Numerical simulations of stationary and transient spray combustion for aircraft gas turbine applications

Le développement des turbines à gaz d’aviation actuelles et futures est principalement axé sur la sécurité, la performance, la minimisation de la consommation de l’énergie, et de plus en plus sur la réduction des émissions d’espèces polluantes. Ainsi, les phases de design de moteurs sont soumises auxaméliorations continues par des études expérimentales et numériques. La présente thèse se consacre à l’étude numérique des phases transitoires et stationnaires de la combustion au sein d’une turbine à gaz d’aviation opérant à divers modes de combustion. Une attention particulière est accordée à la précision des résultats, aux coûts de calcul, et à la facilité de manipulation de l’outil numérique d’un point de vue industriel. Un code de calcul commercial largement utilisé en industrie est donc choisi comme outil numérique. Une méthodologie de Mécanique des Fluides Numériques (MFN) constituée de modèles avancés de turbulence et de combustion jumelés avec un modèle d’allumage sous-maille, est formulé pour prédire les différentes phases de la séquence d’allumage sous différentes conditions d’allumage par temps froid et de rallumage en altitude, ainsi que les propriétés de la flamme en régime stationnaire. Dans un premier temps, l’attention est focalisée sur le régime de combustion stationnaire. Trois méthodologies MFN sont formulées en exploitant trois modèles de turbulence, notamment, le modèle basé sur les équations moyennées de Navier-Stokes instationnaires (URANS), l’adaptation aux échelles de l’écoulement (SAS), et sur la simulation aux grandes échelles (LES). Pour évaluer la pertinence de l’incorporation d’un modèle de chimie détaillée ainsi que celle des effets de chimie hors-équilibre, deux différentes hypothèses sont considérées : l’hypothèse de chimie-infiniment-rapide à travers le modèle d’équilibre-partiel, et l’hypothèse de chimie-finie via le modèle de flammelettes de diffusion. Pour chacune des deux hypothèses, un carburant à une composante, et un autre à deux composantes sont utilisés comme substituts du kérosène (Jet A-1). Les méthodologies MFN résultantes sont appliquées à une chambre de combustion dont l’écoulement est stabilisé par l’effet swirl afin d’évaluer l’aptitude de chacune d’elle à prédire les propriétés de combustion en régime stationnaire. Par la suite, les rapports entre le coût de calcul et la précision des résultats pour les trois méthodologies MFN formulées sont explicitement comparés. La deuxième étude intermédiaire est dédiée au régime de combustion transitoire, notamment à la séquence d’allumage précédant le régime de combustion stationnaire. Un brûleur de combustibles gazeux, muni d’une bougie d’allumage, et dont la flamme est stabilisée par un accroche-flamme, est utilisé pour calibrer le modèle MFN formulé. Ce brûleur, de géométrie relativement simple, peut aider à la compréhension des caractéristiques d’écoulements réactifs complexes, en l’occurrence l’allumabilité et la stabilité. La méthodologie MFN la plus robuste issue de la précédente étude est reconsidérée. Puisque le brûleur fonctionne en mode partiellement pré-mélangé, le modèle de combustion paramétré par la fraction de mélange et la variable de progrès est adopté avec les hypothèses de chimie-infiniment-rapide et de chimie-finie, respectivement à travers le modèle de Bray-Moss-Libby (BML) et un modèle de flammelettes multidimensionnel (FGM). Le modèle d’allumage sous-maille est préalablement ajusté via l’implémentation des propriétés de la flamme considérée. Par la suite, le modèle d’allumage est couplé au solveur LES, puis successivement aux modèles BML et FGM. Pour évaluer les capacités prédictives des méthodologies résultantes, ces dernières sont utilisées pour prédire les évènements d’allumage résultant d’un dépôt d’énergie par étincelles à diverses positions du brûleur, et les résultats sont qualitativement et quantitativement validés en comparant ceux-ci à leurs homologues expérimentaux. Finalement, la méthodologie MFN validée en configuration gazeuse est étendue à la combustion diphasique en la couplant au module de la phase liquide, et en incorporant les propriétés de la flamme de kérosène dans le modèle d’allumage. La méthodologie MFN résultant de cette adaptation, est préalablement appliquée à la chambre de combustion étudiée antérieurement, pour prédire la séquence d’allumage et améliorer les prédictions antérieures des propriétés de la flamme en régime stationnaire. Par la suite, elle est appliquée à une chambre de combustion plus réaliste pour prédire des évènements d’allumage sous différentes conditions d’allumage par temps froid, et de rallumage en altitude. L’aptitude de la nouvelle méthodologie MFN à prédire les