Jet in crossflow (JICF) configurations are often used for secondary fuel injection in staged-fuel combustion systems. The high temperature, vitiated crossflow in these systems is inherently unsteady and characterized by random, turbulent fluctuations and coherent, acoustic oscillations. This thesis presents the results of an experimental investigation into the dynamics of non-reacting and reacting jets injected into unsteady, vitiated crossflow. The flow structure and flame stabilization of jets with different momentum flux and density ratios relative to the crossflow are characterized using simultaneous time-resolved stereoscopic particle image velocimetry (SPIV) synchronized with OH planar laser induced fluorescence (PLIF). A modified trajectory scaling law is developed to account for the influence of near-field heat release on the jet trajectory. The second part of this work focuses on the response of a JICF to crossflow forcing. Acoustic drivers are used to excite natural resonances of the facility, which are characterized using the two-microphone method. Spectral analysis of SPIV results shows that, while the jet response to crossflow velocity fluctuations is often negligible, the fluctuating crossflow pressure induces a significant fluctuating jet exit velocity, which leads to periodic jet flapping. The flame response to crossflow forcing is studied using flame edge tracking. An analytical model is developed that predicts the dependence of the jet injector impedance upon important JICF parameters. In the final part of this work, vortex tracking and Mie scattering flow visualization are used to investigate the effect of near-field heat release on the shear layer dynamics. A phenomenological model is developed to explain the effect of combustion on the shear layer stability of density stratified, reacting JICF. The results of this study demonstrate the important effects of near-field heat release and crossflow acoustics on the dynamics of reacting JICF.

Over the past 25 years, advances in the field of turbulence modeling have been made in an effort to resolve more scales, preserving unsteadiness within a flow. In this research two hybrid models, Scale-Adaptive Simulation (SAS) and Stress-Blended Eddy Simulation (SBES) are implemented in solving the highly unsteady flow over a rotating arrangement of three cylinders. Results are compared to those from wind tunnel experiments carried out at North Dakota State University. Both models show close agreement with first and second order turbulence quantities, and SBES shows much greater flow structure detail due to its ability to resolve smaller scales. The Strouhal number for the flow is found to be a function of the rotational speed of the arrangement with von Karman-like structures resulting from each cylinder's wake over a full rotation. SAS shows a constant computational cost as Re increases while the SBES's computational cost increases relatively linearly.

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The highly competitive gas turbine industry has been motivated by consumer demands for higher power-to-weight ratios, increased thermal efficiencies, and reliability while maintaining affordability. In its continual quest, the industry must continually try to raise the turbine inlet temperature, which according to the well-known Brayton cycle is key to higher engine efficiencies. The desire for increased turbine inlet temperatures creates an extremely harsh environment for the combustor liner in addition to the components downstream of the combustor. Shear layers between the dilution jets and the mainstream, as well as combustor liner film-cooling interactions create a complex mean flow field within the combustor, which is not easy to model. A completely uniform temperature and velocity profile at the combustor exit is desirable from the standpoint of reducing the secondary flows in the turbine. However, this seldom occurs due to a lack of thorough mixing within the combustor. Poor mixing results in non-uniformities, such as hot streaks, and allow non-combusted fuel to exit the combustor. This investigation developed a database documenting the thermal and flow characteristics within a combustor simulator representative of the flowfield within a gas turbine aero-engine. Three- and two-component laser Doppler velocimeter measurements were completed to quantify the flow and turbulence fields, while a thermocouple rake was used to quantify the thermal fields. The measured results show very high turbulence levels due to the dilution flow injection. Directly downstream of the dilution jets, an increased thickness in the film-cooling was noted with a fairly non-homogeneous temperature field across the combustor width. A highly turbulent shear layer was found at the leading edge of the dilution jets. Measurements also showed that a relatively extensive recirculation region existed downstream of the dilution jets. Despite the lack of film-cooling injection at the trailing edge of the dilution hole, there existed coolant flow indicative of a horse-shoe vortex wrapping around the jet. As a result of the dilution jet interaction with the mainstream flow, kidney-shaped thermal fields and counter-rotating vortices developed. These vortices serve to enhance combustor mixing. / Master of Science

