As novas tecnologias FACTS aplicadas ao sistema de transmissão, com base em eletrônica de potência, podem também ser úteis à distribuição. Para tal é preciso conduzir um procedimento de consolidação da utilização e do desempenho destas, para sua aplicação sem riscos. Neste trabalho, dois aspectos serão contemplados. O primeiro se refere à aplicação do dispositivo FACTS atuando como um capacitor série. Em se tendo controle de módulo e da fase da tensão inserida em série com a linha pode-se fazê-la comportar-se como uma queda em uma reatância série capacitiva ou indutiva. O controle dessa reatância série (aumentando/diminuindo) permitirá a aplicação do conceito de compensação série em qualquer ponto do sistema de distribuição, provendo benefícios de um controle contínuo da tensão e também do controle do fluxo de carga no sistema independente da corrente. O segundo aspecto refere-se ao uso dos dispositivos na conexão de alimentadores controlando a potência ativa entre eles. Para esta operação outro dispositivo UPFC, com conceito similar ao descrito acima, entretanto atuando na fase da tensão entre 2 barras, comporta-se como um transformador defasador com variação contínua de ?taps?, podendo controlar a potência ativa entre os alimentadores. A aplicação destas tecnologias propiciarão vários benefícios para a expansão da distribuição tais como, flexibilização do uso da rede, interligação de alimentadores permitindo manobras de blocos de energia sem ?pisca?, ajuste contínuo do suporte de reativos durante a operação, controle dinâmico do fluxo de potência. O objetivo deste trabalho é estudar a aplicabilidade da tecnologia FACTS e estender este conceito para aplicação em sistemas de distribuição e conduzir simulações digitais em redes de distribuição (15kV) identificando o desempenho e os benefícios atingidos. O programa de simulação utilizado é o ATP (Alternative Transients Program). / The new FACTS technologies applied to the transmission system, based on power electronics, can also be useful to the distribution. For that, it is necessary to drive a procedure to consolidate the use and the performance for their application without risks. In this work two aspects will be approached. The first refers to the application of a FACTS device acting as series compensator. This device will be able to control the voltage in module and phase in order to act as a voltage drop in a serie reactance with capacitive or inductive features. The control of this series reactance (increasing/ decreasing) will allow the application of series compensation concept to any point of the distribution system, providing the benefits of continuous control of the voltage added to the load flow control in the system independent of the current. The second aspect refers to its use in the connection of two feeders controlling the active power between them. For this operation other device, UPFC, with similar concept as described previously, acts mainly in the phase of the injected voltage in the line, performing as a phase-shift with continuous taps variation and is able to control the active power flow between feeders. The application of this technology will provide several benefits for the distribution expansion, such as, a greater flexibility in the use of the network, connection of feeders without load flow interruption, continuous adjust of reactive power during the operation and dynamic control of power flow. The purpose of this work is to study the applicability of the FACTS technology, to extend this concept for the application in the distribution system by using digital simulations in distribution network up to 15kV identifying the performance and the reached benefits.

