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Standard eddy-viscosity models lack curvature and system rotation sensitized terms in their formulation. Hence they fail to capture the effects of curvature and system rotation on turbulence anisotropy. As part of this effort, an algebraic expression for a characteristic rotation term is developed and tuned with the help of rotating homogeneous shear flow. This formulation is primarily based upon the rotation and curvature sensitized eddy-viscosity coefficient developed by York et al. (2009). A new scalar transport equation loosely based on Durbin’s wall normal turbulent velocity scale (Durbin, 1991) is introduced to account for the modification in turbulence structure due to system rotation and curvature effects. The added transport equation also introduces history effects and stability in the solution with small increase in computational cost. The eddy-viscosity is redefined based on new turbulent velocity scale and hence the effects of rotation and streamline curvature are introduced into the mean momentum equation. A number of canonical test cases with significant curvature and rotation effects along with a cyclone flow, a representative of complex industrial flows, are considered for model validation. Hybrid modeling framework combines the strength of RANS in boundary layers and LES in separated shear layers to alleviate the weaknesses of RANS and limitations of LES model in some complex flows. A recently proposed hybrid RANS-LES modeling framework uses a weighing parameter that dynamically determines the RANS and LES regions based on solution statistics. The hybrid modeling methodology is implemented on a normal jet in crossflow, and a film cooling case for the purpose of model validation and evaluation. The final goal of the proposed effort is to combine advanced RANS modeling capability with LES using the new hybrid modeling framework. Specifically, the curvature and rotation sensitive RANS model developed here is coupled with commonly used LES models to produce a novel model for complex turbulent flows with the potential to improve accuracy of CFD predictions (versus existing RANS models) as well as significantly reduce the computational expense (versus existing LES models). Performance of the model form hence developed is evaluated on a cyclone flow case.

This paper aims to study how varying crossflow burning temperatures from 1100 C to 1800 C affect the liquid droplet breakup, size distribution, and atomization of a liquid water jet injected into a vitiated crossflow. The LJIC injection mechanism was implemented using the high-pressure axially staged combustion facility at the University of Central Florida. The measurement devices used to gather particle data from the exhaust plume were the TSI Aerodynamic Particle Sizer (APS), which measures particles between 0.523 µm and 20 µm, and the Sensirion SPS30 (SPS30), which measures particles between 0.3 µm and 10 µm. Both measurement devices were placed 3 ft away from the choked exit. Table 3 shows that the 1800 C crossflow temperature behaved as predicted by having the largest particle distribution of 67.97% and the largest particle count of 19,301 at 0.523 µm. The 1100 C crossflow produced the second-largest normalized particle count of 66.69% and raw particle count of 20,209 at 0.523 µm. This result is contrary to the original hypothesis because it shows that the relationship between temperature and particle count is non-linear and that many other factors must be at play in the atomization process, such as the droplet distribution at the nano level. The SPS30 was used to compare the particle size distributions between a 1500 C and 1800 C crossflow. Acquiring number concentration data for particles up to 10 µm in size, the 1800 C crossflow had a distribution peak at 802.76416 N/cm3, and the 1500 C crossflow had a peak of 867.28272 N/cm3. For the 0.5 µm peak, The 1800 C had a 10 µm particle size distribution peak at 674.27.76416 N/cm3, and the 1500C crossflow had a peak of 730.501 N/cm3. The decreased number concentration from 1500 C to 1800 C case grants the water particles in the 1800 C crossflow increased surface area, which allows for increased heat exposure from the vitiated crossflow [7]. Despite some nonlinear particle count results, the highest crossflow temperature of 1800 C produces the best atomization results by reducing the total particle count and having the largest collection of particles at the lowest detectable particle size of 0.523 µm.

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

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.

The Gaseous state of hydrogen at ambient temperature, combined with the fact that hydrogen is highly flammable, results in the requirement of more robust, high pressure storage systems that can meet modern safety standards. To develop these new safety standards and to properly predict the phenomena of hydrogen dispersion, a better understanding of the resulting flow structures and flammable regions from controlled and uncontrolled releases of hydrogen gas must be achieved. In this study the subsonic release of hydrogen was emulated using helium as a substitute working fluid. A sharp-edged orifice round turbulent jet is used to emulate releases in which leak geometry is circular. Effects of buoyancy, crossflow and adjacent surfaces were studied over a wide range of Froude numbers. The velocity fields of turbulent jets were characterized using particle image velocimetry (PIV). The mean and fluctuation velocity components were well quantified to show the effect of buoyancy due to the density difference between helium and the surrounding air. In the range of Froude numbers investigated, increasing effects of buoyancy were seen to be proportional to the reduction of the Fr number. The obtained results will serve as control reference values for further concentration measurement study and for computational fluid dynamics (CFD) validation. / Graduate