A lack of complex analysis for a thermally buoyant jet in a stratified crossflow has motivated the studies presented. A computational approach using the incompressible Navier--Stokes equations (NSE) under the Boussinesq approximation is utilized. Temperature and salinity scalar transport equations are utilized in conjunction with a linear equation of state (EOS) to obtain the density field and thus the buoyancy forcing. Comparing simulation data to experimental data of a point heat source in a stratified environment provides general agreement between the aforementioned computational model and the physics studied. From the literature surveyed, no unified agreement was presented on the selection of turbulence models for the jet--in--crossflow (JICF) problem. For this reason, a comparison is presented for a standard Reynolds--Averaged Navier--Stokes (RANS) and a hybrid Reynolds--Averaged Navier--Stokes/large eddy simulation (HRLES) turbulence model. The mathematical differences are outlined as well as the implications each model has on solving a buoyant jet in stratified crossflow. The RANS model provides a general over prediction of all flow quantities when comparing to the HRLES models. Studies involving the removal of the thermal component inside the jet as well as varying the environmental stratification strength have largely determined that these affects do not alter the near-field in any significant way, at least for a high Reynolds number JICF. The velocity ratio of the jet being the ratio of the jet velocity to the free--stream flow velocity. Deviating from a velocity ratio of one has provided information on the variability of the forcing on the plate the jet exits from, as well as in the integrated energy quantities far downstream of the jet's exit. The departures presented here show that any deviation from the unity value provides an increase in the overall forces seen by the plate. It was also found that the change in the integrated potential and turbulent kinetic energies is proportional to the deviation from a unity velocity ratio. / Master of Science / A lack of complex analysis for a heated jet in a non-uniform crossflow has motivated the studies presented. A computational approach for the fluid dynamics governing equations under specific assumptions is implemented. Additional equations are solved for temperature and salinity in conjunction with a linear equation of state to obtain the density field. Comparing simulations to experimental data of a point heat source in a non-uniform, fluid tank provides general agreement between the aforementioned computational model and the physics studied. Studying the literature yields no unified agreement on the selection of turbulence treatment for the jet-in-crossflow problem. For this reason, a comparison is presented for two various techniques with differing complexity. The mathematical differences as well as the implications each model are outlined, specifically pertaining to a heated jet in a non-uniform crossflow. The simpler model provides a general over prediction when compared to the more complex model. Studies involving the removal of the heat from inside the jet as well as varying the environmental forcing have largely determined that these affects do not alter the flow field near the jet's origin point in any significant way. Changing the jet's velocity has provided information on the variability of the forcing on the plate the jet exits from, as well as in the energy released into the environment far downstream of the jet's exit. The ratios presented show that any deviation from a notional value provides an increase in the overall forces seen by the plate. It was also found that the change in the released energies is proportional to the deviation from the notional jet velocity.

No description available.

No description available.

This thesis deals with the instabilities of the incompressible boundary-layer flow thatis induced by a disk rotating in otherwise still fluid. The results presented include bothwork in the linear and nonlinear regime and are derived from direct numerical sim-ulations (DNS). Comparisons are made both to theoretical and experimental resultsproviding new insights into the transition route to turbulence. The simulation codeNek5000 has been chosen for the DNS using a spectral-element method (SEM) witha high-order discretization, and the results were obtained through large-scale paral-lel simulations. The known similarity solution of the Navier–Stokes equations for therotating-disk flow, also called the von K ́arm ́an rotating-disk flow, is reproduced by theDNS. With the addition of modelled small simulated roughnesses on the disk surface,convective instabilities appear and data from the linear region in the DNS are anal-ysed and compared with experimental and theoretical data, all corresponding verywell. A theoretical analysis is also presented using a local linear-stability approach,where two stability solvers have been developed based on earlier work. Furthermore,the impulse response of the rotating-disk boundary layer is investigated using DNS.The local response is known to be absolutely unstable and the global response, onthe contrary, is stable if the edge of the disk is assumed to be at radius infinity. Herecomparisons with a finite domain using various boundary conditions give a globalbehaviour that can be both linearly stable and unstable, however always nonlinearlyunstable. The global frequency of the flow is found to be determined by the Rey-nolds number at the confinement of the domain, either by the edge (linear case) or bythe turbulence appearance (nonlinear case). Moreover, secondary instabilities on topof the convective instabilities induced by roughness elements were investigated andfound to be globally unstable. This behaviour agrees well with the experimental flowand acts at a smaller radial distance than the primary global instability. The sharpline corresponding to transition to turbulence seen in experiments of the rotating diskcan thus be explained by the secondary global instability. Finally, turbulence datawere compared with experiments and investigated thoroughly. / <p>QC 20170203</p>

