<p>The stability and the receptivity of three-dimensional flat plate boundary layers is studied employing parabolised stability equations. These allow for computationally efficient parametric studies. Two different sets of equations are used. The stability of modal disturbances in the form of crossflow vortices is studied by means of the well-known classical parabolised stability equations (PSE). A new method is developed which is applicable to more general vortical-type disturbances. It is based on a modified version of the classical PSE and describes both modal and non-modal growth in three-dimensional boundary layers. This modified PSE approach is used in conjunction with a Lagrange multiplier technique to compute spatial optimal disturbances in three-dimensional boundary layers. These take the form of streamwise oriented tilted vortices initially and develop into streaks further downstream. When entering the domain where modal disturbances become unstable optimal disturbances smoothly evolve into crossflow modes. It is found that non-modal growth is of significant magnitude in three-dimensional boundary layers. Both the lift-up and the Orr mechanism are identified as the physical mechanisms behind non-modal growth. Furthermore, the modified PSE are used to determine the response of three-dimensional boundary layers to vortical free-stream disturbances. By comparing to results from direct numerical simulations it is shown that the response, including initial transient behaviour, is described very accurately. Extensive parametric studies are performed where effects of free-stream turbulence are modelled by filtering with an energy spectrum characteristic for homogeneous isotropic turbulence. It is found that a quantitative prediction of the boundary layer response to free-stream turbulence requires detailed information about the incoming turbulent flow field. Finally, the adjoint of the classical PSE is used to determine the receptivity of modal disturbances with respect to localised surface roughness. It is shown that the adjoint approach yields perfect agreement with results from Finite-Reynold-Number Theory (FRNT) if the boundary layer is assumed to be locally parallel.  Receptivity is attenuated if nonlocal and non-parallel effects are accounted for. Comparisons to direct numerical simulations and extended parametric studies are presented.</p>

This work is concerned with stability and receptivity analysis as well as studies on control of the laminar-turbulent transition in boundary-layer flows through direct numerical simulations. Various flow configurations are considered to address flow around straight and swept wings. The aim of this study is to contribute to a better understanding of stability characteristics and different means of transition control of such flows which are of great interest in aeronautical applications. Acoustic receptivity of flow over a finite-thickness flat plate with elliptic leading edge is considered. The objective is to compute receptivity coefficient defined as the relative amplitude of acoustic disturbances and TS wave. The existing results in the literature for this flow case plot a scattered image and are inconclusive. We have approached this problem in both compressible and incompressible frameworks and used high-order numerical methods. Our results have shown that the generally-accepted level of acoustic receptivity coefficient for this flow case is one order of magnitude too high. The continuous increase of computational power has enabled us to perform global stability analysis of three-dimensional boundary layers. A swept flat plate of FSC type boundary layer with surface roughness is considered. The aim is to determine the critical roughness height for which the flow becomes turbulent. Global stability characteristics of this flow have been addressed and sensitivity of such analysis to domain size and numerical parameters have been discussed. The last flow configuration studied here is infinite swept-wing flow. Two numerical set ups are considered which conform to wind-tunnel experiments where passive control of crossflow instabilities is investigated. Robustness of distributed roughness elements in the presence of acoustic waves have been studied. Moreover, ring-type plasma actuators are employed as virtual roughness elements to delay laminar-turbulent transition. / <p>QC 20161124</p>