deux types d’allumage considérés est mesurée quantitativement et qualitativement en confrontant les résultats des simulations numériques avec les enveloppes d’allumage expérimentales et les images d’une séquence d’allumage enregistrée avec une caméra infrarouge.The development of current and future aero gas turbine engines is mainly focused on the safety, the performance, the energy consumption, and increasingly on the reduction of pollutants and noise level. To this end, the engine’s design phases are subjected to improving processes continuously through experimental and numerical investigations. The present thesis is concerned with the simulation of transient and steady combustion regimes in an aircraft gas turbine operating under various combustion modes. Particular attention is paid to the accuracy of the results, the computational cost, and the ease of handling the numerical tool from an industrial standpoint. Thus, a commercial Computational Fluid Dynamics (CFD) code widely used in industry is selected as the numerical tool. A CFD methodology consisting of its advanced turbulence and combustion models, coupled with a subgrid spark-based ignition model, is formulated with the final goal of predicting the whole ignition sequence under cold start and altitude relight conditions, and the main flame trends in the steady combustion regime. At first, attention is focused on the steady combustion regime. Various CFD methodologies are formulated using three turbulence models, namely, the Unsteady Reynolds-Averaged Navier-Stokes (URANS), the Scale-Adaptive Simulation (SAS), and the Large Eddy Simulation (LES) models. To appraise the relevance of incorporating a realistic chemistry model and chemical non-equilibrium effects, two different assumptions are considered, namely, the infinitely-fast chemistry through the partial equilibrium model, and the finite-rate chemistry through the diffusion flamelet model. For each of the two assumptions, both one-component and two-component fuels are considered as surrogates for kerosene (Jet A-1). The resulting CFD models are applied to a swirl-stabilized combustion chamber to assess their ability to retrieve the spray flow and combustion properties in the steady combustion regime. Subsequently, the ratios between the accuracy of the results and the computational cost of the three CFD methodologies are explicitly compared. The second intermediate study is devoted to the ignition sequence preceding the steady combustion regime. A bluff-body stabilized burner based on gaseous fuel, and employing a spark-based igniter, is considered to calibrate the CFD model formulated. This burner of relatively simple geometry can provide greater understanding of complex reactive flow features, especially with regard to ignitability and stability. The most robust of the CFD methodologies formulated in the previous configuration is reconsidered. As this burner involves a partially-premixed combustion mode, a combustion model based on the mixture fraction-progress variable formulation is adopted with the assumptions of infinitely-fast chemistry and finite-rate chemistry through the Bray-Moss-Libby (BML) and Flamelet Generated Manifold (FGM) models, respectively. The ignition model is first customized by implementing the properties of the flame considered. Thereafter, the customized ignition model is coupled to the LES solver and combustion models based on the two above-listed assumptions. To assess the predictive capabilities of the resulting CFD methodologies, the latter are used to predict ignition events resulting from the spark deposition at various locations of the burner, and the results are quantitatively and qualitatively validated by comparing the latter to their experimental counterparts. Finally, the CFD methodology validated in the gaseous configuration is extended to spray combustion by first coupling the latter to the spray module, and by implementing the flame properties of kerosene in the ignition model. The resulting CFD model is first applied to the swirl-stabilized combustor investigated previously, with the aim of predicting the whole ignition sequence and improving the previous predictions of the combustion properties in the resulting steady regime. Subsequently, the CFD methodology is applied to a scaled can combustor with the aim of predicting ignition events under cold start and altitude relight operating conditions. The ability of the CFD methodology to predict ignition events under the two operating conditions is assessed by contrasting the numerical predictions to the corresponding experimental ignition envelopes. A qualitative validation of the ignition sequence is also done by comparing the numerical ignition sequence to the high-speed camera images of the corresponding ignition event