Inspired by the pectoral flippers of the humpback whale, the use of spanwise waviness in wings has been considered in the literature as a possible way of delaying the stall, and possibly also reducing the drag coefficient, allowing for improved aerodynamic characteristics. In order to provide a better understanding of this flow control mechanism, the present work investigates numerically the effect of the waviness on the flow around infinite wings with a NACA0012 profile. The study consists of direct numerical simulations employing the spectral/hp method, which is available through the nektar++ library. Considering the high computational cost of the simulations performed, several improvements were introduced to the method, making it more efficient and allowing higher Reynolds numbers to be analysed. These improvements to the method include a coordinate transformation technique to treat the waviness, changes to the parallelism strategy, and an adaptive polynomial order refinement procedure. Initially, simulations were performed for a very low value of the Reynolds number Re = 1, 000, allowing the three-dimensional flow structures to be observed in de- tail. In this case, the results show that the waviness leads to a decrease in the lift-to-drag ratio, accompanied by a strong reduction in the fluctuations of the lift force. The reduction in the lift-to-drag ratio is the combined effect of lower drag and lift forces, and is associated with a regime where the flow remains attached behind the peaks of the leading edge while there are distinct regions of flow separation behind the troughs. Then, simulations with Re = 10, 000 were considered. For high angles of attack, the results for this case are similar to the lower Re, with the waviness leading to separation behind the troughs and reducing both the lift and the drag. However, for a lower angle of attack the waviness leads to a large increase in the lift coefficient. This was observed to be related to the fact that flow around the straight wing is laminar in this case, with the waviness inducing transition to a turbulent state. Finally, the case Re = 50, 000 was considered, with the results showing a good agreement with experiments presented in the literature. / Inspirado na nadadeira peitoral da baleia jubarte, o uso de ondulações ao longo da envergadura de asas tem sido considerado na literatura como uma possível maneira de atrasar o estol, e possivelmente também reduzir o arrasto, levando a melhores características aerodinâmicas. Com o objetivo de obter um melhor entendimento desse mecanismo de controle do escoamento, o presente trabalho investiga numericamente o efeito de ondulações no escoamento ao redor de asas infinitas com o perfil NACA0012. O estudo consiste de simulações diretas do escoamento usando o método espectral/hp, que está disponível através da biblioteca nektar++. Considerando o alto custo computacional das simulações realizadas, diversas melhorias foram introduzidas no método, tornando-o mais eficiente e permitindo que números de Reynolds mais elevados fossem analisados. Essas melhorias ao método incluem uma técnica de mudança de coordenadas para tratar a ondulação, mudanças na estratégia de paralelismo e um procedimento de refinamento usando ordem polinomial variável. Inicialmente, simulações foram realizadas para um número de Reynolds muito baixo Re = 1, 000, o que permitiu observar as estruturas tridimensionais do escoamento em detalhe. Nesse caso, os resultados mostram que a ondulação leva a uma diminuição da razão sustentação-arrasto, combinada com uma forte redução das flutuações da força de sustentação. A redução da razão sustentação-arrasto é consequência de uma combinação de arrasto e sustentação mais baixos e está associada a um regime no qual o escoamento permanece colado atrás dos picos do bordo de ataque, enquanto que regiões distintas de escoamento separado estão presentes atrás dos vales. Em seguida, simulações com Re = 10, 000 foram consideradas. Para ângulos de ataque elevados, os resultados neste caso são similares àqueles com Re mais baixo, com a ondulação levando a separação atrás dos vales e provocando reduções na sustentação e no arrasto. No entanto, para um ângulo de ataque mais baixo a ondulação leva a um grande aumento na força de sustentação. Foi observado que isso está relacionado ao fato de que o escoamento ao redor da asa lisa é laminar neste caso, com a ondulação induzindo a transição para um estado turbulento. Finalmente, o caso Re = 50, 000 foi considerado, com os resultados apresentando uma boa concordância com experimentos apresentados na literatura.

Dans ce mémoire, une étude des conditions de contrôles d’écoulements aérodynamiques par des réseaux de générateurs de tourbillons fluidiques pulsés est menée pour établir un cahier des charges des micro-actionneurs instrumentés de faible coût, indispensables à la réalisation de ce type de contrôle actif à l’échelle industrielle. Une discussion des problématiques rencontrées dans la mise en place de ces dispositifs permet de définir des solutions techniques pertinentes. Une micro-valve encapsulée, constituée d’un canal micro-fluidique en silicium dont l’ouverture est contrôlée par un résonateur annulaire en PDMS, actionnée par différents dispositifs macroscopiques magnétiques, est alors modélisée, fabriquée et caractérisée. Le dispositif permet de générer des jets d’air pulsés complètement contrôlés jusqu’à des vitesses de 150m/s sur la gamme de fréquence [0 ; 500 Hz]. Des réseaux de ces micro-actionneurs polyvalents sont ensuite utilisés en soufflerie pour démontrer sur différents profils aérodynamiques classiques l’intérêt du contrôle par jet pulsé. Le recollement du flux d’air décollé est obtenu sur chacune de ces maquettes pour des conditions réalistes et avec un rendement fluidique supérieur à celui des jets continus.Un débitmètre massique composé d’un capteur de température, d’un capteur de frottement pariétal et d’un capteur de pression de type Pirani, réalisés dans le même procédé de fabrication, est intégré au micro-actionneur. Il permet de caractériser in-situ les jets d’air produits.Enfin un prototype répondant complètement au cahier des charges industriel est obtenu. Sa taille est minimisée par l’optimisation de l’actionneur grâce à un algorithme génétique / This thesis starts with a study of aerodynamic flow control conditions by arrays of pulsed fluidic vortex generators. Detailed specifications are synthesised for the conception of low cost, sensors equipped, micro-actuators required to manage industrial scale active flow control experiments. Devices implementation is discussed to define relevant technical solutions.A packaged micro valve is modelled, fabricated and characterized. It is composed of a micro fluidic channel modulated by an annular membrane resonator made of PDMS. The membrane is controlled by different kinds of magnetic actuation. Fully controlled pulsed air jets are obtained in the frequency range [0; 500 Hz] with velocities up to 150 m/s. Arrays of these micro actuators are used in wind tunnel experiments to demonstrate the ability of pulsed jet to manage control on a wide range of classical separated flows. Reattachment is achieved under industrial flow conditions with improved fluidic yield compared to continuous jets.A mass flow meter constituted of a thermal sensor, a shear flow sensor and a Pirani pressure sensor, all of them built in a single fabrication step, is integrated in the micro-actuator. It allows in-situ characterization of the produced air jets.Finally, a fully satisfying demonstrator is obtained. Its sized is minimized through the use of a genetic algorithm

