Dissertations / Theses on the topic 'Turbina cross-flow'

Estima-se que nos próximos 20 anos a energia hidráulica contribuirá com quase 30% da energia elétrica do planeta, atualmente esta participação é de 19%. Muitos países possuem iniciativas sérias de implementação de Pequenas Centrais Hidrelétricas, quer seja a médio ou a longo prazo. No Brasil, particularmente, um novo programa de incentivo as pequenas centrais hidrelétricas está sendo lançado pela ELETROBRÁS. Porém, a previsão do número de usinas de pequeno porte e a potência total a ser instalada dentro do plano decenal, 1997 2006, de geração é relativamente pequeno (15 PCH somando 93,71 MW de possíveis 2.161 totalizando 3.633 MW Fonte: SIPOT- ELETROBRÁS abr / 98). A média do consumo de energia elétrica por habitante no Brasil está abaixo da média do consumo mundial (1805 kWh/ano para 2160 kWh/ano. (Fontes: SIESE-Síntese anual 1999 e International Energy Outlook 1998 DOE / EIA). Quando comparamos as várias regiões do território brasileiro a discrepância se torna ainda maior. Vários tipos de turbinas hidráulicas podem ser usadas em pequenas, mini e micro centrais hidroelétricas, entre as quais podemos destacar: Pelton, Francis, Turgo, Kaplan, Hélice, Banki etc. No Brasil as mais utilizadas são: Francis e Kaplan seguidas de longe pela Pelton. O uso dos demais tipos é quase que desconhecido, principalmente a Turgo. A turbina de fluxo cruzado, também conhecida pelos nomes de: MichellBanki, Banki e MichellOssberger é definida como uma turbina de ação que pode ser instalada com quedas de 1 a 200 m de altura e vazões de 0,025 a 13 m3/s. Com a evolução apresentada principalmente nas últimas duas décadas por firmas tradicionais como: Ossberger Turbinenfabrick ou mais novas como a CINK, pode alcançar diâmetros de rotores próximos de 1,0 m com largura de até 3,0m e desenvolver potência de até 2000 kW, com rendimentos que já podem chegar a 90%. As principais evoluções estão concentradas em modificações no injetor da turbina, emprego de novos materiais nas pás, eixo e rolamentos do rotor e em tentativas de utilização do tubo de sucção. Um dos estudos de mostra a viabilidade técnica e econômica na implantação de uma turbina de fluxo cruzado em comparação com as turbinas Francis e Kaplan. As conclusões serão relatadas após a análise de viabilidade técnico-econômica entre os três tipos de turbinas.
It is forecasted that in next 20 years the hydraulic energy will contribute with almost 30% of the total electric power of the planet, while this participation is today near 19%. Many countries have firm initiatives of implementation on SHPs, in medium or long terms. In Brazil, a new incentive program for SHPs is being introduced by ELETROBRAS. However, the forecast for the number of small plants and output installed into Ten-Year Expansion Plan of Energy to the year 2006 is relatively small (15 SHP amount to 93.71 MW, compared to feasible levels of 2,161 SHPs and 3,633 MW. (Source: SIPOTELETROBRAS april / 98). The average electric power consumption per inhabitant in Brazil is below of the world average consumption (1,805 kWh/year against 2,160 kWh/year. Source: SIESE - Annual summary 1999 and International Energy Outlook 1998 DOE/EIA) and when compared with the different regions of the Brazilian territory this discrepancy becomes still larger. Several types of hydraulic turbines can be used in small hydropower, as Pelton, Francis, Turgo, Kaplan, Propeller, Banki, etc. In Brazil the more used are Francis and Kaplan followed by Pelton. The usage of the other types is almost that unknown, mainly the Turgo turbine. The cross flow turbine, also known by the names of: MichellBanki, Banki, and MichellOssberger is defined as an action turbine that can be applicable to falls from 1 to 200 m and flows from 0,025 to 13 m3/s. With the evolution technical presented mainly in the last two decades by traditional firms like Ossberger Turbinenfabrik and new firms like CINK, that turbine can reach diameters of rotors of 1,0 m with width of 2,6m and to develop capacity up to 2,000 kW, with efficiency near 90%. The main evolutions are concentrated in modifications presented in the injector of the turbine by several manufacturers, and the use of new materials in the blades of the runner, shafts, bearings and the use of the draft tube. Case study shows the technical and economical implications using a cross flow turbine in comparison to a Francis turbine and a Kaplan. The conclusions will be reported after technical and economical viability analysis among the three types of turbines.

