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While the gas turbine research community is continuously pursuing development of higher cyclic efficiency designs by increasing the combustor firing temperatures and thermally resistant turbine vane / blade materials, a simultaneous effort to reduce the emission levels of high temperature driven thermal NOX also needs to be addressed. Lean premixed combustion has been found as one of the solutions to these objectives. However, since less amount of air is available for backside cooling of liner walls, it becomes very important to characterize the convective heat transfer that occurs on the inside wall of the combustor liners. These studies were explored using laboratory scale experiments as well as numerical approaches for several inlet flow conditions under both non-reacting and reacting flows. These studies may be expected to provide valuable insights for the industrial design communities towards identifying thermal hot spot locations as well as in quantifying the heat transfer magnitude, thus aiding in effective designs of the liner walls. Lean premixed gas turbine combustor flows involve strongly coupled interactions between several aspects of physics such as the degree of swirl imparted by the inlet fuel nozzle, premixing of the fuel and incoming air, lean premixed combustion within the combustor domain, the interaction of swirling flow with combustion driven heat release resulting in flow dilation, the resulting pressure fluctuations leading to thermo-acoustic instabilities there by creating a feedback loop with incoming reactants resulting in flow instabilities leading to flame lift off, flame extinction etc. Hence understanding combustion driven swirling flow in combustors continues to be a topic of intense research. In the present study, numerical predictions of swirl driven combustor flows were analyzed for a specific swirl number of an industrial fuel nozzle (swirler) using a commercial computational fluid dynamics tool and compared against in-house experimental data. The latter data was obtained from a newly developed test rig at Applied Propulsion and Power Laboratory (APPL) at Virginia Tech. The simulations were performed and investigated for several flow Reynolds numbers under non-reacting condition using various two equation turbulence models as well as a scale resolving model. The work was also extended to reacting flow modeling (using a partially premixed model) for a specific Reynolds number. These efforts were carried out in order investigate the flow behavior and also characterize convective heat transfer along the combustor wall (liner). Additionally, several parametric studies were performed towards investigating the effect of combustor geometry on swirling flow and liner hear transfer; and also to investigate the effect of inlet swirl on the jet impingement location along the liner wall under both non-reacting as well as reacting conditions. The numerical results show detailed comparison against experiments for swirling flow profiles within the combustor under reacting conditions indicating a good reliability of steady state modeling approaches for reacting conditions; however, the limitations of steady state RANS turbulence models were observed for non-reacting swirling flow conditions, where the flow profiles deviate from experimental observations in the central recirculation region. Also, the numerical comparison of liner wall heat transfer characteristics against experiments showed a sensitivity to Reynolds numbers. These studies offer to provide preliminary insights of RANS predictions based on commercial CFD tools in predicting swirling, non-reacting and reacting flow and heat transfer. They can be extended to reacting flow heat transfer studies in future and also may be upgraded to unsteady LES predictions to complement future experimental observations conducted at the in-house test facility. / Ph. D.

[ES] En los últimos años, el interés por el desarrollo de motores de aviación limpios y eficientes se ha incrementado debido al impacto perjudicial sobre la salud y el medio ambiente ocasionado por los sistemas de combustión convencionales. En este contexto, la comunidad científica ha ido centrando cada vez más sus esfuerzos en el estudio de la combustión turbulenta y la generación de emisiones contaminantes como las partículas de hollín. Con los recientes avances en lo que respecta a potencia de cálculo, las simulaciones de alta fidelidad emergen como una valiosa alternativa para reproducir y analizar estos fenómenos. En concreto, las simulaciones basadas en el modelado de la turbulencia LES son consideradas como una de las herramientas numéricas más prometedoras a la hora de profundizar en la comprensión sobre los complejos procesos dinámicos que caracterizan el flujo reactivo turbulento y predecir emisiones de hollín en aplicaciones aeronáuticas. En el presente trabajo, se estudia y analiza la combustión turbulenta y producción de hollín en aplicaciones de turbina de gas mediante LES de alta fidelidad. El modelado de la combustión se aborda a través de un método flexible de química tabulada basado en el concepto flamelet, el cual es capaz de representar fenómenos químicos complejos con un coste computacional asequible. Además, se emplea una aproximación Euleriana-Lagrangiana para la descripción de la fase gaseosa y las gotas, de forma que se represente correctamente el flujo reactivo multifásico. Para la predicción de hollín en simulaciones computacionalmente eficientes, se emplea un novedoso enfoque de modelado basada en el método seccional y acoplada al modelo de combustión de química tabulada. Esta estrategia de modelado numérica es utilizada en este trabajo para analizar el proceso de combustión y evaluar sus capacidades para predecir hollín y las características de la llama en quemadores de turbina de gas representativos. En primer lugar, se estudia la combustión de flujo bifásico en una llama atmosférica sin torbellinador con inyección líquida de combustible. Este quemador presenta una estructura doble del frente reactivo y las simulaciones numéricas son capaces de capturar adecuadamente los fenómenos de extinción local que tienen lugar en la zona