NAS Technical Summaries, March 1993 - February 1994

NASA created the Numerical Aerodynamic Simulation (NAS) Program in 1987 to focus resources on solving critical problems in aeroscience and related disciplines by utilizing the power of the most advanced supercomputers available. The NAS Program provides scientists with the necessary computing power to solve today's most demanding computational fluid dynamics problems and serves as a pathfinder in integrating leading-edge supercomputing technologies, thus benefitting other supercomputer centers in government and industry. The 1993-94 operational year concluded with 448 high-speed processor projects and 95 parallel projects representing NASA, the Department of Defense, other government agencies, private industry, and universities. This document provides a glimpse at some of the significant scientific results for the year

High-Performance Parallel Analysis of Coupled Problems for Aircraft Propulsion

Applications are described of high-performance computing methods to the numerical simulation of complete jet engines. The methodology focuses on the partitioned analysis of the interaction of the gas flow with a flexible structure and with the fluid mesh motion driven by structural displacements. The latter is treated by a ALE technique that models the fluid mesh motion as that of a fictitious mechanical network laid along the edges of near-field elements. New partitioned analysis procedures to treat this coupled three-component problem were developed. These procedures involved delayed corrections and subcycling, and have been successfully tested on several massively parallel computers, including the iPSC-860, Paragon XP/S and the IBM SP2. The NASA-sponsored ENG10 program was used for the global steady state analysis of the whole engine. This program uses a regular FV-multiblock-grid discretization in conjunction with circumferential averaging to include effects of blade forces, loss, combustor heat addition, blockage, bleeds and convective mixing. A load-balancing preprocessor for parallel versions of ENG10 was developed as well as the capability for the first full 3D aeroelastic simulation of a multirow engine stage. This capability was tested on the IBM SP2 parallel supercomputer at NASA Ames

Numerical simulation of Newtonian/non-Newtonian multiphase flows : deformation and collision of droplets