Mestrado em Energia
No âmbito das energias renováveis, os aproveitamentos hídricos são uma das soluções para a diminuição das emissões de poluentes resultantes da produção de energia eléctrica. Ao contrário das grandes barragens hidroeléctricas que têm bastantes impactos ambientais, verifica-se que as pequenas hídricas são uma solução mais barata e com menor impacto ambiental, e por isto com um futuro promissor. Neste projecto será efectuado o estudo numérico do escoamento de uma tubeira da turbina cross-flow, bem como do funcionamento de um sistema de controlo de caudal. Para a análise numérica do escoamento na tubeira e na válvula reguladora de caudal, irá ser utilizado um programa computacional já desenvolvido de análise do escoamento. Posteriormente serão analisados os resultados numéricos obtidos, nomeadamente, a velocidade e a pressão nas paredes da tubeira, bem como o ângulo e módulo da velocidade no arco de entrada no rotor e os caudais debitados pela mesma. O estudo dos métodos de desenho utilizados nas tubeiras, bem como o funcionamento dos sistemas de controlo de caudal existentes serão também abordados, com o objectivo de adquirir sensibilidade/experiência para efectuar-se posteriormente os desenhos de detalhe de uma tubeira com válvula reguladora de caudal considerada mais adequada. Será também apresentado um método inovador de construção da tubeira. Finalmente, serão analisados os esforços mecânicos (força e momento), resultantes da acção do escoamento de água na tubeira e válvula reguladora de caudal.

Aquesta tesi doctoral presenta l'estudi que l'autor va realitzar per comprendre l'efecte de l'angle pitch de la pala sobre les interaccions pala-estela que tenen lloc dins el rotor i, per tant, sobre el rendiment d'una turbina de flux creuat amb tres pales rectes. En primer lloc, hem estudiat experimentalment el rendiment d'aquest tipus de turbina en un túnel de vent de capa límit. Ho vam fer per a diferents pitches fixos de les pales, i amb diferents nombres de Reynolds basats en el diàmetre de la turbina que cobreixen la regió de transició en què el parell produït per les pales va superar el parell resistiu oposat. La forma i els valors de la corba de rendiment van canviar dràsticament amb només un increment de l'angle pitch fix. Com més gran sigui el nombre de Reynolds, menor és el tip speed ratio òptim i més cap al toe-out es mou l'angle pitch ideal. Posteriorment, vam estudiar experimentalment la dinàmica de flux dins el rotor per diferents pitches de la pala en un tanc d'aigua amb carro, usant Digital Particle Image Velocimetry. Els assajos es van realitzar a un nombre de Reynolds basat en el diàmetre de la turbina constant, i per a un rang de tip speed ratios. L'atenció se centra en l'anàlisi de les interaccions pala-estela dins el rotor. Angles toe-in i excessius toe-out s'han associat a baixos rendiments d'aquest tipus de turbines. La investigació ens ha permès relacionar les interaccions pala-estela amb les diferències de rendiment en aquest tipus de turbines, en funció del tip speed ratio i de l'angle pitch de la pala.
Esta tesis doctoral presenta el estudio que el autor realizó para comprender el efecto del ángulo pitch de la pala sobre las interacciones pala-estela que tienen lugar dentro del rotor y, por lo tanto, sobre el rendimiento de una turbina de de flujo cruzado con tres palas rectas. En primer lugar, hemos estudiado experimentalmente el rendimiento de este tipo de turbina en un túnel de viento de capa límite. Lo hicimos para diferentes pitches fijos de las palas, y con diferentes números de Reynolds basados en el diámetro de la turbina que cubren la región de transición en la que el par producido por las palas superó al par resistivo opuesto. La forma y los valores de la curva de rendimiento cambiaron drásticamente con sólo un incremento del ángulo pitch fijo. Cuanto mayor sea el número de Reynolds, menor es el tip speed ratio óptimo y más hacia el toe-out se mueve el ángulo pitch ideal. Posteriormente, estudiamos experimentalmente la dinámica de flujo dentro del rotor para diferentes pitches de la pala en un tanque de agua con carro, usando Digital Particle Image Velocimetry. Los ensayos se realizaron a un número de Reynolds basado en el diámetro de la turbina constante, y para un rango de tip speed ratios. La atención se centra en el análisis de las interacciones pala-estela dentro del rotor. Ángulos toe-in y excesivos toe-out se han asociado a bajos rendimientos de este tipo de turbinas. La investigación nos ha permitido relacionar las interacciones pala-estela con las diferencias de rendimiento en este tipo de turbinas, en función del tip speed ratio operativo y del ángulo pitch de la pala.
This doctoral thesis presents the study that the author have carried out in order to understand the effect of the blade pitch angle on the blade-wake interactions that take place inside the rotor, and hence on the performance of a three straight bladed cross-flow turbine. Firstly, we have experimentally studied the performance of this kind of turbine in a boundary layer wind tunnel. We did it for different fixed blade pitches, and at different turbine diameter Reynolds numbers covering the transitional region in which the torque produced by the blades overtook the opposed resistive torque. Shape and values of the performance curve changed drastically with just an increment of the fixed pitch angle. The higher the Reynolds number, the lower the optimal tip speed ratio and the more towards toe-out the ideal pitch angle is moved. Afterwards, we study experimentally the flow dynamics inside the rotor for different blade pitches in a water towing tank, using planar Digital Particle Image Velocimetry. Tests were made at a constant turbine diameter Reynolds number, and for a range of tip speed ratios. The focus is given to the analysis of the blade-wake interactions inside the rotor. Toe-in and excessive toe-out angles have been associated to low performances of this type of turbines. The investigation has allowed us to relate the blade-wake interactions with the performance differences in this type of turbines, as a function of both the operational tip speed ratio and the blade pitch angle.