Estudos aplicados ao processo de filtração tangencial têm sido o objetivo de muitos trabalhos devido a sua ampla capacidade de adequação aos mais diversos processos industriais. Os mecanismos de transferência associados a esse processo envolvem basicamente o escoamento em tubos permeáveis (ou membranas) com fenômenos de transferência de massa presentes junto à superfície. Esta tese de doutorado apresenta uma modelagem numérica capaz de representar o escoamento de fluidos newtonianos e não-newtonianos em tubos permeáveis aplicada ao processo de filtração tangencial, para os regimes de escoamento laminar e turbulento. No regime turbulento, utilizou-se o modelo de comprimento de mistura de Prandtl. O modelo numérico envolveu as equações de conservação da massa, da quantidade de movimento e das espécies químicas, acopladas a adequadas condições de fronteira. Em particular, por se tratar de um modelo numérico, analisou-se a discretização dos termos convectivos por meio da implementação de três esquemas: WACEB, CUBISTA e QUICKEST adaptativo. Os resultados produzidos pela implementação dos esquemas convectivos foram analisados por meio de comparações com resultados analíticos e experimentais da literatura, para regimes de escoamento laminar e turbulento. De acordo com as comparações realizadas, o esquema QUICKEST adaptativo apresentou melhor desempenho na modelagem desse escoamento. Diversas simulações numéricas geraram resultados, os quais foram comparados com expressões analíticas e dados experimentais da literatura e com dados produzidos pelo laboratório do Núcleo de Engenharia Térmica e Fluidos (NETeF) da USP São Carlos. Verificou-se, assim, que o modelo matemático produziu resultados compatíveis com o fenômeno estudado, tendo-se, portanto, uma ferramenta para descrição do problema convectivo mássico do escoamento em tubos permeáveis. / Studies applied to the crossflow filtration process have been the goal of several researches due to its large capacity for adaptation to the various industrial processes. The mechanism of transfer associated with this process basically involves fiows in permeable tubes (or membranes) with the phenomenon of mass transfer on the surface. This doctoral thesis presents a numerical modeling able to represent the fiow of Newtonian and non-Newtonian fiuids in permeable tubes applied to the process of crossflow filtration, in laminar and turbulent flow regimes. In the turbulent regime the Prandtl mixing length model was used. The numerical model involved the mass conservation, momentum conservation and mass transport equations coupled to the appropriate boundary conditions. In particular, as it is a numerical model, the discretization of convective terms was analyzed through the implementation of three schemes: WACEB, CUBISTA and adaptative QUICKEST. The results produced by the implementation of the convective schemes were analyzed through comparisons with experimental and analytical results from the literature, for laminar and turbulent flow regImes. According to the comparisons made, adaptative QUICKEST scheme showed the best performance in the modeling in this flow. Several numerical simulations generated results, which were compared with experimental data and analytical expressions of the literature and with data produced by the laboratory of the Center of Thermal Thermal and Fluids Engineering (NETeF) of the EESC- USP/São Cados. It was possible to verify, that the mathematical model produced results consistent with the phenomenon studied, and can be considered a tool for the description of the mass convective problem flow in permeavel tubes.