The complex nature of multiphase flows, particularly in the presence of non-Newtonian rheologies in the phases, limits the applicability of theoretical analysis of physical equations as well as setting up laboratory experiments. As a result, Computational Fluid Dynamics (CFD) techniques are essential tools to study these problems. Despite the advances in numerical simulation techniques in this field in the past decade, the applicability of these approaches are limited by challenges appearing in specific applications, and particular consideration must be taken into account for each of these problems. The present thesis aims at three-dimensional numerical solution of Newtonian/non-Newtonian multiphase flow problems in the context of finite-volume discretization approach with applications in different natural and industrial processes. This thesis is organized in five chapters. The first chapter aims at providing an introduction to the motivation behind this work. We also present some application of the context of this thesis in industrial processes, followed by a small introductory on the CTTC research group, objectives and the outline of the thesis. The core of this thesis lays within chapters two, three and four. In chapter 2, using a conservative level-set method, three-dimensional direct numerical simulation of binary droplets collision is performed. A novel lamella stabilization approach is introduced to numerically resolve the thin lamella film appeared during a broad range of collision regimes. This approach demonstrates to be numerically efficient and accurate compared with experimental data, with a significant save-up on computational costs in three-dimensional cases. The numerical tools introduced are validated and verified against different experimental results for a wide range of collision regimes where very good agreement is seen. Besides, for all the cases studied in this chapter, a detailed study of the energy budgets are provided. In chapter 3, the physics of a single droplet subjected to shear flow is studied in details, with a primary focus on the effect of viscosity on walls critical confinement ratio. First, we highly validate the ability of the numerical tools on capturing the correct physics of droplet deformation. This chapter continues by three-dimensional DNS study of subcritical (steady-state) and supercritical (breakup) deformations of the droplet for a wide range of walls confinement in different viscosity ratios. The results indicate the existence of two steady-state regions in a viscosity ratio-walls confinement ratio graph, which are separated by a breakup region. Overall, these achievements indicate a promising potential of the current approach for simulating droplet deformation and breakup, in applications of dispersion science and mixing processes. In chapter 4, with the help of experience gained in the previous chapters, a finite-volume based conservative level-set method is used to numerically solve the non-Newtonian multiphase flow problems. One set of governing equations is written for the whole domain where different rheological properties may appear. Main challenging areas of numerical simulation of multiphase non-Newtonian fluids, including tracking of the interface, mass conservation of the phases, small timestep problems encountered by non-Newtonian fluids, numerical instabilities regarding the high Weissenberg Number Problem (HWNP), instabilities encouraged by low solvent to polymer viscosity ratio in viscoelastic fluids and instabilities encountered by surface tensions are discussed and proper numerical treatments are provided in the proposed method. The numerical method is validated for different types of non-Newtonian fluids, e.g. shear-thinning, shear-thickening and viscoelastic fluids using structured and unstructured meshes, where the extracted results are compared against analytical, numerical and experimental data available in the literature.La naturaleza compleja de los flujos multifásicos, particularmente en presencia de reologías no newtonianas, limita la aplicabilidad del análisis teórico de ecuaciones físicas y también de los experimentos de laboratorio. Por lo tanto, las técnicas de dinámica de fluidos computacional (CFD) son esenciales para estudiar estos problemas. A pesar de los avances en las técnicas de simulación numérica en esta área durante la última década, la aplicabilidad de estos enfoques está limitada por los desafíos que aparecen en las aplicaciones específicas, y se debe considerar de forma particular cada uno de estos problemas. La presente tesis tiene como objetivo la solución numérica tridimensional de los problemas de flujo multifase newtoniano / no newtoniano en el contexto del enfoque de discretización de volúmenes finitos con aplicaciones en diferentes procesos naturales e industriales. Esta tesis está organizada en cinco capítulos. El primer capítulo proporciona una introducción y la motivación de este trabajo. También presentamos alguna aplicación de esta tesis en procesos industriales, seguida de una corta introducción al grupo de investigación del CTTC, los objetivos y el resumen de la tesis. En el capítulo 2, utilizando un método CLS, se realiza una simulación numérica directa (DNS) tridimensional de colisión de gotitas binarias. Se introduce un nuevo enfoque de estabilización de lamella para resolver numéricamente la capa delgada de fluido ("lamella") que aparece durante muchos regímenes de colisión. Este enfoque demuestra ser numéricamente eficiente y preciso en comparación con los datos experimentales, con una importante reducción de costos computacionales en casos tridimensionales. Las herramientas numéricas introducidas se validan y verifican con diferentes resultados experimentales para diferentes casos de colisión en los que se observa un muy buen acuerdo. Además, para todos los casos estudiados en este capítulo, se proporciona un estudio detallado de los balances de energía. En el capítulo 3, se estudia en detalle la física de una sola gota sometida a flujo de cizallamiento, con un enfoque principal en el efecto de la viscosidad en el confinamiento crítico de las paredes. Primero, validamos la capacidad de las herramientas numéricas para capturar la física correcta de la deformación de las gotitas. Este capítulo continúa con el estudio tridimensional DNS de las deformaciones subcríticas (estado estable) y supercríticas (ruptura) de la gota para un amplio rango de confinamiento de paredes en diferentes relaciones de viscosidad. Los resultados indican la existencia de dos regiones de estado estable en un gráfico de una relación de confinamiento de las paredes y la viscosidad, que están separados por una región de ruptura. En general, estos logros indican un potencial importante del enfoque actual para simular la deformación y ruptura de las gotitas, en aplicaciones de la ciencia de la dispersión y los procesos de mezcla. En el capítulo 4, con la ayuda de la experiencia adquirida en los capítulos anteriores, se utiliza un método CLS de volumen finito para resolver numéricamente los problemas de flujo multifase no newtonianos. Las principales áreas desafiantes de la simulación numérica de fluidos multifásicos no newtonianos incluso el seguimiento de la interfaz, la conservación de masa de las fases, los problemas de pequeños paso de tiempo encontrados por los fluidos no newtonianos, las inestabilidades numéricas relacionadas con el problema del alto número de Weissenberg (HWNP), inestabilidades fomentadas por una baja relación de viscosidad de disolvente a polímero en fluidos viscoelásticos y las inestabilidades encontradas por las tensiones superficiales son discutidos y se proporcionan tratamientos numéricos adecuados para el método propuesto. El método numérico se valida para diferentes tipos de fluidos no newtonianos, utilizando diluyentes de cizallamiento, espesamiento de cizallamiento y fluidos viscoelásticos utilizando mallas estructuradas y no estructuradas, donde los resultados extraídos se comparan con los datos analíticos, numéricos y experimentales disponibles en la literatura.Postprint (published version

