O estudo de métodos de modelagem de escoamentos aerodinâmicos em regime transônico é de grande importância para a engenharia aeronáutica. O maior desafio no tratamento desses escoamentos está na sua característica não linear devido aos efeitos de compressibilidade e formação de ondas de choque. Tais efeitos não lineares influenciam no desempenho de superfícies aerodinâmicas em geral, bem como são responsáveis pelo aparecimento de fenômenos danosos para a resposta aeroelástica de aeronaves. O equacionamento para esses tipos de escoamentos pode ser obtido via as equações básicas da mecânica dos fluidos. No entanto, apenas soluções numéricas de tais equações são possíveis de ser obtidas de forma prática no presente momento. Para o caso específico do tratamento de problemas transônicos, as equações de Euler formam um conjunto de equações diferenciais a derivadas parciais capazes de capturar os efeitos não lineares de escoamentos compressíveis, porém os efeitos da viscosidade não são levados em consideração. O objetivo desse trabalho é implementar uma rotina computacional capaz de resolver numericamente escoamentos em regime transônico em torno de aerofólios. Para isso as equações de Euler não lineares são utilizadas e o campo de fluido ao redor de um perfil aerodinâmico é discretizado pelo método das diferenças finitas. Uma malha estruturada do tipo C discretizando o fluido ao redor de um aerofólio NACA0012 é considerada. A metodologia para solução numérica é baseada no método explícito de MacCormack de segunda ordem de precisão no tempo e espaço. Baseados na aproximação upwind, termos de dissipação artificial com coeficientes não lineares também são adicionados ao método. A solução do escoamento transônico estacionário ao redor do aerofólio NACA0012 é obtida e as principais propriedades do escoamento são apresentadas. Observa-se a formação de ondas de choque através de contornos de número de Mach ao redor do aerofólio. Gráficos das distribuições de pressão no intra e extradorso do aerofólio são mostrados, onde se identificam aos efeitos da brusca variação de pressão devido as ondas de choque. Os resultados são validados com valores de distribuição de pressão para o mesmo aerofólio encontradas na literatura técnica. Os resultados obtidos combinam bem com os fornecidos em códigos computacionais para solução do mesmo problema aerodinâmico / The study of aerodynamic modeling methods for the transonic flow regime is of great importance in aeronautical engineering. Major challenge on the treatment of those flows is on their nonlinear features due to compressibility effects and shock waves (appearance). Such nonlinear effects present a strong influence on aerodynamic performance, as well as they are responsible for harmful aeroelastic response phenomena in aircraft. Equations for transonic flows can be obtained from the basic fluid mechanic equations. However, only numerical methods are able to attain practical solutions for those set of differential equations at the present moment. For the specific case of treating transonic flow problems, the nonlinear Euler equations provide a set of partial differential equations with features to capture nonlinear effects of typical compressible flows, despite of not accounting for viscous flows effects. The aim of this work is to implement a computational routine for the numerical solution of transonic flows around airfoils. The Euler equations are used and the flow field around a aerodynamic profile is discretized by finite difference method. A C-type structured mesh is used to discretize the flow around a NACA0012 airfoil. The methodology for numerical solution is based on the explicit MacCormack method which has second order accuracy in time and space. Based on the upwind approximation, artificial dissipation with nonlinear coefficients is incorporated to the method. The steady transonic flow around the NACA0012 airfoil numerical solution is assessed and the main flow properties are presented. Shock wave structure can also be observed by means of the Mach number contours around the airfoil. Pressure distributions on upper and lower surfaces for different flow conditions are also shown, thereby allowing the observation of the effects of the abrupt pressure change due to shock waves. The results are validated using data presented in the technical literature. The present code solutions agree well with the solution obtained in other computational codes used for the same problem

<p>Ispitivana je zavisnost brzine fronta udarnih talasa u T-cevi od vi&scaron;e parametara. Izvr&scaron;eno je povezivanje ICCD kamere sa spektrometrom. Ispitane su karakteristike celokupnog sistema i izvr&scaron;ena je njegova optimizacija i kalibracija. Izmerene su &Scaron;tarkove polu&scaron;irine 45 spektralnih linija OII, 13 spektralnih linija Si II i 14 spektralnih linija Si III. Dobijene vrednosti su upoređene sa vrednostima koje se mogu naći u literature, kao i sa teorijskim vrednostima. Urađena je detaljna analiza rezultata iz ovog rada kao i svih dostupnih prethodno dobijenih eksperimentalnih podataka.</p> / <p>The dependence of shock front velocity on different parameters was examined. The ICCD camera was mounted on the spectrometer. The characteristics of the whole system were examined and the system was optimized and calibrated. The Stark halfwidths of 45 O II spectral lines, 13 Si II spectral lines and 14 Si III spectral lines were measured. The obtained values were compared with the data available in the literature, as well as with theoretical values. A detailed analysis of both the experimental results given in this dissertation and previously published experimental data was done.</p>