A constante exploração dos recursos hídricos para os mais diferentes usos sem um planejamento adequado, tem levado ao comprometimento desses recursos, verificando-se cada vez mais aumento no número de pesquisas e investimentos, visando o estudo de alternativas que viabilizem o tratamento avançado de águas residuárias e sua reutilização. Entre essas alternativas, estão as técnicas de separação dos materiais contaminantes por membranas. Neste trabalho estudou-se a viabilidade da utilização da microfiltração tangencial como alternativa de pós-tratamento de efluente de Reator Anaeróbio de Leito Expandido alimentado com esgoto sanitário, analisando-se a influência da utilização de cloreto férrico como coagulante, bem como, membranas com diferentes tamanhos de poro (0,2 e 1,0 &#956m), no desempenho da microfiltração tangencial. Os ensaios no sistema de microfiltração tangencial foram realizados em batelada, com amostras de efluente do reator anaeróbio de leito expandido (RALEX). Verificou-se que para os ensaios realizados com a membrana de 0,2 &#956m, o aumento das dosagens de cloreto férrico, contribuiu para diminuição nos valores de luxo de permeado. Esta relação não ocorreu de forma direta com a membrana de 1,0 &#956m. Os processos de coagulação e floculação foram essenciais para ambas membranas no aumento na eficiência de remoção da demanda química total de oxigênio (mg/l), fosfato total (mg P/l) e turbidez, no entanto, em relação aos valores de fluxo do permeado,foi prejudicial, pois nos ensaios em que as amostras de efluente do RALEX não foram previamente coaguladas e floculadas, a permeabilidade das membranas foi bem maios. O sistema de microfiltração tangencial operando com a membrana de 0,2 &#956m apresentou melhor desempenho, com valores de fluxo do permeado, em geral superiores a 100 L/m2.h, eficiência de 100% na remoção de coliformes totais e fecais, e a dosagem de 40 mg/l de cloreto férrico, já foi suficiente para uma eficiência média de remoção de DQOt de 95%; P.PO4-3 (89,5%) e Turbidez (96,4%). Portanto, a microfiltração tangencial pode ser considerada uma alternativa eficaz como unidade de pós-tratamento de efluente de reator anaeróbio de leito expandido, produzindo efluente que atende os padrões de reuso na agricultura, para coliforme totais e fecais. / The constant exploration of water resources for the most different uses, without an appropriate planning, has lead to the exhaustion of this resources. This scenery has showed the need of increasing researches and investments on alternative forms of wastewater treatment. This work studied the viability of using crossflow microfiltration as an alternative form of advanced treatment of effluents of Anaerobic Reactor Expanded Bed feed with sewage, examining the effect of the use of ferric chloride as coagulam, as well as of different pore size membranes (0,2 and 1,0 &#956m) on the performance of crossflow microfiltration. The experiments on crossflow microfiltration system were carried out in batch, using effluent samples of anaerobic reactor expanded bed. The results obtained with the 0,2 &#956m membrane showed that the increase of ferric chloride dosages contributed for the reduction on flux values. The 1,0 &#956m membrane did not presented this relation. The flocculation and coagulation processes were essentials for increasing the removal efficiency of Total Chemical Oxygen Demand, Total Phosphorus and Turbidity for both membranes, however, for the flux values the effect was harmful, because when the samples of the Anaerobic Reactor Expanded Bed were not previously coagulated and flocculated, the membranes penneability were higher. The Crossflow Microfiltration System, operating with the 0,2 &#956m membrane, presented better performance, with flux values generally superior than 100 L/m2.h, efficiency around 100% on the removal of Total and Fecal Coliforms. For this membrane (0,2 &#956m) the dosage of 40 mg/l of FeCl3 (first stage) was enough for an average of removal efficiency of Total Chemical Oxygen Demand (95%); Turbidity (96.4%); and P.PO4-3 (89,5%). Therefore, crossflow mocrofiltration can be considered an effective alternative for advanced treatment of effluents of Anaerobic Reactor Expanded Bed, producing a final effluent with large potentiality to be used in agriculture.

