O objetivo desta pesquisa é o estudo do uso potencial de multi-winglets adaptativas para obter reduções no arrasto induzido através da variação do diedro das winglets. Os vórtices gerados nas pontas das asas são um produto inevitável da presença da sustentação, ou seja, é um custo a pagar pela força que mantém as aeronaves no ar. Diferentes estudos têm demonstrado que o escoamento presente nas pontas das asas pode ser redirecionado usando pequenas superfícies aerodinâmicas reduzindo assim o arrasto induzido. O modelo testado era constituído por uma asa retangular construída a partir de um perfil NACA 653 - 018 dotado de três winglets tipo \"tip-sails\", que são pequenas asas sem enflechamento ao 25% da corda. Os testes realizados foram para um regime de Número de Reynolds de 357.000. Os resultados foram analisados através da análise da sustentação, arrasto e mapeamento da esteira através da técnica de anemometria de fio quente. / The aim of this research is the study of the potential use of adaptive multi-winglets to reduce induced drag through variations of winglet cant angles. The vortices generated at the wing tips are an inevitable product of the presence of lift, that is, they represent the price paid for the presence for the force that keeps the aircraft in the air. Different studies have shown that the flow over the wing-tip can be redirected using small aerodynamics surfaces, thereby reducing the induced drag. The model tested is composed of a rectangular wing using a NACA 653 - 018 profile with three winglets called \"tip-sails\", which are small wings without sweep at 25% chord. The tests were made at a Reynolds number of 350,000. The results are analyzed in terms of lift and drag and mapping of the wake using hot wire anemometry techniques.

Orientador: Edvaldo Sabadini / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-23T10:56:52Z (GMT). No. of bitstreams: 1 Strauss_DarleneLuziaFelix_M.pdf: 3817957 bytes, checksum: 2557a153a7468c4a1f482e242b50bfea (MD5) Previous issue date: 2013 / Resumo: É conhecido que surfactantes agregam-se através de interações hidrofóbicas, formando espontaneamente estruturas supramoleculares em solução aquosa. A formação destas macroestruturas pode alterar significativamente a viscoelasticidade da solução. Essas estruturas diferem dos polímeros por serem sistemas que estão num processo constante de quebra e recombinação numa escala finita de tempo que é dependente das propriedades físico-químicas dos sistemas. Foram estudados os efeitos do cisalhamento intenso de soluções aquosas de micelas gigantes formadas pela combinação de CTAB com salicilato de sódio em diferentes concentrações do co-soluto (NaSal). Os experimentos foram realizados em um reômetro, sendo que a estabilidade térmica das micelas gigantes foi avaliada usando a propriedade deste sistema supramolecular em produzir significativas reduções de atrito hidrodinâmico. Três temperaturas características foram observadas, T0, T1 e T2, que são atribuídas respectivamente à fusão de cadeias, ruptura dos pontos de fusão e quebra das micelas em menores fragmentos. A concentração de co-soluto afeta diretamente a estabilidade térmica das soluções, quanto maior a razão co-soluto/surfactante maior a temperatura de quebra das micelas (T2). Outro fator importante é a taxa de cisalhamento, pois até certo limite, quanto maior a taxa de cisalhamento maior a T2. Foi estudado também o comportamento de estruturas induzidas por cisalhamento (SIS), que é uma propriedade característica desses sistemas, utilizando o reômetro, em que se aplicou um cisalhamento intenso e depois se monitorou o comportamento de relaxação das estruturas formadas durante o cisalhamento. Para entender melhor este comportamento foi realizado um estudo cinético em função da temperatura para verificar a cinética de relaxação das mesmas às estruturas iniciais. A temperatura tem grande influência sobre a manutenção das estruturas induzidas por cisalhamento, pois quanto maior a temperatura aplicada ao sistema mais rápida e a volta à estrutura inicial. Assim, o Modelo de Arrhenius foi aplicado para determinar a energia de ativação de uma das etapas / Abstract: It is known that surfactants spontaneously self-assemble through hydrophobic interactions in aqueous solutions generating supramolecular structures. The formation of these macrostructures can modify significantly the solution viscoelasticity. These structures differ from polymers because these systems are in a constant break and recombination process in a limited time scale dependent of its physical-chemistry properties. The effects of intense shear on aqueous solution of wormlike micelles formed by CTAB and sodium salicylate combination in different co-solute (NaSal) concentrations were studied. The experiments were performed in a rheometer, where the thermal stability of worm-like micelles was evaluated applying drag reduction studies that is a particular property of this supramolecular system. Three characteristic temperatures are observed, T0, T1 e T2, that correspond respectively to the chains fusion, break of fusion points and micelles break into minor fragments. The co-solute concentration directly affects the solutions thermal stability, as higher the co-solute/surfactant ratio as higher the micelles break temperature (T2). Other important factor is the shear rate, until certain limit, the higher the shear rates the higher T2. The behavior of shear induced structures (SIS), that is a characteristic property of these systems, was also studied using the rheometer where an intense shear was applied and then the relaxation behavior of the formed structures was monitored under shear. For better understanding of this behavior, a kinetic study as a function of the temperature was accomplished to verify the relaxation kinetics of the SIS to the initial structures. The temperature has a critical influence under the maintenance of shear induced structures, because the higher the temperature applied at the system the faster the return to the initial structures. Thus, Arrhenius model was applied to determine the activation energy from one of the steps / Mestrado / Físico-Química / Mestra em Química

