracy that can be expected from the results. Essentially, it is composed of three parts, each one deals with different set of tasks associated with model development and simulation. The first part investigates the computational practices to the fields of turbulence in urban environments implemented in the open-source CFD library OpenFOAM. It examines the performance of a turbulence model, known as DES, which has not been previously used for external flows in complex urban environments and concludes that this approach offers improved robustness and accuracy over a range of wind conditions. It offers improved prediction of flows in wake regions compared to RANS methods and is less computationally demanding than full LES approaches. The validity of DES implementation is tested using data sets derived from both wind tunnel experiments and field measurements. In the second part, a procedure is developed to identify the optimum location for mounting wind turbines, based on the spatial variations in mean annual wind speed and the corresponding annual energy production (AEP). The procedure utilizes one year of measured wind data for one site to extrapolate (using the `Wind Atlas Methodology') the annual wind speed at the site of interest. Then combining the climate data with the CFD results and the power characteristics of the micro wind turbines, it estimates the mean wind speed and the annual energy yield. Essentially, this methodology leads to the formation of three dimensional fields of the average annual wind speed and the AEP (3d wind maps), which will enable identification of the effects of the complex urban topography on the wind flow, and the potential locations for micro wind turbines installation. The third part examines the accuracy that can be expected from the annual energy production estimation techniques and provides guidelines on the calculations. In particular, it investigates the validity of the standard power curves for the site-specific air density and evaluates their effect on the annual energy production estimations. Differences of the order of 10-3 between the default and the site specific mean air density (ρ), do not change substantially the energy production. However, for higher discrepancies of the order of 10-2 the power output can differ more than 10%. Turbulence affects the wind energy in two ways: through power performance impacts and through effects on turbine loads and fatigue. In the operational range of each turbine, TI increases the output at low wind speeds, while in the transition region to rated power it decreases the power output. In the context of this study, the DES approach was implemented to examine the flow at the De Montfort university campus in Leicester. The 3d wind maps for the mean wind speed and the annual energy production were developed and the optimum locations for micro wind turbines installation were identified. Although the rooftops of the higher buildings have mostly the potential for wind energy applications, the effect of the urban topography on the wind potential is not always apparent. Lower building can occasionally have higher potential for micro wind turbines installation than taller and roofs of the same height and close each other may differ substantially in their predicted energy output. Using the field measurements by two 3d ultrasonic anemometers placed in the campus, the site specific air density and turbulence intensity were considered to correct the energy yield estimations and evaluate their effect on the results.

Three novel multicomponent fuel spray droplet evaporation models are developed by employing the theory of continuous thermodynamics(CT) with the aim of applying them in the design and analysis of various energy conversion devices such as, aircraft jet engines, liquid-fuel rocket engines, diesel engines, and industrial furnaces. The CT methodology seeks to represent complex mixtures - for example,aviation kerosene or JP8 that typically comprise blends of a large number of chemical compounds by using probability distribution functions (PDFs). The components of JP8, which is constituted by the homologous series of paraffin, naphthene, and aromatic hydrocarbons; are each represented by the Pearson-Shultz type three-parameter gamma PDF, where the three (shape, scale, and origin) parameters characterise changes in the mixture composition. The phase transition of the liquid droplet due to evaporation is modelled using both low-pressure (LP) and high-pressure (HP) vapour-liquid equilibrium (VLE) models employing various mixing and combining rules by applying a general cubic equation of state (CEOS). Interestingly enough, the phase transition of the liquid fuel into vapour mixture is characterised by a change in the PDF scale parameter alone. Once the description of the fuel mixture is complete, the traditional species and energy transport equations both for the liquid and vapour phases respectively, are re-written using the composition PDF moments under Lagrangian and Eulerian frameworks. In order to solve the governing equations for the three droplet evaporation models, which characteristically involve phase change and a moving interface, a novel fully Adaptive Method Of Lines using B-Spline Collocation (AMOLBSC) is developed. The models are tested at various pressures, temperatures and convective conditions, including at a lean, premixed, prevaporised (LPP) combustor operating condition. In general, the computational results at an ambient pressure close to atmospheric showed good to excellent agreement against available experimental data in the literature. However, for ambient conditions with elevated-high pressures and temperatures only models that employ the HP formulation gave reliable results. In particular, when the liquid is at or near its critical pressure and temperature it is characterised by faster vaporisation and shorter droplet lifetime, including some evidence of liquid mass diffusion. The liquid model that incorporates the effects of liquid core circulation using semiempirical approximation and adaptive mesh refinement (AMR) technique is the most accurate and computationally efficient, although further work is required to establish its ranges of applicability.