The objective of this research is to present a theoretical study of the compressibility effects on the performance of an electric D/C motor driven synthetic jet actuator for flow separation control. Hot wire anemometer experiments were conducted to validate the jet exit velocities predicted by the theoretical model. The optimal jet exit velocity required to achieve maximum flow reattachment at reasonable blowing momentum coefficients is predicted. A dynamic electro-acoustic model of the D/C motor driven actuator is developed to accurately predict its performance and efficiency. This model should help formulate a feedback optimal control strategy for real-time flow control using an array of actuators. This model is validated by comparing with hot wire anemometer experiments conducted under similar conditions. The effects of geometric parameters like the slot width, slot geometry, and cavity volume on the performance of the actuator are also tested using this model.

Flow control of transitional shear flows is investigated by means of numerical simulations. The attenuation of three-dimensional wavepackets of Tollmien-Schlichting (TS) and streaks in the boundary layer is obtained using active control in combination with localised sensors and actuators distributed near the rigid wall. Due to the dimensions of the discretized Navier-Stokes operator, reduced-order models are identified, preserving the dynamics between the inputs and the outputs of the system. Balanced realizations of the system are computed using balanced truncation and system identification. We demonstrate that the energy growth of the perturbations is substantially and efficiently mitigated, using relatively few sensors and actuators. The robustness of the controller is analysed by varying the number of actuators and sensors, the Reynolds number, the pressure gradient and by investigating the nonlinear, transitional case. We show that delay of the transition from laminar to turbulent flow can be achieved despite the fully linear approach. This configuration can be reproduced in experiments, due to the localisation of sensing and actuation devices. The closed-loop system has been investigated for the corresponding twodimensional case by using full-dimensional optimal controllers computed by solving an iterative optimisation based on the Lagrangian approach. This strategy allows to compare the results achieved using open-loop model reduction with model-free controllers. Finally, a parametric analysis of the actuators/ sensors placement is carried-out to deepen the understanding of the inherent dynamics of the closed-loop. The distinction among two different classes of controllers – feedforward and feedback controllers - is highlighted. A second shear flow, a confined turbulent jet, is investigated using particle image velocimetry (PIV) measurements. Proper orthogonal decomposition (POD) modes and Koopman modes via dynamic mode decomposition (DMD) are computed and analysed for understanding the main features of the flow. The frequencies related to the dominating mechanisms are identified; the most energetic structures show temporal periodicity. / <p>QC 20130207</p>

