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Widlund, Ola. "Modeling of magnetohydrodynamic turbulence." Doctoral thesis, Stockholm, 2000. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3065.
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Tera, Sridhar R. "Turbulence modeling of solar convection." abstract and full text PDF (free order & download UNR users only), 2007. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1446423.
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PASINATO, HUGO DARIO. "TURBULENCE IN WALL REGION MODELING." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1998. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=19290@1.
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CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICONeste trabalho são apresentados de uma pesquisa orientada à modelagem da turbulência de baixos números de Reynolds. Com esse objetivo foi caracterizado o escoamento turbulento de baixos números de Reynolds na região viscosa vizinha a uma parede, na base de dados experimentais e correlação empírica. Sobre essa caracterização foi feita uma análise dos valores médios de interesse para modelos de turbulência de duas equações, a qual permitiu obter conclusões sobre o comportamento da turbulência de baixos Reynolds e propor modelos para a mesma. Essa modelagem implica em fornecer um fechamento para a equação de dissipação de energia cinética turbulenta e uma expressão para a viscosidade efetiva da turbulência, na região viscosa. O fechamento da equação de dissipação foi feito analisando os termos fontes de vorticidade, usando resultados prévios da ordem de grandeza relativa dos mesmos. A equação de dissipação obtida desse modo não contém funções de amortecimento. Com relação à expressão proposta para calcular a viscosidade efetiva de turbulência, considera-se que a transferência de quantidade de movimento devido à turbulência pode ser obtida em função da energia cinética do escoamento médio. Considera-se que a modelagem proposta é uma complementação para modelos de turbulência de duas equações, para simular zonas de baixos Reynolds incluídos os casos em sub-camada logarítmica aparente. Problemas de escoamentos turbulentos com cisalhamento médio com diferentes características, usualmente utilizadas para avaliar modelos de turbulência, foram usados como testes. Como resultados relevantes desta pesquisa, considera-se o fato de se usar em forma sistemática informação experimental para o desenvolvimento de modelos de turbulência, a obtenção de um fechamento para a equação de dissipação sem funções de amortecimento e uma expressão para a viscosidade da turbulência na região viscosa. No caso da viscosidade da turbulência, a expressão proposta permite obter a distribuição da velocidade média na região amortecedora, apresentando boa concordância com dados experimentais.
This thesis presents the results of research work aiming at low Reynolds turbulence modeling. For an stablished boundary layer turbulent low Reynolds flow in the viscous layer near a wall was characterized based on experimental data and empirical polynomials. On this basis an analysis of the distribuition of the mean values in the near-wall region was performed allowing for the proposal of a low Reynolds turbulence model within a two-equation model methodolgy. The low Reynolds proposal involves a closure to the dissipation equation and the proposal of an effective turbulence viscosity expression. The dissipation equation closure like as the effective viscosity proposal were made based on previous results of scale time rate analysis through the viscous region. On the other hand, the effective turbulence viscosity expression allows for the representation of the Reynolds stress as a function of mean flow kinetic energy. The low Reynolds turbulence modeling proposal can be seen as a complementation of two eqaution models for low Reynolds turbulence. The model was tested in several case tests of turbulent flow with different kind of mean shear, frequently used for turbulence model assessment. As main results of this work can be mentioned the systematic use of experimental data to build, analyze and test turbulence models; the closure of the dissipation equation without damping functions and the turbulence effective viscosity expression for the viscous region. This last proposed relation allows for the attainment of a mean velocity distribuition profile in the buffer region, which adequately fits experimental data.
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Ajmani, Kumud. "Turbulence modeling in hypersonic inlets." Thesis, Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/101365.
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A study is conducted to analyze the performance of different turbulence models when applied to flow through a Mach 7.4 hypersonic inlet. The analysis, which is two-dimensional, is done by comparing computational results from a Parabolized Navier Stokes code, with experimental data. The McDonald Camarata (MC) and Baldwin Lomax (BL) models were the two zero-equation models used in the study. The Turbulent Kinetic Energy (TKE) model was chosen as a representative higher order model. The MC model, when run with transition of flow, provides a solution which compares excellently with the data. Transition has a first order effect on the overall solution provided by the code. The BL model predicts separation of flow in the inlet, which contradicts experimental findings. The TKE model does not perform any better than the MC and BL models, despite the fact that it is a higher order turbulence model. The BL and TKE models predict transition in the inlet at a location which is much earlier than observed in the experiment. This may be attributed to the empirical constants used to determine the point of transition.M.S.
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Bakosi, József. "PDF modeling of turbulent flows on unstructured grids." Fairfax, VA : George Mason University, 2008. http://hdl.handle.net/1920/3083.
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Thesis (Ph.D.)--George Mason University, 2008.Vita: p. 178. Thesis director: Zafer Boybeyi. Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Computational Sciences and Informatics. Title from PDF t.p. (viewed June 30, 2008). Includes bibliographical references (p. 168-177). Also issued in print.
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Cotela, Dalmau Jordi. "Applications of turbulence modeling in civil engineering." Doctoral thesis, Universitat Politècnica de Catalunya, 2016. http://hdl.handle.net/10803/383754.