A proposta desta pesquisa consistiu na avaliação da microfiltração tangencial para o tratamento avançado de efluente gerado em sistema de tratamento de esgoto sanitário constituído de reator UASB (Upflow Anaerobic Sludge Blanket) seguido de tanque de aeração. Neste trabalho foram avaliados métodos de limpeza física (retrolavagem com ar comprimido) e química (ácida e básica) das membranas, bem como análise comparativa da colmatação e do desempenho de membranas de tamanhos de poro de 0,2 e 1,0 'mü'm, quando aplicadas ao pós-tratamento de efluentes do tanque de aeração em diferentes concentrações de SST. Foram contemplados ainda estudos de desinfecção de efluentes da microfiltração por radiação UV e aplicação do processo de coagulação antecedendo a microfiltração tangencial. Os experimentos foram realizados em unidade piloto com membranas tubulares de polipropileno com área efetiva de filtração de 0,036 'M POT.2'. Constatou-se que a limpeza física foi essencial para obtenção de maiores valores de fluxo de permeado na unidade de microfiltração. A limpeza química das membranas por solução básica foi mais eficiente quando comparada a limpeza ácida. Foram obtidos melhores resultados com a membrana de 0,2 'mü'm, quando comparada a membrana de 1 'mü'm, a qual apresentou intensa colmatação interna de seus poros. Para membrana de 0,2 'mü'm obteve-se permeado de excelente qualidade microbiológica (E.Coli < 1 UFC/100 mL e Colifagos < 16 UFP/100 mL), bem como valores de turbidez inferiores a 1,46 uT e remoção praticamente completa de SST. A prévia coagulação das amostras de licor misto do tanque de aeração contribuiu para obtenção de maiores taxas e melhor remoção de P-'PO IND.4'POT.3-' e DQOt na unidade de microfiltração. Para dosagem de 40 mg/L de cloreto férrico obteve-se a maior taxa média (139,7 L/'M POT.2'.h), concentrações residuais de P-'PO IND.4'POT.3-' inferiores a 1,4 mgP/L e DQOt menor que 33 mg/L. A radiação UV permitiu inativação completa de E.Coli e Colifagos das amostras de permeado. Concluiu-se que a microfiltração tangencial apresentou grande potencialidade para ser aplicada no tratamento avançado de efluente gerado em sistema de tratamento de esgoto sanitário constituído de reator UASB (Upflow Anerobic Sludge Blanket) seguido de tanque de aeração. / The proposal of this research was to evaluate the crossflow microfiltration as an alternative for an advanced treatment of effluent generated in a system of sewage treatment composed by a UASB (Upflow Anaerobic Sludge Blanket) reactor followed by an aeration tank. This work aimed to evaluate the membranes physical cleaning methods (backwashing with compressed air) and the chemical ones (acid and basic), as well as the comparative analysis between the fouling event and the 0,2 and 1,0 'mü'm pore size membranes performance, when applied to the aeration tank effluents in a post-treatment stage at TSS different concentrations. Studies for microfiltration effluents disinfection by UV radiation and the application of the coagulation process preceding the crossflow microfiltration were also developed. The experiments were performed in a pilot unit with polypropylene tubular membranes with 0.036 'M POT.2' of effective filtration area. It was verified that the physical cleaning was essential to the attainment of higher permeate flux values in the microfiltration unit. The chemical cleaning of the membranes through basic solution was more efficient when compared to their acid cleaning. Better results were attained when the 0,2 'mü'm membrane was employed in comparison with the 1 'mü'm membrane, which presented intense internal blocking of its pores. It was attained an excellent microbiological quality (E.Coli < 1 FCU/100 mL and Coliphages < 16 FPU/100 mL) for the 0,2 'mü'm membrane, as well as turbidity levels under 1,46 uT and almost total removal of TSS. The previous mixed liquor samples coagulation of the aeration tank contributed to the attainment of higher rates and better removal of P-'PO IND.4'POT.3-' and CODt in the microfiltration unit. It was attained, for the ferric chloride 40 mg/L dosage, the higher mean rate (139,7 L/'M POT.2'.h), P-'PO IND.4'POT.3-' remaining concentrations under 1,4 mgP/L and CODt lesser than 33 mg/L. The UV radiation allowed the complete inactivation of E.Coli and Coliphages from the permeate samples. It was concluded that the crossflow microfiltration presents great possibilities of application in the advanced treatment of effluent generated in a system of sewage treatment composed by a UASB (Upflow Anaerobic Sludge Blanket) reactor followed by an aeration tank.