Numerical simulation of Newtonian/non-Newtonian multiphase flows : deformation and collision of droplets

The complex nature of multiphase flows, particularly in the presence of non-Newtonian rheologies in the phases, limits the applicability of theoretical analysis of physical equations as well as setting up laboratory experiments. As a result, Computational Fluid Dynamics (CFD) techniques are essential tools to study these problems. Despite the advances in numerical simulation techniques in this field in the past decade, the applicability of these approaches are limited by challenges appearing in specific applications, and particular consideration must be taken into account for each of these problems. The present thesis aims at three-dimensional numerical solution of Newtonian/non-Newtonian multiphase flow problems in the context of finite-volume discretization approach with applications in different natural and industrial processes. This thesis is organized in five chapters. The first chapter aims at providing an introduction to the motivation behind this work. We also present some application of the context of this thesis in industrial processes, followed by a small introductory on the CTTC research group, objectives and the outline of the thesis. The core of this thesis lays within chapters two, three and four. In chapter 2, using a conservative level-set method, three-dimensional direct numerical simulation of binary droplets collision is performed. A novel lamella stabilization approach is introduced to numerically resolve the thin lamella film appeared during a broad range of collision regimes. This approach demonstrates to be numerically efficient and accurate compared with experimental data, with a significant save-up on computational costs in three-dimensional cases. The numerical tools introduced are validated and verified against different experimental results for a wide range of collision regimes where very good agreement is seen. Besides, for all the cases studied in this chapter, a detailed study of the energy budgets are provided. In chapter 3, the physics of a single droplet subjected to shear flow is studied in details, with a primary focus on the effect of viscosity on walls critical confinement ratio. First, we highly validate the ability of the numerical tools on capturing the correct physics of droplet deformation. This chapter continues by three-dimensional DNS study of subcritical (steady-state) and supercritical (breakup) deformations of the droplet for a wide range of walls confinement in different viscosity ratios. The results indicate the existence of two steady-state regions in a viscosity ratio-walls confinement ratio graph, which are separated by a breakup region. Overall, these achievements indicate a promising potential of the current approach for simulating droplet deformation and breakup, in applications of dispersion science and mixing processes. In chapter 4, with the help of experience gained in the previous chapters, a finite-volume based conservative level-set method is used to numerically solve the non-Newtonian multiphase flow problems. One set of governing equations is written for the whole domain where different rheological properties may appear. Main challenging areas of numerical simulation of multiphase non-Newtonian fluids, including tracking of the interface, mass conservation of the phases, small timestep problems encountered by non-Newtonian fluids, numerical instabilities regarding the high Weissenberg Number Problem (HWNP), instabilities encouraged by low solvent to polymer viscosity ratio in viscoelastic fluids and instabilities encountered by surface tensions are discussed and proper numerical treatments are provided in the proposed method. The numerical method is validated for different types of non-Newtonian fluids, e.g. shear-thinning, shear-thickening and viscoelastic fluids using structured and unstructured meshes, where the extracted results are compared against analytical, numerical and experimental data available in the literature.La naturaleza compleja de los flujos multifásicos, particularmente en presencia de reologías no newtonianas, limita la aplicabilidad del análisis teórico de ecuaciones físicas y también de los experimentos de laboratorio. Por lo tanto, las técnicas de dinámica de fluidos computacional (CFD) son esenciales para estudiar estos problemas. A pesar de los avances en las técnicas de simulación numérica en esta área durante la