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This thesis explores the use of stabilized finite element formulations for the incompressible Navier-Stokes equations to simulate turbulent flow problems. Turbulence is a challenging problem due to its complex and dynamic nature and its simulation if further complicated by the fact that it involves fluid motions at vastly different length and time scales, requiring fine meshes and long simulation times. A solution to this issue is turbulence modeling, in which only the large scale part of the solution is retained and the effect of smaller turbulent motions is represented by a model, which is generally dissipative in nature.
In the context of finite element simulations for fluids, a second problem is the apparition of numerical instabilities. These can be avoided by the use of stabilized formulations, in which the problem is modified to ensure that it has a stable solution. Since stabilization methods typically introduce numerical dissipation, the relation between numerical and physical dissipation plays a crucial role in the accuracy of turbulent flow simulations. We investigate this issue by studying the behavior of stabilized finite element formulations based on the Variational Multiscale framework and on Finite Calculus, analyzing the results they provide for well-known reference problems, with the final goal of obtaining a method that both ensures numerical stability and introduces physically correct turbulent dissipation.
Given that, even with the use of turbulence models, turbulent flow problems require significant computational resources, we also focused on programming and implementation aspects of finite element codes, specially in ensuring that our solver can perform efficiently on distributed memory architectures and high-performance computing clusters.
Finally, we have developed an adaptive mesh refinement technique to improve and optimize unstructured tetrahedral meshes, again with the goal of enabling the simulation of large turbulent flow problems. This technique combines an error estimator based on Variational Multiscale principles with a simple refinement procedure designed to work in a distributed memory context and we have applied it to the simulation of both turbulent and non-Newtonian flow problems.Aquesta tesi estudia la possibilitat d'utilitzar formulacions estabilitzades d'elements finits de les equacions de Navier-Stokes incompressibles per a la simulació de problemes de flux turbulent. La descripció de la turbulència és un repte, ja que es tracta d'un problema altament dinàmic i complex i la seva simulació numèrica es veu complicada pel fet que hi intervenen moviments de masses fluides amb dimensions i temps característics molt diferents i per tant requereix malles de càlcul molt fines i temps de simulació llargs. Això s'ha provat de resoldre mitjançant l'ús de models de turbulència, mantenint únicament la part de la solució de més gran escala i introduint un model de l'efecte dels moviments de petita escala, que acostuma a tenir un efecte dissipatiu. En el context de la simulació de fluids amb elements finits es planteja un segon problema amb l'aparició d'inestabilitats numèriques. Aquestes es poden evitar amb l'ús de formulacions estabilitzades, en les quals el problema es modifica per assegurar que tingui una solució estable. Ja que els mètodes d'estabilització típicament introdueixen dissipació addicional, la relació entre la dissipació numèrica i la dissipació física té un paper fonamental en la qualitat de la solució. Per investigar aquest fenomen hem estudiat el comportament de diferents formulacions d'elements finits basades en mètodes variacionals de subescala (VMS) i en el càlcul finit (FIC) en termes del seu comportament en la simulació de problemes turbulents de referència, amb l'objectiu final de trobar un mètode que a la vegada garanteixi l'estabilitat de la solució i introdueixi la dissipació turbulenta físicament necessària. Tenint en compte que, fins i tot quan s'utilitzen models de turbulència, la simulació de problemes de flux turbulent requereix molts recursos de càlcul, també hem estudiat aspectes de la implementació paral·lela de programes d'elements finits per tal de garantir que el nostre codi pot treure partit d'arquitectures de memòria distribuïda i servidors de càlcul d'alt rendiment. Finalment, hem desenvolupat una tècnica de refinament adaptatiu de malla que permeti millorar la qualitat de malles de càlcul tetraèdriques, novament amb la intenció de facilitar la simulació de grans problemes de flux turbulent. Aquesta tècnica combina un estimador d'error basat en els principis de la formulació variacional de subescala amb un procediment de refinament dissenyat per funcionar fàcilment en un context de memòria distribuïda i s'ha utilitzat per simular problemes de flux turbulent i no-Newtonià.
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Jeong, Eun-Hwan. "Selected problems in turbulence theory and modeling." Diss., Texas A&M University, 2003. http://hdl.handle.net/1969.1/523.
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Three different topics of turbulence research that cover modeling, theory and model computation categories are selected and studied in depth. In the first topic, "velocity gradient dynamics in turbulence" (modeling), the Lagrangian linear diffusion model that accounts for the viscous-effect is proposed to make the existing restricted-Euler velocity gradient dynamics model quantitatively useful. Results show good agreement with DNS data. In the second topic, "pressure-strain correlation in homogeneous anisotropic turbulence subject to rapid strain-dominated distortion" (theory), extensive rapid distortion calculation is performed for various anisotropic initial turbulence conditions in strain-dominated mean flows. The behavior of the rapid pressure-strain correlation is investigated and constraining criteria for the rapid pressure-strain correlation models are developed. In the last topic, "unsteady computation of turbulent flow past a square cylinder using partially-averaged Navier-Stokes method" (model computation), the basic philosophy of the PANS method is reviewed and a practical problem of flow past a square cylinder is computed for various levels of physical resolution. It is revealed that the PANS method can capture many important unsteady flow features at an affordable computational effort.