Orientadores: Edvaldo Sabadini, Marcelo G. de Oliveira / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-04T14:22:34Z (GMT). No. of bitstreams: 1 Alkschbirs_MelissaInger_D.pdf: 20703558 bytes, checksum: 093e76dc07818947b87478f9a799ad47 (MD5) Previous issue date: 2004 / Resumo: O efeito da redução de atrito hidrodinâmico em soluções poliméricas nas estruturas produzidas pelo impacto de gotas foi determinado por meio da análise de imagens obtidas utilizando uma câmera CCD e um programa de tratamento de imagens. O impacto de uma gota contra uma superficie líquida causa o fenômeno conhecido como splash, onde duas principais estruturas são formadas: a coroa e o jato Rayleigh. A altura máxima atingida pelo jato Rayleigh foi utilizada como parâmetro para determinar a redução de atrito hidrodinâmico, proporcionada pela presença de pequenas quantidades (ppm) de polímeros de elevada massa molar presentes em solução. A capacidade redutora de atrito hidrodinâmico do poli( óxido de etileno ), PEO, o mais eficiente agente redutor de atrito, foi estudada em função da qualidade do solvente, da temperatura, da concentração, da massa molar e da flexibilidade intrínsica da cadeia polimérica. As modificações decorrentes de alguns destes fatores sobre o raio de giração do polímero e, conseqüentemente sobre o tempo de relaxação e a viscosidade elongacional, são responsáveis pelas modificações morfológicas observadas no jato Rayleigh. Estudos temporais da evolução do splash também foram desenvolvidos, onde se procurou correlacionar a taxa de deformação do líquido com o tempo de relaxação da cadeia polimérica. O presente trabalho mostra, de forma inédita, que é possível utilizar o splash nos estudos sobre a redução de atrito hidrodinâmico / Abstract: The presence of very small amounts (ppm) of high-molecular weight polymers in a solution produces high levels of drag reduction in a turbulent flow. This phenomenon, termed as the Toms Effect, was studied using images of the impact of a small drop against shallows liquid surfaces, both liquids containing a drag reducer agent. After the impact a crown and a cavity are created and the collapse of these structures impels a liquid column, named as Rayleigh jet. This phenomenon is termed splash. The amplitude reached by the Rayleigh jet was used to estimate the energy of the drop stored in the liquid; therefore, the maximum height of the jet allow us to determine the percentage of drag reduction. The results were discussed in terms of different parameters such as polymer concentration, molecular weight in the poly(ethylene oxide), PEO, the most efficient drag reducer agent in aqueous system. The splash in aqueous polymeric solution is dominated by the elongational viscosity and therefore, the polymer relaxation time has an important role in the process. We consider that the main contribution of this work to the drag reduction field is the new approach proposed to investigate this old hydrodynamic phenomenon / Doutorado / Físico-Química / Doutor em Quimica

Studiens syfte är att undersöka attityder till, samt användande av, dialektalt språkbruk bland studenter i olika årskurser på en språkinriktad högskoleutbildning. Undersökningen genomförs med en direkt metod i form av en enkätstudie. Resultatet visar att informanterna svarar enligt samma mönster men med lite olika värden på skalorna, vilket överensstämmer med tidigare forskning. Åk 1 är mer positiva till sin dialekt men visar mindre skillnader i sitt språkbruk i olika situationer och sällskap. Åk 3 visar en antydan till att vara neutrala till sin dialekt men visar även indikationer på en större variation av sitt språkbruk. Slutsatsen är att det inte finns påtagliga skillnader men att åk 3 visar tecken på en större medvetenhet om sitt språkbruk, sannolikt för att de har studerat längre på högskolan.

