The accurate prediction of turbulent transport and its effect on tokamak operation is vital for the performance and development of operational scenarios for present and future fusion devices. For problems of this complexity, a common approach is integrated modelling where multiple, well-benchmarked codes are coupled together to form a code that covers a larger domain and range of physics than each of the constituents. The main goal of this work is to develop such a code that integrates core and edge physics for long-time simulation of the tokamak plasma. Three questions are addressed that contribute to the ultimate end goal of this core/edge coupling, each of which spans a chapter. Firstly, the choice of model for edge and core must be fluid for the time scales of interest, but the validity of a common further simplification to the physics models (i.e. the drift-reduction) is explored for regions of interest within a tokamak. Secondly, maintaining a high computational efficiency in such integrated frameworks is challenging, and increasing this while maintaining accurate simulations is important. The use of sub-grid dissipation models is ubiquitous and useful, so the accuracy of such models is explored. Thirdly, the challenging geometry of a tokamak necessitates the use of a field-aligned coordinate system in the edge plasma, which has limitations. A new coordinate system is developed and tested to improve upon the standard system and remove some of its constraints. Finally, the investigation of these topics culminates in the coupling of an edge and core code (BOUT++ and CENTORI, respectively) to produce a novel, three-dimensional, two-fluid plasma turbulence simulation.

Engine components are commonly exposed to air temperatures exceeding the thermal material limit in order to increase the overall engine performance and to maximise the engine specific fuel consumption. To prevent the overheating of the materials and thus the reduction of the component life, an internal flow system must be designed to cool the critical engine parts and to protect them. As the coolant flow is bled from the compressor and not used for the combustion an important goal is to minimise the amount of coolant in order to optimise the overall engine performance. Predicting the metal temperatures is of paramount importance as they are a major factor in determining the component stresses and lives. In addition, as modern engines operate in ever harsher conditions due to efficiency requirements, the ability to predict thermo-mechanical displacements becomes very relevant: on the one hand, to prevent damage of components due to excessive rubbing, on the other hand, to understand how much air is flowing internally within the secondary air system for cooling and sealing purposes, not only in the design condition but throughout the engine life-span. In order to achieve this aero-engine manufacturers aim to use more and more accurate numerical techniques requiring multi-physics models, including thermo-mechanical finite elements and CFD models, which can be coupled in order to investigate small variations in temperatures and displacements. This thesis shows a practical application and extension of a numerical methodology for predicting conjugate heat transfer. Extensive use is made of FEA (solids) and CFD (fluid) modeling techniques to understand the thermo-mechanical behaviour of a turbine stator well cavity, due to the interaction of cooling air supply with the main annulus. Previous work based on the same rig showed diffculties in matching predictions to thermocouple measurements near the rim seal gap. In this investigation, further use is made of existing measurements of hot running seal clearances in the rig. The structural deflections are applied to the existing model to evaluate the impact in flow interactions and heat transfer. Furthermore, for one test case unsteady CFD simulations are conducted in order to take into account the flow unsteadiness in the heat transfer predictions near the rim. In addition to a baseline test case without net ingestion, a case simulating engine deterioration with net ingestion is validated against the available test data, also taking into account cold and hot running seal clearances. Furthermore an additional geometry with a stationary deflector plate is modelled and validated for the same flow cases. Experiments as well as numerical simulations have shown that due to the deflector plate the cooling flow is fed more directly into the disc boundary layer, allowing more effective use of less cooling air, leading to improved engine efficiency. Therefore, the deflector plate geometry is embedded in a CFD-based automated optimisation loop to further reduce the amount of cooling air. The optimisation strategy concentrates on a flexible design parameterisation of the cavity geometry with deflector plate and its implementation in an automatic 3D meshing system with respect of finally executing an automated design optimisation. Special consideration is given to the flexibility of the parameterisation method in order to reduce design variables to a minimum while also increasing the design space flexibility & generality. The parameterised geometry is optimised using a metamodel-assisted approach based on regressing Kriging in order to identify the optimum position and orientation of the deflector plate inside the cavity. The outcome of the optimisation is validated using the benchmarked FEA-CFD coupling methodology.

No description available.

The increasing trend towards large-scale deployment of wind energy imposes numerous operational challenges regarding large integration of wind power to the transmission system including the maintenance of system stability due to the uncertain nature of wind power. Thus, the traditional way of operating and controlling wind turbines and wind power plants are becoming less acceptable. Furthermore, wind power plants are progressively being subjected to the Transmission network operators (TSO's) regulations and are required to operate as a single controllable unit, similar to the conventional power plants, to provide active power regulation. To provide such a functionality, wind turbines in a wind farm must provide more flexible output power control in a quick and safe operating manner. Additionally, the operation of the wind turbines must be coordinated so as to operate the whole wind power plant as a single controllable entity. The main goal of this thesis is to generate a wind farm Simulink model that captures all the essential dynamics for the wind farm controller design and load analysis. To achieve this main aim, a mathematic wind farm model has been developed which offers sufficiently fast simulation for iterative controller design task, and contains a suitable wind-field model that provides a suitable representation of the wind-field and wake propagation through the wind farm. The wind farm controller design with the objectives of primary frequency response and power optimisation has also been investigated.