Nesta tese estudamos dois problemas diferentes na área de átomos ultra frios: Ondas de choque em condensados de Bose-Einstein e Espalhamento inelástico de átomos em um potencial de dois poços. No primeiro problema, estudamos o fluxo supersônico de um condensado de Bose-Einstein (BEC) através de um obstáculo macroscópico impenetrável delgado no sistema da equação de Schrödinger não-linear (NLS) bidimensional. Assumindo-se que a velocidade do fluxo é suficientemente alta, reduzimos assintoticamente o problema bidimensional original de valor de contorno para o fluxo estacionário através de um obstáculo alongado ao problema do pistão dispersivo unidimensional descrito pela NLS 1D dependente do tempo, no qual a coordenada original x reescalonada faz o papel de tempo e o movimento do pistão está vinculado à geometria do obstáculo. Duas ondas de choque dispersivas (DSWs) são geradas no fluxo, cada uma sendo formada em uma extremidade (frontal e traseira) do obstáculo. A DSW frontal é descrita analiticamente construindo-se soluções de modulação exatas para as equações de Whitham e a para a DSW traseira, empregamos a regra de quantização de Bohr-Sommerfeld generalizada para descrever a distribuição dos sólitons escuros. Propomos uma extensão da solução de modulação tradicional, a fim de incluir o padrão de ship-wave linear formado fora da região da DSW frontal. Realizamos simulações numéricas 2D completas e verificamos a validade das previsões analíticas. Os resultados deste problema podem ser relevantes para experimentos recentes sobre o fluxo de BECs através de obstáculos. No segundo problema, estudamos uma mistura atômica de dois átomos fermiônicos leves de spin 1/2 e dois átomos pesados em um potencial de dois poços. Processos de espalhamento inelástico entre ambas as espécies atômicas excitam os átomos pesados e renormalizam a taxa de tunelamento e a interação entre os átomos leves (efeito polarônico). A interação efetiva dos átomos leves muda de sinal e se torna atrativa quando o espalhamento inelástico é forte. Observamos também o cruzamento de níveis de energia, de um estado onde cada poço contém apenas um férmion (espalhamento inelástico fraco) para um estado onde um poço contém um par de férmions e ou outra está vazio (espalhamento inelástico forte). Identificamos o efeito polarônico e o cruzamento dos níveis de energia estudando-se a dinâmica quântica do sistema. / In this thesis we study two different problems in the field of ultracold atoms: Shock waves in Bose-Einstein condensates and Inelastic scattering of atoms in a double well. In the first problem, we study the supersonic flow of a Bose-Einstein condensate (BEC) past a slender impenetrable macroscopic obstacle in the framework of the twodimensional (2D) defocusing nonlinear Schr¨odinger equation (NLS). Assuming the oncoming flow speed sufficiently high, we asymptotically reduce the original boundary-value problem for a steady flow past a slender body to the one-dimensional dispersive piston problem described by the nonstationary NLS equation, in which the role of time is played by the stretched x-coordinate and the piston motion curve is defined by the spatial body profile. Two steady oblique spatial dispersive shock waves (DSWs) spreading from the pointed ends of the body are generated in both half-planes. These are described analytically by constructing appropriate exact solutions of the Whitham modulation equations for the front DSW and by using a generalized Bohr-Sommerfeld quantization rule for the oblique dark soliton fan in the rear DSW. We propose an extension of the traditional modulation description of DSWs to include the linear ship-wave pattern forming outside the nonlinear modulation region of the front DSW. Our analytic results are supported by direct 2D unsteady numerical simulations and are relevant to recent experiments on Bose-Einstein condensates freely expanding past obstacles. In the second problem, we study a mixture of two light spin-1/2 fermionic atoms and two heavy atoms in a double well potential. Inelastic scattering processes between both atomic species excite the heavy atoms and renormalize the tunneling rate and the interaction of the light atoms (polaron effect). The effective interaction of the light atoms changes its sign and becomes attractive for strong inelastic scattering. This is accompanied by a crossing of the energy levels from singly occupied sites at weak inelastic scattering to a doubly occupied and an empty site for stronger inelastic scattering. We are able to identify the polaron effect and the level crossing in the quantum dynamics.