L'estimation précise de la traînée est aujourd'hui un enjeu majeur pour les avionneurs. Il est nécessaire d'identifier et de quantifier ses sources phénoménologiques dans le cadre d'un processus de design efficace. Les méthodes champ lointain, qui permettent une telle décomposition, sont cependant limitées aux applications stationnaires.Cette étude consiste à développer une méthode d'extraction champ lointain destinée à permettre une décomposition phénoménologique de la traînée pour des écoulements instationnaires. La première étape a consisté à généraliser la formulation stationnaire de Van der Vooren aux écoulements instationnaires. Des axes pour l'amélioration de la robustesse et du contenu physique ont ensuite été explorés, avec la mise en évidence de phénomènes acoustiques. La formulation ainsi obtenue a ensuite été appliquée à des cas tests simples, dans le but de valider la décomposition phénoménologique. Le comportement des composantes de traînée s'est avéré cohérent avec la physique de l'écoulement. Enfin, la méthode a été appliquée à des cas complexes afin de démontrer ses capacités : un cas instationnaire 3D ainsi qu'un écoulement simulé en ZDES.Dans l'avenir, il serait intéressant de continuer à explorer la définition de la composante de traînée induite, par exemple en utilisant les formulations basées sur le vecteur vitesse. En ce qui concerne les cas d'application, l'évaluation de la performance d'un doublet d'hélices contra-rotatives pourrait fortement bénéficier de l'utilisation d'une méthode comme celle-ci. Enfin, des applications en vol d'ailes battantes pourraient être d'intéressantes perspectives. / Accurate drag prediction is now of a major issue for aircraft designers. Its phenomenological sources need to be identified and quantified for an efficient design process. Far-field methods, which allow such phenomenological drag breakdown, are however restricted to steady flows. This study consists in developing a far-field drag prediction method aiming at a phenomenological breakdown of drag for unsteady flows. The first step has consisted in generalizing the steady formulation of Van der Vooren to unsteady flows, starting from a new rigorous proof. Axes for the improvement of the robustness and physical background have then been explored. Acoustic contributions have in particular been highlighted and quantified. The resulting five-components formulation has then been applied to simple cases, in order to validate as best as possible the phenomenological breakdown. The behavior of the drag components has proved to be consistent with the physics of the flow. Finally, the method has been applied to complex cases in order to demonstrate its capabilities: a 3-D case and a flow simulated by the ZDES method. In the future, it would be interesting to further improve the definition of the induced drag component, for example by using velocity-based formulations. As far as the application cases are concerned, the performance evaluation of a Counter-Rotating-Open-Rotor would strongly benefit from such a method. Unsteady optimization of one of the drag component could also be contemplated. Finally, applications in aeroelasticity or flapping flight would be an interesting perspective.

The remarkable efficacy with which normal surface mass transpiration (blowing and suction) alters a given base flow to achieve a desired predefined objective has motivated several investigations on drag reduction, self-propulsion and suppression of separation and wake unsteadiness in bluff body flows. However, the energetic efficiency, a critical parameter that determines the true efficacy and in particular practical feasibility of this control strategy, has received significantly less attention. In this work, we determine the optimal zero net mass transpiration blowing and suction profiles that minimize net power consumption while reducing drag or enabling self-propulsion in typical bluff body flows. We establish the influence of prescribed blowing and suction profiles on the hydrodynamic loads and net power consumption for a representative bluff body flow involving flow past a stationary two-dimensional circular cylinder. Using analysis based on Oseen’s equations, we find that all the symmetric modes, except the first one, lead to an increase in the net power consumption without affecting hydrodynamic drag. The optimal blowing and suction profile that yields minimum power consumption is such that the normal stress acting on the cylinder surface vanishes identically. Furthermore, we show that a self-propelling state corresponding to zero net drag force is attained when the first mode of blowing and suction profile is such that the flow field be-comes irrigational. Based on these findings we employ direct numerical simulation tools to decipher the Reynolds number dependence of the optimal profiles and the associated power consumption for both drag reduction and self-propulsion. For a typical Reynolds number, the time-averaged drag coefficient first decreases due to vortex shedding suppression, then increases and eventually decreases again after attaining a local maximum as the strength of the first mode is increased. The net power consumption continues to decrease with an increase in the strength of the first mode before reaching a minima after which it rises continuously. For a Reynolds number of 1000 over fifteen fold reduction in drag is achieved for an optimal blowing and suction profile with a maximum radial surface velocity that is nearly 1.97 times the free stream velocity. Next, to establish whether or not higher modes play a role in decreasing net power consumption at finite Reynolds number, we perform theoretical analysis of a configuration similar to the one described above for a spherical body. At zero Reynolds number, as a result of mode independence, we show that surface blow-ing and suction of any form that involves second or higher order axisymmetric or non-axisymmetric modes does not contribute to drag and only leads to an increase in total power consumption. However, at finite Reynolds number, using analysis based on Oseen’s equations, we find that the second and higher modes contribute substantially to the optimal profiles. Finally to understand the effects of a change in shape we consider generalization of the above analysis to axisymmetric prolate and oblate spheroidal bodies. We find that for a general axisymmetric body with non-constant curvature, the optimal drag reducing and self-propelling blowing and suction profiles for minimum power consumption contain second and higher-order modes along with the first mode even when the Reynolds number is zero. The net decrease in power consumption with the use of second and higher order modes exceeds 33% for a disk-like low aspect ratio self-propelling oblate spheroid. Moreover, we perform comparisons between blowing and suction and tangential surface velocity based boundary deformation propulsion mechanisms. Below an aspect ratio of 0.56 we find blowing and suction mechanism to be more efficient for self-propulsion of an oblate spheroid. In contrast, for a self-propelling pro-late spherical micro-swimmer, we show that the tangential surface tread milling consumes less power irrespective of the aspect ratio.