This study presents a numerical investigation of a generic horizontal axis cross-flow marine turbine. The numerical tool used is the commercial Computational Fluid Dynamics package ANSYS FLUENT 12.0. The numerical model, using the SST k-w turbulence model, is validated against static, dynamic pitching blade and rotating turbine data. The work embodies two main investigations. The first is concerned with the influence of turbine solidity (ratio of net blade chord to circumference) on turbine performance, and the second with the influence of blockage (ratio of device frontal area to channel crosssection area) and free surface deformation on the hydrodynamics of energy extraction in a constrained channel. Turbine solidity was investigated by simulating flows through two-, three- and four-bladed turbines, resulting in solidities of 0.019, 0.029 and 0.038, respectively. The investigation was conducted for two Reynolds numbers, Re = O(10^5) & O(10^6), to reflect laboratory and field scales. Increasing the number of blades from two to four led to an increase in the maximum power coefficient from 0.43 to 0.53 for the lower Re and from 0.49 to 0.56 for the higher Re computations. Furthermore, the power curve was found to shift to a lower range of tip speed ratios when increasing solidity. The effects of flow confinement and free surface deformation were investigated by simulating flows through a three-bladed turbine with solidity 0.125 at Re = O(10^6) for channels that resulted in cross-stream blockages of 12.5% to 50%. Increasing the blockage led to a substantial increase in the power and basin efficiency; when approximating the free surface as a rigid lid, the highest power coefficient and basin efficiency computed were 1.18 and 0.54, respectively. Comparisons between the corresponding rigid lid and free surface simulations, where Froude number, Fr = 0.082, rendered similar results at the lower blockages, but at the highest blockage an increase in power and basin efficiency of up to 7% for the free surface simulations over that achieved with a rigid lid boundary condition. For the free surface simulations with Fr = 0.082, the energy extraction resulted in a drop in water depth of up to 0.7%. An increase in Fr from 0.082 to 0.131 resulted in an increase maximum power of 3%, but a drop in basin efficiency of 21%.

The challenge of tackling global climate change and our increasing reliance on power means that new and diverse renewable energy generation technologies are a necessity for the future. From a number of technologies reviewed at the outset, the cross-flow tidal turbine was chosen as the focus of the research. The numerical investigation begins by choosing to model flow around a circular cylinder as a challenging benchmarking and evaluation case to compare two potential solvers for the ongoing research, ANSYS CFX and OpenFOAM. A number of meshing strategies and solver limitations are extracted, forming a detailed guide on the topic of cylinder lift, drag and Strouhal frequency prediction in its own right. An introduction to cross-flow turbines follows, setting out turbine performance coefficients and a strategy to develop a robust numerical modelling environment with which to capture and evaluate hydrodynamic phenomena. The validation of a numerical model is undertaken by comparison with an experimentally tested lab scale turbine. The resultant numerical model is used to explore turbine performance with varying Reynolds number, concluding with a recommended minimum value for development purposes of Re = 350 × 103 to avoid scalability errors. Based on this limit a large scale numerical simulation of the turbine isconducted and evaluated in detail, in particular, a local flow sampling method is proposed and presented. The method captures flow conditions ahead of the turbine blade at all positions of motion allowing local velocities and angles of attack to be interrogated. The sampled flow conditions are used in the final chapter to construct a novel blade pitching strategy. The result is a highly effective optimisation method which increases peak turbine power coefficient by 20% for only two further case iterations of the numerical solution.

The cross-flow turbine is unique due to the generation of power during two stages. The water flows through the rectangular cross-section nozzle and enters the runner, where the first stage power is generated. The water then flows diametrically through the center of the runner, before it hits the blades on the way out, generating the second stage power. This type of turbine is often used in small hydropower plants located in less-developed countries. The turbine has a simple design, which is economical and easy to manufacture. A cross-flow turbine manufactured by Remote HydroLight in Afghanistan was installed in The Waterpower Laboratory at The Norwegian University of Science and Technology in September 2008. During the fall of 2008, efficiency measurements were performed on the turbine. A maximum efficiency of 78.6% was obtained at 5 meter head. However, although the efficiency is high for a turbine with such a simple design, there is a desire to improve it for better utilization of the resources. An open question is if the flow through the runner behaves like the manufacturers of this turbine type claim. It is therefore of interest to investigate the flow pattern through the runner and the distribution of torque transferred during the two stages. This is the objective of this thesis. Two experiments are performed in this thesis. The objective of the first experiment was to visualize the flow through the runner with use of a high-speed camera. This required an extensive remodeling of the turbine in order to obtain a clear view of the flow. However, the high--speed camera had to be replaced by a single-lens reflex camera and stroboscopes, due to low quality pictures. The second experiment measured the torque transfer to the runner by the use of strain gages. The strain gages could not be calibrated within the time frame of this thesis, but a relative measure of the distribution of torque was obtained. During both experiments the efficiency was measured, but the main objective was to determine the flow pattern and torque transfer through the runner. The results show that the turbine works well for large nozzle openings. The water enters the runner close to the nozzle outlet, leading to a cross flow entering the inside of the runner at a short distance from the nozzle. This gives good conditions for the flow, as the direction of the absolute velocity when entering the second stage corresponds well with the blade inlet angle. At best efficiency point the second stage contributes to 53.7% of the total amount of torque transferred. With decreasing nozzle opening, the cross flow enters the inside of the runner further away from the nozzle. This give a direction of the cross flow which corresponds poorly with the inlet angle of the blades at the second stage, which increases the incidence losses and gives a lower efficiency.