Despite significant advancements in the understanding of fluid flows, combustion and material technologies, hypersonic flight still presents numerous technological challenges. In hypersonic vehicles turbulence is critical in controlling heat generation in the boundary layer, mixing inside the combustor, generation of acoustic noise, and mass flow in the intake. The study of turbulence in highly compressible flows is challenging compared to incompressible due to a drastic change in the behavior of pressure and a relaxation of the incompressibility constraint. In addition fluid flow inside a flight vehicle is complicated by wall-effects, heat generation and complex boundary conditions. Homogeneous shear flow contains most of the relevant physics of boundary and mixing layers without the aforementioned complicating effects. In this work we aim to understand and characterize the role of pressure, velocity-pressure interaction, velocity-thermodynamics interaction in the late-stage transition-to-turbulence regime in a high speed shear dominated flow by studying the evolution of perturbations in in a high Mach number homogeneous shear flow. We use a modal-analysis based approach towards understanding the statistical behavior of turbulence. Individual Fourier waves constituting the initial flow field are studied in isolation and in combination to understand collective statistical behavior. We demonstrate proof of concept of novel acoustic based strategies for controlling the onset of turbulence. Towards this goal we perform direct numerical simulations (DNS) in three studies: (a) development and evaluation of gas kinetic based numerical tool for DNS of compressible turbulence, and perform detailed evaluation of the efficacy of different interpolation schemes in capturing solenoidal and dilatational quantities, (b) modal investigation in the behavior of pressure and isolation of linear, non-linear, inertial and pressure actions, and (c) modal investigation in the possible acoustic based control strategies in homogeneously sheared compressible flows. The findings help to understand the manifestation of the effects of compressibility on transition and turbulence via the velocity-pressure interactions and the action of individual waves. The present study helps towards the design of control mechanisms for compressible turbulence and the development of physically consistent pressure strain correlation models.

Demonstration of spanwise-periodic discrete roughness element laminar flow control (DRE LFC) technology at operationally relevant flight regimes requires extremely stable flow conditions in flight. A balance must be struck between the capabilities of the host aircraft and the scientific apparatus. A safe, effective, and efficient flight experiment is described to meet the test objectives, a flight test technique is designed to gather research-quality data, flight characteristics are analyzed for data compatibility, and an experiment is designed for data collection and analysis. The objective is to demonstrate DRE effects in a flight environment relevant to transport-category aircraft: [0.67 – 0.75] Mach number and [17.0M – 27.5M] Reynolds number. Within this envelope, flight conditions are determined which meet evaluation criteria for minimum lift coefficient and crossflow transition location. The angle of attack data band is determined, and the natural laminar flow characteristics are evaluated. Finally, DRE LFC technology is demonstrated in the angle of attack data band at the specified flight conditions. Within the angle of attack data band, a test angle of attack must be maintained with a tolerance of ± 0.1° for 15 seconds. A flight test technique is developed that precisely controls angle of attack. Lateral-directional stability characteristics of the host aircraft are exploited to manipulate the position of flight controls near the wing glove. Directional control inputs are applied in conjunction with lateral control inputs to achieve the desired flow conditions. The data are statistically analyzed in a split-plot factorial that produces a system response model in six variables: angle of attack, Mach number, Reynolds number, DRE height, DRE spacing, and the surface roughness of the leading edge. Predictions on aircraft performance are modeled to enable planning tools for efficient flight research while still producing statistically rigorous flight data. The Gulfstream IIB aircraft is determined to be suitable for a laminar flow control wing glove experiment using a low-bank-angle-turn flight test technique to enable precise, repeatable data collection at stabilized flight conditions. Analytical angle of attack models and an experimental design were generated to ensure efficient and effective flight research.

