Calculation of the blade tip clearances of the high-pressure-compressor rotors in aeroengines involves calculating the radial growth of the corotating compressor discs. This requires the calculation of the thermal growth of the discs, which in turn requires a knowledge of the disc temperatures and Nusselt numbers for the buoyancy-induced flow in the cavity between the discs. This is a strongly conjugate problem in which the equations for the fluid flow and the disc temperature are coupled. In this thesis, the buoyancy-induced flow and heat transfer inside the compressor rotors is modelled assuming laminar Ekman-layer flow on the discs and compressible flow in the fluid core between the Ekman layers; conduction in the discs is modelled using a one-dimensional fin equation. The theoretical predictions are compared with Nusselt numbers and temperatures obtained from two independent sets of temperature measurements, obtained on a multi-cavity compressor rig, and the ‘experimental’ Nusselt numbers were calculated using a Bayesian model for the inverse solution of the fin equation. For most of the experimental cases, with Grashof numbers up to 1012, mainly good agreement was achieved between the theoretical predictions and experimental values of the disc temperatures and Nusselt numbers. As predicted by the model, increasing the rotational Reynolds number can, under certain conditions, cause a decrease in the Nusselt numbers. Importantly, the results suggest that laminar Ekman-layer flow could occur even at the high Grashof numbers found in the compressor rotors of aeroengines. An extension of the buoyancy model included empirical correlations for the Nusselt numbers for the compressor shroud and disc cobs. This extended model was used to predict the temperature rise of the axial throughflow of cooling air in the compressor rotor, and reasonable agreement was achieved between the predicted and measured throughflow temperatures. This is the first time a theoretical model (rather than CFD) has been used to predict the temperatures of a compressor disc and the axial throughflow, and the model takes only seconds to predict the temperatures that would take days or even weeks to predict using CFD. Some suggestions are made for future research to improve the extent and accuracy of the model.

The inboard-winglet concept was examined for its flow characteristics by testing for pressure coefficients over the wing and winglet surface in the Virginia Tech Stability Wind Tunnel over a range of freestream velocity and angle of attack. The results were analytically applied to calculate aircraft performance of a roadable aircraft, Pegasus II, which used the inboard-winglet concept in its design. The results proved that this concept has the potential to increase a wing lift coefficient at the right combination of thrust setting and freestream velocity better than a conventional wing-propeller arrangement. The lift coefficient inside the winglet channel was approximated as 2D in behavior. It is also shown that the winglets produce thrust at a positive-lift wing configuration. In the Pegasus II, the vertical stabilizers act like inboard winglets and produce a thrust component from its resultant force, giving 5.2% improvement in its effective aspect ratio and resulting in an induced-drag decrease. With an application of the new wing concept, the Pegasus II performance is comparable to other general aviation aircraft. / Master of Science

Air velocities induced by underground vehicles in complex metro systems are obtained using artificial neural networks. Complex tunnel shaft-systems with any number of tunnels and shafts and with most of the practically possible geometries encountered in underground structures can be simulated with the proposed method. A single neural network, of type feed-forward back propagation, with a single hidden layer is trained for modelling a single tunnel segment. Train and tunnel parameters that have influence on the vehicle induced flow characteristics are used together to obtain non-dimensional input and target parameters. First input parameter is the major head loss coefficient of tunnel, (L/D)_Tunnel. Blockage ratio A_Train/A_Tunnel and train aspect ratio (D/L)_Train are selected to be non-dimensional input parameters to represent the system geometry. As the final input parameter, skin friction coefficient of the train, f_Train drag coefficient of the train, C_D / frontal area of the train, A_Train and lateral area of the train, A_Lateral are combined into a single overall drag coefficient based on the train frontal area. Non-dimensional V_Air/V_Train speed ratio is selected to be the target parameter. Using maximum air velocity predicted by the trained neural network together with non dimensional system parameters and time, an additional neural network is trained for predicting the deceleration of air in case of train stoppage within the tunnel system and departure of the train from the system. A simulation tool for predicting time dependent velocity profile of air in metro systems is developed with the trained neural networks.