An experimental investigation has been carried out into the mixing of a row of jets injected into a confined cross-flow. Measurements were made on a fully annular test facility, the geometry of the rig simulating that found in the dilution zone of a gas turbine combustion chamber. A small temperature difference of 44°C between the cross-flow and dilution fluid allowed the mixing characteristics to be assessed, with hot jets being injected into a relatively cold cross-flow at a jet to cross-flow momentum flux ratio of 4.0. The investigation concentrated on differences in the mixing of individual dilution jets, as indicated by the regularity of the temperature patterns around the cross-flow annulus. Despite the uniform conditions approaching the dilution holes there were significant differences in the temperature patterns produced by the dilution jets around the annulus.

Control of pollutants and emissions has become a major factor in the design of modern combustion systems. The “Liquid Hydrogen Fueled Aircraft - System Analysis” project funded in 2000 by the European Commission can be seen as such an initiative. Within the framework of this project, the Aachen University of Applied Sciences developed experimentally the “Micromix” hydrogen combustion principle and implemented it successfully in the Honeywell APU GTCP 36-300 gas turbine engine. Lowering the reaction temperature, eliminating hot spots from the reaction zone and keeping the time available for the formation of NOx to a minimum are the prime drivers towards NOx reduction. The “Micromix” hydrogen combustion principle meets those requirements by minimizing the flame temperature working at small equivalence ratios, improving the mixing by means of Jets In Cross-Flow and reducing the residence time in adopting a combustor geometry that provides a very large number of very small diffusion flames. In terms of pollutant emissions, compared to the unconverted APU, an essential reduction in emitted NOx was observed, stressing the potential of this innovative burning principle.

The objective of this thesis is to investigate the “Micromix” hydrogen combustion principle with the ultimate goal of an improved prediction during the design process. Due to the complex interrelation of chemical kinetics and flow dynamics, the “Micromixing” was analyzed first. Stereoscopic Particle Image Velocimetry was used to provide insight into the mixing process. A “simplified” set-up, that allowed to investigate the flow characteristics in great detail while retaining the same local characteristics of its “real” counterparts, was considered. The driving vortical structures were identified. To further investigate the physics involved and to extend the experimental results, numerical computations were carried out on the same “simplified” set-up as on a literature test case. In general, a number of physical issues were clarified. In particular, the interaction between the different vortical structures was looked into, and a kinematically consistent vortex model is proposed. After demonstrating the development of the mixing, the “cold flow” study was extended to a single injector. The double backward-facing step injector geometry was addressed experimentally and numerically. At design geometry, the flow appeared to behave single backward-facing like, with respect to the first gradation. In terms of varying step configurations, the flow was seen to be dependent on the periodic perturbation arising from the graded series of backward-facing steps. During the second part of the investigation, the “hot flow” was analyzed. Considering combustor similar operating conditions, a test burner was experimented on an atmospheric test rig. NOx emissions were traced by exhaust gas analysis for different working conditions. Particular flame patterns, such as a regular attached flame as well as lifted flames were observed. In parallel with the experimental work, numerical computations on a pair of opposite injectors, permitted to classify the combustion regime and the main factors involved in the NOx formation. Accordingly, NOx emission enhancing design changes are proposed. Finally, the demanding computational effort, worthy of acceptance for academic purposes, is found not agreeable as future design tool and improvements to speed up the design process are projected.

Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished

A lot of research effort is spent worldwide in order to reduce the environmental impact of the transportation and power generation sector. To minimize the environmental pollution the role of hydrogen fuelled gas turbines is intensively discussed in several research scenarios, like the IGCC-technology or the application of hydrogen as large scale storage for renewable energy sources. The adaptation of the applied gas turbine combustion chamber technology and control technology is mandatory for a stable and secure low NOx operation of a hydrogen fuelled gas turbine.

The micromix combustion principle was invented at Aachen University of Applied Sciences and achieves a significant reduction of the NOx-emissions by the application of multi miniaturized diffusion-type flamelets. Based on the research experiences, gained during the two European hydrogen research programs EQHHPP and Cryoplane at Aachen University of Applied Sciences, the intention of this thesis was to continue the scientific research work on low NOx hydrogen fuelled gas turbines. This included the experimental characterization of the micromix combustion principle, the design of an improved combustion chamber, based on the micromix combustion principle, for industrial gas turbine applications and the improvement of the gas turbine’s control and metering technology.

The experimental characterization of the micromix combustion principle investigated the impact of several key parameters, which influence the formation of the NOx-emissions, and allows therefore the definition of boundary conditions and design laws, in which a low NOx operation of the micromix combustion principle is practicable. In addition the ability of the micromix combustion principle to operate at elevated energy densities up to 15 MW/(m2bar) was successfully demonstrated. The improved combustion chamber design concept includes the experiences gained during the experimental characterization and covers the industrial needs regarding scalability and manufacturability.