The increasing nationwide interest in intelligent transportation systems (ITS) and the need for more efficient transportation have led to the expanding use of variable message sign (VMS) technology. VMS panels are substantially heavier than flat panel aluminum signs and have a larger depth (dimension parallel to the direction of traffic). The additional weight and depth can have a significant effect on the aerodynamic forces and inertial loads transmitted to the support structure. The wind induced drag forces and the response of VMS structures is not well understood. Minimum design requirements for VMS structures are contained in the American Association of State Highway Transportation Officials Standard Specification for Structural Support for Highway Signs, Luminaires, and Traffic Signals (AASHTO Specification). However the Specification does not take into account the prismatic geometry of VMS and the complex interaction of the applied aerodynamic forces to the support structure. In view of the lack of code guidance and the limited number research performed so far, targeted experimentation and large scale testing was conducted at the Florida International University (FIU) Wall of Wind (WOW) to provide reliable drag coefficients and investigate the aerodynamic instability of VMS. A comprehensive range of VMS geometries was tested in turbulence representative of the high frequency end of the spectrum in a simulated suburban atmospheric boundary layer. The mean normal, lateral and vertical lift force coefficients, in addition to the twisting moment coefficient and eccentricity ratio, were determined using the measured data for each model. Wind tunnel testing confirmed that drag on a prismatic VMS is smaller than the 1.7 suggested value in the current AASHTO Specification (2013). An alternative to the AASHTO Specification code value is presented in the form of a design matrix. Testing and analysis also indicated that vortex shedding oscillations and galloping instability could be significant for VMS signs with a large depth ratio attached to a structure with a low natural frequency. The effect of corner modification was investigated by testing models with chamfered and rounded corners. Results demonstrated an additional decrease in the drag coefficient but a possible Reynolds number dependency for the rounded corner configuration.

Classical approaches to evaluate the stability of large woody debris (LWD) introduced in streams for habitat restoration or flood management purposes are usually based on inappropriate assumptions and hydraulic equations. Results suggest that the physics of small cylindrical elements located in large channels cannot be transferred to the case of a large roughness elements placed in small channels. The introduction of LWD in a small channel can generate a significant modification of the upstream hydraulic conditions. This modification has direct implications on the stability of the LWD. Experiments were performed in a controlled environment: a small stream section was represented by a low roughness rectangular flume and LWD were modeled with smooth PVC cylinders. Direct force measurements were performed with a load cell and results were used to identify an equation that evaluates the drag force acting on a large cylindrical element place in a rectangular channel. This equation does not depend on a drag coefficient. Water depths were also measured during the experiments and results were used to develop an approach that evaluates the upstream hydraulic impacts of a large cylinder introduced in a rectangular channel. The effect of the variation of the unit discharge (discharge per unit of width), cylinder size, cylinder elevation from the channel bed, and downstream hydraulic conditions, could be related to the upstream hydraulic conditions with relative success. Dimensionless parameters were developed to increase the versatility of the approach. The application of this approach to field cases is expected to require adjustments, mainly because of the roughness of natural environments differs from the smoothness of the controlled environment described in this work. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

