Battery charging wind turbines like, Hybrid Field Generator, have become more popular in the growing renewable energy market. With wind energy, voltage and current control is generally provided by means of power electronics. The paper describes the analytical investigation in to control aspects of a hybrid field generator controller for optimized performance. The project objective is about maintaining the generated voltage at 28V through out a generator speed range, between 149 rpm and 598 rpm. The over voltage load, known as dump load, is connected to the control circuit to reduce stress on the bypass transistor for speeds above 598 rpm. Maintaining a stable voltage through out the speed range, between 149rpm and 598rpm, is achieved by employing power electronics techniques. This is done by using power converters and inverters to vary the generator armature excitation levels hence varying its air gap flux density. All these take place during each of the three modes of generator operation, which are: buck, boost and permanent magnet modes. Although the generator controller is power electronics based, it also uses software to optimize its performance. In this case, a PIC16F877 microcontroller development system has been used to test the controller function blocks.

This thesis presents a computational fluid dynamic (CFD) study of high pressure gas turbine blade design with different realistic inlet temperature and velocity boundary conditions. The effects of blade shaping and inlet conditions can only be fully understood by considering the aerodynamics and heat transfer concurrently; this is in contrast to the sequential method of blade design for aerodynamics followed by cooling. The inlet boundary conditions to the NGV simulations are governed by the existence of discrete fuel injectors in the combustion chamber. An appreciation of NGV shaping design under engine realistic inflow conditions will allow for an identification of the correct three dimensional shaping parameters that should be considered for design optimisation. The Rolls-Royce efficient Navier-Stokes solver, HYDRA, was employed in all computational results for a transonic turbine stage. The single passage unsteady method based on the Fourier Shape Correction is adopted. The solver is validated under both rich burn (hot steak only) and the case with swirl inlet profiles for aerothermal characteristics; good agreement is noted with the validation data. Post processing methods were used in order to obtain time-averaged results and blade visualisations. Subsequently, a surrogate design optimisation methodology using machine learning combined with a Genetic Algorithm is implemented and validated. A study of the effect of NGV compound lean on stage performance is carried out and contrasted for uniform and rich burn inlets, and subsequently for lean burn. Compound lean is shown to produce a tip uploading at the rotor inlet, which is beneficial for rich burn, but detrimental for lean burn. It is also found that for rich burn, fluid driving temperature is more dominant than HTC in determining rotor blade heat transfer, the opposite sense to the uniform inlet. Also, for a lean burn inlet, there is another role reversal, with HTC dominating fluid driving temperature in determining heat transfer. A novel NGV design methodology is proposed that seeks to mitigate the combined effects of inlet hot streak and swirling flow. In essence, the concept two NGVs in a pair are shaped independently of each other, thus allowing the inlet flow non uniformity to be suitably accommodated. Finally, two numerical NGV optimisation studies are undertaken for the combined hot streak and swirl inlet for two clocking positions; vane impinging and passage aligned. Due to the prohibitive cost of unsteady CFD simulations for an optimisation strategy, a suitable objective function at the NGV exit plane is used to minimise rotor tip heat flux. The optimised shape for the passage case resulted in the lowest tip heat flux distribution, however the optimum shape for the impinging case led to the highest gain in stage efficiency. This therefore suggests that NGV lean and clocking position should be a consideration for future optimisation and design of the HP stage.

Many reactions carried out in the chemical industry are exothermic. The heat liberated by the reaction is often transferred to another medium such as steam by heat exchange. This heat can then be used elsewhere or be used to generate power via a steam cycle. In this work the focus is on another method of reaction heat recovery. When an exothermic reaction is conducted at elevated pressures, a turbine expander can be placed directly behind the reactor. The hot, high-pressure product gas from the reactor can then be expanded in the turbine. During the expansion process the physical energy of the product gas is converted to kinetic energy (or electricity if the turbine is connected to a generator). Three chemical processes were studied to determine the feasibility of turbine integration into the processes. They are ethylene oxide production, phthalic anhydride production and the hydrodealkylation of alkylaromatic compounds. The chosen processes differ in terms of reactor operation, reactant conversion as well as the presence or absence of recycle loops. Simulation models were developed for the mentioned processes with the process simulator Aspen Plus®. Results from the simulations show that, without the turbine, the processes require power from external sources. They can however operate independently from external power sources when a turbine is present. Excess power can be exported or used for electricity generation. It is therefore feasible• to incorporate turbine expansion units in all the processes considered. The operating conditions of some unit operations have to be changed to accommodate the turbine expander. With the additional product namely power, a re-evaluation of all the operating conditions and tradeoffs in the process is necessary. Further investigation into the impact of turbine integration on the optimal operating conditions of the process is therefore recommended. Traditional definitions used to evaluate the performance of a process generating or consuming power, were found to be inadequate for use in processes where power and chemicals are produced together. New performance parameters are required for the evaluation of processes where power and chemicals are produced simultaneously. An exergy analysis was performed for one of the cases. This analysis method provides insight as to where thermodynamic losses occur in a process. The exergy analysis was useful to quantify the losses occurring in an isenthalpic expansion valve, and the savings obtained by replacing such a valve with an expansion turbine. / Dissertation (MEng (Chemical Engineering))--University of Pretoria, 2006. / Chemical Engineering / unrestricted

