Flow control is an area of research of particular interest within automotive and aerospace industries since methods used to affect the fluid flow around vehicles can reduce drag and therefore lower their fuel consumption. One of these methods, which has generated a lot of interest in later years, is called active flow control and uses different types of actuators to impact the surrounding flow. In this thesis a model of a piezoelectric actuator for active flow control has been developed using Lumped Element Modelling and equivalent circuits. This approach, together with the chosen software for implementation, Simulink, provides models which are easy to simulate and evaluate. The actuator model has been validated using a novel methodology with sub-models with the purpose of reducing computational costs. The actuator is therefore divided into two submodels,one for structural and one for fluid dynamics, which are validated separately. This enables the use of simple yet accurate FEM and CFD models instead of time consuming FSI software which the complete model requires. The three implemented models have been validated using cases presented in previous studies and data from CFD-simulations. The results show that the decoupled models can be validated separately and its results can be integrated into the complete model, although further tests with a real actuator is needed. In addition to the modelling, a parameter study of the actuator has been performed in order to prepare for prototype design.

Active flow control of a precessing jet is the focus of this work. A round jet confined by a round cavity exhibits a self-excited rotational motion, precession, for a specific range of cavity lengths. Active flow control of this unstable flow provides the ability to control near-field mixing of the precessing jet. Twelve micro-jets on the periphery of the nozzle inlet are used as actuation and near-field pressure data is measured by four pressure probes at the chamber exit to monitor the flow behavior. A phase plane, based on pressure signals, is used to find a Reynolds number and actuation frequency range where actuation stabilizes the flow motion. Phase-locked stereoscopic PIV is also used to validate the pressure processing tool. The results confirm the pressure measurement and micro-jet actuation can be employed to develop a future closed-loop flow control on a precessing jet.

A new experimental setup for studies on wake flow instability and its control that successfully has been designed and manufactured, is introduced and de- scribed. The main body is a dual-sided flat plate with an elliptic leading edge and a blunt trailing edge. Permeable surfaces enable boundary layer suction and/or blowing that introduce the unique feature of adjusting the inlet condition of the wake created behind the plate. This, in combination with a trailing edge that is easily modified, makes it an ideal experiment for studies of different control methods for the wake flow instability as well as extensive parameter studies. Experimental validation of the setup has been performed by means of measurements of the wake symmetry and boundary layer velocity profiles at the trailing edge. Some preliminary results on the Strouhal number versus different inlet conditions are reported. Additionally, an in-house vortex detection (VD) program has been developed in order to detect, analyse and compare small-scale vortical structures in instantaneous velocity fields from flow measurements. This will be a powerful tool for comparison of wake characteristics for varying inlet conditions and control methods in the new experimental setup. Measurements from three completely separate experimental setups with different geometries and flow cases, have been analysed by the VD-program.          i.     In order to obtain improved ventilation we have studied the effect of pulsating inflow into a closed volume compared to having the inflow at a constant flow rate. We show that the number of small-scale eddies is significantly increased and that the stagnation zones are reduced in size, which enhances the mixing.         ii.     Instantaneous velocity fields in the wake behind a porous cylinder subjected to suction or blowing through the entire cylinder surface have also been analysed using the VD-program. The results show that the major change for different levels of blowing or suction is the location of vortices while the most common vortex size and strength are essentially unchanged.        iii.     Another study on how the geometry of a V-shaped mixer in a pipe flow affects the mixing have also been examined, where no general differences were found between different thicknesses, why a thickness that is favourable from an acoustic point of view can be chosen.   We also propose a new method, using global mode analysis on experimental data, showing that randomly ordered snapshots of the velocity field behind the porous cylinder can be re-ordered and phase-averaged. / QC 20111108 / Active control of vortex shedding behind bluff bodies

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.