As a contribution towards understanding the impact of free-stream perturbations on laminar-to-turbulent boundary layer transition, we calculate the signature of unsteady disturbances engendered by the interaction of free-stream vortical fluctuations with a laminar boundary layer over a flat and a curved plate. We concentrate on low-frequency perturbations which, in the case of a flat plate, induce strong streamwise-elongated components of the boundary-layer signature, known as Klebanoff modes or streaks. In boundary layers over suitably curved concave walls, Klebanoff modes are expected to develop into Gortler vortices. The generation and nonlinear evolution of the induced perturbations, which acquire an O(1) magnitude, are described on a self-consistent and first-principle basis using the mathematical framework of the nonlinear unsteady boundary-region equations (NUBREs), subject to appropriate upstream and far-field boundary conditions. The nonlinear response of a compressible flat-plate boundary layer to free-stream vorticity is investigated first. The problem is governed by the compressible NUBREs, which are derived herein for the first time. The free-stream flow is studied by including the boundary-layer displacement effect and the solution is matched asymptotically with the boundary-layer flow. The nonlinear interactions inside the boundary layer drive an unsteady two-dimensional flow of acoustic nature in the outer inviscid region through the displacement effect. Analytical solutions are derived by exploiting the well-known analogy with the flow over a thin oscillating airfoil, which is used herein for the first time to study unsteady boundary layers. In the subsonic regime the perturbation is felt from the plate in all directions, while at supersonic speeds the disturbance only propagates within the dihedron defined by the Mach line. Numerical computations are performed for carefully chosen parameters that characterize three practical applications: turbomachinery systems, supersonic flight conditions and wind-tunnel experiments. The results show that nonlinearity plays a marked stabilizing role on the velocity and temperature streaks, and this is found to be the case for low-disturbance environment such as flight conditions. Increasing the free-stream Mach number inhibits the kinematic fluctuations but enhances the thermal streaks, relative to the free-stream velocity and temperature respectively, and the overall effect of nonlinearity becomes weaker. An abrupt deviation of the nonlinear solution from the linear one is observed in the case pertaining to a supersonic wind tunnel. Large-amplitude thermal streaks and the strong abrupt stabilizing effect of nonlinearity are two new features of supersonic flows. In the second part of the thesis, the generation and nonlinear development of unsteady Gortler vortices in an incompressible boundary layer over a concave plate is studied. The centrifugal force caused by the concavity of the wall is included in the incompressible NUBREs. The results show that the stabilizing effect on nonlinearity is significantly intensified in the presence of centrifugal forces. Sufficiently downstream the nonlinear vortices generated at different free-stream turbulence levels Tu are stabilized to the same amplitude, suggesting that the initial intensity of the forcing becomes unimportant. At low Tu the perturbation undergoes a quasi-exponential growth with the growth rate being enhanced for lower frequencies and more curved plates. At higher Tu, in the typical range of turbomachinery applications, the Gortler vortices do not exhibit an exponential growth as nonlinearity saturates rapidly, and the wall curvature does not influence the boundary-layer response. Good quantitative agreement with direct numerical simulations and experimental data is obtained.