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Fan, Chen. "ENHANCING FLUID MODELING WITH TURBULENCE AND ACCELERATION." Kent State University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=kent1426072265.
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Hickel, Stefan. "Implicit turbulence modeling for large-eddy simulation." kostenfrei, 2008. http://mediatum2.ub.tum.de/doc/654921/654921.pdf.
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Uddin, Naseem. "Turbulence modeling of complex flows in CFD." München Verl. Dr. Hut, 2008. http://d-nb.info/990811263/04.
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Bose, Jyoti Sankar. "Modeling turbulence anisotropy using algebraic Reynolds stress models." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp04/mq22277.pdf.
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Le, Roy Pascal. "Cascade inverse et dispersion turbulente en turbulence bidimensionnelle." Phd thesis, Ecole Nationale des Ponts et Chaussées, 1988. http://tel.archives-ouvertes.fr/tel-00529772.
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Cette thèse étudie la turbulence bidimensionnelle au moyen de simulations numériques. La turbulence bidimensionnelle intéresse surtout les météorologues et les océanographes car elle constitue une première approximation de leurs écoulements. Mon travail sur le modèle de turbulence bidimensionnelle du Laboratoire de Météorologie Dynamique a consisté à la fois en l'amélioration du modèle et la réalisation de diverses expériences sur ce modèle. La principale amélioration apportée au modèle est la mise au point d'une bonne modélisation de la cascade inverse d'énergie, i.e. une simulation plus réaliste des plus grandes échelles de l'écoulement. Les expériences réalisées sur ce modèle amélioré concernent la dispersion (absolue ou relative), i.e. nous simulons l'advection de flotteurs lagrangiens par l'écoulement. Les résultats obtenus diffèrent sensiblement des conjectures théoriques et nous obligent à envisager une approche différente de la dispersion turbulente. J'ai ajouté le travail d'une année, réalisé comme scientifique du contingent à l'Institut de Mécanique de Grenoble, sur les instabilités qui se développent dans une couche de mélange bidimensionnelle.
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Horne, Jimmy D. Jr. "Modeling optical turbulence with COAMPS during two observation periods at Vandenberg AFB." Thesis, Monterey, California. Naval Postgraduate School, 2004. http://hdl.handle.net/10945/1671.
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Approved for public release, distribution is unlimitedThe objective of this thesis is to investigate the forecastability of optical turbulence using the U.S. Navy's Coupled Ocean Atmosphere Mesoscale Prediction System (COAMPS). First, a detailed synoptic study was performed over the Eastern Pacific region for observation periods in October 2001 and March 2002 to focus on mesoscale features affecting Vandenberg AFB. Second, a modified version of COAMPS version 2.0.16 model output was evaluated to ensure reasonable modeling of the mesoscale. Next, temperature and dewpoint temperature vertical profiles of COAMPS, modified with the Turbulent Kinetic Energy (TKE) Method, were compared with balloon-launched rawinsondes, initially, then with higher resolution thermosondes. Optical turbulence parameters were then calculated from the data and a comparison between synthetic profiles and thermosonde-derived profiles were qualitatively and quantitatively studied. Then the vertical resolution of the model was increased for selected forecasts to determine the potential for forecast improvement.
Lieutenant Commander, United States Navy
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Sainte-Rose, Bruno. "Simulations numériques d'écoulements réactifs massivement décollés par une approche hybride RANS/LES." Phd thesis, Ecole Centrale Paris, 2010. http://tel.archives-ouvertes.fr/tel-00635538.
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Les premières simulations numériques d'écoulements réactifs sur des configurationscomplexes ont été réalisées à l'aide d'approches RANS (Reynolds Averaged Navier Stokes). Ces dernières, bien adaptées aux écoulements de type couches limites attachées et relativement peu coûteuses en temps de calcul, ne donnent accès qu'à des résultats stationnaires qui s'éloignent parfois de la réalité. Pour réaliser des simulations instationnaires d'écoulements, les méthodes de type LES (Large Eddy Simulation) -- plus précises mais plus coûteuses -- sont de plus en plus utilisées. Cependant, ces méthodes sont mal adaptées à la simulation de la dynamique pariétale, car elles nécessitent un effort de maillage souvent prohibitif près de la paroi. Cette thèse est consacrée au développement dans le code CEDRE (code de simulation d'écoulements réactifs complexes de l'Onera) d'une méthode hybride RANS/LES, appelée Delayed Detached Eddy Simulation (DDES), et à son application à des écoulements réactifs massivement décollés. Après une étape de validation sur des couches limites attachées, la DDES a été appliquée à la simulation des écoulements inerte et réactif dans une chambre de combustion en forme de marche descendante (A3C) et comparée aux résultats des approches RANS et LES classiques, ainsi qu'aux résultats expérimentaux. Cette méthode a ensuite permis de réaliser l'étude de la dynamique de l'écoulement réactif décollé dans la tuyère ATAC montée sur le banc cryotechnique MASCOTTE de l'Onera.
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Vilmin, Stéphane. "Turbulence modeling on unstructured meshes for 3D turbomachinery CFD /." Lausanne : EPFL, 1998. http://library.epfl.ch/theses/?nr=1864.