A voz é a principal ferramenta de comunicação da espécie humana e quase 70% da população economicamente ativa dos países desenvolvidos dependem direta ou indiretamente dela em sua profissão. Sua produção deve-se ao funcionamento harmônico de sistemas fisiológicos distintos, nos quais a laringe desempenha um importante papel. É nela que as funções de deglutição, respiração e fonação se encontram e também onde o pulso glotal é formado durante a passagem do ar pelas pregas vocais. Se os nervos e músculos da região por alguma razão são lesionados, o funcionamento dessas funções é prejudicado, causando sérios danos à qualidade de vida do indivíduo. Em virtude disso, diversas pesquisas tem sido realizadas visando adquirir informações que auxiliem as tomadas de decisões clínicas e cirúrgicas. Embora diversos avanços tenham sido realizados no campo de modelagens das pregas vocais e nos estudos da laringe, modelos baseados em geometrias de pacientes específicos que possam colaborar mais ativamente no planejamento cirúrgico, permanecem um desafio. Nesse sentido, este trabalho apresenta o desenvolvimento de um modelo computacional tridimensional, com base em imagens de tomografia computacional. Tendo por objetivo impulsionar a modelagem das características fisiológicas de pacientes reais e assim proporcionar maiores informações para tomadas de decisões. Esse modelo foi utilizado em simulações de escoamento de fluido solucionadas por elementos finitos, apresentando possibilidades satisfatórias de contribuir para avanços na modelagem de pacientes com patologias e em abordagens interativas, tal como interferências nos modelos virtuais por interfaces hápticas e simulações virtuais de cirurgia da laringe. / The voice is the main instrument for communication of human beings and almost 70% of the economically active population in the developed countries depends, directly or indirectly, on it for their profession. Its production is due to the harmonious interaction of different physiological systems, in which the larynx plays an important role. The larynx is involved in the deglutition, breathing and phonation functions and it is where the glottal pulse is formed during airflow through the vocal folds. If the nerves and muscles in this region for some reason are injured, this functions are adversely affected, causing serious damages to the individuals quality of life. As a result, several researches have been carried out, aiming at acquiring information that help in the clinical and surgical decision making. Although many progresses had been reached in the field of vocal folds modeling and in larynx studies, patientspecific geometry modeling that may take an active part in the surgical planning are still a challenge. In this regard, this work presents the development of a threedimensional computational model, based on images from computed tomography (CT) scans. This model was used in fluid flow simulations, solved by finite element analysis, showing satisfactory possibilities for contributions to progresses in the modeling of patients with lesions and in interactive approaches, such as interferences in the models with haptic interface and virtual surgery of the larynx.