Plasma actuators are devices which function by creating a discharge in air at atmospheric conditions. These devices have been demonstrated to effectively delay flow separation and enhance the lift- drag characteristics of wing sections. They have also been shown to have potential applications in controlling dynamic stall, flow separation control over turbine blades, flow vectoring, boundary layer manipulation and bluff body flow control. This study examines the characteristics of the plasma actuator, its working and the optimization of its configuration for its use as a lift enhancing device. A single actuator connected to a high-voltage, high-frequency power supply was studied in quiescent conditions. It was demonstrated by means of flow visualization experiments and hot-wire anemometry that the plasma actuator functions by inducing a flow, thus behaving as a source of momentum flux in any system that it is introduced into. Further, it was inferred that the flow induced is a wall jet and that the magnitude of the velocity achieved is maximum within a few millimeters of the surface of the actuator. A parametric investigation of the actuator was conducted next. The variation of the peak velocity induced in quiescent conditions with the variation of configuration parameters was studied by means of photographic studies and hot-wire anemometry. These experiments indicated that there is a strong correlation between the visible extent of the plasma along the direction of the induced _ow (plasma width) and the peak velocity achieved. The peak velocity achieved is found to increase with the increase in the plasma width as long as the discharge created is in the uniform glow discharge regime. The development of localized high intensity streamers, which destroy the uniformity of the plasma, lead to a loss in the peak velocity. Hot-wire tests indicated that the peak velocity increases with a decrease in the spanwise overlap of the electrodes, with the other parameters kept constant. Also, in the uniform glow discharge regime, the velocity increases with the increase in the thickness of the dielectric placed between the two electrodes. After a particular optimum thickness, further increase of the thickness leads to formation of streamers. The velocity increased with a decrease in streamwise overlap, with the maximum being reached for a overlap of approximately 2mm, after which it remained a constant. It was observed that the absence of overlap leads to a loss of uniformity of the discharge created. The velocity was found to be independent of the variations in the electrode widths. Particle Image Velocimetry (PIV) was conducted to study the characteristics of the jet produced. It was observed that when the actuator is switched on, a low pressure region is created near the surface of the actuator, vertically above it, leading to a flow towards this region from above the actuator. Furthermore, a vortex is shed, which is convected downstream, after which a wall jet is established close to the dielectric surface.

Recent tsunami disasters caused devastating damages to well-engineered coastal infrastructures. In fact, the current design guidelines are not able to provide realistic estimations of tsunami loads in order to design structures to withstand tsunamis. Tsunami hydrodynamic forces are estimated using the drag coefficient. This coefficient is traditionally calculated based on a steady flow analogy. However, tsunami bores behave like unsteady flows. The present work aims at investigating the tsunami forces for different structure geometries to provide realistic guidelines to estimate drag coefficients considering unsteady flows. In the present paper, the dam-break approach is used to investigate the tsunami-like bore interaction with structures. A three-dimensional multiphase numerical model is implemented to study the tsunami induced forces on rectangular shape structures with various aspect ratios (width/depth) and orientations. The numerical model results are validated using measured forces and bore surface elevations of the physical experiments. A scaled-up domain is modeled in order to eliminate the effects of domain sidewalls in the simulation results. The drag coefficient relations with structure geometries and bore depths are provided. The obtained hydrodynamic forces and drag coefficients are compared with existing data in the literature and design codes. For the second topic, a multi-phase three-dimensional numerical reproduction of a large scale laboratory experiment of tsunami-like bores interaction with a surface-piercing circular column is presented. The numerical simulation is conducted in OpenFOAM. The dam-break mechanism is implemented in order to generate tsunami-like bores. The numerical model is validated using the experimental results performed at Canadian Hydraulics Center of the National Research Council (NRC-CHC) in Ottawa. The unsteady Reynolds Averaged Navier-Stokes equations (RANS) are used in order to treat the turbulence effects. The Shear Stress Transport (SST) k-ω turbulence model showed high level of accuracy in replication of the bore-structure interaction. Further, a scaled-up domain is used to investigate the influence of the bed condition in terms of various downstream depths and roughness. Finally, a broad investigation on the bore propagation characteristics is performed. The resulting stream-wise forces exerted on the structural column as well as the bore velocity are compared and analyzed for smooth, rough, dry and wet beds with varying depths.