This thesis presents the battery thermal management systems (BTMS) modelling of Li-ions batteries and investigates the design and modelling of different passive cooling management solutions from single battery to module level. A simplified one-dimensional transient computational model of a prismatic lithium-ion battery cell is developed using thermal circuit approach in conjunction with the thermal model of the heat pipe. The proposed model is compared to an analytical solution based on variable separation as well as three-dimensional (3D) computational fluid dynamics (CFD) simulations. The three approaches, i.e. the 1D computational model, analytical solution, and 3D CFD simulations, yielded nearly identical results for the thermal behaviours. Therefore the 1D model is considered to be sufficient to predict the temperature distribution of lithium-ion battery thermal management using heat pipes. Moreover, a maximum temperature of 27.6ºC was predicted for the design of the heat pipe setup in a distributed configuration, while a maximum temperature of 51.5ºC was predicted when forced convection was applied to the same configuration. The higher surface contact of the heat pipes allows a better cooling management compared to forced convection cooling. Accordingly, heat pipes can be used to achieve effective thermal management of a battery pack with confined surface areas. In addition, the thermal management of a cylindrical battery cell by a phase change material (PCM) / compressed expanded natural graphite (CENG) is investigated. The transient thermal behaviour of both the battery and the PCM/CENG is described with a simplified onedimensional model taking into account the physical and phase change properties of the PCM/CENG composite. The 1D analytical/computational model predicted nearly identical results to the three-dimensional simulation results for various cooling strategies. Therefore, the 1D model is sufficient to describe the transient behaviour of the battery cooled by a PCM/CENG composite. Moreover, the maximum temperature reached by the PCM/CENG cooling strategy is much lower than that by the forced convection in the same configuration. In the test case studied, the PCM showed superior transient characteristics to forced convection cooling. The PCM cooling is able to maintain a lower maximum temperature during the melting process and to extend the transient time for temperature rise. Furthermore, the graphite-matrix bulk density is identified as an important parameter for optimising the PCM/CENG cooling strategy. Finally, the lithium-ion battery cooling using a passive cooling material (PCM) / compressed expanded natural graphite (CENG) composite is investigated for the battery module scale. An electrochemistry model (average model) is coupled to the thermal model, with the addition of a one-dimensional model for the solution and solid diffusion using the nodal network method. The analysis of the temperature distribution of the battery module scale has shown that a twodimensional model is sufficient to describe the transient temperature rise. In consequence, a two-dimensional cell-centred finite volume code for unstructured meshes is developed with additions of the electrochemistry and the phase change. This two-dimensional thermal model is used for investigating a new and usual battery module configurations cooled by PCM/CENG at different discharge rates. The comparison of both configurations with a constant source term and heat generation based on the electrochemistry model, showed the superiority of the new design. In this study, comparisons between the predictions from different analytical and computational tools as well as open-source packages were carried out, and close agreements have been observed.

With the fast growth in wind energy, the performance and reliability of the wind power generation system has become a major issue in order to achieve cost-effective generation. Integration of condition monitoring system (CMS) in the wind turbine has been considered as the most viable solution, which enhances maintenance scheduling and achieving a more reliable system. However, for an effective CMS, large number of sensors and high sampling frequency are required, resulting in a large amount of data to be generated. This has become a burden for the CMS and the fault detection system. This thesis focuses on the development of variable selection algorithm, such that the dimensionality of the monitoring data can be reduced, while useful information in relation to the later fault diagnosis and prognosis is preserved. The research started with a background and review of the current status of CMS in wind energy. Then, simulation of the wind turbine systems is carried out in order to generate useful monitoring data, including both healthy and faulty conditions. Variable selection algorithms based on multivariate principal component analysis are proposed at the system level. The proposed method is then further extended by introducing additional criterion during the selection process, where the retained variables are targeted to a specific fault. Further analyses of the retained variables are carried out, and it has shown that fault features are present in the dataset with reduced dimensionality. Two detection algorithms are then proposed utilising the datasets obtained from the selection algorithm. The algorithms allow accurate detection, identification and severity estimation of anomalies from simulation data and supervisory control and data acquisition data from an operational wind farm. Finally an experimental wind turbine test rig is designed and constructed. Experimental monitoring data under healthy and faulty conditions is obtained to further validate the proposed detection algorithms.