De-centralised renewable energy power generation is proposed to be a significant part of the future of electricity generation technology, with wind energy playing a significant role. With half of the global population residing in urban and suburban areas, the opportunity for individuals or small organisations to generate power locally facilitates the decrease in losses associated with long distance electricity generation and transmission. Small-scale wind turbine applications within suburban/urban areas are exposed to high level of gust and turbulence compared to flow over less rough surfaces (e.g. coastal/offshore areas, open grasslands, rural areas, etc.). There is, therefore, a need for such systems not only to cope with, but to thrive under such rapidly fluctuating, complex urban wind conditions. Assessing the potential of a proposed urban wind turbine project is hindered by insufficient assessment of both the urban wind resource and power capabilities of certain turbine designs within a potential suburban/urban site. This, however, requires estimation of important factors such as local atmospheric turbulence, total energy available to the turbine system and the potential power output to be generated should a certain turbine system design be installed within a potential site. The research presented in this thesis proposes a methodology for scoping the potential of small wind turbines within a built environment through effective assessment of the urban wind resource and power capabilities of small turbine systems. The aim is to address the lack of accurate and affordable methods for site viability assessment of small wind turbines within a built environment. This methodology encompasses three sub-models which estimate the local atmospheric turbulence (represented by the turbulence intensity, T.I.), additional energy within the gusty urban wind (represented by the excess energy content, EEC) and the turbine power capability at different heights within a potential site. Firstly, to quantify the influence of location on the total energy available to a small wind turbine at a potential site, an in-depth evaluation of the urban wind resource is completed. This includes the development of methods to predict the local atmospheric turbulence at a given turbine mast height, and the additional energy available to the turbine which is usually under represented when using assessments based only on mean wind speeds. This is achieved using high temporal resolution wind measurement datasets from eight potential turbine sites within the urban and suburban environments and LiDAR building height datasets from three major UK cities namely, Leeds, Manchester and London. Subsequently, new analytical models are developed that allow the mapping of atmospheric turbulence and excess energy at different heights over Leeds, Edinburgh, Manchester and London by combining the T.I. and EEC estimation models with currently available methods of predicting mean wind speeds over urban areas. The results from these two models highlight the importance of including building height variation and changes in wind direction within the assessment, and also the value of employing detailed building geometric data as model inputs. A simple low-cost 2-D multiple streamtube vertical axis wind turbine (VAWT) model capable of simulating turbine performance in a fluctuating wind isdeveloped. Combining this VAWT model with dynamic stall features and variable speed control strategy, enables a system based design of wind turbines operating within suburban/urban environment. A method of estimating the performance of a turbine operation within an urban wind resource is developed by assessing the power capabilities of the VAWT model using high-resolution wind measurement datasets as model inputs. This is combined with the T.I. and EEC estimation models in developing a new model known as the turbine power estimation (TPE) model used in mapping turbine performance at different heights over Leeds, Edinburgh, Manchester and London. Comparison between the TPE model and a generic power curve is made, hence suggesting the possibility of using a simple model to estimate the power capabilities of a certain turbine design while accounting for local turbulence within an urban wind resource. Finally, the investigation of the cumulative potential of small wind turbine power generation in Leeds, Edinburgh, Manchester and London indicates a largely untapped wind resource available (represented by high EEC values estimated within small distances in each city) which could be harnessed if gust tracking solutions were to be commercially available. It also highlights the importance of site viability assessment and its financial implications illustrated by capacity factor maps over the four cities, which has practical value for turbine manufacturers and urban planners alike. Thus, for urban wind applications to achieve their optimum deployment potential, this research study proposes a simple, effective and affordable tool for preliminary scoping the potential of certain small wind turbine designs within a suburban/urban environment, and hence encouraging effective carbon savings. In order to maximize the impact of this research study, it would be valuable that these maps be extended to other towns/cities and made available and easily accessible to individuals and interested parties, and hence this is a major objective of future work.