ABSTRACT A theoretical and experimental study of the vibrational and chemical relaxation rates of diatomic gases, in flows behind shock waves and along nozzles,is made here. ¶ The validity of the conventional relaxation rate models, which are generally used to analyse experiments, is tested by developing a detailed microscopic description of the diatomic relaxation processes. Assuming the diatomic molecules to be represented by the anharmonic Morse Oscillator, the vibrational Master equation, which describes the time variation of each vibrational energy level population, is constructed by allowing one-quantum vibration to translation (V-T) energy exchanges and vibration to vibration (V-V) energy exchanges between the molecules. Dissociation and recombination are allowed to occur from, and to, the uppermost vibrational level. Solving the Master equation, it is found that a number of effects are explained by the inclusion of V-V transitions. In particular it is found that V-V energy exchanges cause the induction time for H2 dissociation to be increased; suggest that the linear rate law, for H2 and Ar mixtures, fails for a H2 mole fraction above 20%; give an acceleration of vibrational excitation as equilibrium is approached for H2 and N2; cause the vibrational temperature to be lower than the value found without V-V transitions for vibrational de-excitation in nozzle flows of H2 and N2, and conversely for recombination of H2 in nozzle flows. The most important result is the demonstration that conventional nozzle flow calculations, with shock-tube-determined dis-sociation and vibrational excitation rates, appear to be valid for the recombining and vibrationally de-excitating flows considered. ¶ The dissociation rates of undiluted nitrogen are measured in the free-piston shock tube DDT, using time-resolved optical interferometry, over a temperature range of 6000-14000K and confirm the strong temperature dependence of the pre-exponential factor observed by Hanson and Baganoff (1972). ¶ The vibrational de-excitation and excitation rates are determined in the small free-piston shock tunnel T2 over temperature ranges of 2000-4000K and 7000-10300K, respectively, by measuring the shock angles and curvatures, from optical interferograms, of flow over an inclined flat plate in the nonequilibrium nozzle flow. The de-excitation rate is found to be within a factor of ten of the excitation rate, while the excitation rate of N2 by collision with N is found to be less than about 50 times the excitation rate of N2 by N2. The dissociation rates of nitrogen, in the flow behind a shock attached to a wedge, are investigated in the large free-piston shock tunnel, using the shock curvature technique. The discrepancy, reported by Kewley and Hornung (1974b), between theory and experiment at the highest enthalpy is found to be resolved by including the measured helium contamination (Crane 1975) in the free-stream. Reasonable agreement is obtained between experimental shock curvatures and calculations using accepted dissociation rates.

