DNS of multiphase flows: study of atomization and free-surface phenomena

The present thesis focuses on the numerical analysis of some diverse physical set-up that involve the interaction of two -or three immiscible and incompressible phases. The simulations are carried out by means of finite-volume algorithms developed on the in-house Computational Fluid Dynamics platform TermoFluids, developed by the Heat and Mass Transfer Technological Center (CTTC). They are intended to give detailed insights on the physics of the analyzed phenomena by carrying out Direct Numerical Simulations (DNS). In the context of multiphase flows, namely, Computational Multi-Fluid Dynamics (CMFD) field, DNS means that all the interfacial and turbulent scales of the phenomenon must be fully resolved. In the Introduction, a general overview of the engineering applications and the computational methods related to multiphase flows is proposed. The various types of physics analyzed in this work and the numerical approaches applied here to carry out efficient simulations are introduced. In Chapter 2, a low-dissipation convection scheme for the stable discretization of multiphase flow by means of interface-capturing schemes is analyzed. The hybrid form of the convective operator proposed incorporates localized low-dispersion characteristics to limit the growth of spurious flow solutions. Moreover, in comparison to pure-dissipative schemes, the discretization aims at minimizing the differences in kinetic energy preservation with respect to the continuous governing equations. This property plays a fundamental role in the case of flows presenting significant levels of turbulence. The simulation of a turbulent 2D coaxial jet with the low-dissipation convection scheme demonstrates its capability of solving correctly the two-phase turbulent problems. In Chapter 3, all the work carried out on the simulation of two-phase flow with the aid of Adaptive Mesh Refinement (AMR) strategies is described. The model is globally addressed at improving the representation of interfacial and turbulent scales in general multiphase flows. It is first applied to the simulation of simple multiphase phenomena, as 2D and 3D rising bubbles, to demonstrate the convergence of the method and the important computational savings in comparison to static mesh computations. However, its adoption becames essential in the simulation of instability and break-up phenomena, where the necessity of representing accurately the complex structures that appear at the interface, as ligaments and droplets, make the simulation particularly expensive in terms of computational cost. In Chapter 4, we analyze in detail the simulations of 3-D atomizing phenomena, including the coaxial jet case, characterized by the parallel injection of high speed liquid and gas fluxes, and the liquid spray case, characterized by the injection of a high speed liquid inside a still air chamber. In Chapter 5, an original single-phase scheme for the DNS of free-surface problems on 3-D unstructured meshes is presented. The scheme is based on a novel treatment of the interface for the deactivation of the light-phase, allowing an optimization of the classic two-phase model for the cases in which the influence of the lighter phase is negligible. Consequently, the model is particularly addressed at analyzing problems involving the movement of free-surfaces, as the evolution of waves on the sea, and their interaction with fixed and moving obstacles. Some practical cases of application are proposed, as the evaluation of stresses on an object due to the action of a dam-break event, and the interaction of linear waves with an oscillating water column device. In the same Chapter we describe the procedure to couple the single-phase model to the Immersed Boundary Method. The method is aimed at representing the interaction of a solid moving with prescribed velocity and the two-phase flow. The most significant example consists in the simulation of a sliding wedge into