京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第19677号 / 工博第4132号 / 新制||工||1638(附属図書館) / 32713 / 京都大学大学院工学研究科都市社会工学専攻 / (主査)教授 五十嵐 晃, 准教授 米山 望, 准教授 森 信人 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

<p>A new model for simulating non-Brownian flexible fibres suspended in a Newtonian fluid has been developed. Special attention has been given to include realistic flow conditions found in the industrial papermaking process in the key features of the model; it is the intention of the author to employ the model in simulations of the forming section of the paper machine in future studies.</p><p>The model considers inert fibres of various shapes and finite stiffness, interacting with each other through normal, frictional and lubrication forces, and with the surrounding fluid medium through hydrodynamic forces. Fibre-fluid interactions in the non-creeping flow regime are taken into account, and the two-way coupling between the solids and the fluid phase is included by enforcing momentum conservation between phases. The incompressible three-dimensional Navier-Stokes equations are employed to model the motion of the fluid medium.</p><p>The validity of the model has been tested by comparing simulation results with experimental data from the literature. It was demonstrated that the model predicts the motion of isolated fibres in shear flow over a wide range of fibre flexibilities. It was also shown that the model predicts details of the orientation distribution of multiple straight, rigid fibres in a sheared suspension. Model predictions of the viscosity and first normal stress difference were in good agreement with experimental data found in the literature. Since the model is based solely on first-principles physics, quantitative predictions could be made without any parameter fitting.</p> / <p>En ny modell för simulering av rörelserna hos icke-Brownska böjliga fibrer dispergerade i en Newtonsk vätska har utvecklats. Eftersom det är författarens avsikt att modellen skall kunna tillämpas vid simulering av arkformning under de förhållanden som råder i en modern pappersmaskin, har särskilt omsorg givits till att inkludera motsvarande flödesvillkor i modellens giltighetsområde.</p><p>Modellen hanterar fibrer av varierande form, massa och styvhet, som växelverkar sinsemellan via normal-, friktions- och smörjkrafter. Deras växelverkan med den omgivande vätskan sker via hydrodynamiska krafter vid finita Reynolds-tal. Den så kallade tvåvägskopplingen mellan fibrerna och vätskefasen har tagits i beaktande genom att kräva att rörelsemängden bevaras vid interaktionen mellan faserna. Vidare har Navier-Stokes ekvationer för inkompressibla vätskor använts för att beskriva mediets rörelser.</p><p>Modellens giltighet har undersökts genom att jämföra resultat från simuleringar med experimentella data från litteraturen. Det har påvisats att modellen förutsäger rörelsen hos ensamma fibrer i ett skjuvflöde, för vitt skilda fiberflexibiliteter. Det visades också att modellen förutsäger detaljer hos fiberorienteringsdistributionen i suspensioner utsatta för skjuvflöde. Det kunde också konstateras att modellens förutsägelser av fibersuspensioners viskositet och första normalspänningsdifferens under skjuvning väl överensstämde med experimentella data i litteraturen. Kvantitativa förutsägelser har kunnat göras utan någon parameteranpassning, då modellen bygger uteslutande på väletablerade fysikaliska samband inom klassisk mekanik och strömningslära.</p>

Made available in DSpace on 2016-06-02T19:55:37Z (GMT). No. of bitstreams: 1 5587.pdf: 3066852 bytes, checksum: 17d88d3ab913d61bb315842b57ec5a74 (MD5) Previous issue date: 2013-09-30 / Universidade Federal de Sao Carlos / Cyclones are used to separate suspended particles from gas streams. The analysis of flow inside the cyclone is complex due to the large number of parameters and operating variables that influence the dynamics of the system. Due to its versatility of use and its robustness, results in computational fluid dynamic are an important alternative often used to study the dynamics of flow in the cyclone. In the literature, several works make use of computational fluid dynamics in order to study the pressure drop of cyclones. However, the works about the efficiency of collection are fewer. For the cyclone, computational fluid dynamics allows an accurately simulation of the collection efficiency of particles with diameter greater than 5 µm; but for particles with smaller diameters the simulated results diverge from experimental values. In this work, Stairmand s cyclone was numerically simulated with injected particles with diameters from 1 to 5 µm. The results were verified using available experimental data reported in the literature. The experimental data taken from literature belong to Zhao and Shen Kang (2004) and Zhao (2005). The simulation mesh was analyzed before and after the simulations. The turbulence models used in the simulation of flow in the cyclone were: Reynolds Stress Model (RSM) and Large Eddy Simulation (LES). The dispersed phase was simulated considering one and two way couplings. The equation of motion of the particles was integrated using the integration schemes: implicit, analytic, trapezoidal, and Runge-Kutta. The results showed that the methodology was adequate to reproduce the behavior of the flow in the cyclone. The error