The optimization and testing is done with an Auxiliary Power Unit GTCP 36-300. The original kerosene fuelled gas turbine was modified for the hydrogen application. Therefore several hardware and software modifications were realized. The improved gas turbine’s control and metering technology enables stable and comparable operational characteristics as in kerosene reference. An improved hydrogen metering unit, which is controlled by the industrial Versatile Engine Control Box, was successfully implemented.

The combination of the micromix combustion technology and of the optimized control and metering technology allows a stable, secure and low NOx hydrogen fuelled gas turbine operation.

Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished

The goal of the present work was to identify and implement modifications to a density-based unstructured RANS CFD algorithm, as typically used in turbomachinery flows (represented here via the RoIIs-Royce 'Hydra' code), for application to Iow Mach number gas-turbine combustor flows. The basic algorithm was modified to make it suitable for combustor relevant problems. Fixed velocity and centreline boundary conditions were added using a characteristic based method. Conserved scalar mean and variance transport equations were introduced to predict scalar mixing in reacting flows. Finally, a flarnelet thermochemistry model for turbulent non-premixed combustion with an assumed shape pdf for turbulence-chemistry interaction was incorporated. A method was identified whereby the temperature/ density provided by the combustion model was coupled directly back into the momentum equations rather than from the energy equation. Three different test cases were used to validate the numerical capabilities of the modified code, for isothermal and reacting flows on different grid types. The first case was the jet in confined cross flow associated with combustor liner-dilution jetcore flow interaction. The second was the swirling flow through a multi-stream swirler. These cases represent the main aerodynamic features of combustor primary zones. The third case was a methane-fueled coaxial jet combustor to assess the combustion model implementation. This study revealed that, via appropriate modifications, an unstructured density-based approach can be utilised to simulate combustor flows. It also demonstrated that unstructured meshes employing nonhexahedral elements were inefficient at accurate capture of flow processes in regions combining rapid mixing and strong convection at angles to cell edges. The final version of the algorithm demonstrated that low Mach RANS reacting flow simulations, commonly performed using a pressure-based approach, can successfully be reproduced using a density-based approach.

This dissertation addresses the design, simulation, prototype, and test of a new energy generation system, which transforms rotational motion into electricity by the use of an innovative turbine-generator. The system is divided in two assembled subsystems that interact to finally transform kinetic energy into electricity. The first subsystem is a miniaturized notched impulse turbine system, and the second one is a millimeter permanent magnet generator (PMG) assembled into the turbine. The conversion of biomechanical energy to electric energy, using clean and free energy produced by a living organism, is being increasingly researched [1]-[11]. These are all viable options, but advantages and disadvantages of each type of energy conversions should be evaluated individually to determine key factors such as efficiency as an energy harvesting method, the implementation cost, size, and the final applications where they will be used. Through this dissertation, a new option of green energy conversion is made available; focusing on the use of turbines to extract energy from microfluidics, with diverse application in biomedical, military/aerospace, and home areas. These systems have the potential of converting mechanical movement energy, and hydraulic energy into electric energy that may be sufficient for self-powering nano/micro devices and nano/micro systems. A flow, with constant pressure, a magnetic generator, and a novel impulse turbine design are combined to form a self-contained miniaturized generator system. The turbine consists of two main parts: a bearingless rotor and the enclosure or casing; while the miniaturized magnetic generator is a permanent magnet brushless machine, consisting of permanent magnets in a ring configuration and radial coils. A permanent pressure, from microfluidic pressure system, is the force used to move the blades. This rotational motion of the turbine is transformed into electricity using magnetic induction, formed by permanent magnets on the rotor and nine coils fixed in the holder of the turbine. The electricity is generated when the magnetic field rotates and moves past the conductor, which induces a current according to Faraday's Law [1-3]. The system has potential uses not only in medical equipment, but in automotive applications, home appliances, and aquatic and ventilation systems.

This thesis details the development, verification and validation of an unsteady unstructured high order (≥ 3) h/p Discontinuous Galerkin - Fourier solver for the incompressible Navier-Stokes equations on static and rotating meshes in two and three dimensions. This general purpose solver is used to provide insight into cross-flow (wind or tidal) turbine physical phenomena. Simulation of this type of turbine for renewable energy generation needs to account for the rotational motion of the blades with respect to the fixed environment. This rotational motion implies azimuthal changes in blade aero/hydro-dynamics that result in complex flow phenomena such as stalled flows, vortex shedding and blade-vortex interactions. Simulation of these flow features necessitates the use of a high order code exhibiting low numerical errors. This thesis presents the development of such a high order solver, which has been conceived and implemented from scratch by the author during his doctoral work. To account for the relative mesh motion, the incompressible Navier-Stokes equations are written in arbitrary Lagrangian-Eulerian form and a non-conformal Discontinuous Galerkin (DG) formulation (i.e. Symmetric Interior Penalty Galerkin) is used for spatial discretisation. The DG method, together with a novel sliding mesh technique, allows direct linking of rotating and static meshes through the numerical fluxes. This technique shows spectral accuracy and no degradation of temporal convergence rates if rotational motion is applied to a region of the mesh. In addition, analytical mappings are introduced to account for curved external boundaries representing circular shapes and NACA foils. To simulate 3D flows, the 2D DG solver is parallelised and extended using Fourier series. This extension allows for laminar and turbulent regimes to be simulated through Direct Numerical Simulation and Large Eddy Simulation (LES) type approaches. Two LES methodologies are proposed. Various 2D and 3D cases are presented for laminar and turbulent regimes. Among others, solutions for: Stokes flows, the Taylor vortex problem, flows around square and circular cylinders, flows around static and rotating NACA foils and flows through rotating cross-flow turbines, are presented.