<p>Problems in the area of land/biosphere-atmosphere interaction, hydrology, climate modeling etc. can be systematically organized as a study of turbulent flow in presence of boundary conditions in an increasing order of complexity. The present work is an attempt to study a few subsets of this general problem of turbulence in natural environments- in the context of neutral and thermally stratified atmospheric surface layer, the presence of a heterogeneous vegetation canopy and the interaction between air flow and a static water body in presence of flexible protruding vegetation. The main issue addressed in the context of turbulence in the atmospheric surface layer is whether it is possible to describe the macro-states of turbulence such as mean velocity and turbulent velocity variance in terms of the micro-states of the turbulent flow, i.e., a distribution of turbulent kinetic energy across a multitude of scales. This has been achieved by a `spectral budget approach' which is extended for thermal stratification scenarios as well, in the process unifying the seemingly different and unrelated theories of turbulence such as Kolmogorov's hypothesis, Heisenberg's eddy viscosity, Monin Obukhov Similarity Theory (MOST) etc. under a common framework. In the case of a more complex scenario such as presence of a vegetation canopy with edges and gaps, the question that is addressed is in what detail the turbulence is needed to be resolved in order to capture the bulk flow features such as recirculation patterns. This issue is addressed by a simple numerical framework and it has been found out that an explicit prescription of turbulence is not necessary in presence of heterogeneities such as edges and gaps where the interplay between advection, pressure gradients and drag forces are sufficient to capture the first order dynamics. This result can be very important for eddy-covariance flux calibration strategies in non-ideal environments and the developed numerical model can be used in related dispersion studies and coupled land atmosphere interaction models. For other more complex biosphere atmosphere interactions such as greenhouse gas emissions from wetlands, the interplay between air and water, often in presence of flexible aquatic vegetation, controls turbulence in water, which in turn affect the gas transfer processes. This process of wind shear induced wave-turbulent-vegetation interaction is studied for the first time in the laboratory and the state of turbulence as well as the bulk flow is found to be highly sensitive to environmental controls such as water height, wind speed, vegetation density and flexibility. This dissertation describes and gradually develops these concepts in an increasing order of complexity of boundary conditions. The first three chapters address the neutral and thermally stratified boundary layers and the last two chapters address the canopy edge problem and the air-water-vegetation experiments respectively.</p> / Dissertation

A voz é a principal ferramenta de comunicação da espécie humana e quase 70% da população economicamente ativa dos países desenvolvidos dependem direta ou indiretamente dela em sua profissão. Sua produção deve-se ao funcionamento harmônico de sistemas fisiológicos distintos, nos quais a laringe desempenha um importante papel. É nela que as funções de deglutição, respiração e fonação se encontram e também onde o pulso glotal é formado durante a passagem do ar pelas pregas vocais. Se os nervos e músculos da região por alguma razão são lesionados, o funcionamento dessas funções é prejudicado, causando sérios danos à qualidade de vida do indivíduo. Em virtude disso, diversas pesquisas tem sido realizadas visando adquirir informações que auxiliem as tomadas de decisões clínicas e cirúrgicas. Embora diversos avanços tenham sido realizados no campo de modelagens das pregas vocais e nos estudos da laringe, modelos baseados em geometrias de pacientes específicos que possam colaborar mais ativamente no planejamento cirúrgico, permanecem um desafio. Nesse sentido, este trabalho apresenta o desenvolvimento de um modelo computacional tridimensional, com base em imagens de tomografia computacional. Tendo por objetivo impulsionar a modelagem das características fisiológicas de pacientes reais e assim proporcionar maiores informações para tomadas de decisões. Esse modelo foi utilizado em simulações de escoamento de fluido solucionadas por elementos finitos, apresentando possibilidades satisfatórias de contribuir para avanços na modelagem de pacientes com patologias e em abordagens interativas, tal como interferências nos modelos virtuais por interfaces hápticas e simulações virtuais de cirurgia da laringe. / The voice is the main instrument for communication of human beings and almost 70% of the economically active population in the developed countries depends, directly or indirectly, on it for their profession. Its production is due to the harmonious interaction of different physiological systems, in which the larynx plays an important role. The larynx is involved in the deglutition, breathing and phonation functions and it is where the glottal pulse is formed during airflow through the vocal folds. If the nerves and muscles in this region for some reason are injured, this functions are adversely affected, causing serious damages to the individuals quality of life. As a result, several researches have been carried out, aiming at acquiring information that help in the clinical and surgical decision making. Although many progresses had been reached in the field of vocal folds modeling and in larynx studies, patientspecific geometry modeling that may take an active part in the surgical planning are still a challenge. In this regard, this work presents the development of a threedimensional computational model, based on images from computed tomography (CT) scans. This model was used in fluid flow simulations, solved by finite element analysis, showing satisfactory possibilities for contributions to progresses in the modeling of patients with lesions and in interactive approaches, such as interferences in the models with haptic interface and virtual surgery of the larynx.