This study involved experimental and equivalent computational investigations into the automobile-type 3―D flow physics of a diffuser bluff body in ground-effect and novel passive flow-control methods applied to the diffuser flow to enhance the diffuser’s aerodynamic performance. The bluff body used in this study is an Ahmed-like body employed in an inverted position with the slanted section together with the addition of side plates along both sides forming the ramped diffuser section. The first part of the study confirmed reported observations from previous studies that the downforce generated by the diffuser in proximity to a ground plane is influenced by the peak suction at the diffuser inlet and subsequent static pressure-recovery towards the diffuser exit. Also, when the bluff body ride height is gradually reduced from high to low, the diffuser flow as indicated by its force curve and surface flow features undergoes four distinct flow regimes (types A to D). The types A and B regimes are reasonably symmetrical, made up of two low-pressure core longitudinal vortices travelling along both sides of the diffuser length and they increase downforce and drag with reducing ride height. However, below the ride heights of the type B regime, types C and D regimes are asymmetrical because of the breakdown of one vortex; consequently a significant loss in downforce and drag occurs. The second part of the study involved the use ― near the diffuser exit ― of a convex bump on the diffuser ramp surface and an inverted wing between the diffuser side plates as passive flow control devices. The modification of the diffuser geometry with these devices employed individually or in combination, induced a second-stage pressure-drop and recovery near the diffuser exit. This behaviour was due to the radial pressure gradient induced on the diffuser flow by the suction surface ii curvature of the passive devices. As a result of this aerodynamic phenomenon, the diffuser generated across the flow regimes additional downforce, and a marginal increase in drag due to the profile drag induced by the devices.

Shock control bumps (SCBs) are considered promising flow control devices for transonic commercial aircraft. By generating a λ-shock structure, 2D SCBs offer large drag savings, but perform poorly when that structure breaks down off-design. Milder-performing 3D devices produce weak vortices, that may offer some boundary layer control, and SCBs also affect buffet via direct impact on shock motions and separation. To date however, design studies have largely ignored complications from the swept, spanwise-varying flows, so this thesis tackles the question of whether SCB arrays can offer useful benefits to the performance of transonic commercial aircraft. Using a numerical infinite-wing model, a simple rotation adaptation is shown to redress deficient on-design drag performance of 3D SCBs under swept flows. With the correct rotation (dependent on height, planform and spacing) bumps follow performance-design trends similar to those in unswept flow. With this knowledge, an array design method is developed to tailor 2D and 3D devices to local flow conditions on an aircraft model, aiming to maximise on-design drag performance. Careful infinite-wing setup means the influence of rotation and array height on performance is replicated on the aircraft. Predicted array designs achieve 74-87% of their estimated local drag savings. However, with wave drag being a smaller percentage of the total, the influence of arrays on lift is more significant and makes the optimal designs shorter than predicted. Strategies for improving off-design drag performance are then evaluated. Stagger, an alternating chordwise translation applied to 3D arrays, broadens operating range and lowers drag penalties by better accommodating off-design shock movements, but offers a less favourable trade-off against on-design drag than simply reducing the array height. However, a 2D array can always outperform a 3D on drag objectives. Lastly, buffet performance is inferred using steady indicators based on trailing edge pressure and shock location. These disagree regarding the impact on buffet onset, unresolvably due to a lack of validation data, but agree that arrays could alleviate flow development post-onset. Optimal array designs depend on prioritised objectives: considering buffet severity and on-design drag, tall 2D (or 3D) arrays; for buffet and minimum off-design drag penalties (similar to the motivation behind vortex generator application), 3D arrays of varying height and stagger. A simple flight fuel consumption model utilising the computed drag data shows that many arrays are neutral or offer small savings (up to 0.3%) across a range of mission profiles. While likely too small to merit application for solely drag purposes, this implies buffet benefits without cost to efficiency. Unsteady tests and proper assessment of buffet onset are needed to confirm this.

Les écoulements décollés sont omniprésents dans la nature comme dans les écoulements industriels (aérodynamique externe des véhicules, des bâtiments, écoulements autour d’aubes de turbines, aérodynamique interne dans des tuyaux...) où ils sont en général sources de nuisances (vibrations, bruit aéroacousitque, forces de traînée ou de portance). Les enjeux associés à la compréhension et à la maîtrise de tels écoulements, caractérisés par une bulle de recirculation, sont donc considérables.Un capteur "visuel" non invasif développé au laboratoire PMMH est d'abord amélioré afin d'accéder en temps réel aux champs de vitesses - et à leurs grandeurs dérivées - des écoulements rencontrés en soufflerie industrielle. Basé sur un algorithme de flot optique issu de la vision par ordinateur, cette approche expérimentale novatrice permet de faciliter les études paramétriques et peut être implémenté dans des boucles de contrôle réactif.Ensuite, les mesures obtenues pour un écoulement sur une plaque plane sont analysées dans le cadre de l'identification de système. Un modèle d’ordre réduit est alors construit par apprentissage, permettant de prédire la dynamique de la transition de la couche limite laminaire vers la turbulence.Enfin, le sillage pleinement turbulent derrière une géométrie modélisant une voiture simplifiée est caractérisé, de façon classique et en tant que système dynamique. Différentes modifications de l'écoulement à l'aide de micro-jets sont testées. Une loi de contrôle réactif consistant à suivre et forcer la recirculation est mise en œuvre avec succès. / Separated flows are ubiquitous in nature and industrial systems, such as diffusers, airfoils, air conditioning plants, moving vehicles... As the separation can strongly influence the performances of such devices, investigating their dynamics and their control is of great interest.A visual sensor developed at PMMH laboratory is first improved to measure in real time the velocity fields and its derived values for flows available in wind tunnels. Based on an optical flow algorithm from the computer vision domain, this new experimental approach makes easier parametric studies and may be used in closed-loop controls.The dynamics of the flow over a flat plate are then investigated. A system identification method - the dynamic observer - is successfully implemented to build a reduced-order model of the transient flow, which captures and predicts well the instabilities generated.Finally, the fully turbulent wake of the square-back Ahmed body is described. Dynamical system tools are applied to characterize it. Using continuous and pulsed micro-jets, different forcing strategies are analyzed. An opposition closed-loop control is implemented, tracking and driving the recirculation.