a liquid basin.Esta tesis se focaliza en la simulación numérica de algunos set-up físicos que involucran la interacción entre dos o tres fluidos incompresibles y immiscibles. Las simulaciones se realizan por medio de algoritmos de volúmenes-finitos desarrollados en la plataforma propia de Fluido-Dinámica Computacional (CFD) denominada TermoFluids, desarrollada en el Centro Tecnologico de Trasferencia de Calor (CTTC). Las simulaciones quieren estudiar en detalle la física de los fenómenos analizados, realizando su Simulación Numérica Directa (DNS). En el contexto de los flujos multifase, DNS significa que todas las escalas interfaciales y turbulentas del fenómeno han de ser totalmente resueltas. En la Introducción, se propone una panorámica general de las aplicaciones de ingeniería y de los métodos computacionales relacionados con flujos multifases. Se introducen los varios tipos de física analizados en este trabajo y las estrategias numéricas aplicadas aquí para efectuar su simulación de manera eficiente. En el Capitulo 2 se analiza un esquema convectivo de baja-disipación para la discretization de flujo multifase por medio de métodos de interface-capturing. La forma híbrida del operador convectivo propuesto incorpora la característica de una baja dispersión localizada, focalizada en limitar el crecimiento de soluciones numéricas espurias. Además, en comparación con métodos disipativos puros, la discretización apunta a minimizar las diferencias en la conservación de energía cinética en respeto a las ecuaciones continuas que gobiernan el flujo. Esta propiedad juega un papel fundamental en el caso de flujo caracterizado por un alto nivel de turbulencia. La simulación de un jet 2D coaxial turbulento con el método convectivo de baja disipación demuestra su capacidad de resolver correctamente un flujo de dos fases turbulentos. En el Capitulo 3 se reporta todo el trabajo realizado sobre la simulación de flujo multifase con el auxilio de técnicas de refinamiento adaptativo de malla (AMR). El modelo es globalmente dirigido a la mejora de la representación de las escalas turbulentas y interfaciales en flujos multifases en general. Se aplica inicialmente a la simulación de flujos sencillos, como unos casos de burbujas flotantes 2D y 3D, demostrando la convergencia del método y los importantes ahorros computacional en comparación con los cálculos de mallas estáticas. La adopción de la técnica se hace esencial en la simulación de fenómenos de inestabilidad y de ruptura, donde la necesidad de representar sacramentalmente las estructuras complejas que aparecen en la interfaz, como ligamentos o pequeñas gotas, hacen que la simulación sea particularmente pesada en términos de coste computacional. En el Capitulo 4 se reportan en detalle las simulaciones de fenómenos de atomización 3D. Esas incluyen el caso del jet coaxial, caracterizado por la inyección paralela de flujos de aire y liquido de altas velocidades, y el caso del spray liquido, que consiste en la inyección de un liquido dentro de una cámara de aire. En el Capitulo 5 se presenta un esquema de single-phase original, para el DNS de problemas de superficie libre en mallas 3D no-estructuradas. El esquema se basa en un nuevo tratamiento de la interfase para la desactivación de la fase ligera, permitiendo la optimización del solver clásico de dos fases para los casos en que la influencia de la fase mas ligera sea despreciable. En consecuencia, el modelo es particularmente indicado para la análisis de problemas que involucran el movimiento de superficies libres, como la evolución de olas en la superficie marina y su interacción con obstáculos fijos o muebles. Se proponen algunos casos prácticos de aplicación, como la evaluación de las fuerzas sobre un objeto debidos a un episodio de dam-break, o el estudio de las olas generadas por el impacto de un solido deslizante (representado integrando la tecnica de Immersed Boundary con el presente metodo de single-phase) con un embalse de agua.Postprint (published version