Environmentally friendly and efficiently produced energy from sustainable and renewable resources is of great importance. Carbon dioxide (CO2) and nitric oxides (NOx) are the main emissions of air-breathing gas turbines in power plants. Gas turbines of the power generation industry are normally fueled with liquid fuels, natural gas or syngas in changing qualities. Syngas can be produced by gasification processes in IGCC power plants and consist of varying percentages of the main fractions hydrogen (H2) and carbon monoxide (CO). CO2 emissions can be reduced by a decrease of the CO-share and an increase of the hydrogen-share in the syngas fuel, and by using pre-combustion carbon capture and sequestration (CCS) technology. For low NOx, current gas turbine combustion chamber technologies require diluents, a rather low H2 content and modifications of the combustor hardware. A feasible solution for low NOx hydrogen and syngas combustion in gas turbines is the Micromix principle developed at Aachen University of Applied Sciences. The goal of this doctoral thesis is the research on a Micromix combustor with increased power densities fueled with hydrogen-rich syngas with about 90% by volume hydrogen, and going up to 100% hydrogen in the fuel. Test burner experiments are used to characterize the combustion and emission properties of a multitude of key drivers. Based on this optimization with a variety of scaled model test burners, a prototype dual-fuel hydrogen/syngas Micromix combustor is designed and integrated into the annular combustion chamber of an industrial gas turbine. In the gas turbine, the performance characteristics of the prototype-combustor are investigated under real operational conditions with hydrogen-rich syngas and pure hydrogen. / Doctorat en Sciences de l'ingénieur et technologie / info:eu-repo/semantics/nonPublished

Estudos aplicados ao processo de filtração tangencial têm sido o objetivo de muitos trabalhos devido a sua ampla capacidade de adequação aos mais diversos processos industriais. Os mecanismos de transferência associados a esse processo envolvem basicamente o escoamento em tubos permeáveis (ou membranas) com fenômenos de transferência de massa presentes junto à superfície. Esta tese de doutorado apresenta uma modelagem numérica capaz de representar o escoamento de fluidos newtonianos e não-newtonianos em tubos permeáveis aplicada ao processo de filtração tangencial, para os regimes de escoamento laminar e turbulento. No regime turbulento, utilizou-se o modelo de comprimento de mistura de Prandtl. O modelo numérico envolveu as equações de conservação da massa, da quantidade de movimento e das espécies químicas, acopladas a adequadas condições de fronteira. Em particular, por se tratar de um modelo numérico, analisou-se a discretização dos termos convectivos por meio da implementação de três esquemas: WACEB, CUBISTA e QUICKEST adaptativo. Os resultados produzidos pela implementação dos esquemas convectivos foram analisados por meio de comparações com resultados analíticos e experimentais da literatura, para regimes de escoamento laminar e turbulento. De acordo com as comparações realizadas, o esquema QUICKEST adaptativo apresentou melhor desempenho na modelagem desse escoamento. Diversas simulações numéricas geraram resultados, os quais foram comparados com expressões analíticas e dados experimentais da literatura e com dados produzidos pelo laboratório do Núcleo de Engenharia Térmica e Fluidos (NETeF) da USP São Carlos. Verificou-se, assim, que o modelo matemático produziu resultados compatíveis com o fenômeno estudado, tendo-se, portanto, uma ferramenta para descrição do problema convectivo mássico do escoamento em tubos permeáveis. / Studies applied to the crossflow filtration process have been the goal of several researches due to its large capacity for adaptation to the various industrial processes. The mechanism of transfer associated with this process basically involves fiows in permeable tubes (or membranes) with the phenomenon of mass transfer on the surface. This doctoral thesis presents a numerical modeling able to represent the fiow of Newtonian and non-Newtonian fiuids in permeable tubes applied to the process of crossflow filtration, in laminar and turbulent flow regimes. In the turbulent regime the Prandtl mixing length model was used. The numerical model involved the mass conservation, momentum conservation and mass transport equations coupled to the appropriate boundary conditions. In particular, as it is a numerical model, the discretization of convective terms was analyzed through the implementation of three schemes: WACEB, CUBISTA and adaptative QUICKEST. The results produced by the implementation of the convective schemes were analyzed through comparisons with experimental and analytical results from the literature, for laminar and turbulent flow regImes. According to the comparisons made, adaptative QUICKEST scheme showed the best performance in the modeling in this flow. Several numerical simulations generated results, which were compared with experimental data and analytical expressions of the literature and with data produced by the laboratory of the Center of Thermal Thermal and Fluids Engineering (NETeF) of the EESC- USP/São Cados. It was possible to verify, that the mathematical model produced results consistent with the phenomenon studied, and can be considered a tool for the description of the mass convective problem flow in permeavel tubes.