Made available in DSpace on 2014-06-11T19:31:36Z (GMT). No. of bitstreams: 0 Previous issue date: 2003Bitstream added on 2014-06-13T21:02:55Z : No. of bitstreams: 1 carvalho_wpa_dr_botfca.pdf: 2182270 bytes, checksum: b0a113bf2a899d4f009e726458c0469f (MD5) / A aplicação de defensivos é uma das etapas mais importantes do processo de produção agrícola. O sucesso da atividade depende de diversos parâmetros, entre os quais destaca-se o volume de aplicação, o qual depende diretamente da velocidade de deslocamento do pulverizador. Nos sistemas convencionais, o operador precisa manter a velocidade constante para garantir uniformidade de volume aplicado ao longo da faixa. Visando maior acurácia na definição da dose aplicada e melhor qualidade geral da aplicação, os sistemas controlados eletronicamente permitem o ajuste automático do volume aplicado ao longo da área quando ocorre variação da velocidade durante a aplicação. Os objetivos do presente trabalho foram desenvolver metodologia para avaliação do desempenho de sistemas controladores de fluxo ligados a DGPS e avaliar o desempenho de um controlador de fluxo Satloc Airstar 99.5 em condições de campo e de laboratório. Para tanto foram avaliados os seguintes parâmetros: acurácia de determinação de velocidade para deslocamentos em curvas e linha reta; tempo de resposta a mudanças de velocidade; tempo de resposta a mudanças de intensidade de bombeamento e acurácia na determinação do fluxo de calda. Nos ensaios de laboratório foi utilizado um sistema de simulação dos sinais de DGPS para possibilitar o uso estático do equipamento. Nas etapas de campo e de laboratório, os valores registrados pelo controlador de fluxo foram confrontados com dados coletados através de um sensor de pressão acoplado a um coletor de dados. Os resultados mostraram que o sistema estudado possui acurácia adequada para a determinação da velocidade de deslocamento quando comparado ao radar e a cronometragem manual, pois não houve diferença estatisticamente significativa nos valores indicados entre as metodologias, tanto para deslocamento em retas como em curvas... . / Chemical application is one of the most important parts of the agricultural production process. The success of this activity depends on several parameters, including the total volume rate, which is directly related to the forward speed. On conventional systems the operator needs to keep constant speed in order to guaranty volume rate uniformity across the field. Aiming more accuracy and general quality of the application, electronic control systems allows automatic flow control against changes on forward speed. The objectives of this work were to develop methods for evaluation of flow control systems linked to DGPS and to analyze the performance of a Satloc Airstar 99.5 flow control system on laboratory and field conditions. The following parameters were evaluated: accuracy of speed measurement on curves and strait line movements; time response for changes on forward speed and pump speed; accuracy on flow rate measurement. Laboratory tests were performed using DGPS simulation software. On laboratory and field tests the flow data from the Airstar 99.5 were compared to data acquired using a pressure sensor and a data logger system. The results showed that the system was accurate to determine forward speed compared to radar and time measurement because there was no statistically significant difference for both strait lines and curves. Time response for changes on forward speed was in average between 6 and 20 seconds. Changes on the total flow rate and on the adjustment of the control algorithm constant had influence on the time response and there were cases of interaction between those factors. There was a tendency of better results on time response using a constant for the control algorithm different from the one indicated by the manufacturer. The average error was bellow 2% in all the operational conditions giving good accuracy on the flow rate definition. In terms of methodology all the procedures developed for this work can be considered adequate.