DNS of multiphase flows: study of atomization and free-surface phenomena

The present thesis focuses on the numerical analysis of some diverse physical set-up that involve the interaction of two -or three immiscible and incompressible phases. The simulations are carried out by means of finite-volume algorithms developed on the in-house Computational Fluid Dynamics platform TermoFluids, developed by the Heat and Mass Transfer Technological Center (CTTC). They are intended to give detailed insights on the physics of the analyzed phenomena by carrying out Direct Numerical Simulations (DNS). In the context of multiphase flows, namely, Computational Multi-Fluid Dynamics (CMFD) field, DNS means that all the interfacial and turbulent scales of the phenomenon must be fully resolved. In the Introduction, a general overview of the engineering applications and the computational methods related to multiphase flows is proposed. The various types of physics analyzed in this work and the numerical approaches applied here to carry out efficient simulations are introduced. In Chapter 2, a low-dissipation convection scheme for the stable discretization of multiphase flow by means of interface-capturing schemes is analyzed. The hybrid form of the convective operator proposed incorporates localized low-dispersion characteristics to limit the growth of spurious flow solutions. Moreover, in comparison to pure-dissipative schemes, the discretization aims at minimizing the differences in kinetic energy preservation with respect to the continuous governing equations. This property plays a fundamental role in the case of flows presenting significant levels of turbulence. The simulation of a turbulent 2D coaxial jet with the low-dissipation convection scheme demonstrates its capability of solving correctly the two-phase turbulent problems. In Chapter 3, all the work carried out on the simulation of two-phase flow with the aid of Adaptive Mesh Refinement (AMR) strategies is described. The model is globally addressed at improving the representation of interfacial and turbulent scales in general multiphase flows. It is first applied to the simulation of simple multiphase phenomena, as 2D and 3D rising bubbles, to demonstrate the convergence of the method and the important computational savings in comparison to static mesh computations. However, its adoption becames essential in the simulation of instability and break-up phenomena, where the necessity of representing accurately the complex structures that appear at the interface, as ligaments and droplets, make the simulation particularly expensive in terms of computational cost. In Chapter 4, we analyze in detail the simulations of 3-D atomizing phenomena, including the coaxial jet case, characterized by the parallel injection of high speed liquid and gas fluxes, and the liquid spray case, characterized by the injection of a high speed liquid inside a still air chamber. In Chapter 5, an original single-phase scheme for the DNS of free-surface problems on 3-D unstructured meshes is presented. The scheme is based on a novel treatment of the interface for the deactivation of the light-phase, allowing an optimization of the classic two-phase model for the cases in which the influence of the lighter phase is negligible. Consequently, the model is particularly addressed at analyzing problems involving the movement of free-surfaces, as the evolution of waves on the sea, and their interaction with fixed and moving obstacles. Some practical cases of application are proposed, as the evaluation of stresses on an object due to the action of a dam-break event, and the interaction of linear waves with an oscillating water column device. In the same Chapter we describe the procedure to couple the single-phase model to the Immersed Boundary Method. The method is aimed at representing the interaction of a solid moving with prescribed velocity and the two-phase flow. The most significant example consists in the simulation of a sliding