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Lagha, Maher. "Modeling the transition to turbulence in plane Couette flow." Phd thesis, Ecole Polytechnique X, 2006. http://pastel.archives-ouvertes.fr/pastel-00675068.
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The Galerkin method is used to derive a realistic model of plane Couette flow in terms of partial differential equations governing the space-time dependence of the amplitude of a few cross-stream modes. Numerical simulations show that it reproduces the globally sub-critical behavior typical of this flow. In particular, the statistics of turbulent transients at decay from turbulent to laminar flow displays striking similarities with experimental findings.
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Grigoriev, Igor. "Turbulence modeling of compressible flows with large density variation." Doctoral thesis, KTH, Turbulens, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-183452.
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In this study we highlight the influence of mean dilatation and mean density gradient on the Reynolds stress modeling of compressible, heat-releasing and supercritical turbulent flows.Firstly, the modeling of the rapid pressure-strain correlation has been extended to self-consistently account for the influence of mean dilatation.Secondly, an algebraic model for the turbulent density flux has been developed and coupled to the tensor equationfor Reynolds stress anisotropy via a 'local mean acceleration',a generalization of the buoyancy force. We applied the resulting differential Reynolds stress model (DRSM) and the corresponding explicit algebraic Reynolds stress model (EARSM) to homogeneously sheared and compressed or expanded two-dimensional mean flows. Both formulations have shown that our model preserves the realizability of the turbulence, meaning that the Reynolds stresses do not attain unphysical values, unlike earlier approaches. Comparison with rapid distortion theory (RDT) demonstrated that the DRSM captures the essentials of the transient behaviour of the diagonal anisotropies and gives good predictions of the turbulence kinetic energy. A general three-dimensional solution to the coupled EARSM has been formulated. In the case of turbulent flow in de Laval nozzle we investigated the influence of compressibility effects and demonstrated that the different calibrations lead to different turbulence regimes but with retained realizability. We calibrated our EARSM against a DNS of combustion in a wall-jet flow. Correct predictions of turbulent density fluxes have been achieved and essential features of the anisotropy behaviour have been captured.The proposed calibration keeps the model free of singularities for the cases studied. In addition, we have applied the EARSM to the investigation of supercritical carbon dioxide flow in an annulus. The model correctly captured mean enthalpy, temperature and density as well as the turbulence shear stress. Hence, we consider the model as a useful tool for the analysis of a wide range of compressible flows with large density variation.QC 20160314
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Cerminara, Matteo. "Modeling dispersed gas-particle turbulence in volcanic ash plumes." Doctoral thesis, Scuola Normale Superiore, 2016. http://hdl.handle.net/11384/86206.
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This PhD thesis focuses on numerical and analytical methods for simulating the dynamics of volcanic ash plumes. The study starts from the fundamental balance laws for a multiphase gas– particle mixture, reviewing the existing models and developing a new set of Partial Differential Equations (PDEs), well suited for modeling multiphase dispersed turbulence. In particular, a new model generalizing the equilibrium–Eulerian model to two-way coupled compressible flows is developed. The PDEs associated to the four-way Eulerian-Eulerian model is studied, investigating the existence of weak solutions fulfilling the energy inequalities of the PDEs. In particular, the convergence of sequences of smooth solutions to such a set of weak solutions is showed. Having explored the well-posedness of multiphase systems, the three-dimensional compressible equilibrium–Eulerian model is discretized and numerically solved by using the OpenFOAM® numerical infrastructure. The new solver is called ASHEE, and it is verified and validated against a number of well understood benchmarks and experiments. It demonstrates to be capable to capture the key phenomena involved in the dynamics of volcanic ash plumes. Those are: turbulence, mixing, heat transfer, compressibility, preferential concentration of particles, plume entrainment. The numerical solver is tested by taking advantage of the newest High Performance Computing infrastructure currently available. Thus, ASHEE is used to simulate two volcanic plumes in realistic volcanological conditions. The influence of model configuration on the numerical solution is analyzed. In particular, a parametric analysis is performed, based on: 1) the kinematic decoupling model; 2) the subgrid scale model for turbulence; 3) the discretization resolution. In a one-dimensional and steady-state approximation, the multiphase flow model is used to derive a model for volcanic plumes in a calm, stratified atmosphere. The corresponding Ordinary Differential Equations (ODEs) are written in a compact, dimensionless formulation. The six non-dimensional parameters characterizing a multiphase plume are then written. The ODEs is studied both numerically and analytically. Different regimes are analyzed, extracting the first integral of motion and asymptotic solutions. An asymptotic analytical solution approximating the model in the general regime is derived and compared with numerical results. Such a solution is coupled with an electromagnetic model providing the infrared intensity emitted by a volcanic ash plume. Key vent parameters are then retrieved by means of inversion techniques applied to infrared images measured during a real volcanic eruption.
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Cook, Andrew W. "On the simulation and modeling of turbulent reacting flows /." Thesis, Connect to this title online; UW restricted, 1996. http://hdl.handle.net/1773/7040.
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Franceschini, Lucas. "Modeling Strategies for Aerodynamic Flow Reconstruction from partial measurements." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLX092.