percentages obtained in pressure drop were under 5% and the average collection efficiency was reproduced with good accuracy for diameters of 3, 4 and 5 µm. / O ciclone é um equipamento utilizado para separar partículas suspensas em correntes gasosas. A análise do escoamento dentro do ciclone é complexa devido ao grande número de parâmetros e variáveis operacionais que influenciam na dinâmica do sistema. Devido a sua versatilidade de uso e a sua robustez nos resultados a fluidodinâmica computacional é uma alternativa importante utilizada com frequência no estudo da dinâmica do escoamento no ciclone. Na literatura existem vários trabalhos que fazem uso da fluidodinâmica computacional no estudo da queda de pressão. Entretanto, no estudo da eficiência de coleta, os artigos são em menor quantidade. No ciclone, a fluidodinâmica computacional permite simular a eficiência de coleta de partículas com diâmetro maiores que 5 µm com bastante precisão; a modelagem da eficiência de coleta para partículas com diâmetros menores ainda resultam em valores diferentes dos valores experimentais. Neste trabalho foram realizadas as simulações numéricas no ciclone tipo Stairmand; foram injetadas partículas de 1 a 5 µm. Para a verificação foram tomados dados experimentais disponíveis na literatura. Os dados experimentais foram obtidos por Zhao, Shen e Kang (2004) e Zhao (2005). A malha utilizada nas simulações, foi analisada antes e depois das simulações. Os modelos de turbulência utilizados para simular o escoamento no ciclone foram: Reynolds Stress Model (RSM) e Large Eddy Simulation (LES). A fase dispersa foi simulada considerando acoplamento de uma via e acoplamento de duas vias. Para integrar as equações de movimento das partículas, foram utilizados os esquemas de integração: implícito, analítico, trapezoidal e Runge-Kutta. Os resultados mostraram que a metodologia empregada mostrou-se adequada para reproduzir o comportamento do escoamento no ciclone. As porcentagens de erro obtidos na queda de pressão foram em média menores que 5% e na eficiência de coleta foram reproduzidas com boa precisão para os diâmetros de 3, 4 e 5 µm.

A new model for simulating non-Brownian flexible fibres suspended in a Newtonian fluid has been developed. Special attention has been given to include realistic flow conditions found in the industrial papermaking process in the key features of the model; it is the intention of the author to employ the model in simulations of the forming section of the paper machine in future studies. The model considers inert fibres of various shapes and finite stiffness, interacting with each other through normal, frictional and lubrication forces, and with the surrounding fluid medium through hydrodynamic forces. Fibre-fluid interactions in the non-creeping flow regime are taken into account, and the two-way coupling between the solids and the fluid phase is included by enforcing momentum conservation between phases. The incompressible three-dimensional Navier-Stokes equations are employed to model the motion of the fluid medium. The validity of the model has been tested by comparing simulation results with experimental data from the literature. It was demonstrated that the model predicts the motion of isolated fibres in shear flow over a wide range of fibre flexibilities. It was also shown that the model predicts details of the orientation distribution of multiple straight, rigid fibres in a sheared suspension. Model predictions of the viscosity and first normal stress difference were in good agreement with experimental data found in the literature. Since the model is based solely on first-principles physics, quantitative predictions could be made without any parameter fitting. / En ny modell för simulering av rörelserna hos icke-Brownska böjliga fibrer dispergerade i en Newtonsk vätska har utvecklats. Eftersom det är författarens avsikt att modellen skall kunna tillämpas vid simulering av arkformning under de förhållanden som råder i en modern pappersmaskin, har särskilt omsorg givits till att inkludera motsvarande flödesvillkor i modellens giltighetsområde. Modellen hanterar fibrer av varierande form, massa och styvhet, som växelverkar sinsemellan via normal-, friktions- och smörjkrafter. Deras växelverkan med den omgivande vätskan sker via hydrodynamiska krafter vid finita Reynolds-tal. Den så kallade tvåvägskopplingen mellan fibrerna och vätskefasen har tagits i beaktande genom att kräva att rörelsemängden bevaras vid interaktionen mellan faserna. Vidare har Navier-Stokes ekvationer för inkompressibla vätskor använts för att beskriva mediets rörelser. Modellens giltighet har undersökts genom att jämföra resultat från simuleringar med experimentella data från litteraturen. Det har påvisats att modellen förutsäger rörelsen hos ensamma fibrer i ett skjuvflöde, för vitt skilda fiberflexibiliteter. Det visades också att modellen förutsäger detaljer hos fiberorienteringsdistributionen i suspensioner utsatta för skjuvflöde. Det kunde också konstateras att modellens förutsägelser av fibersuspensioners viskositet och första normalspänningsdifferens under skjuvning väl överensstämde med experimentella data i litteraturen. Kvantitativa förutsägelser har kunnat göras utan någon parameteranpassning, då modellen bygger uteslutande på väletablerade fysikaliska samband inom klassisk mekanik och strömningslära.