Increasing awareness of the issues of climate change and sustainable energy use has led to growing levels of interest in small-scale, decentralised power generation. Small-scale wind power has seen significant growth in the last ten years, partly due to the political support for renewable energy and the introduction of Feed In Tariffs, which pay home owners for generating their own electricity. Due to their ability to respond quickly to changing wind conditions, small-scale vertical axis wind turbines (VAWTs) have been proposed as an efficient solution for deployment in built up areas, where the wind is more gusty in nature. If VAWTs are erected in built up areas they will be inherently close to people; consequently, public acceptance of the turbines is essential. One common obstacle to the installation of wind turbines is noise annoyance, so it is important to make the VAWT rotors as quiet as possible. To date, very little work has been undertaken to investigate the sources of noise on VAWTs. The primary aim of this study was therefore to gather experimental data of the noise from various VAWT rotor configurations, for a range of operating conditions. Experimental measurements were carried out using the phased acoustic array in the closed section Markham wind tunnel at Cambridge University Engineering Department. Beamforming was used in conjunction with analysis of the measured sound spectra in order to locate and identify the noise sources on the VAWT rotors. Initial comparisons of the spectra from the model rotor and a full-scale rotor showed good qualitative agreement, suggesting that the conclusions from the experiments would be transferable to real VAWT rotors. One clear feature observed in both sets of spectra was a broadband peak around 1-2kHz, which spectral scaling methods demonstrated was due to laminar boundary layer tonal noise. Application of boundary layer trips to the inner surfaces of the blades on the model rotor was found to eliminate this noise source, and reduced the amplitude of the spectra by up to 10dB in the region of the broadband peak. This method could easily be applied to a full-scale rotor and should result in measurable noise reductions. At low tip speed ratios (TSR) the blades on a VAWT experience dynamic stall and it was found that this led to significant noise radiation from the upstream half of the rotor. As the TSR was increased the dominant source was seen to move to the downstream half of the rotor; this noise was thought to be due to the interaction of the blades in the downstream half of the rotor with the wake from the blades in the upstream half. It was suggested that blade wake interaction is the dominant noise source in the typical range of peak performance for the full-scale QR5 rotor. Different solidity rotors were investigated by using 2-, 3- and 4-bladed rotors and it was found that increasing the solidity had a similar effect to increasing the TSR. This is due to the fact that the induction factor, which governs the deflection of the flow through the rotor, is a function of both the rotor solidity and the TSR. With a large body of experimental data for validation, it was possible to investigate computational noise prediction methods. A harmonic model was developed that aimed to predict the sound radiated by periodic fluctuations in the blade loads. This model was shown to agree with similar models derived by other authors, but to make accurate predictions very high resolution input data was required. Since such high resolution blade loading data is unlikely to be available, and due to the dominance of stochastic sources, the harmonic model was not an especially useful predictive tool. However, it was used to investigate the importance of the near-field components of the sound radiated by the wind tunnel model to the acoustic array. It was shown that the near-field terms were significant over a wide range of frequencies, and the total spectrum was always greater than that of the far-field component. This implied that the noise levels measured by the acoustic array represented an upper bound on the sound radiated to the far-field, and hence that the latter would also be dominated by stochastic components. An alternative application of the harmonic model, which attempted to determine the blade loading harmonics from the harmonics in the sound field was proposed. This inversion method utilised a novel convex optimisation technique that was found to generate good solutions in the simulated test cases, even in the presence of significant random noise. The method was found to be insensitive at low frequencies, which made it ineffective for inverting the real microphone data, although this was shown to be at least partly due to the limitations imposed by the array size. In addition to the harmonic models, an empirical noise prediction method using the spectral scaling laws derived by \citet*{Brooks_1989} was trialled, and was found to be capable of making predictions that were in agreement with the measured data. The model was shown to be sensitive to the exact choice of turbulence parameters used and was also found to require good quality aerodynamic data to make accurate noise predictions. If such data were available however, it is expected that this empirical model would be able to make useful predictions of the noise radiated by a VAWT rotor.