Abstract Permeable reactive barrier technology is a cost effective means of treating near surface groundwater contaminant plumes. However, current reactive barrier technology lacks the capacity to manipulate flow rates and thus hydraulic retention time (HRT) within the barriers in order to maximize the effectiveness and longevity of the media. This study examines the effectiveness of tile drains as passive controls on the flow rate of ground-water through an existing wood particle media permeable reactive barrier treating agricultural nitrate. The use of upgradient and downgradient tile drains allowed HRT to be increased from 4.5 to 10 days in one trial and then to be decreased from 11.1 to 0.8 days in a second trial. Influent groundwater NO3-N concentrations of ~100 mg/L were attenuated to detection limit (0.02 mg/L) only 12% of the 4 m long barrier with HRTs of 4.5 to 10 days. During the second trial, HRT was decreased to 0.8 days and NO3-N penetrated to the downgradient edge of the PRB at 1.8 mg/L. The behaviour of SO4 in the PRB was also affected by flow rate. SO4 entered the PRB at 60 to 71 mg/L during the first trial. Under a HRT of 10 days it was depleted to detection limit after traveling through only 13% of the barrier. When HRT was decreased to 4.5 days, SO4 was able to penetrate the downgradient edge of the PRB at concentrations from 4 to 6 mg/L. With a 0.8 day HRT SO4 reduction was highly restricted as calculations showed 90% of available carbon in the PRB was being used to reduce NO3-N, compared to 7.5% being used for SO4 reduction at that time. In comparison, at the 10 day HRT, 61% of carbon being used for NO3-N reduction, 8.7% for SO4 reduction, 0.7 for dissolved oxygen and 29% was lost through DOC leaching. These calculations suggest that barrier efficiency can be greatly enhanced by manipulation of HRT through use of tile drains.

Abstract Permeable reactive barrier technology is a cost effective means of treating near surface groundwater contaminant plumes. However, current reactive barrier technology lacks the capacity to manipulate flow rates and thus hydraulic retention time (HRT) within the barriers in order to maximize the effectiveness and longevity of the media. This study examines the effectiveness of tile drains as passive controls on the flow rate of ground-water through an existing wood particle media permeable reactive barrier treating agricultural nitrate. The use of upgradient and downgradient tile drains allowed HRT to be increased from 4.5 to 10 days in one trial and then to be decreased from 11.1 to 0.8 days in a second trial. Influent groundwater NO3-N concentrations of ~100 mg/L were attenuated to detection limit (0.02 mg/L) only 12% of the 4 m long barrier with HRTs of 4.5 to 10 days. During the second trial, HRT was decreased to 0.8 days and NO3-N penetrated to the downgradient edge of the PRB at 1.8 mg/L. The behaviour of SO4 in the PRB was also affected by flow rate. SO4 entered the PRB at 60 to 71 mg/L during the first trial. Under a HRT of 10 days it was depleted to detection limit after traveling through only 13% of the barrier. When HRT was decreased to 4.5 days, SO4 was able to penetrate the downgradient edge of the PRB at concentrations from 4 to 6 mg/L. With a 0.8 day HRT SO4 reduction was highly restricted as calculations showed 90% of available carbon in the PRB was being used to reduce NO3-N, compared to 7.5% being used for SO4 reduction at that time. In comparison, at the 10 day HRT, 61% of carbon being used for NO3-N reduction, 8.7% for SO4 reduction, 0.7 for dissolved oxygen and 29% was lost through DOC leaching. These calculations suggest that barrier efficiency can be greatly enhanced by manipulation of HRT through use of tile drains.

The ultimate objective of this research is to investigate the effectiveness of cathode gas (air) recirculation for the thermal management of a solid oxide fuel cell (SOFC) stack. SOFCs conventionally operate at high temperatures (>600o C); and recovering heat from stack exhaust is critical to improving the stack and system performance. Prevalent approaches implement bulky and expensive high temperature gas-to-gas heat exchangers. Also, ejectors are being investigated for recirculation of the air; however, an ejector with typically large velocity gradients would incur large viscous losses. An alternative recirculation approach is being developed for distributed entrainment via active flow control. The entrainment would allow recuperative thermal mixing to occur that may be more effective than the preceding two approaches. The ultimate goal of this research thrust is to reduce, or even exclude, the need of an air preheater in a SOFC system. The cathode air preheat contributes to a large portion of the cost of a SOFC system. Verifying and demonstrating the efficacy of the Coand and #259; effect has been the initial focus, and positive results have been demonstrated in a test environment from a fluid mechanics standpoint. This has been based upon three stages of experimental development, inclusive of cross-sectional area and activated blowing degrees-of-freedom. Seed thermal testing of the system has demonstrated legitimate thermal mixing capabilities. EES thermodynamic modeling developments confirm that the approach can reduce or even exclude the air preheat. It is concluded that recuperative thermal mixing with this recirculation approach is indeed feasible and has the potential to greatly reduce the cost and efficiency of the SOFC system.