The transport or the separation of solid particles or droplets suspended in a fluid flow is a common task in mechanical and process engineering. To improve machinery and physical processes (e.g. for coal combustion, reduction of NO_x and soot) an optimization of complex phenomena by simulation applying the fundamental conservation equations is required. Fluid-particle flows are characterized by the ratio of density of the two phases gamma=rho_P/rho_F, by the Stokes number St=tau_P/tau_F and by the loading in terms of void and mass fraction. Those numbers (Stokes number, gamma) define the flow regime and which relevant forces are acting on the particle. Dependent on the geometrical configuration the particle-wall interaction might have a heavy impact on the mean flow structure. The occurrence of particle-particle collisions becomes also more and more important with the increase of the local void fraction of the particulate phase. With increase of the particle loading the interaction with the fluid phase can not been neglected and 2-way or even 4-way coupling between the continous and disperse phases has to be taken into account. For dilute to moderate dense particle flows the Euler-Lagrange method is capable to resolve the main flow mechanism. An accurate computation needs unfortunately a high number of numerical particles (1,...,10^7) to get the reliable statistics for the underlying modelling correlations. Due to the fact that a Lagrangian algorithm cannot be vectorized for complex meshes the only way to finish those simulations in a reasonable time is the parallization applying the message passing paradigma. Frank et al. describes the basic ideas for a parallel Eulererian-Lagrangian solver, which uses multigrid for acceleration of the flow equations. The performance figures are quite good, though only steady problems are tackled. The presented paper is aimed to the numerical prediction of time-dependend fluid-particle flows using the simultanous particle tracking approach based on the Eulerian-Lagrangian and the particle-source-in-cell (PSI-Cell) approach. It is shown in the paper that for the unsteady flow prediction efficiency and load balancing of the parallel numerical simulation is an even more pronounced problem in comparison with the steady flow calculations, because the time steps for the time integration along one particle trajectory are very small per one time step of fluid flow integration and so the floating point workload on a single processor node is usualy rather low. Much time is spent for communication and waiting time of the processors, because for cold flow particle convection not very extensive calculations are necessary. One remedy might be a highspeed switch like Myrinet or Dolphin PCI/SCI (500 MByte/s), which could balance the relative high floating point performance of INTEL PIII processors and the weak capacity of the Fast-Ethernet communication network (100 Mbit/s) of the Chemnitz Linux Cluster (CLIC) used for the presented calculations. Corresponding to the discussed examples calculation times and parallel performance will be presented. Another point is the communication of many small packages, which should be summed up to bigger messages, because each message requires a startup time independently of its size. Summarising the potential of such a parallel algorithm, it will be shown that a Beowulf-type cluster computer is a highly competitve alternative to the classical main frame computer for the investigated Eulerian-Lagrangian simultanous particle tracking approach.

Lors d’un lancement spatial, le bruit des jets supersoniques chauds, générés par les moteurs-fusées au décollage et en interaction avec le pas de tir, est dommageable pour le lanceur et en particulier sa charge utile. Par conséquent, les acteurs du spatial cherchent à renforcer leur compréhension et leur maîtrise de cette ambiance acoustique, entre autres grâce à des méthodes et outils numériques. Toutefois, ils ne disposent pas d’une approche numérique globale capable de prendre en compte simultanément la génération fidèle du bruit, la propagation acoustique non-linéaire, les effets d’installation complexes et les géométries réalistes, pourtant inhérents aux applications spatiales. Dans cette optique, cette étude consiste à mettre en place et valider une méthodologie de simulation numérique par couplage fort Navier-Stokes − Euler, puis à l’appliquer à des cas réalistes de bruit de jet supersonique. L’objectif est d’affiner les capacités de prévision et de contribuer à la compréhension des mécanismes de génération de bruit dans de tels jets. Le solveur Navier-Stokes repose sur une méthode LES sur maillage non-structuré et le solveur acoustique sur une méthode de Galerkine discontinue d’ordre élevé sur maillage non-structuré. La méthodologie est tout d’abord évaluée sur des cas académiques visant à valider la simulation par couplage fort. Après des calculs préliminaires, la méthodologie est appliquée à la simulation du bruit d’un jet libre supersonique à Mach 3.1. Une méthode de déclenchement géométrique de la turbulence est implémentée sous la forme d’une marche à la paroi de la tuyère. La simulation aboutit à des estimations du bruit très proches des mesures réalisées au banc MARTEL et met en évidence des effets non-linéaires significatifs ainsi qu’un mécanisme singulier de rayonnement des ondes de Mach. Dans une démarche de progression vers des cas toujours plus réalistes, l’ensemble de l’approche numérique est finalement adaptée avec succès à la simulation du bruit d’un jet en présence d’un carneau. À terme, elle pourra être étendue à des