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Dans un premier temps, nous nous intéresserons à la récupération du champ moyen à partir d'informations partielles ou éparses, allant des sondes de vitesse ponctuelles à la pression ou frottement de paroi. Pour le réaliser, on considère les équations de Reynolds-Averaged Navier-Stokes (RANS), complétées par un modèle, ici le Spalart-Allmaras. Ce type de modélisation a été conçu pour quelques configurations d'écoulement de référence et peut manquer de généralité, ce qui conduit à des prédictions erronées, surtout lorsqu'il y a recirculation. Nous proposons la modification de ce modèle avec un paramètre de contrôle tel que la solution qui en découle corresponde le mieux aux données de champ moyen mentionnées ci-dessus. La configuration considérée est une marche descendente à Re=28275, avec des données réelles provenant d'un DNS.Ensuite, nous nous intéressons à l'analyse linéaire de champ moyen et à son utilisation pour prédire la fluctuation non linéaire instationnaire. En particulier, nous concevons un modèle d'ordre réduit, composé de l'équation du champ moyen couplé aux modes de résolvent, qui prédit la fluctuation pour chaque fréquence existante. Les énergies de ces modes sont utilisées comme paramètres à régler par la procédure d'assimilation des données, qui nécessite généralement (très) peu de donnée, typiquement des signaux résolus en temps issus de sondes ponctuelles. Cette technique sera appliquée dans des écoulements transitoires tels que celui autour d'un cylindre à section carrée, un cas de référence pour les écoulements oscillateurs, et un pas orienté vers l'arrière, un écoulement type d'amplificateur de bruit.Nous considérons ensuite un cas turbulent correspondant à l'écoulement autour d'un cylindre à section carrée à Re=22000, ayant à la fois des caractéristiques d'oscillateur (émission périodique de vortices) et d'amplificateur de bruit (représenté par les structures Kelvin-Helmholtz). L'analyse classique de stabilité de champ moyen est utilisée pour récupérer le mode d'emission de vortex et une technique de résolvent, basée sur les équations linéarisées autour de la composante périodique, est utilisée pour récupérer la dépendance des modes Kelvin-Helmholtz avec l'emission de vortexIn a first moment we will be interested in the recovery of the mean-flow quantities from partial or sparse information, ranging from point-wise velocity probes to wall-pressure and friction. This will be achieved by considering the Reynolds-Averaged Navier-Stokes (RANS) equations, completed with a model, here the Spalart-Allmaras. This kind of modeling has been conceived for a few benchmark flow configurations and may lack generality, leading to erroneous predictions, especially when re-circulation is present. We propose the modification of this model with a tuning parameter such that its solution matches the best the aforementioned mean-flow data. The configuration considered was a Backward-Facing Step at Re=28275, with actual data stemming from a DNS.Then, we turn our attention to linear mean-flow analysis and its use to predict the nonlinear unsteady fluctuation. In particular, we design a reduced-order model, composed by the mean-flow equation coupled with the resolvent modes, predicting the fluctuation for each existing frequency. The energies of those modes are used as tuning parameters for the data-assimilation procedure, that will take as input typically (very) few point-wise time-resolved information. This technique will be applied in transitional flows such as the one around a squared-section cylinder, a benchmark case for oscillator flows, and a backward-facing-step, a typical noise-amplifier flow.We then consider a turbulent case corresponding to the flow around a squared-section cylinder at Re=22000, having both oscillator (periodic vortex-shedding) and noise-amplifier-like characteristics (represented by the Kelvin-Helmholtz structures). Classical mean-flow stability analysis is used to recover the the vortex-shedding mode and a resolvent technique, based on the linearized equations around the periodic component, is used to recover the dependency of the Kelvin-Helmholtz modes with the vortex-shedding
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Glawe, Christoph [Verfasser]. "ODTLES: Turbulence Modeling Using a One-Dimensional Turbulence Closed Extended Large Eddy Simulation Approach / Christoph Glawe." Berlin : Freie Universität Berlin, 2016. http://d-nb.info/1100388214/34.
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Zeren, Zafer. "Lagrangian stochastic modeling of turbulent gas-solid flows with two-way coupling in homogeneous isotropic turbulence." Thesis, Toulouse, INPT, 2010. http://www.theses.fr/2010INPT0106/document.