Shock waves create a unique environment of high pressure, high temperature and high strain-rates. It has been observed that chemical reactions that occur in this regime are exothermic and can lead to the synthesis of new materials that are not possible under other conditions. The exothermic reaction is used in the development of binary energetic materials. These materials are of significant interest to the energetic materials community because of its capability of releasing high heat content during a chemical reaction and the relative insensitivity of these types of energetic materials. Synthesis of these energetic materials, at nano grain sizes with structural reinforcements, provides an opportunity to develop a dual functional material with both strength and energetic characteristics. Shock-induced chemical reactions pose challenges in experiment and instrumentation. This thesis is addressed to the theoretical development of constitutive models of shock-induced chemical reactions in energetic composites, formulated in the framework of non-equilibrium thermodynamics and mixture theories, in a continuum scale. Transition state-based chemical reaction models are introduced and incorporated with the conservation equations that can be used to calculate and simulate the shock-induced reaction process. The energy that should be supplied to reach the transition state has been theoretically modeled by considering both the pore collapse mechanism and the plastic flow with increasing yield stress behind the shock wave. A non-equilibrium thermodynamics framework and the associated evolution equations are introduced to account for time delays that are observed in the experiments of shock-induced or assisted chemical reactions. An appropriate representation of the particle size effects is introduced by modifying the initial energy state of the reactants. Numerical results are presented for shock-induced reactions of mixtures of Al, Fe2O3 and Ni, Al with epoxy as the binder. The theoretical model, in the continuum scale, requires parameters that should be experimentally determined. The experimental characterization has many challenges in measurement and development of nano instrumentation. An alternate approach to determine these parameters is through ab-initio calculations. Thus, this thesis has initiated ab-initio molecular dynamics studies of shock-induced chemical reactions. Specifically, the case of thermal initiation of chemical reactions in aluminum and nickel is considered.

No description available.

The near field blast–wave propagation dynamics has been a subject of intense research in recent past. Since experiments on a large scale are difficult to carry out, focus has been directed towards recreating these blast waves inside the laboratory by expending minuscule amounts of energy(few joules),which have been termed here as micro–blast waves. In the present study, micro-blast waves are generated from the open end of a small diameter polymer tube (Inner Diameter of 1.3 mm)coated on its inner side with negligible amounts of HMX explosive (~18 mg/m), along with traces of aluminium powder. Experimental, numerical, and analytical approaches have been adopted in this investigation to understand the generation and subsequent propagation of these micro–blast waves in the open domain. Time–resolved schlieren flow visualization experiments, using a high speed digital camera, and dynamic pressure measurements (head–on and side–on pressures) have been carried out. Quasi one dimensional numerical modeling of the detonation process inside the tube, has been carried out by considering the reaction kinetics of a single(HMX) reaction to account for the reaction dynamics of HMX. The one dimensional numerical model is then coupled to a commercial Navier– Stokes equation solver to understand the propagation of the blast wave from the open end of the tube. A theory that is valid for large scale explosions of intermediate strength was then used for the first time to understand the propagation dynamics of these micro–blast waves. From the experiments, the trajectory of the blast wave was mapped, and its initial Mach number was found to be about 3.7. The side–on overpressure was found to be 5.5 psi at a distance of 20 mm from the tube, along an axis, offset by 30 mm from the tube axis. These values were found to compare quite well with the numerically obtained data in the open domain. From the numerical model of the tube, the energy in the blast wave was inferred to be 1.5 J. This value was then used in the analytical theory and excellent correlation was obtained, suggesting the exciting possibility of using such theories, validated for large-scale explosions, to describe these micro–blasts. Considering the uncertainties in the approximate model, a better estimate of energy was obtained by working back the energy(using the analytical model) from the trajectory data as 1.25 J. The average TNT equivalent, a measure of its strength relative to a TNT explosion, was found to be 0.3. A few benchmark experiments, demonstrating the capability of this novel blast device have also been done by comparing them against the extant large–scale explosion database, suggesting the possibility of using these micro–blast waves to study certain aspects of large–scale explosions.