Quelque soit la zone de culture, l'anacardier (Anacardium occidentale L.) est essentiellement cultivé pour la production de noix de cajou, filière d'une grande importance socio-économique notamment au Brésil. Le jus de cajou est un produit secondaire qui résulte du pressage du pédoncule hypertrophié de la noix appelé pomme de cajou (pseudo-fruit). Le traitement des pommes engendre de grands volumes de déchets solides qui sont soit mis en décharge, soit utilisés pour l'alimentation animale. Dans ce contexte, le travail a pour objectif de proposer et d'évaluer un nouveau procédé permettant d'accroître la valeur ajoutée de ce sous-produit en extrayant les caroténoïdes qu'il contient. Le procédé comporte 3 opérations successives : une extraction par pressage associée à une macération enzymatique, une concentration à froid de l'extrait par microfiltration tangentielle et une purification par diafiltration. La première opération a été optimisée à l'aide de 2 plans d'expériences : un plan de criblage de facteurs de Plackett-Burmam (matrice de Hadamard) pour sélectionner les paramètres opératoires les plus influents suivi d'un plan central composite pour les optimiser. La dose de pectinase utilisée durant la macération et la force appliquée lors du pressage sont les paramètres les plus influents sur le profil caroténoïdique de l'extrait. De fortes doses de pectinase associées à une force de pressage élevée permettent d'obtenir à la fois un extrait plus riche en caroténoïdes et une meilleure densité de flux de perméat en microfiltration. L'utilisation de plusieurs cycles successifs de pressage permet d'augmenter les teneurs en caroténoïdes de l'extrait mais augmente également son pouvoir colmatant en microfiltration. L'étude de la concentration de l'extrait par microfiltration tangentielle a montré qu'il est possible d'atteindre un facteur de réduction volumique (FRV) de 20 en maintenant des densité de flux de perméat supérieures à 100 L.h-1.m-2. Les caroténoïdes sont concentrés à hauteur du FRV choisi (jusqu'à 20 fois). La diafiltration a permis de purifier 5 fois les caroténoïdes par rapport à la matière sèche. Un modèle simple basé sur des bilans matières pour prévoir l'impact du FRV et du diavolume sur la composition de l'extrait a été développé et validé. L'extrait final obtenu présente une teneur en caroténoïdes de 70 mg.kg-1. Parmi les 11 molécules identifiées par HPLC-DAD, les caroténoïdes majoritaires sont les isomères cis et trans de l'auroxanthine, la β-cryptoxanthine et le β-carotène. Les extraits finaux obtenus se présentent sous forme de liquides visqueux de couleur jaune intense, faciles à disperser dans l'eau. Ils possèdent un fort potentiel d'utilisation dans la formulation des aliments comme colorant naturel. / Whatever is the area of plantation, cashew (Anacardium occidentale L.) is grown primarily for the production of nuts, a supply chain that has great socioeconomic importance, especially in Brazil. The cashew juice is a by-product that results from pressing the nut hypertrophied peduncle, known as cashew apple, a juicy pseudo fruit. Peduncle processing generates large volumes of industrial solid waste that are usually discarded or sometimes used as animal feed. In this context, this work aimed to propose and evaluate a new process that provides an added value to this industrial byproduct, extracting carotenoids that were contained therein. The process comprised three successive operations: an extraction by pressing associated to an enzymatic maceration, a cold concentration of the extract by crossflow microfiltration and a purification by diafiltration. The first operation was optimized with the use of two experimental designs: a Plackett-Burmam (Hadamard matrix) plan for factors screening to select the most influential operating parameters, followed by a central composite design for optimization. The dose of pectinase used during maceration and the applied force used during the pressing operation were the most influential parameters on the carotenoid extract profile. High doses of pectinase associated with a high pressing force led to a richer carotenoid extract and enhanced the permeate flux in microfiltration. The use of several successive cycles of compression increased the carotenoid content of the extract but also increased its fouling properties during microfiltration. The extract concentration by crossflow microfiltration study showed that it was possible to reach values of volumetric reduction ratio (VRR) of about 20, maintaining the permeate flux above 100 Lh-1.m-2. The carotenoids were concentrated in the same levels of FRV (up to 20 times). The diafiltration allowed purification of carotenoids 5 times in relation to the dry matter. A simple model, based on a mass balance to predict the impact of VRR and diavolume on the extract composition was developed and validated. The final extract obtained presented a carotenoid content of 70 mg.kg-1. Among the 11 compounds identified by HPLC-DAD, the main carotenoids were cis and trans isomers of auroxanthine, β-cryptoxanthin and β-carotene. The final extracts obtained were in the form of viscous liquids of a yellow intense color, and easily dispersed in water. These concentrates have a strong potential for use in the formulation of foods and beverages as a natural dye.

The effect of superheat on the disruption of liquid droplets in a compressible gas flow was investigated experimentally in a small-scale, supersonic wind tunnel. Aerodynamically generated ethanol droplets of an average diameter of 0.1 mm were injected via a normal sonic jet into a Mach 1.8 freestream. Both nonsuperheated and superheated droplets were injected with initial Weber numbers of approximately 700. The droplets and flow structure were photographed using the shadowgraph method. The relatively high momentum of the liquid droplets typically caused them to pass out of the sonic jet structure. Nonsuperheated droplets showed no signs of disrupting after traveling over 200 mm downstream from the injection point. Only droplets with injection temperatures above the predicted boiling point at tunnel freestream static pressure (48°C) showed signs of disruption, typically after they left the sonic jet structure (30 to 100 mm downstream of the injection point). Droplets in this range of temperatures appeared to begin to boil from the downstream side of the droplet, shedding a vapor cloud before disrupting completely in the chaotic mode. Droplets with temperatures above the boiling point at the exit plane of the sonic jet began to disrupt in the chaotic mode almost instantly (within 1 exit nozzle diameter).