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Dans ce travail de thèse, réalisé à l'IMFT, nous nous sommes intéressés aux écoulements turbulents diphasiques gaz-solides et plus particulièrement au phénomène de couplage inverse qui correspond à la modulation de la turbulence par la phase dispersée. Ce mécanisme est crucial pour les écoulements à forts chargements massiques. Dans cette thèse, nous avons considéré une turbulence homogène isotrope stationnaire sans gravité dans laquelle des particules sont suivies individuellement d'une façon Lagrangienne. La turbulence du fluide porteur est obtenue par des simulations directes (DNS). Les particules sont sphériques, rigides et d'une taille inférieure aux plus petites échelles de la turbulence. Leur densité est bien plus grande que la densité du fluide. Dans ce cadre, la force la plus importante agissant sur les particules est celle de traînée. Les interactions inter-particules ainsi que la gravité ne sont pas prises en compte. Pour modéliser ce type d'écoulement, une approche stochastique est utilisée pour laquelle l'accélération du fluide est modélisée par une équation de Langevin. L'originalité de ce travail est la prise en compte de l'effet de la modulation de la turbulence par un terme additionnel. Nous avons proposé deux modèles : une force de couplage moyenne qui est définie à partir des vitesses moyennes des phases, et une force instantanée qui est définie à l'aide du formalisme mésoscopique Eulérien. La fermeture des modèles s’appuie sur la fonction d’autocorrélation Lagrangienne et l’équation de transport de l’énergie cinétique. Les modèles sont testés en terme de prédiction de la vitesse de dérive et des corrélations fluide-particule. Les résultats montrent que le modèle moyen, plus simple, prend en compte les effets principaux du couplage inverse. Cependant, le problème de fermeture pratique est reporté sur la modélisation de l’échelle intégrale Lagrangienne et l’énergie cinétique de la turbulence du fluide vue par les particulesIn this thesis, performed in IMFT, we are interested in the turbulent gas-solid flows and more specifically, in the phenomenon of turbulence modulation which is the modification of the structure of the turbulence due to the solid particles. This mechanism is crucial in flows with high particle mass-loadings. In this work, we considered a homogeneous isotropic turbulence without gravity kept stationary with stochastic type forcing. Discrete particles are tracked individually in Lagrangian manner. Turbulence of the carrier phase is obtained by using DNS. The particles are spherical, rigid and of a diameter smaller than the smallest scales of turbulence. Their density is very large in comparison to the density of the fluid. In this configuration the only force acting on the particles is the drag force. Volume fraction of particles is very small and inter-particle interactions are not considered. To model this type of flow, a stochastic approach is used where the fluid element accel- eration is modeled using stochastic Langevin equation. The originality in this work is an additional term in the stochastic equation which integrates the effect of the particles on the trajectory of fluid elements. To model this term, we proposed two types of modeling: a mean drag model which is defined using the mean velocities from the mean transport equations of the both phases and an instantaneous drag term which is written with the help of the Mesoscopic Eulerian Approach. The closure of the models is based on the Lagrangian auto- correlation function of the fluid velocity and on the transport equation of the fluid kinetic energies. The models are tested in terms of the fluid-particle correlations and fluid-particle turbulent drift velocity. The results show that the mean model, simple, takes into account the principal physical mechanism of turbulence modulation. However, practical closure problem is brought forward to the Lagrangian integral scale and the fluid kinetic energy of the fluid turbulence viewed by the particles
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Kudla, Thomas Lucas. "Implementation and Validation of a Modified Non-Equilibrium Wilcox K Omega Turbulence Model in Subsonic and Transonic Flow Regimes." University of Dayton / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1373481080.
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Chung, Daniel Pullin Dale Ian Pullin Dale Ian. "Numerical simulation and subgrid-scale modeling of mixing and wall-bounded turbulent flows." Diss., Pasadena, Calif. : California Institute of Technology, 2009. http://resolver.caltech.edu/CaltechETD:etd-05292009-123828.
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Thesis (Ph.D.) -- California Institute of Technology,2009.Advisor name found in the Acknowledgments pages of the thesis. Title from home page (viewed 05/04/2010). Includes bibliographical references.
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YODER, DENNIS ALLEN. "ALGEBRAIC REYNOLDS STRESS MODELING OF PLANAR MIXING LAYER FLOWS." University of Cincinnati / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1115637717.
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Martin, Scott Montgomery. "The conditional moment closure method for modeling lean premixed turbulent combustion /." Thesis, Connect to this title online; UW restricted, 2003. http://hdl.handle.net/1773/7088.
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Pajayakrit, Palanunt. "Turbulence modeling for curved wall jets under adverse pressure gradient." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ26861.pdf.
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Acton, Michael (Michael John). "Scale adaptive turbulence modeling for in-vessel sodium thermal hydraulics." Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/107022.
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Thesis: S.M., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2016.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 72-76).
Computational fluid dynamics is a powerful tool for the simulation of nuclear reactor coolant flows, such as in sodium fast reactors. In these reactors, the phenomenon of thermal striping -- characterized by oscillatory turbulent mixing of non-isothermal coolant flows -- has the potential to damage the structural integrity of reactor instrumentation and structural materials. At present, large eddy simulation is the only turbulence modeling approach which can sufficiently resolve and predict the mixing behavior of thermal striping, including temperature fluctuation and fluctuation frequencies. The extreme computational cost requirements of large eddy simulation application preclude the use of CFD for large engineering applications. In this work, the performance of the newly developed STRUCT hybrid turbulence model (Lenci, 2016) is evaluated on three representative test cases in comparison to traditional unsteady Reynolds-Averaged Navier-Stokes (URANS) and large eddy simulation (LES) models. Results indicate excellent potential for application of the STRUCT approach to sodium thermal striping flows. Best practice guidelines are developed and discussed.
by Michael Acton.
S.M.
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Wells, Jesse Buchanan. "Effects of Turbulence Modeling on RANS Simulations of Tip Vortices." Thesis, Virginia Tech, 2009. http://hdl.handle.net/10919/34343.