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The present work refers to the characterization of the sound field generated by subsonic jets in crossflow (JICF). This phenomenon that results from a jet of fluid discharged perpendicularly to a moving medium has a very complex, but well established, fluid dynamics and a sound field yet unexplored. For the complete characterization of this phenomenon, a hybrid methodology of low computational cost that uses a combination of commercial and open source packages is used. The fluid dynamics part is solved by the commercial code CFD ++ by Metacomp Inc. through Reynolds Average Navier-Stokes Equations (RANS), and the noise calculations are performed on an open source code using the Lighthill Ray-Tracing method (LRT). An extensive validation step is performed to demonstrate the ability and highlight the limitations of the methods used for predicting the jet s behavior. This work brings a large contribution to the development of JICF noise research by showing the existence of a region of relative silence in these jets. / O presente trabalho refere-se ao estudo da caracterização do campo acústico de jatos subsônicos submetidos a escoamento cruzado (JSEC). Este fenômeno que resulta de um jato de fluido descarregado perpendicularmente a um meio em movimento, possui uma dinâmica muito complexa, mas bem estabelecida, e um campo acústico ainda inexplorado. Para a completa caracterização deste fenômeno, utiliza-se uma metodologia híbrida de baixo custo computacional, que associa pacotes comerciais e códigos abertos. A parte fluidodinâmica é solucionada pelo código computacional comercial CFD++ da empresa Metacomp Inc. por meio das Equações Médias de Reynolds (RANS), e os cálculos de ruído são realizados em código aberto utilizando o método de Lighthill Ray-Tracing (LRT). Uma extensa etapa de validações é realizada para comprovar a capacidade e evidenciar as limitações dos métodos utilizados na previsão do comportamento do jato. Este trabalho contribui para o avanço das pesquisas na área de ruído de JSEC, tendo identificado a existência de uma região de silêncio nesses jatos. / Mestre em Engenharia Mecânica

The mixing performance of multiple transverse jets has been evaluated experimentally. Measurement techniques included laser Doppler velocimetry and planar laser induced fluorescence. Basic findings are consistent with results presented in literature for single jet mixing behavior. Mixing performance has been compared to literature for the single jet case and the Holdeman parameter has been re-evaluated for effectiveness at low jet numbers. A single jet in a confined crossflow was found to have a local minimum at B(d⁄D) = 0.721. Results for two jets indicate monotonically decreasing unmixedness for the range of conditions tested, with no local optimum apparent. Data for three jets indicate a local optimum at B(d⁄D) = 0.87and relatively flat range of mixing performance in the range of 0.75 < B(d⁄D) < 1.5. Six jets indicate a minimum unmixedness near B(d⁄D) = 0.5, but exhibited poorer mixing performance than all other configurations at the highest values of B(d⁄D)tested. The most optimum configuration tested was six jets at B(d⁄D) = 0.5, resulting in an unmixedness of 0.0192. This value was 76% lower than the next lowest configuration (three jets) at the same B(d⁄D).Total momentum was found to collapse the data well, as configurations more closely matched a historical correlation for second moment of a single confined jet more closely.

La réduction des émissions polluantes est actuellement un enjeu majeur au sein du secteur aéronautique. Parmi les solutions développées par les motoristes, la combustion en régime pauvre apparaît comme une technologie efficace pour réduire l’impact de la combustion sur l’environnement.Or, ce type de technologie favorise l’apparition d’instabilités de combustion issues d’un couplage thermo-acoustique. Des études expérimentales précédemment menées à l’ONERA ont mis en évidence l’importance de l’atomisation au sein d’un injecteur multipoint sur le phénomène d’instabilités de combustion. L’objectif de cette thèse est de mettre en place la méthodologie multi-échelle pour reproduire les phénomènes de couplage entre l’atomisation du jet liquide en présence d’un écoulement gazeux transverse (configuration simplifiée d’un point d’injection d’un injecteur multipoint) et d’une perturbation acoustique imposée, représentative de l’effet d’une instabilité de combustion. Ce type d’approche pourra, à terme, être utilisé pour la simulation instationnaire LES d’un système de combustion, et permettra de déterminer les temps caractéristiques de convection du carburant liquide pouvant affecter les phénomènes d’évaporation et de combustion, et donc l’apparition des instabilités de combustions. Afin de valider cette approche,les résultats issus des simulations sont systématiquement comparés aux observations expérimentales obtenues dans le cadre du projet SIGMA. Dans un premier temps, une simulation du jet liquide en présence d’un écoulement gazeux transverse est réalisée. Cette simulation a permis de valider l’approche multi-échelle : pour cela, les grandes échelles du jet, ainsi que les mécanismes d’atomisation reproduits par les simulations, sont analysés. Ensuite, l’influence d’une perturbation acoustique sur l’atomisation du jet liquide est étudiée. Les comportements instationnaires du jet et du spray issu de l’atomisation sont comparés aux résultats expérimentaux à l’aide des moyennes temporelles et des moyennes de phase. / The reduction of polluting emissions is currently a major issue in the aeronautics industry.Among the solutions developed by the engine manufacturers, lean combustion appears as an effectivetechnology to reduce the impact of combustion on the environment. However, this type oftechnology enhances the onset of combustion instabilities, resulting from a thermo-acoustic coupling.Experimental studies previously conducted at ONERA have highlighted the importanceof atomization in a multipoint injector to the combustion instabilities. The aim of this thesis isto implement the multi-scale methodology to reproduce the coupling phenomena between theatomization of the liquid jet in the presence of a crossflow (which is a simplified configuration ofan injection point of a multipoint injector) and an imposed acoustic perturbation, representativeof the effect of combustion instabilities. This type of approach can ultimately be used for the unsteadysimulation of a combustion system, and will determine the characteristic convection timesof the liquid fuel that can affect the phenomena of evaporation and combustion, and therefore theappearance of combustion instabilities. In order to validate this approach, the results obtainedfrom the simulations are systematically compared with the experimental observations obtainedwithin the framework of the SIGMA project. First, a simulation of the liquid jet in gaseous crossflowis performed. This simulation enabled us to validate the multi-scale approach : to this end,the large scales of the jet, as well as the atomization mechanisms reproduced by the simulations,are analyzed. Then, the influence of an acoustic perturbation on the atomization of the liquidjet is studied. The unsteady behavior of the jet and the spray resulting from the atomization arecompared with the experimental results using time averages and phase averages.

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