Vertical Axis Tidal Turbines (VATTs) have become the subject of increased interest in recent decades, but the development of this type of hydrokinetic turbine has faced several challenges that have not yet been overcome. The influence of rotor parameters on turbine performance is one of these challenges. No axiom can be found in the literature about the effect of these parameters on the turbine behaviour, and sometimes research projects even show contradictory results. As a consequence, parameters that define turbine rotors may differ substantially from each other but have performed similarly in terms of efficiency. In relation to this matter, experimental modelling has been carried out in the School of Engineering facility at Cardiff University. Using small-scale set-ups, experimental testing provided useful and reliable information that shed light into these design uncertainties. Blade roughness has been found to have a great impact on the turbine behaviour, and the influence of this parameter has been tested and analysed in depth in a subsequent chapter of the thesis. Apart from the parametric analysis, a mechanical and an electrical system were utilised for the turbine set up. Thanks to these different systems of energy conversion, it was possible to compare the extracted power and to evaluate their inherent losses. Electricity was generated from the electrical approach, which was very useful in order to accurately evaluate the turbine efficiency. Taking into account the results coming from physical testing, an optimised prototype of a VATT was designed and manufactured; estimated to be a 1:15 scale device. Not just the rotor but the whole super structure was built, in order to analyse both the efficiency and the performance of the rotor, as well as the 1 structural response of the entire device. Performing experimental testing without removing the effect that a blocked channel provides to the turbine rotation is no trivial issue, and intermediate scale tests will become a fundamental step for recognition of the technology. Aiming to achieve a reliable source of information, the manufactured tidal turbine prototype has been tested in a water sports centre (White Water Rafting Centre, Cardiff). There is a clear lack of information in the literature about testing tidal turbines on an intermediate scale, and the chance to test a tidal turbine is a very valuable opportunity. The experiments were accomplished in a very similar environment to a real tidal stream, but with the related advantages of complete control over the turbine deployment. Thus, these experiments are considered to provide very useful data for scientific knowledge and also the tidal stream energy sector. Finally, the study of the hydrodynamic turbine wake in small scale was carried out. Not only velocity measurements were collected at the turbine operating point, but also water elevations upstream and downstream were measured by using depth gauges based on water conductivity. At the time of writing and to the best of the authors’ knowledge, not many research articles have studied the wake characteristics of vertical axis tidal stream turbines, and none have used this equipment. The quality of the data is deemed to be excellent and the following process of the information described perfectly the near and far wake. This could be extremely useful for a future scale-up of the turbine, and the development of an array.

This thesis explores the mesh-free numerical method, Smooth Particle Hydrodynamics (SPH), presents improvements to the algorithm and studies its application in solid mechanics problems. The basic concept of the SPH method is introduced and the governing equations are discretised using the SPH method to simulate the elastic solid problems. Special treatments are discussed to improve the stability of the method, such as the treatment for boundary problems, artificial viscosity and tensile instability. In order to improve the stability and efficiency, (i) the classical SPH method has been combined with the Runge-Kutta Chebyshev scheme and (ii) a new time-space Adaptive Smooth Particle Hydrodynamics (ASPH) algorithm has been developed in this thesis. The SPH method employs a purely meshless Lagrangian numerical technique for spatial discretisation of the domain and it avoids many numerical difficulties related to re-meshing in mesh-based methods such as the finite element method. The explicit Runge-Kutta Chebyshev (RKC) scheme is developed to accurately capture the dynamics in elastic materials for the SPH method in the study. Numerical results are presented for several test examples applied by the RKC-SPH method compared with other different time stepping scheme. It is found that the proposed RKC scheme offers a robust and accurate approach for solving elastodynamics using SPH techniques. The new time-space ASPH algorithm which is combining the previous ASPH method and the RKC schemes can achieve not only the adaptivity of the particle distribution during the simulation, but also the adaptivity of the number of stage in one fixed time step. Numerical results are presented for a shock wave propagation problem using the time-space ASPH method compared with the analytical solution and the results of standard SPH. It is found that using the dynamic adaptive particle refinement procedure with adequate refinement criterion, instead of adopting a fine discretisation for the whole domain, can achieve a substantial reduction in memory and computational time, and similar accuracy is achieved.