Renewable energy is an environmentally friendly alternative to the use of fossil fuels. In response to reducing the dependency on fossil fuels, the European Wind Energy Association (EWEA) has made a policy to increase the overall renewable energy consumption by three times the current amount by the year 2020. Critical to achieving this target will be the use of wind turbines. There is a scope to increase the performance of wind turbines by utilising the existing techniques from the aeronautical industry. One of these techniques is the use of passive flow control which involves no moving parts that has a reduced complexity compared to active flow control techniques. Initially eleven flow control devices applicable for a wind turbine were identified. Out of the eleven devices four possible flow control devices were selected for this research project (vortex generator, vortex trapping, passive ventilation and sinusoidal leading edge wing). These four concepts have been evaluated for their applicability for a wind turbine. A novel CFD work was conducted for a wedge type vortex generator for wind turbine blade. A number of different configurations as well as its performance over different operating conditions were assessed. The wedge type vortex generator (VG) showed the most benefit for a wind turbine blade and it is recommended for wind turbine application, specifically for the root part of the blade. It was found that up to 0.2% increase in AEP is possible with integration of this VG at the blade root, which corresponds to about €30,000 worth of additional energy production of a 5MWturbine per annum. A series of theoretical studies using Blade Element Momentum (BEM) theory was conducted to establish the requirements for an optimum wind turbine blade. Based on this investigation it was found that the current root geometry is unable to attain the optimum lift force and in fact it produces negative torque. One of the interests of this project was to identify ways to reduce the blade loads. This simple BEM based investigation was conducted to quantify potential the chord reduction available with the use of conventional vane and passive air-jet vortex generators (PAJVG). Findings from this exercise showed that large chord reductions are possible with the use of these devices. Only the PAJVGs were able to attain chord reduction up to 10% while allowing the blade to operate within a safe stall margin. Extensive number of 2D CFD simulations was conducted to validate the current 2D CFD methods. Baseline 2D CFD methods have been successfully validated for the pre-stall angle of attack. The effect of modelling transition for a 2D and 3D wind turbine simulation has been established using the Menter’s SST γ-θ transition model.

No description available.

The design, modelling and testing of a film cooling system intended for the casing of an unshrouded HP turbine rotor is described in this thesis. Due to the dense network of small film cooling holes employed in such a system, this is often referred to as a casing effusion cooling scheme. Though there are patent references to such systems, there is as yet very limited published material on the aero thermal performance of such film cooling schemes. The casing of an unshrouded HP rotor is an incredibly hostile environment, witnessing the periodic passing of the HP rotor tips within close proximity at a frequency of ∼10 kHz. These blade passing events subject the casing to extremely large amplitude fluctuations of pressure and heat load, which may at first seem to preclude the use of a film cooling scheme. This thesis details many theoretical, computational and experimental advancements related to the research topic. Highlights include: The introduction of a new fundamental mechanism to the field of film cooling, the propagation and reflection of pressure waves within film cooling holes and the impact on film cooling performance. The development of new miniature thin film heat flux gauges manufactured using a new process. Sensor resolution is improved by a factor of seven. The first published computational model reporting heat transfer data on a film cooled rotor casing. Improvements to heat transfer data processing techniques and theory. These are applied to experimental work to produce the highest resolution heat transfer data obtained on the casing of a scaled rotating transonic HP rotor for both uncooled and cooled geometries. Computational models are used to demonstrate that coolant injection on the rotor casing reduces the over-tip leakage mass flow, offsetting the spoiling and mixing losses that film cooling schemes introduce. Much of the work in this thesis is based on papers that have been submitted to or are pending submission. To date three papers have been presented at conference with two published in journals and the third recommended and pending journal publication. Two other papers are pending submission. A patent has also been filed with the European and American patent office regarding novel film cooling hole shapes designed to make use of acoustic effects.

No description available.

Wind turbines are leading the way in helping to reduce the dependency on fossil fuel energy sources. However to compete with other energy sources there is a need to reduce the cost of energy from wind turbines. It has been shown in the literature that as wind turbines increase in size their reliability decreases. As wind turbines move further offshore and into deeper water this becomes more of an issue as carrying out maintenance becomes more challenging and costly. One way of improving the reliability of wind turbines is through the use of condition monitoring systems (CMS) which can continually monitor the health of the machine and allow more optimised maintenance and repair scheduling. Although the benefits of using a CMS may seem evident, operators have been slow in the uptake of such systems. One reason for this is due to issues with the reliability of CMS themselves. As stated in the literature, CMS must accurately detect 60-80% of faults to be economically justifiable. Not detecting faults or the occurrence of false alarms is detrimental to the effectiveness of CMS. The work presented in this thesis aims to address the issue of CMS reliability. Through the installation of two CMS in operational wind turbines the author of this thesis has gained valuable insight into the design, build and installation of CMS which has facilitated the novel contributions from this work. The first contribution comes from the formulation of an engineering design process which incorporates five categories of robustness which were identified by the author through Failure-Mode Effects Analysis on a wind turbine CMS that was installed in an operational wind turbine. The engineering design process incorporating the robustness categories will allow wind turbine CMS to be designed which are capable of operating reliably in the harsh environment they are subjected to. The second contribution comes from the development of three techniques which will increase CMS reliability by reducing false alarms and introducing the ability to detect erroneous data.