In 1937 the Manchester Engineering Firm Metropolitan Vickers (Metrovick) were awarded a development contract by the Air Ministry to develop a gas turbine for aircraft propulsion in conjunction with the Royal Aircraft Establishment at Farnborough. Over the next decade and a half, the company developed a number of gas turbine designs for a variety of applications in the air, at sea, and on land. This thesis examines the gas turbine work of Metropolitan Vickers, and how the company interacted with a variety of partners across both the military and the civilian realms. These included government research establishments such as the Royal Aircraft Establishment and the Admiralty Engineering Laboratory; commercial partners, such as the aero-engine manufacturer Armstrong Siddeley, Yarrow Shipbuilders, and the Great Western Railway, and state institutions such as the Ministries of Aircraft Production and Fuel and Power. It argues that Metrovick’s technical style was formed by the company’s existing heavy engineering plant business, which privileged design over development and production engineering. Compared to competitors such as Power Jets and Rolls Royce, Metrovick’s progress on aero-engine work was hampered by the lack of a development organisation; though technically advanced, its aircraft engines took a long time to be developed and would not reach production; a factor which was influential in the post-war sale of Metrovick’s aero-engine designs to Armstrong Siddeley. Metrovick did use its gas turbine experience to gain post-war contracts for both naval and civilian gas turbines. The Royal Navy adopted gas turbines for two roles: as lightweight powerplants for short-ranged fast-attack craft, and as part of major warship propulsion systems that were intended to overcome the perceived flaws of the Navy’s interwar steam plants. Metrovick was selected as a development partner because of the company’s existing naval business, as well as its gas turbine expertise. In the civilian realm, the company produced gas turbines for a wide range of applications ranging from railway locomotives to electrical power generation. Most of the customers for these designs were state or quasi-state institutions; this thesis argues that the postwar British state’s support for the civilian gas turbine shows that it was seen as a crucially British technology that could help improve industrial efficiency, as well as utilising indigenous energy resources. However, again Metrovick was content to rely on development contracts rather than commit itself to large-scale production. The company’s gas turbine designs were somewhat marginal to the wider heavy electrical business, and Metrovick never committed the kind of development resources to the gas turbine division that would have been required to produce successful products, nor did it attempt to sell its designs widely to relevant markets.

Wind farm operators utilize various financial agreements to generate revenue and mitigate risk. These agreements are often based on some estimate of the energy production from the wind farm. A power purchase agreement (PPAs), which is a long-term fixed volume fixed price arrangement, was the most common type of agreement for much of the growth of wind energy in the U.S. Recently, wind turbine power production estimations are relying less on fixed production volumes and PPAs as the basis for energy estimation in financial agreements and more on proxy generation, or an estimate of what the wind farm should make given a set of inflow conditions. These newer types of financial agreements are shifting the focus to when power is produced rather than just how much, and so it is imperative to understand and analyze the errors arising in proxy generation and how it may impact the financial agreements that use proxy generation. This work quantifies the errors in proxy generation and compares two methods of estimating power production, examining the financial impacts of both, for one wind project. These two methods are the nacelle transfer function (NTF) method and the reanalysis data method, which may be used if onsite data is unavailable. The different methods of estimating power production have varying impacts on the financial outcome of the project. Errors in power production estimates that coincide with large price events can result in significant financial impacts for the wind project, and this is more likely to occur with the reanalysis method compared to the NTF method. The results show that the Nacelle Transfer Function (NTF) method of estimating power production via onsite measurements has much less risk of being impacted by a price excursion than the reanalysis data method.

Wind energy is recognized as a sustainable source of energy that is both reliable and capable of dramatically reducing pollution to the environment and dependency on non-renewable fuels, leading to research on wind turbines. Nowadays, the demand for electricity increases. Considering that the greater the distance from shore, the greater the wind, more electricity will be generated along the coast. It is necessary and beneficial to study large scale offshore wind turbines. The National Renewable Energy Lab (NREL) 5-MW offshore wind turbine is simulated using a three-dimensional computational fluid dynamics (CFD) model in this article. A realizable k-ε viscous model is used to simulate turbulence flow. The work is validated by comparing the torque with published simulated data, and satisfied consistency is observed. Further simulation and comprehensive analysis demonstrate the flow features and aerodynamic performances of 5-MW offshore wind turbine under various wind and rotor speeds. The velocity profiles, total pressure distribution, pressure coefficient, rotor thrust, torque and aerodynamic properties are obtained in detail.