Cette thèse s'inscrit dans le cadre des énergies renouvelables au sein du programme HARVEST centré sur le développement d'un concept d'hydrolienne dérivé des turbines Darrieus et Gorlov. L'ajout d'un dispositif appelé carénage à la turbine permet à celle-ci d'extraire une portion de l'énergie cinétique du courant plus grande. Toutefois ce dernier peut favoriser la cavitation qui nuit à la turbine. Parmi les différents axes du programme, les travaux de thèse se situent dans cette problématique. En régime subcavitant et cavitant, l'analyse de l'hydrolienne a été menée suivant une approche numérique et expérimentale. Pour ce faire deux outils ont été mis en place. Du coté expérimental, le tunnel hydrodynamique du LEGI a été équipé d'une balance qui donne la mesure instantanée des forces et du couple qui s'exercent sur la turbine. Du coté numérique, les efforts ont été orientés sur l'amélioration et le développement du code de calcul universitaire, CAVKA. L'utilisation intensive de ces deux moyens, couplée à des modèles théoriques, a permis de mettre en évidence d'une part le fonctionnement de la turbine libre ou carénée et, d'autre part, les limites de fonctionnement vis-à-vis de la cavitation.

There is a growing interest in tidal energy, owing to its predictable nature in comparison to other renewable sources. In the case of the UK, its importance also lies on the availability of exploitable areas as well as their total capacity, which is estimated to cover more than 20% of the country demand. However, the level of development of this kind of technology is still far behind other types of renewable energy. However, several studies focused on a variety of individual devices, followed by more recent research on the deployment of large arrays or tidal farms. Potential sites for energy extraction can be found in narrows between islands and the coast or estuaries. The latter present some advantages for the installation and the connection to the grid but estuaries are often prone to flood risk from tides and surges. Therefore, the objective of this thesis is to evaluate the effect that very large groups of turbines could have on peak water levels during flooding events in the case of being deployed in estuarine areas. For that purpose, a new methodology has been developed, which implies the use of a numerical model (MIKE 21 by DHI), and it has been demonstrated against a real case study in the UK: the Solway Firth estuary. Another objective has consisted of integrating in this thesis the results from detailed CFD modelling and optimisation techniques involved in the project. A literature review has been carried out in order to identify the current state of the art for the different subjects considered in the thesis. Different aspects of the numerical model used for this study (MIKE 21) have been presented and the modelling of the turbines within the code has been validated against experimental and CFD data. The procedure to include large numbers of turbines in the code is also developed. An analysis has been done of the different estuaries existing in the UK suitable for tidal energy extraction, identifying their main geometrical features. Based on this, idealised models of estuaries have been used to assess the influence that the channel geometry could have on the impact of tidal farms under extreme water levels. The effect has been measured by comparing the results of the numerical model between the case with and without turbines under different flooding scenarios. Finally, the same methodology has been applied to a real case study selected from the previous group of estuaries namely the Solway Firth. An initial model has been created, according to the available data at the start of the research, which contained some errors related to the water depth at the intertidal areas in the upper estuary. Therefore, when a more realistic dataset became available, an improved model was created. The improved model has been used to assess the effects of tidal farms in the estuary under a coastal flooding event. It is concluded that there is significant influence of the channel geometry over the locations where the maximum changes in water levels due to the tidal farms will happen. Nevertheless, the effects seem to be more relevant in terms of the decrease rather than the increase of peak water levels for all geometries and the maximum changes seem to be in the order of dm. This is in agreement with the results of the Solway Firth models and can be summarised as a positive net effect over flood risk. On the other hand, a concern has been raised about the impact on intertidal areas, which could be the subject of future research.