A proposta desta pesquisa consistiu na avaliação da microfiltração tangencial para o tratamento avançado de efluente gerado em sistema de tratamento de esgoto sanitário constituído de reator UASB (Upflow Anaerobic Sludge Blanket) seguido de tanque de aeração. Neste trabalho foram avaliados métodos de limpeza física (retrolavagem com ar comprimido) e química (ácida e básica) das membranas, bem como análise comparativa da colmatação e do desempenho de membranas de tamanhos de poro de 0,2 e 1,0 'mü'm, quando aplicadas ao pós-tratamento de efluentes do tanque de aeração em diferentes concentrações de SST. Foram contemplados ainda estudos de desinfecção de efluentes da microfiltração por radiação UV e aplicação do processo de coagulação antecedendo a microfiltração tangencial. Os experimentos foram realizados em unidade piloto com membranas tubulares de polipropileno com área efetiva de filtração de 0,036 'M POT.2'. Constatou-se que a limpeza física foi essencial para obtenção de maiores valores de fluxo de permeado na unidade de microfiltração. A limpeza química das membranas por solução básica foi mais eficiente quando comparada a limpeza ácida. Foram obtidos melhores resultados com a membrana de 0,2 'mü'm, quando comparada a membrana de 1 'mü'm, a qual apresentou intensa colmatação interna de seus poros. Para membrana de 0,2 'mü'm obteve-se permeado de excelente qualidade microbiológica (E.Coli < 1 UFC/100 mL e Colifagos < 16 UFP/100 mL), bem como valores de turbidez inferiores a 1,46 uT e remoção praticamente completa de SST. A prévia coagulação das amostras de licor misto do tanque de aeração contribuiu para obtenção de maiores taxas e melhor remoção de P-'PO IND.4'POT.3-' e DQOt na unidade de microfiltração. Para dosagem de 40 mg/L de cloreto férrico obteve-se a maior taxa média (139,7 L/'M POT.2'.h), concentrações residuais de P-'PO IND.4'POT.3-' inferiores a 1,4 mgP/L e DQOt menor que 33 mg/L. A radiação UV permitiu inativação completa de E.Coli e Colifagos das amostras de permeado. Concluiu-se que a microfiltração tangencial apresentou grande potencialidade para ser aplicada no tratamento avançado de efluente gerado em sistema de tratamento de esgoto sanitário constituído de reator UASB (Upflow Anerobic Sludge Blanket) seguido de tanque de aeração. / The proposal of this research was to evaluate the crossflow microfiltration as an alternative for an advanced treatment of effluent generated in a system of sewage treatment composed by a UASB (Upflow Anaerobic Sludge Blanket) reactor followed by an aeration tank. This work aimed to evaluate the membranes physical cleaning methods (backwashing with compressed air) and the chemical ones (acid and basic), as well as the comparative analysis between the fouling event and the 0,2 and 1,0 'mü'm pore size membranes performance, when applied to the aeration tank effluents in a post-treatment stage at TSS different concentrations. Studies for microfiltration effluents disinfection by UV radiation and the application of the coagulation process preceding the crossflow microfiltration were also developed. The experiments were performed in a pilot unit with polypropylene tubular membranes with 0.036 'M POT.2' of effective filtration area. It was verified that the physical cleaning was essential to the attainment of higher permeate flux values in the microfiltration unit. The chemical cleaning of the membranes through basic solution was more efficient when compared to their acid cleaning. Better results were attained when the 0,2 'mü'm membrane was employed in comparison with the 1 'mü'm membrane, which presented intense internal blocking of its pores. It was attained an excellent microbiological quality (E.Coli < 1 FCU/100 mL and Coliphages < 16 FPU/100 mL) for the 0,2 'mü'm membrane, as well as turbidity levels under 1,46 uT and almost total removal of TSS. The previous mixed liquor samples coagulation of the aeration tank contributed to the attainment of higher rates and better removal of P-'PO IND.4'POT.3-' and CODt in the microfiltration unit. It was attained, for the ferric chloride 40 mg/L dosage, the higher mean rate (139,7 L/'M POT.2'.h), P-'PO IND.4'POT.3-' remaining concentrations under 1,4 mgP/L and CODt lesser than 33 mg/L. The UV radiation allowed the complete inactivation of E.Coli and Coliphages from the permeate samples. It was concluded that the crossflow microfiltration presents great possibilities of application in the advanced treatment of effluent generated in a system of sewage treatment composed by a UASB (Upflow Anaerobic Sludge Blanket) reactor followed by an aeration tank.