configurations multi-jets réactifs, avec injection d’eau, voire à l’échelle 1. / During a space launch, the noise from hot supersonic jets, generated by rocket engines at liftoff and interacting with the launch pad, is harmful to the launcher and in particular its payload. Consequently, space actors are seeking to strengthen their understanding and control of this acoustic environment through numerical methods and tools, among the others. However, they do not dispose of a comprehensive numerical strategy that can simultaneously take into account accurate noise generation, nonlinear acoustic propagation, complex installation effects and realistic geometries, which are inherent to space applications. For this purpose, the present study consists in setting up and validating a numerical simulation methodology using a Navier-Stokes − Euler two-way coupling approach, then applying it to realistic cases of supersonic jet noise in order to improve prediction capabilities and contribute to the understanding of the noise generation mechanisms in such jets. The Navier-Stokes solver is based on an LES method on unstructured mesh and the acoustic solver on a high-order discontinuous Galerkin method on unstructured mesh. The methodology is first assessed on academic cases to validate the use of the two-way coupling. After preliminary computations, the methodology is applied to the simulation of the noise from a supersonic free jet at Mach 3.1. A geometric turbulence tripping method is implemented via a step at the nozzle wall. The computation leads to noise predictions very close to the experimental measurements performed at the MARTEL test bench and highlights significant nonlinear effects as well as a quite particular Mach waves radiation mechanism. Targeting even more realistic cases, the entire numerical approach is finally successfully adapted to the simulation of the noise from a supersonic jet configuration including a flame trench. In the future, it may be extended to configurations with clustered reactive jets, water injection devices or even at full scale.

The transport or the separation of solid particles or droplets suspended in a fluid flow is a common task in mechanical and process engineering. To improve machinery and physical processes (e.g. for coal combustion, reduction of NO_x and soot) an optimization of complex phenomena by simulation applying the fundamental conservation equations is required. Fluid-particle flows are characterized by the ratio of density of the two phases gamma=rho_P/rho_F, by the Stokes number St=tau_P/tau_F and by the loading in terms of void and mass fraction. Those numbers (Stokes number, gamma) define the flow regime and which relevant forces are acting on the particle. Dependent on the geometrical configuration the particle-wall interaction might have a heavy impact on the mean flow structure. The occurrence of particle-particle collisions becomes also more and more important with the increase of the local void fraction of the particulate phase. With increase of the particle loading the interaction with the fluid phase can not been neglected and 2-way or even 4-way coupling between the continous and disperse phases has to be taken into account. For dilute to moderate dense particle flows the Euler-Lagrange method is capable to resolve the main flow mechanism. An accurate computation needs unfortunately a high number of numerical particles (1,...,10^7) to get the reliable statistics for the underlying modelling correlations. Due to the fact that a Lagrangian algorithm cannot be vectorized for complex meshes the only way to finish those simulations in a reasonable time is the parallization applying the message passing paradigma. Frank et al. describes the basic ideas for a parallel Eulererian-Lagrangian solver, which uses multigrid for acceleration of the flow equations. The performance figures are quite good, though only steady problems are tackled. The presented paper is aimed to the numerical prediction of time-dependend fluid-particle flows using the simultanous particle tracking approach based on the Eulerian-Lagrangian and the particle-source-in-cell (PSI-Cell) approach. It is shown in the paper that for the unsteady flow prediction efficiency and load balancing of the parallel numerical simulation is an even more pronounced problem in comparison with the steady flow calculations, because the time steps for the time integration along one particle trajectory are very small per one time step of fluid flow integration and so the floating point workload on a single processor node is usualy rather low. Much time is spent for communication and waiting time of the processors, because for cold flow particle convection not very extensive calculations are necessary. One remedy might be a highspeed switch like Myrinet or Dolphin PCI/SCI (500 MByte/s), which could balance the relative high floating point performance of INTEL PIII processors and the weak capacity of the Fast-Ethernet communication network (100 Mbit/s) of the Chemnitz Linux Cluster (CLIC) used for the presented calculations. Corresponding to the discussed examples calculation times and parallel performance will be presented. Another point is the communication of many small packages, which should be summed up to bigger messages, because each message requires a startup time independently of its size. Summarising the potential of such a parallel algorithm, it will be shown that a Beowulf-type cluster computer is a highly competitve alternative to the classical main frame computer for the investigated Eulerian-Lagrangian simultanous particle tracking approach.