L'étude développée dans cette thèse concerne le contrôle des performances et des lâchers tourbillonnaires au cours du cycle de rotation d'une hydrolienne à axe vertical de type Darrieus. L'élaboration d'une famille de lois de commande d'incidence de pales exploitant le principe de conservation de la circulation autour de profils en mouvement permet ici le contrôle du fonctionnement de l'hydrolienne ainsi que la maîtrise de son sillage tourbillonnaire afin de préserver l'environnement.L'écoulement 2D est simulé à l'aide du solveur incompressible de Star CCM+ afin de mettre en évidence l'effet de ce type de contrôle sur le rendement de la turbine pour différents points de fonctionnement. Ce modèle CFD a été utilisé pour améliorer l'analyse analytique en ce qui concerne l'extraction de l'énergie, la compréhension de l'écoulement autour de l'hydrolienne et le contrôle des tourbillons générés. La nouveauté de cette étude est l'élaboration de lois de commande de pales d'hydrolienne, basées sur des valeurs constantes et transitoires de la circulation, afin d'augmenter la puissance de la turbine tout en garantissant un contrôle efficace de la vorticité et ainsi prévenir de l'interaction entre les tourbillons et les pales. Une bonne comparaison est réalisée entre les résultats analytiques et numériques concernant les forces hydrodynamiques.En outre, une campagne d'essais a été menée afin d'acquérir des mesures quantitatives sur une hydrolienne de type Darrieus à pales fixes en terme de puissance, mais aussi des résultats qualitatifs pertinents comme la visualisation de l'écoulement autour des pales à différentes positions et pour différents points de fonctionnement. La mise en place complète d'un système PTV pour les mesures qualitatives et les étapes de traitement sont discutées et les divers paramètres obtenus à partir des études CFD sont validées en utilisant ces résultats PIV.L'étude expérimentale dans la présente recherche appo11e des informations détaillées sur les gradients de pression et de vitesse, les contours de vorticité et le critère Q qui ont servi à valider les visualisations obtenues numériquement
With key applications in marine renewable energy. the vertical axis water turbine can use current or tidal energy in an eco-friendly manner. However, it is difficult to reconcile optimal performance of hydrokinetic turbines and compliance wilh the aquatic environment as the main drawback of the turbines is the formation of non-linear flow structures caused by the unsteady movement of the blades. Eddies in the flow are advected and can interact with other blades, which leads to a reduction in power output. To limit this phenomenon, the turbines operate at high speeds, which are likely to reduce the shaft power. High speeds of rotational so forbid the passage of aquatic animais, and are the cause of a suction effect on the sediments.The objective of this thesis work is twofold. First, it aims to develop a blade pitch control to get the flow adjusted around the blade profile at any given flow configuration by incorporatin.g the profile's motion with respect to incident flow. Such a system intends to achieve the objective of operating at reduced speeds without vortical releases, which should allow achieving a high torque without causing damage to the environment.This thesis work is mainly carried out in three phases. ln the first phase, the irrotational flow over an arbitrary profile is formulated using conforma] mapping. Prospective potential flow application on the basis of Couchet theory (1976) is involved in the development of a control law that decides the blade pitching in a constant circulation framework. In the second phase, a numerical validation of the developed analytical work is presented using CFD to examine how the theoretical fomulation can be effectively applied to Darricus turbines. In the final phase, two prototypes are developed, one is classical Darrieus turbine with fixed blades, and other is the turbine with pitching blades for experimental measurements of performance as well as flow fields(by PIV) in order to validate the computational results

Le but de cette thèse est le développement et l'optimisation de la chaine électrique d'une hydrolienne fluviale. L'approche est d'abord traitée en simulation pour ensuite finir par la conception et la mise au point d'un prototype. La partie simulation concerne la modélisation des ensembles turbines, génératrices et électronique de puissance mais aussi le développement des diverses lois de commandes. Ces commandes peuvent intervenir à différents niveaux du contrôle jusqu'à la supervision complète du système, permettant de gérer des défauts, des algorithmes de MPPT (extraction maximale de puissance), des synchronisations entre colonne, ... Le prototype d'hydrolienne fluviale sera ensuite présenté, de la mise au point des parties mécaniques jusqu'aux résultats expérimentaux. Les travaux nombreux autour de ce prototype ont permis d'obtenir des résultats satisfaisants et encourageants qui corroborent la théorie.

The dissertation investigates the approach of open source hardware and its potential for a “post-growth” transformation of society, which, from an environmentalist perspective, seems necessary. Hereby it elaborates the paradigm shift attached to the idea of open source, compares them with living systems in nature and practically contributes to the open source movement in the field of rural electrification. By doing so, it compares renewable energy technologies for rural electrification from the perspective of open source applicability. The practical output hereby is the design of an open source licensed hydro power turbine, called “Pico Cross Flow”. The dissertation covers the hydraulic and mechanical design as well as the manufacturing of a prototype and the testing at the hydrodynamic laboratory of the University of Viena
La disertación investiga la idea de “open source hardware” (hardware de código abierto) y su potencial para una transformación social de "post-capitalismo", la cual, desde una perspectiva ambientalista, parece necesaria. Se elabora el cambio de paradigma asociado a las ideas de código abierto, se compara con los sistemas vivos en la naturaleza y prácticamente contribuye al movimiento de fuente abierta (open source) en el campo de la electrificación rural. El resultado práctico es el diseño de una turbina hidroeléctrica licenciado código abierto, denominada "Pico Cross Flow". La parte práctica de la disertación abarca el diseño hidráulico y mecánico, así como la fabricación de un prototipo y las pruebas en el laboratorio hidrodinámico de la Universidad de Viena.