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The primary purpose of this thesis is to quantify the effects of RANS turbulence modeling on the resolution of free shear vortical flows. The simulation of aerodynamic wing-tip vortices is used as a test bed. The primary configuration is flow over an isolated finite wing with aspect ratio, , and Reynolds number, . Tip-vortex velocity profiles, vortex core and wake turbulence levels, and Reynolds stresses are compared with wind tunnel measurements. Three turbulence models for RANS closure are tested: the Lumley, Reece, and Rodi full Reynolds stress transport model and the Sparlart-Allmaras model with and without a proposed modification. The main finding is that simulations with the full Reynolds stress transport model show remarkable mean flow agreement in the vortex and wake due to the proper prediction of a laminar vortex core. Simulations with the Spalart-Allmaras model did not indicate a laminar core and predicted over-diffusion of the tip-vortex.
Secondary investigations in this work include the study of wall boundary layer treatment and simulating the wake-age of an isolated rotorcraft in hover using a steady-state RANS solver. By comparing skin friction plots over the NACA 0012 airfoil, it is shown that wall functions are most effective in the trailing edge half of the airfoil, while high velocity gradient and curvature of the leading edge make them more vulnerable to discrepancies. The rotorcraft simulation uses the modified Spalart-Allmaras turbulence model and shows proper, qualitative, resolution of the interaction between the vortex sheet and the tip vortex.Master of Science
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Barrows, Sean Thomas. "TURBO Turbulence Model Validation with Recommendations to Tip-Gap Modeling." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1213373781.
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Pajayakrit, Palanunt Carleton University Dissertation Engineering Mechanical and Aerospace. "Turbulence modeling for curved wall jets under adverse pressure gradient." Ottawa, 1997.
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Santoriello, Andrea. "Multiscale finite element methods for turbulence modeling in turbomachinery CFD." Doctoral thesis, La Sapienza, 2006. http://hdl.handle.net/11573/916915.
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Cai, Jiayi. "Turbulence modeling using machine learning driven by direct numerical simulations." Electronic Thesis or Diss., université Paris-Saclay, 2024. http://www.theses.fr/2024UPAST171.
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En simulation numérique de la turbulence, les modèles RANS (Reynolds-Averaged Navier-Stokes) permettent de résoudre les grandeurs moyennes des écoulements pour un coût de calcul très inférieur à la résolution "exacte" par simulation numérique directe (DNS). Ils exigent cependant un effort de modélisation considérable. L'une des problématiques habituellement rencontrées est celle de la modélisation du tenseur de Reynolds (RST), qui apparaît lors de l'application aux équations de Navier-Stokes d'un opérateur de moyenne statistique. Le modèle le plus couramment utilisé pour ce tenseur est l'hypothèse linéaire de Boussinesq, mais il souffre de nombreux défauts. Diverses généralisations ont été proposées dans la littérature, bien qu'elles manquent également d'universalité. Alors que ces fermetures complexes sont souvent basées sur des considérations semi-empiriques, il est désormais possible, grâce à l'accroissement des ressources informatiques, d'établir des modèles de fermeture neuronaux basés à la fois sur la physique et sur les données et notamment les données DNS. Ces dernières années, plusieurs modèles d'apprentissage automatique ont été développés dans ce domaine et ont montré des résultats prometteurs. Un modèle particulièrement pertinent pour cette thèse est celui des réseaux de neurones à base tensorielle (TBNN), s'appuyant sur des réseaux de neurones profonds qui vise à prédire le tenseur d'anisotropie (une version adimensionnée du RST). L'avantage principal de ce modèle est qu'il garantit l'invariance galiléenne et rotationnelle, en incorporant le modèle physique, le Modèle Généralisé de Viscosité Turbulente (GEVM), dans l'architecture du réseau neuronal. En prenant en compte les forces et les limites des études TBNN existantes, l'objectif principal de cette thèse est de développer et valider un TBNN augmenté (aTBNN) pour deux types d'écoulements confinés : l'écoulement de canal plan (PCF) et l'écoulement de canal carré (SDF). Ce travail est divisé en deux phases : la phase a priori et la phase a posteriori. La phase a priori se concentre sur la configuration, l'entraînement et l'évaluation de l'aTBNN. Dans cette phase, des entrées supplémentaires du réseau, une base tensorielle optimisée et des stratégies d'apprentissage avancées sont utilisées pour obtenir des prédictions équilibrées et physiquement correctes du tenseur d'anisotropie. Ensuite, l'aTBNN entraîné est intégré dans le code maison TrioCFD afin d'évaluer ses performances dans la prédiction de l'écoulement, en particulier le champ de vitesse. La validation a posteriori est particulièrement importante car plusieurs études ont montré que, même avec des entrées RST haute-fidélité, les solveurs RANS peuvent produire des prédictions de champ de vitesse insatisfaisantes. Pour répondre à cela, divers modèles de propagation de données haute-fidélité et modèles neuronaux sont implémentés et comparés aux modèles RANS de référence dans TrioCFD. Deux stratégies de couplage, la substitution itérative et la substitution figée, sont testées pour intégrer l'aTBNN avec les modèles RANS de référence, en combinaison avec des réseaux neuronaux supplémentaires pour corriger l'énergie cinétique turbulente et le taux de dissipation. Pour le cas du PCF, les simulations a priori et a posteriori montrent des résultats prometteurs, les modèles neuronaux dépassant les modèles RANS classiques dans plusieurs cas et montrant une forte concordance avec les données DNS. En revanche, le