interna de la llama debido a la interacción de las gotas y la turbulencia con el frente reactivo. Posteriormente, se investiga la combustión y producción de hollín en un quemador presurizado con torbellinador que incluye aire secundario de dilución en el interior de la cámara de combustión. La validación del flujo reactivo y hollín se lleva a cabo tanto en la configuración del quemador con aire secundario como sin el mismo, mostrando unas excelentes capacidades predictivas en ambos casos. La presente estrategia de modelado reproduce de forma precisa el complejo patrón de flujo, la estructura de la llama y la dinámica de generación de hollín, además de que es capaz de proporcionar diferentes distribuciones de tamaño de partícula dependiendo de las variaciones en los procesos de formación y oxidación del hollín. En resumen, los diferentes casos prácticos estudiados permiten consolidar y validar la metodología computacional seguida en la presente tesis. La estrategia de modelado basada en química tabulada propuesta demuestra ser lo suficientemente válida y adecuada para reproducir los complejos fenómenos de la combustión y la formación de hollín, en vista de la consistencia del análisis, las precisas predicciones y la concordancia satisfactoria con las medidas experimentales. / [CA] En els últims anys, l'interés pel desenvolupament de motors d'aviació nets i eficients s'ha incrementat a causa de l'impacte perjudicial sobre la salut i el medi ambient ocasionat pels sistemes de combustió convencionals. En aquest context, la comunitat científica ha anat centrant cada vegada més els seus esforços en l'estudi de la combustió turbulenta i la generació d'emissions contaminants com les partícules de sutge. Amb els recents avanços pel que fa a potència de càlcul, les simulacions d'alta fidelitat emergeixen com una valuosa alternativa per a reproduir i analitzar aquests fenòmens. En concret, les simulacions basades en el modelatge de la turbulència LES són considerades com una de les eines numèriques més prometedores a l'hora d'aprofundir en la comprensió sobre els complexos processos dinàmics que caracteritzen el flux reactiu turbulent i predir emissions de sutge en aplicacions aeronàutiques. En el present treball, s'estudia i analitza la combustió turbulenta i la producció de sutge en aplicacions de turbina de gas mitjançant LES d'alta fidelitat. El modelatge de la combustió s'aborda a través d'un mètode flexible de química tabulada basat en el concepte flamelet, el qual és capaç de representar fenòmens químics complexos amb un cost computacional assequible. A més, s'empra una aproximació Euleriana-Lagrangiana per a la descripció de la fase gasosa i les gotes, de manera que es represente correctament el flux reactiu multifàsic. Per a la predicció de sutge en simulacions computacionalment eficients, s'empra un nou plantejament de modelatge basat en el mètode seccional i acoblat al model de combustió de química tabulada. Aquesta estratègia de modelatge numèrica és utilitzada en aquest treball per a analitzar el procés de combustió en cremadors de turbina de gas representatius, i avaluar les seues capacitats per a predir sutge i les característiques de la flama. En primer lloc, s'estudia la combustió de flux bifàsic en una flama atmosfèrica sense remolinador amb injecció líquida de combustible. Aquest cremador presenta una estructura doble del front reactiu i les simulacions numèriques són capaces de capturar adequadament els fenòmens d'extinció local que tenen lloc en la zona interna de la flama a causa de la interacció de les gotes i la turbulència amb el front reactiu. Posteriorment, s'investiga la combustió i producció de sutge en un cremador pressuritzat amb remolinador que inclou aire secundari de dilució a l'interior de la cambra de combustió. La validació del flux reactiu i sutge es duu a terme tant en la configuració del cremador amb aire secundari com sense aquest, mostrant unes estupendes capacitats predictives en tots dos casos. La present estratègia de modelatge reprodueix de manera precisa el complex patró de flux, l'estructura de la flama i la dinàmica de generació de sutge, a més de que és capaç de proporcionar diferents distribucions de grandària de partícula depenent de les variacions en els processos de formació i oxidació del sutge. En resum, els diferents casos pràctics estudiats permeten consolidar i validar la metodologia computacional seguida en la present tesi. L'estratègia de modelatge basada en química tabulada proposada demostra ser prou vàlida i adequada per a reproduir els complexos fenòmens de la combustió i la formació de sutge, en vista de la consistència de l'anàlisi, les precises prediccions i la concordança satisfactòria amb les mesures experimentals. / [EN] In recent years, interest in the development of efficient and clean aviation powerplants has increased due to the detrimental impact on health and the environment caused by conventional combustion systems. In this context, the research community has increasingly focused its efforts on the study of turbulent combustion and the generation of pollutant emissions such as soot particulates. With recent advances in computational power, high-fidelity simulations emerge as a valuable alternative to reproduce and analyze these phenomena. Specifically, Large Eddy Simulations (LES) are considered as one of the most promising numerical tools to provide further insight into the complex dynamic processes that characterize reactive turbulent flows and predict soot emissions in aeronautical applications. In the present work, turbulent combustion and soot production is studied and analyzed in gas turbine engine applications by means of high-fidelity LES. Combustion modelling is addressed by a flexible tabulated chemistry method based on the flamelet concept, which is able to represent complex chemical phenomena with an affordable computational cost. In addition, an Eulerian- Lagrangian description is employed for the gas phase and droplets in order to correctly represent the multiphase flow in spray flames. A recently developed approach based on the sectional method and coupled to the tabulated chemistry framework is considered for soot prediction in computationally efficient