Les hydroliennes représentent une des ressources d'énergie renouvelable qui a encore besoin d'études exploratoires et d'une réelle finalité pratique. Les hydroliennes sont des turbines qui récupèrent l'énergie cinétique des courants fluviaux ou marins. Equivalentes quelque part aux éoliennes, elles seront plus compactes à puissance égale car l'eau est mille fois plus dense que l'air. L'étude présentée dans le cadre de cette thèse s'inscrit dans un programme de recherche multidisciplinaire et a pour objet le concept HARVEST basé sur une structure verticale nommée colonne qui est composée d'un empilement de turbines "Achard" solidaires sur un même axe de rotation. Cette thèse fait partie des travaux menés sur les aspects génération électrique et porte sur les possibilités de contrôle commande et de pilotage pour les hydroliennes en mode connecté au réseau de puissance infinie ou en mode ilôté
Cross-flow water turbines represent a potential renewable energy resource which needs more exploring study and eventually real scale finality. Cross-flow water turbines harvest the water kinetic energy. Somehow equivalents to wind turbines these water turbines are more compact at equal power as water is a thousand times denser than air. The study here presented is part of a multidisciplinary research program focused on the HARVEST concept. The latter is based on vertical structure composed of piled up Achard turbines locked on the same rotational shaft. This Ph. D. Thesis concerns electrical generation issues and its main developed topics are control possibilities of this generation system in a grid connected or islanded mode of operation

La récupération, grâce aux hydroliennes, de l’énergie cinétique de courants marins et fluviaux constitue une source d’énergie renouvelable considérable et prédictible. La simulation fine, par une description statistique instationnaire de type URANS, de l’écoulement autour d’une hydrolienne isolée à axe vertical, bi-rotor et munie d’un carénage (hydrolienne de type HARVEST) donne accès à une estimation précise de la puissance produite. Cependant, le coût élevé de cette approche URANS la rend inadaptée à la simulation d’un parc de machines. Une analyse de la littérature conduit à retenir un modèle basse-fidélité de type Blade Element Momentum (BEM) pour décrire à moindre coût l’effet du rotor de la turbine sur l’écoulement, dans le contexte d’une description 2D (coupe horizontale). La performance de l’hydrolienne est alors prédite par un calcul RANS incluant des termes sources distribués dans un anneau rotor virtuel et conservant le maillage des parties fixes (carénage). Ces termes sources sont construits grâce à une procédure originale exploitant les conditions locales de l’écoulement en amont des cellules du rotor virtuel et le débit de l’écoulement traversant l’hydrolienne. Les coefficients hydrodynamiques utilisés pour le calcul des termes sources BEM-RANS sont construits une fois pour toutes en exploitant une série de simulations URANS préliminaires ; ils intègrent les effets du carénage et le fonctionnement de chaque rotor à une vitesse de rotation optimale (maximisant la puissance produite) grâce au système de régulation de l’hydrolienne. Le modèle BEM-RANS développé est validé par comparaison avec des simulations URANS de référence : il fournit une estimation fiable de la puissance produite (erreur de quelques % par rapport à l’approche URANS) pour un coût réduit de plusieurs ordres de grandeur. Ce modèle est appliqué à l'analyse de la puissance produite par une rangée d’hydroliennes HARVEST dans un canal pour différents facteurs de blocage et d’espacement latéral ainsi qu’à une ferme marine composée de trois hydroliennes
The capture, thanks to hydrokinetic turbines, of the kinetic energy generated by sea and river currents provides a significant and predictable source of renewable energy. The detailed simulation, using an unsteady statistical description of URANS type, of the flow around an isolated water turbine of HARVEST type (cross flow vertical axis ducted water turbine) provides an accurate estimate of the power output. However, the cost of the URANS approach is much too expensive to be applied to a farm of several turbines. A review of the literature leads to select a low-fidelity model of Blade Element Momentum (BEM) type to describe at a reduced cost the rotor effect on the flow, in a 2D context (horizontal cross-section). The turbine performance is then predicted using a steady RANS simulation including source terms distributed within a virtual rotor ring and preserving the mesh of the turbine fixed parts (duct). These source terms are derived using an original procedure which exploits both the local flow conditions upstream of the virtual rotor cells and the flow rate through the turbine. The hydrodynamic coefficients used to compute the BEM-RANS source terms are built once for all from a series of preliminary URANS simulations; they include the effects of the duct on the flow and the rotor operating at optimal rotational speed (maximizing the power output) thanks to the turbine regulation system. The BEM-RANS model is validated against reference URANS simulations: it provides a reliable prediction for the power output (within a few % of the URANS results) at a computational cost which is lowered by several orders of magnitude. This model is applied to the analysis of the power produced by a row of Vertical Axis Water Turbines in a channel for various values of the blockage ratio and lateral spacing as well as to a 3-machine sea farm

碩士
國立中興大學
土木工程學系所
105
In the appeals to carbon reduction, micro-hydropower technology developments have become a topic of concern to the world community gradually.In Taiwan in terms of the hydroelectric power facilities.Because of the reservoir development has become saturated.Therefore, The future of hydropower in Taiwan will also develop in the direction of micro-hydroelectric power. The study decided to introduce the Japanese open-type cross-flow turbine manufacturing technology, and manufacture the scaled-down prototype by our manufacturers. The power generation experiment was carried out using the improved experimental channel of NCHU to facilitate the collection of performance test data through conditional control, to evaluate the efficiency of power generation, and to preliminary calculate what the actual micro hydropower generating units can achieve the benefits. From the experimental results, the scaled-down prototype runs smoothly with power generation efficiencies of up to 22%, Pumped at 5 hp. In the fixed-flow power generation experimental results show that the effective drop is proportional to the power generation efficiency.But the power generation potential of the calculation can be clearly seen that the effect is far less than the size of the magnification model.The results show that the installation of the generator is best to the size of the magnification model as much as possible.