The proposed hybrid system generates AC power by combining solar and wind energy converted by a doubly-fed induction generator (DFIG). The DFIG, driven by a wind turbine, needs rotor excitation so the stator can supply a load or the grid. In a variable-speed wind energy system, the stator voltage and its frequency vary with wind speed, and in order to keep them constant, variable-voltage and variable-frequency rotor excitation is to be provided. A power conversion unit supplies the rotor, drawing power either from AC mains or from a PV panel depending on their availability. It consists of a multilevel inverter which gives lower harmonic distortion in the stator voltage. Maximum power point tracking techniques have been implemented for both wind and solar power. The complete hybrid renewable energy system is implemented in a PSIM-Simulink interface and the wind energy conversion portion is realized in hardware using dSPACE controller board.

<div>Yttria-stabilized zirconia (YSZ) thermal barrier coatings (TBCs) provide thermal and environmental protection to superalloy components operating within the combustor and high pressure sections of a gas turbine. However, calcium-magnesium-aluminum silicate (CMAS) deposits originated from particulate matter ingested through the air intake degrade YSZ TBCs, ultimately decreasing the overall efficiency of the engines. With the introduction of biofuels into gas turbines, a new list of impurities with no precedent in jet engines may interact with TBCs, arising the possibility to form CMAS deposits without flying in a particular environment and to exacerbate CMAS negative effect through the addition of other contaminants.</div><div><br></div><div>In this work, a cyclic thermal gradient rig was developed to test TBCs in similar conditions as in a gas turbine. The heat flux and non-contact surface temperature measurements were validated with a thermal transient model. The effect of biofuel impurities on YSZ TBCs was evaluated by spraying the coatings with impurity cocktails, solutions containing the impurities of interest, and subsequently testing their lifetimes in the ablation rig.</div><div><br></div><div>Detailed microstructure analysis revealed that APS and EB-PVD TBCs fail in different ways when exposed to equal concentrations of CMAS. When contaminating APS TBCs with varying combinations of CMAS constituents (e.g., S, C-S, C-A, C-A-S, C-M-S, and C-M-A-S), it was possible to identify that coatings delaminated at different rates depending on the combination of CMAS constituents. Finally, the effect of CMAS in combination with contaminants exclusive of biofuels was analyzed on YSZ TBCs. X-ray diffraction (XRD) analysis and micrographs revealed that glass modifiers (e.g., K₂O and ZnO) accelerated the degradation of YSZ TBCs.</div>

Within a gas turbine engine, the turbine nozzle guide vanes are subjected to very harsh conditions from the highly turbulent and hot gases exiting the combustor. The temperature and pressure fields exiting combustors are highly nonuniform and dictate the heat transfer and aero losses that occur in the turbine passages. To better understand these effects, the goal of this work was to develop an adjustable combustor exit profile simulator for the Turbine Research Facility (TRF) at the Air Force Research Laboratory. The TRF is a high temperature, high pressure, short duration blow-down test facility that is capable of matching several aerodynamic and thermal nondimensional engine parameters including Reynolds number, Mach number, pressure ratio, corrected mass flow, gas to metal temperature ratio, and corrected speed. The primary research objective was to design, install, and verify a non-reacting simulator device that can provide representative combustor exit total pressure and temperature profiles to the inlet of the TRF turbine test section. This required the upstream section of the facility to be redesigned into multiple concentric annuli that serve the purpose of injecting high momentum dilution jets and low momentum film cooling jets into a central annular chamber, similar to a turbine engine combustor. The design of the section allows for variations in injection levels to generate different pressure profiles with elevated turbulence. The dilution and film cooling temperatures can also be varied to create a variety of exit temperature profiles similar to real combustors. The impact of the generated temperature and pressure profiles on turbine heat transfer and secondary flow development was ultimately investigated. Proposed optimal inlet conditions for the turbine tested in this research effort were determined based on the measured data corresponding to the combustor simulator exit profiles that minimized vane heat transfer and total pressure loss. / Ph. D.