Growing interest in biomedical applications of nonthermal plasmas inspires the development of new plasmas sources. Dielectric barrier (DBD) and corona discharges produced in ambient air or in noble gas flow are typically applied. Direct production of plasma in liquids has a great potential for sterilization of liquid substances and extracorporeal blood treatment. The physical mechanisms of discharge formation in liquid medium are not fully understood.The first part of this thesis deals with the initiation and development of the nanosecond discharge in liquid dielectrics (deionized water, ethanol and n-pentane). Time-resolved shadowgraph visualization, optical emission spectroscopy and electrical diagnostics are applied to investigate the discharge formation on point anode.We have shown that depending on the applied voltage amplitude three different scenario can occur in the polar dielectric, namely, cavitation of a bubble, discharge development in the gaseous cavity (bush-like mode) and initiation of the filamentary discharge (tree-like mode) propagating in bulk liquid. Formation of the bush-like and the tree-like discharges is governed by distinct physical mechanisms, resulting in strongly different plasma parameters.In the second part of this work we address the question of how cold atmospheric plasma interacts with living cells in-vitro and in-vivo, and what is the mechanism of plasma induced cell death. Flowcytometry based cell viability assay with two markers AnnexinV (AV) and Propidium iodide (PI), demonstrates a dose dependent induction of the apoptosis for human T lymphocyte (Jurkat) and epithelial (HMEC) cells treated with DBD plasma. In nude mice model, induction of apoptosis and necrosis in dose dependant manner is observed by electron microscopy in thin epidermis sections. Histological analysis shows significant lesions appeared in epidermis, dermis, hypodermis and muscle as a function of treatment duration. Production of hydrogen peroxide in culture medium (PBS) exposed to DBD plasma is measured using selective fluorescent probe (Amplex® Red). Cell viability of human thyroid epithelial (HTori-3) and melanoma (1205Lu) cells demonstrates nonmonotonous dependence on H2O2 concentration. The major role of plasma produced hydrogen peroxide and DBD electric field is suggested.

The emerging paradigms of shockwave research have opened up new horizons for interdisciplinary applications. This has inevitably driven research towards studying the propagation of shockwaves in miniature shock tubes (tube diameters typically in the range of 1−10 ). Studies have revealed that while operating at this diameter range and low initial pressures (typically 1 < 100 ) leading to low values of characteristic Reynolds numbers (typically ′ < 23,000 −1), results in the boundary layer playing a major role in shockwave attenuation. But there are very few studies addressing shockwave attenuation when shock tubes are operated at higher Reynolds number. Pressure measurements and visualization studies in shock tubes of these length scales are also seldom attempted due to practical difficulties. Given that premise, in the present work the shockwave attenuation due to wall effects and non-ideal diaphragm rupture in shock tubes of hydraulic diameters 2 , 6 and 10 has been investigated at ambient initial driven section conditions ( 1 = 300 and 1 = 1 resulting in Reynolds number in the range 70,212 −1 – 888,627 −1). In this study pressure measurements and high-speed visualization have been carried out to find the effect of the pressure ratio, temperature ratio and molecular weights of driver gas on the shock attenuation processes. In order to study the effects of the driver/driven gas temperature ratios on the shock attenuation process, a new in-situ oxyhydrogen (hydrogen and oxygen gases in the ratio 2:1) generator has been developed. Using this innovative device, the miniature shock tubes are also run in the detonation mode (forward facing detonation wave). The results obtained using helium and nitrogen driver gases for these shock tubes reveal that as the hydraulic diameter of the shock tube is reduced, a larger diaphragm pressure ratio is required to obtain a particular strength of shockwave. The attenuation in the shockwave is found to be a function of the driver gas properties namely specific heat ratio ( 4), molecular weight ( 4), temperature ( 4) as well as the diaphragm opening time of the shock tube in addition to the parameters , 21, / , and 1 as already suggested in previous reports. The visualization studies reveal that the effect of diaphragm opening time leading to longer shock formation distances appears to influence the shockwave attenuation process at these shock tube diameters. Further, it is also found that the strength of the shockwave reduces when the ratio 4/ 1 is higher. It is also seen that the length of the driven sections must be less than twice the length of the