última década, la aplicabilidad de estos enfoques está limitada por los desafíos que aparecen en las aplicaciones específicas, y se debe considerar de forma particular cada uno de estos problemas. La presente tesis tiene como objetivo la solución numérica tridimensional de los problemas de flujo multifase newtoniano / no newtoniano en el contexto del enfoque de discretización de volúmenes finitos con aplicaciones en diferentes procesos naturales e industriales. Esta tesis está organizada en cinco capítulos. El primer capítulo proporciona una introducción y la motivación de este trabajo. También presentamos alguna aplicación de esta tesis en procesos industriales, seguida de una corta introducción al grupo de investigación del CTTC, los objetivos y el resumen de la tesis. En el capítulo 2, utilizando un método CLS, se realiza una simulación numérica directa (DNS) tridimensional de colisión de gotitas binarias. Se introduce un nuevo enfoque de estabilización de lamella para resolver numéricamente la capa delgada de fluido ("lamella") que aparece durante muchos regímenes de colisión. Este enfoque demuestra ser numéricamente eficiente y preciso en comparación con los datos experimentales, con una importante reducción de costos computacionales en casos tridimensionales. Las herramientas numéricas introducidas se validan y verifican con diferentes resultados experimentales para diferentes casos de colisión en los que se observa un muy buen acuerdo. Además, para todos los casos estudiados en este capítulo, se proporciona un estudio detallado de los balances de energía. En el capítulo 3, se estudia en detalle la física de una sola gota sometida a flujo de cizallamiento, con un enfoque principal en el efecto de la viscosidad en el confinamiento crítico de las paredes. Primero, validamos la capacidad de las herramientas numéricas para capturar la física correcta de la deformación de las gotitas. Este capítulo continúa con el estudio tridimensional DNS de las deformaciones subcríticas (estado estable) y supercríticas (ruptura) de la gota para un amplio rango de confinamiento de paredes en diferentes relaciones de viscosidad. Los resultados indican la existencia de dos regiones de estado estable en un gráfico de una relación de confinamiento de las paredes y la viscosidad, que están separados por una región de ruptura. En general, estos logros indican un potencial importante del enfoque actual para simular la deformación y ruptura de las gotitas, en aplicaciones de la ciencia de la dispersión y los procesos de mezcla. En el capítulo 4, con la ayuda de la experiencia adquirida en los capítulos anteriores, se utiliza un método CLS de volumen finito para resolver numéricamente los problemas de flujo multifase no newtonianos. Las principales áreas desafiantes de la simulación numérica de fluidos multifásicos no newtonianos incluso el seguimiento de la interfaz, la conservación de masa de las fases, los problemas de pequeños paso de tiempo encontrados por los fluidos no newtonianos, las inestabilidades numéricas relacionadas con el problema del alto número de Weissenberg (HWNP), inestabilidades fomentadas por una baja relación de viscosidad de disolvente a polímero en fluidos viscoelásticos y las inestabilidades encontradas por las tensiones superficiales son discutidos y se proporcionan tratamientos numéricos adecuados para el método propuesto. El método numérico se valida para diferentes tipos de fluidos no newtonianos, utilizando diluyentes de cizallamiento, espesamiento de cizallamiento y fluidos viscoelásticos utilizando mallas estructuradas y no estructuradas, donde los resultados extraídos se comparan con los datos analíticos, numéricos y experimentales disponibles en la literatura

Aeronautical engineering: A continuing bibliography with indexes (supplement 270)

This bibliography lists 600 reports, articles, and other documents introduced into the NASA scientific and technical information system in September, 1991. Subject coverage includes: design, construction and testing of aircraft and aircraft engines; aircraft components, equipment and systems; ground support systems; and theoretical and applied aspects of aerodynamics and general fluid dynamics

Summary of research in progress at ICASE

This report summarizes research conducted at the Institute for Computer Applications in Science and Engineering in applied mathematics, fluid mechanics, and computer science during the period October 1, 1992 through March 31, 1993