This thesis describes an experimental investigation of the breakup processes involved in the formation of a spray created by a liquid jet injected into a gaseous crossflow. This work is motivated by the utilization of this method to inject fuel in combustors and afterburners of airplane engines. This study aims to develop better understanding of the spray breakup processes and provide better experimental inputs to improve the fidelity of numerical models. This work adresses two key research areas: determining the time required for a liquid column to break up in the crossflow (i.e., primary breakup time) and the effect of injector geometry on spray properties. A new diagnostic technique, the liquid jet light guiding technique that utilizes ability of the liquid jet to act as a waveguide for laser light was developed to determine the location where the liquid column breaks up, in order to obtain the primary breakup time. This study found that the liquid jet Reynolds number was an important factor that governed the primary breakup time and improved the existing correlation. Optical diagnostic techniques such as Phase Doppler Particle Analyzer, Liquid Jet Light Guiding Technique, Particle Image Velocimetry and Imaging techniques were employed to measure the spray properties that include spray penetration, droplet sizes and velocities, velocity field on the surface of the liquid jet and the location of the primary breakup time. These properties were measured for two injectors: one with a sharp transition and the other with a smooth transition. It was found that the spray created by the injector with a sharp transition forms large irregular structures while one with smooth transition produces a smooth liquid jet. The spray transition creates a spray that penetrates deeper into the crossflow, breakup up earlier and produces larger droplets. Additionally, this study reports the phenomenon of the liquid jet splitting into two or more jets in sprays created by the injector with a smooth transition.

A lot has changed since that day on December 17, 1903 when the Wright brothers made the first powered manned flight. Even though the concepts behind flying are unaltered, appearance of stat-of-the-art modern aircrafts has undergone a massive evolution. This is mainly owed to our deeper understanding of how to harness and optimize the interaction between fluid flows and aircraft bodies. Flow passing over wings and different junctions on an aircraft faces numerous local features, for instance, acceleration or deceleration, laminar or turbulent state, and interacting boundary layers. In our study we aim to characterize some of these flow features and their physical roles. Primarily, stability characteristics of flow over a wing subject to a negative pressure gradient are studied. This is a common condition for flows over swept wings. Part of the current numerical study conforms to existing experimental studies where a passive control mechanism has been tested to delay laminarturbulent transition. The same flow type has also been considered to study the receptivity of three-dimensional boundary layers to freestream turbulence. The work entails investigation of effects of low-level freestream turbulence on crossflow instability, as well as interaction with micron-sized surface roughness elements. Another common three-dimensional flow feature arises as a resultof stream-lines passing through a junction, the so-calledcorner-flow. For instance, thisflow can be formed in the junction between the wing and fuselage on aplane.A series of direct numerical simulations using linear Navier-Stokes equationshave been performed to determine the optimal initial perturbation. Optimalrefers to perturbations which can gain the maximum energy from the flow overa period of time. In other words this method seeks to determine theworst-casescenario in terms of perturbation growth. Here, power-iterationtechnique hasbeen applied to the Navier-Stokes equations and their adjoint to determine theoptimal initial perturbation. Recent advances in super-computers have enabled advance computational methods to increasingly contribute to design of aircrafts, in particular for turbulent flows with regions of separation. In this work we investigate theturbulentflow on an infinite wing at a moderate chord Reynolds number of Re= 400,000 using a well resolved direct numerical simulation. A conventional NACA4412 has been chosen for this work. The turbulent flow is characterizedusing statistical analysis and following time history data in regions with interesting flow features. In the later part of this work, direct numerical simulation has been chosen as a tool to mainly investigate the effect of freestream turbulence on the transition mechanism of flow from laminar to turbulent around a turbine blade. / <p>QC 20151125</p>