wedge into a liquid basin.Esta tesis se focaliza en la simulación numérica de algunos set-up físicos que involucran la interacción entre dos o tres fluidos incompresibles y immiscibles. Las simulaciones se realizan por medio de algoritmos de volúmenes-finitos desarrollados en la plataforma propia de Fluido-Dinámica Computacional (CFD) denominada TermoFluids, desarrollada en el Centro Tecnologico de Trasferencia de Calor (CTTC). Las simulaciones quieren estudiar en detalle la física de los fenómenos analizados, realizando su Simulación Numérica Directa (DNS). En el contexto de los flujos multifase, DNS significa que todas las escalas interfaciales y turbulentas del fenómeno han de ser totalmente resueltas. En la Introducción, se propone una panorámica general de las aplicaciones de ingeniería y de los métodos computacionales relacionados con flujos multifases. Se introducen los varios tipos de física analizados en este trabajo y las estrategias numéricas aplicadas aquí para efectuar su simulación de manera eficiente. En el Capitulo 2 se analiza un esquema convectivo de baja-disipación para la discretization de flujo multifase por medio de métodos de interface-capturing. La forma híbrida del operador convectivo propuesto incorpora la característica de una baja dispersión localizada, focalizada en limitar el crecimiento de soluciones numéricas espurias. Además, en comparación con métodos disipativos puros, la discretización apunta a minimizar las diferencias en la conservación de energía cinética en respeto a las ecuaciones continuas que gobiernan el flujo. Esta propiedad juega un papel fundamental en el caso de flujo caracterizado por un alto nivel de turbulencia. La simulación de un jet 2D coaxial turbulento con el método convectivo de baja disipación demuestra su capacidad de resolver correctamente un flujo de dos fases turbulentos. En el Capitulo 3 se reporta todo el trabajo realizado sobre la simulación de flujo multifase con el auxilio de técnicas de refinamiento adaptativo de malla (AMR). El modelo es globalmente dirigido a la mejora de la representación de las escalas turbulentas y interfaciales en flujos multifases en general. Se aplica inicialmente a la simulación de flujos sencillos, como unos casos de burbujas flotantes 2D y 3D, demostrando la convergencia del método y los importantes ahorros computacional en comparación con los cálculos de mallas estáticas. La adopción de la técnica se hace esencial en la simulación de fenómenos de inestabilidad y de ruptura, donde la necesidad de representar sacramentalmente las estructuras complejas que aparecen en la interfaz, como ligamentos o pequeñas gotas, hacen que la simulación sea particularmente pesada en términos de coste computacional. En el Capitulo 4 se reportan en detalle las simulaciones de fenómenos de atomización 3D. Esas incluyen el caso del jet coaxial, caracterizado por la inyección paralela de flujos de aire y liquido de altas velocidades, y el caso del spray liquido, que consiste en la inyección de un liquido dentro de una cámara de aire. En el Capitulo 5 se presenta un esquema de single-phase original, para el DNS de problemas de superficie libre en mallas 3D no-estructuradas. El esquema se basa en un nuevo tratamiento de la interfase para la desactivación de la fase ligera, permitiendo la optimización del solver clásico de dos fases para los casos en que la influencia de la fase mas ligera sea despreciable. En consecuencia, el modelo es particularmente indicado para la análisis de problemas que involucran el movimiento de superficies libres, como la evolución de olas en la superficie marina y su interacción con obstáculos fijos o muebles. Se proponen algunos casos prácticos de aplicación, como la evaluación de las fuerzas sobre un objeto debidos a un episodio de dam-break, o el estudio de las olas generadas por el impacto de un solido deslizante (representado integrando la tecnica de Immersed Boundary con el presente metodo de single-phase) con un embalse de agua