Wind turbine gearbox bearings are the component that leads to the most downtime of operating wind turbines due to their high failure rates. Failures occur within 10 % of bearing design life, despite the fact that they are designed to the same bearing standards that satisfactorily predict bearing lifetime in many other industrial applications. No theory has yet been widely accepted to explain the reasons for this premature failure, despite intensive research effort and many theories have been suggested both from industrial and academic researchers alike. The most widely accepted theory at the current time is that the bearing subsurface is weakened by what have been termed as white etching cracks that eventually lead to material removal from the bearing contact surfaces. Extreme loading conditions caused by a number of possible sources, which expose bearings to higher than designed contact pressures and surface traction in wind turbine operation, are investigated throughout this project. A dynamic model of a wind turbine gearbox was developed in order to calculate bearing contact stresses during transient operating conditions, which found that bearings were loading to above recommended values, even during normal operating conditions. A failed bearing from a wind turbine gearbox was then destructively investigated, leading to the conclusion that manganese sulphide inclusions were the primary cause of white etching crack initiation. These inclusions were investigated in greater detail to determine the geometry and depth of the most damaging inclusions, both in the failed bearing and on bench top test rigs. A series of hammering impact test and rolling contact fatigue tests were designed and led to the successful recreation of white etching cracks in test specimens. It was found that white etching cracks certainly initiate at MnS inclusions. These microcracks initiate due to a tensile load across inclusion tips, which are thought to be further propagated by shear loading along the cracks. Inclusion initiated microcracks have been found to develop into white etching cracks, which may link up and weaken the subsurface of bearing raceways sufficiently to cause eventual failure. Testing is carried out to find thresholds in terms of contact pressure, surface traction, impact and fatigue loading cycles, required for the formation of white etching cracks. The key contributions of this study are identification and recreation of four different types of subsurface damage at MnS inclusions by examining a failed WTGB and carrying out testing using a reciprocating hammering impact rig and a rolling contact fatigue twin disc machine. A hypothesis of the order and mechanism of these damage events is proposed in this study, as well as the development of testing methods to investigate the damage in order to support the hypotheses. Test methods are also developed to investigate the effects of some key bearing loading parameters, including impact loading, levels of contact pressure, surface traction and number of load cycles.

Wind turbines have been developed for more than a century and nowadays wind turbines are still facing some challenges such as efficiency and maintenance problems. Load control is considered to be one of the most important parts for future horizontal axis wind turbine (HAWT) designs. Deploying effective flow control devices on the blades could either increase loads at off-design wind speed conditions or reduce the extreme loads, leading to either higher energy output or a more stable energy output from the wind turbine. This study reports a research into the performance of trailing edge flow control devices of HAWT by solving the Reynolds averaged Navier-Stokes equations. The validation case selected for this work is the NREL Phase VI blade with experimental data. The trailing edge flow control devices studied include microtabs and microjets installed near the trailing edge of the rotating blade. The divergent trailing edge is also included in the study as a passive flow control device due to its practical interest. These trailing edge devices are implemented on the fixed-pitch NREL Phase VI blade, using the original performance and flow characteristics as a benchmark. Both 2D and 3D simulations are carried out in order to investigate the suitability of the 2D blade sectional design analysis and control for the actual 3D rotating framework. Moreover, the study is extended to an active pitch-regulated offshore wind turbine, NREW 5MW wind turbine. Firstly the code to code comparison is carried out for validation purpose. Then the trailing edge flow control devices are also deployed on this wind turbine to find out their effectiveness. The results show there are significant differences when compared to the conclusions from the CFD study on the NREL Phase VI blade.