driver sections to reduce attenuation. Based on the understanding of the nature of supersonic flow in a miniature shock tubes, a novel shock/blast wave device has been developed for certain innovative biotechnology applications such as needleless vaccine delivery and cell transformations. The new device has an internal diameter of 6 and by varying the length of the driver/driven sections either shock or blast waves of requisite strength and impulse can be generated at the open end of the tube. In the shock tube mode of operation, shockwaves with steady time duration of up to 30 have been generated. In the blast tube mode of operation, where the entire tube is filled with oxyhydrogen mixture, shockwaves with peak pressures of up to 550 have been obtained with good repeatability. An attempt to power this device using solar energy has also given successful results. Visualization of the open end of the detonation driven shock tube reveals features typical of flow from the open end of shock tubes and has helped in quantifying the density field. The subsequent instants of the flow resemble a precursor flow in gun muzzle blast and flash. Typical energy levels of the shock/blast waves coming out this device is found to be about 34 for an oxyhydrogen fill pressure of 5.1 in the shock tube operation mode. Transformation of E.coli, Salmonella Typhimurium and Pseudomonas aeruginosa bacterial strains using the device by introducing plasmid DNA through their cell walls has been successfully carried out. There is more than twofold increase in the transformation efficiency using the device as compared to conventional methods. Using the same device, needleless vaccine delivery in mice using Salmonella has also been demonstrated successfully. Overall, in the present thesis, a novel method for generating shockwaves in a repeatable and controllable manner in miniature scales for interdisciplinary applications has been proposed. Also, it is the first time that experiments with the different diameter miniature shock tubes have been carried out to demonstrate the attenuation of shockwaves as the hydraulic diameter of the shock tube decreases. Future research endeavors will focus on quantitative measurement of the particle velocity behind the shock waves, and also on the nature of the boundary layers to further resolve the complex flow physics associated with supersonic flows in these miniature shock tubes.

La sécurité des biens et des personnes est, de nos jours, une préoccupation première, en particulier lorsqu'elle concerne l'usage des explosifs. Afin de répondre à ces exigences de sécurité, il est nécessaire de pouvoir prédire le comportement des ondes de pression issues d'une explosion, que ce soit à l'intérieur ou à l'extérieur du bâtiment, et leur interaction avec leur environnement. Une importante quantité d'informations sur les ondes de choc se propageant en champ libre est disponible dans la littérature, de sorte que leur comportement est maintenant bien connu. Toutefois, il y a très peu de données disponibles en littérature ouverte sur les explosions en milieu confiné. Les travaux présentés dans ce mémoire de thèse s'inscrivent dans le cadre de l'étude du comportement des ondes de choc en milieu confiné multi-chambres et de l'effet de différents paramètres tels que le volume des cellules ou la largeur du couloir sur les profils de pression à l'intérieur d'un bâtiment. La propagation de l'onde de choc est analysée par l'évolution de certains paramètres du choc (temps d'arrivée, surpression maximale et impulsion positive).Plusieurs essais à échelle réduite ont été réalisés à l'aide d'une maquette modulable, représentative d'un bâtiment pyrotechnique de plein pied, composé de quatre pièces alignées et reliées entre elles par un couloir. / Security is nowadays a real and major concern, especially when explosives are involved. To address this security issue, an accurate prediction of the behavior of shock waves caused by a detonation propagating inside or outside a building and interacting with the surrounding environment is required. Extensive knowledge regarding shock waves in free field can be found in the literature so that their behavior is now well known. However, there is very few information available in the open literature for confined configuration. This study focuses on the behavior of a shock wave within a confined multi-chamber system and on the impact of different parameters such as the size of the rooms and the width of the corridor on the pressure history inside the building. The shock wave propagation is analyzed through the evolution of some of the shock parameters (arrival time, maximum overpressure and positive impulse). Several small-scale experiments have been carried out using an adjustable model of a four-roomed single-story building. The rooms are connected to a single corridor and all on the same side. This model is representative of a pyrotechnic workshop.