Development of a design environment for integrated concurrent engineering (DE-ICE) in university education : integrating student designers, design tools, and active learning

Thesis (M.Eng.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2000.Also available online at the MIT Theses Online homepage .Includes bibliographical references (p. 93-95).The development of an operational framework for a design center to enhance learning in MIT's Department of Aeronautics and Astronautics is described. The results of research at MIT, which included a survey of students and faculty in the Department, is summarized. Visits to aerospace industry design centers are considered with respect to their implications toward engineering education. DE-ICE needs are explained and mapped to technical requirements through quality function deployment. Functional analysis with use case diagrams and a product matrix mapping requirements to implementations are used to generate architectural variants. These variants are synthesized into a suggested architecture for the design center. An enabling prototype for the DE-ICE system is characterized: an On-Line Teaching Assistant (OLTA) that provides guidance and project management to student designers. A part of the OLTA is the project navigator, which provides a roadmap through a design process by depicting the dependencies between documents associated with a project.by Alex Manka.M.Eng

Improving Structural Features Prediction in Protein Structure Modeling

Proteins play a vital role in the biological activities of all living species. In nature, a protein folds into a specific and energetically favorable three-dimensional structure which is critical to its biological function. Hence, there has been a great effort by researchers in both experimentally determining and computationally predicting the structures of proteins. The current experimental methods of protein structure determination are complicated, time-consuming, and expensive. On the other hand, the sequencing of proteins is fast, simple, and relatively less expensive. Thus, the gap between the number of known sequences and the determined structures is growing, and is expected to keep expanding. In contrast, computational approaches that can generate three-dimensional protein models with high resolution are attractive, due to their broad economic and scientific impacts. Accurately predicting protein structural features, such as secondary structures, disulfide bonds, and solvent accessibility is a critical intermediate step stone to obtain correct three-dimensional models ultimately. In this dissertation, we report a set of approaches for improving the accuracy of structural features prediction in protein structure modeling. First of all, we derive a statistical model to generate context-based scores characterizing the favorability of segments of residues in adopting certain structural features. Then, together with other information such as evolutionary and sequence information, we incorporate the context-based scores in machine learning approaches to predict secondary structures, disulfide bonds, and solvent accessibility. Furthermore, we take advantage of the emerging high performance computing architectures in GPU to accelerate the calculation of pairwise and high-order interactions in context-based scores. Finally, we make these prediction methods available to the public via web services and software packages

Large-Scale Light Field Capture and Reconstruction

This thesis discusses approaches and techniques to convert Sparsely-Sampled Light Fields (SSLFs) into Densely-Sampled Light Fields (DSLFs), which can be used for visualization on 3DTV and Virtual Reality (VR) devices. Exemplarily, a movable 1D large-scale light field acquisition system for capturing SSLFs in real-world environments is evaluated. This system consists of 24 sparsely placed RGB cameras and two Kinect V2 sensors. The real-world SSLF data captured with this setup can be leveraged to reconstruct real-world DSLFs. To this end, three challenging problems require to be solved for this system: (i) how to estimate the rigid transformation from the coordinate system of a Kinect V2 to the coordinate system of an RGB camera; (ii) how to register the two Kinect V2 sensors with a large displacement; (iii) how to reconstruct a DSLF from a SSLF with moderate and large disparity ranges. To overcome these three challenges, we propose: (i) a novel self-calibration method, which takes advantage of the geometric constraints from the scene and the cameras, for estimating the rigid transformations from the camera coordinate frame of one Kinect V2 to the camera coordinate frames of 12-nearest RGB cameras; (ii) a novel coarse-to-fine approach for recovering the rigid transformation from the coordinate system of one Kinect to the coordinate system of the other by means of local color and geometry information; (iii) several novel algorithms that can be categorized into two groups for reconstructing a DSLF from an input SSLF, including novel view synthesis methods, which are inspired by the state-of-the-art video frame interpolation algorithms, and Epipolar-Plane Image (EPI) inpainting methods, which are inspired by the Shearlet Transform (ST)-based DSLF reconstruction approaches

Thermodynamic Approach to Fatigue Failure Analysis in Metals and Composite Materials

Fatigue is a dissipative process and must obey the laws of thermodynamics. In general, it can be hypothesized that the degradation of machinery components is a consequence of irreversible thermodynamic processes that disorder a component, and that degradation is a time dependent phenomenon with increasing disorder. This suggests that entropy —a fundamental parameter in thermodynamics that characterizes disorder— offers a natural measure of component degradation. The majority of the existing methods for prediction of fatigue are limited to the study of a single fatigue mode, i.e., bending or torsion or tension-compression. Further, the variability in the duty cycle in a practical application may render many of these existing methods incapable of reliable performance. During this research, we put forward the idea that fatigue is a degradation process and that entropy is the most suitable index for assessing degradation. That is, tallying irreversible entropy is more reliable and accurate than many of the other methods presented in the existing papers. We show that in processes involving fatigue, for a given material (metal and composite laminate), there exists a unique threshold of the cumulative thermodynamic entropy beyond which fatigue fracture takes place. This threshold is shown to be independent of the type of the fatigue process and the loading history. This exciting result is the basis of the development of a Fatigue Monitoring Unit (FMU) described in this research. We also propose a general procedure for assessment of damage evolution based on the concept of entropy production. The procedure is applicable to both constant- and variable amplitude loading. Empirical relations between entropy generation and damage evolution for two types of metals (Alumunium 6061-T6 and Stainless steel 304) and a woven Glass/Epoxy composite laminate are proposed and their potential for evaluation of fatigue damage are investigated