simulations. This numerical modelling framework is used in this work to analyze the combustion process and evaluate its capabilities to predict soot and flame characteristics in representative gas turbine burners. First, an atmospheric non-swirled spray flame is studied in terms of two-phase flow combustion. This burner shows a double reaction front structure and local extinction occurs in the inner layer due to both droplet-flame and turbulence-flame interactions, which is properly characterized by LES. Subsequently, combustion and soot production is investigated in a pressurized swirled model combustor which includes secondary dilution jets inside the combustion chamber. The assessment of the reacting flow field and soot is addressed for burner configurations with and without secondary air, showing excellent predictive capabilities in both cases. The present modelling approach accurately reproduce the complex swirled flow field, flame structure and soot dynamics and is able to provide different particle size distributions depending on the variations of the soot formation and oxidation processes. In summary, the different practical cases studied allow to consolidate and validate the computational methodology followed in the present thesis. The proposed tabulated modelling strategy is sufficiently valid and suitable for reproducing complex combustion and soot formation phenomena, in view of the consistency of the analysis, the accurate predictions and the satisfactory agreement with the experimental measurements. / El desarrollo de la presente tesis ha sido posible gracias a una ayuda para la Formación de Profesorado Universitario (FPU 18/03065) perteneciente al Subprograma Estatal de Formación del Ministerio de Ciencia, Innovación y Universidades de España. Además, el trabajo desarrollado está enmarcado en el proyecto ESTiMatE (Emissions SooT ModEl), que ha sido financiado por el consorcio Clean Sky 2 bajo el programa de investigación e innovación Horizonte 2020 de la Unión Europea (acuerdo No. 821418). Las actividades de simulación numérica han sido posibles gracias a la Red Española de Supercomputación y al Centro de Supercomputación de Barcelona por los recursos computacionales proporcionados en MareNostrum, además del grupo PRACE por conceder el acceso a HAWK (GCS, HLRS, Alemania) a través del proyecto SootAero. / Olmeda Ramiro, I. (2023). Assessment of Detailed Combustion and Soot Models for High-Fidelity Aero-Engine Simulations [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/202284

In modern, low emission, gas turbine combustion systems the amount of air available for cooling of the flame tube liner is limited. This has led to the development of more complex cooling systems such as cooling tiles i.e. a double skin system, as opposed to the use of more conventional cooling slots i.e. a single skin system. An isothennal experimental facility has been constructed which can incorporate 10 times full size single and double skin (cooling tile) test specimens. The specimens can be tested with or without effusion cooling and measurements have been made to characterise the flow through each cooling system along with the velocity field and cooling effectiveness distributions that subsequently develop along the length of each test section. The velocity field of the coolant film has been defined using pneumatic probes, hot-wire anemometry and PIV instrumentation, whilst gas tracing technique is used to indicate (i) the adiabatic film cooling effectiveness and (ii) mixing of the coolant film with the mainstream flow. Tests have been undertaken both with a datum low turbulence mainstream flow passing over the test section, along with various configurations in which large magnitudes and scales of turbulence were present in the mainstream flow. These high turbulence test cases simulate some of the flow conditions found within a gas turbine combustor. Results are presented relating to a variety of operating conditions for both types of cooling system. The nominal operating condition for the double skin system was at a coolant to mainstream blowing ratio of approximately 1.0. At this condition, mixing of the mainstream and coolant film was relatively small with low mainstream turbulence. However, at high mainstream turbulence levels there was rapid penetration of the mainstream flow into the coolant film. This break up of the coolant film leads to a significant reduction in the cooling effectiveness. In addition to the time-averaged characteristics, the time dependent behaviour of the .:coolantfilm was. also investigated. In particular, unsteadiness associated with large scale structures in the mainstream flow was observed within the coolant film and adjacent to the tile surface. Relative to a double skin system the single skin geometry requires a higher coolant flow rate that, along with other geometrical changes, results in typically higher coolant to mainstream velocity ratios. At low mainstream turbulence levels this difference in velocity between the coolant and mainstream promotes the generation of turbulence and mixing between the streams so leading to some reduction in cooling effectiveness. However, this higher momentum coolant fluid is more resistant to high mainstream turbulence levels and scales so that the coolant film break up is not as significant under these conditions as that observed for the double skin system. For all the configurations tested the use of effusion cooling helped restore the coolant film along the rear of the test section. For the same total coolant flow, the minimum value of cooling effectiveness observed along the test section was increased relative to the no effusion case. In addition the effectiveness of the effusion patch depends on the amount of coolant injected and the axial location of the patch. The overall experimental data suggested the importance of the initial cooling film conditions together with better understanding of the possible mechanisms that results in the rapid cooling film break-up, such as high turbulence mainstream flow and scales, and this will lead to a more effective cooling system design. This experimental data is also thought to be ideal for the validation of numerical predictions.