Orientador: Ulisses Rocha Antuniassi / Resumo: A aplicação de defensivos é uma das etapas mais importantes do processo de produção agrícola. O sucesso da atividade depende de diversos parâmetros, entre os quais destaca-se o volume de aplicação, o qual depende diretamente da velocidade de deslocamento do pulverizador. Nos sistemas convencionais, o operador precisa manter a velocidade constante para garantir uniformidade de volume aplicado ao longo da faixa. Visando maior acurácia na definição da dose aplicada e melhor qualidade geral da aplicação, os sistemas controlados eletronicamente permitem o ajuste automático do volume aplicado ao longo da área quando ocorre variação da velocidade durante a aplicação. Os objetivos do presente trabalho foram desenvolver metodologia para avaliação do desempenho de sistemas controladores de fluxo ligados a DGPS e avaliar o desempenho de um controlador de fluxo Satloc Airstar 99.5 em condições de campo e de laboratório. Para tanto foram avaliados os seguintes parâmetros: acurácia de determinação de velocidade para deslocamentos em curvas e linha reta; tempo de resposta a mudanças de velocidade; tempo de resposta a mudanças de intensidade de bombeamento e acurácia na determinação do fluxo de calda. Nos ensaios de laboratório foi utilizado um sistema de simulação dos sinais de DGPS para possibilitar o uso estático do equipamento. Nas etapas de campo e de laboratório, os valores registrados pelo controlador de fluxo foram confrontados com dados coletados através de um sensor de pressão acoplado a um coletor de dados. Os resultados mostraram que o sistema estudado possui acurácia adequada para a determinação da velocidade de deslocamento quando comparado ao radar e a cronometragem manual, pois não houve diferença estatisticamente significativa nos valores indicados entre as metodologias, tanto para deslocamento em retas como em curvas... (Resumo completo, clicar acesso eletrônico abaixo). / Abstract: Chemical application is one of the most important parts of the agricultural production process. The success of this activity depends on several parameters, including the total volume rate, which is directly related to the forward speed. On conventional systems the operator needs to keep constant speed in order to guaranty volume rate uniformity across the field. Aiming more accuracy and general quality of the application, electronic control systems allows automatic flow control against changes on forward speed. The objectives of this work were to develop methods for evaluation of flow control systems linked to DGPS and to analyze the performance of a Satloc Airstar 99.5 flow control system on laboratory and field conditions. The following parameters were evaluated: accuracy of speed measurement on curves and strait line movements; time response for changes on forward speed and pump speed; accuracy on flow rate measurement. Laboratory tests were performed using DGPS simulation software. On laboratory and field tests the flow data from the Airstar 99.5 were compared to data acquired using a pressure sensor and a data logger system. The results showed that the system was accurate to determine forward speed compared to radar and time measurement because there was no statistically significant difference for both strait lines and curves. Time response for changes on forward speed was in average between 6 and 20 seconds. Changes on the total flow rate and on the adjustment of the control algorithm constant had influence on the time response and there were cases of interaction between those factors. There was a tendency of better results on time response using a constant for the control algorithm different from the one indicated by the manufacturer. The average error was bellow 2% in all the operational conditions giving good accuracy on the flow rate definition. In terms of methodology all the procedures developed for this work can be considered adequate. / Doutor

L'amélioration de la performance des turbomachines fonctionnant loin de leur point d'adaptation passe par la maîtrise des phénomènes instationnaires qui se produisent dans ces différents organes. L'étude présentée ici se concentre sur les interactions entre une roue de ventilateur centrifuge et son diffuseur. Elle vise, par des mesures de pression sur les différentes parois du diffuseur, ainsi que par des sondages dans les canaux inter-aubages à analyser finement ces phénomènes instationnaires et notamment les décollements fluctuants apparaissant sur les aubes à sur débit, et à mesurer leur influence sur la performance du diffuseur. Dans un second temps, un dispositif de contrôle passif de ces décollements utilisant des générateurs de vortex est proposé. Plusieurs configurations sont testés et leurs résultats sont comparés / The performance improvement of turbomachinery operating at off-design conditions can be achieved by the understanding of unsteady phenomena which are occuring in its components. The present study is focussing on the interaction between a centrifugal impeller fan and its vaned diffuser. It aims at analysing precisely these unsteady phenomena (and especially the fluctuating separated region identified on the vanes wall) and their consequences on the diffuser performance by three holes probe and unsteady pressure measurements. In a second step, devices for a passive control of the separation are introduced. Several configurations are tested and their results are compared