cas SDF présente de plus grands défis en raison de la complexité physique des écoulements secondaires et du manque de données d'entraînement couvrant différents régimes turbulents. En particulier, la méthode de couplage itératif s'est révélée instable dans ce scénario. Cependant, la méthode de substitution figée a montré un potentiel pour obtenir des résultats cohérents, et mérite une investigation plus approfondie pour exploiter pleinement ses capacitésIn the field of computational fluid dynamics, the Reynolds-Averaged Navier-Stokes (RANS) models allow the resolution of mean flow quantities at a much lower computational cost than the "exact" resolution provided by Direct Numerical Simulation (DNS). However, these models require significant modeling efforts. One major challenge is the modeling of the Reynolds Stress Tensor (RST), which emerges when applying a statistical averaging operator to the Navier-Stokes equations. The most commonly used model for this tensor is the linear Boussinesq hypothesis, but it suffers from some well-known limitations. Numerous generalizations have been proposed in the literature, though they also lack universality. While these complex closures are often based on semi-empirical considerations, advances in computational power now make it possible to establish physics-informed and DNS data-driven neural network-based closure models. In recent years, various machine-learning frameworks have been developed in this domain, showing promising results. Of particular relevance to this thesis is the Tensor Basis Neural Network (TBNN) framework, based on deep neural networks which aims to predict the anisotropy tensor (a scaled version of the RST). A key advantage of this framework is its incorporation of Galilean and rotational invariances, achieved by embedding the General Eddy Viscosity Model into the neural network architecture. Building upon the TBNN framework, this work aims to develop and validate an augmented Tensor Basis Neural Network (aTBNN) for two canonical wall-bounded flows: Plane Channel Flow (PCF) and Square Duct Flow (SDF). The research is divided into two phases: a priori and a posteriori phases. The a priori phase focuses on configuring, training, and evaluating the aTBNN. In this phase, additional input features, an optimized tensor basis, and advanced training strategies are employed to produce balanced and physically accurate predictions of the anisotropy tensor. Following this, the trained aTBNN is integrated into the in-house CFD code TrioCFD to assess its performance in predicting realistic flow behavior, such as velocity profiles. The a posteriori validation is particularly important, as previous studies have shown that even with high-fidelity RST inputs, RANS solvers can produce unsatisfactory velocity field predictions. To address this, various high-fidelity data propagation models and neural network models are implemented and compared with baseline RANS models in TrioCFD. Two coupling strategies, iterative and frozen substitution, are tested to integrate the aTBNN with baseline RANS models, along with extra neural networks for turbulent kinetic energy and dissipation rate corrections. For the PCF case, both a priori and a posteriori results from the proposed framework demonstrate promising outcomes, outperforming classical RANS models in certain cases and showing strong agreement with the DNS data. The SDF case presents more challenges due to the physical complexity of secondary flows and the limited availability of training data across different turbulence regimes. The iterative coupling method, in particular, proved to be unstable in this case. However, the frozen substitution method has shown potential for achieving accurate results, which requires further investigation
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Ching, Wing-han Michael. "Modeling of contaminant dispersion by statistical mechanics." Click to view the E-thesis via HKUTO, 2009. http://sunzi.lib.hku.hk/hkuto/record/B42664500.
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Qin, Zecong. "Transitions in Axisymmetric Turbulence." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSEC023/document.
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La turbulence axisymétrique est un écoulement bidimensionnel trois-composantes. L’étude de ce type de turbulence est motivée par le fait que celle-ci représente la limite asymptotique des écoulements anisotropes, et qu’elle a été le sujet des investigations théoriques dans le passé. Dans ce manuscrit, la turbulence axisymétrique a étudié en géométrie fermée en utilisant des simulations numériques spectrales et pseudo-spectrales.Études antérieures concernant la génération des structures cohérentes, obtenues dans les écoulements en déclin libre, sont considérées ici dans le contexte des écoulements statistiquement stationnaires, où l’énergie est injectée soit par un forçage spectralement localisé ou par une rotation des disques en haut et en bas du cylindre. On montre que les structures observées sont conformes aux prédictions théoriques.Lorsqu’un protocole de forçage anisotrope est utilisé, une bifurcation est observée entre un état non-tourbillonnant (bidimensionnel deux-composantes, 2D2C) et un écoulement tourbillonnant turbulent (bidimensionnel trois-composante, 2D3C). Cette transition est modélisée à travers un système de deux équations différentielles ordinaires (ODE), et on montre que ce modèle retient la physique essentielle de cette transition. La transition de l’écoulement axisymétrique à un écoulement tridimensionnel (3D3C) est ensuite étudiée à l’aide d’une dimension non-entière, en introduisant de façon continue la variation azimutale dans le système. On montre que la limite 2D2C est singulière et qu’une petite variation azimutale permet une redistribution d’énergie sur les différentes composante énergétiques. Le modèle ODE est adapté pour ce système et on montre que pour l’écoulement considéré la corrélation pression-déformation est responsable d'un niveau approximativement proportionnel à la dimension non-entière. Des Simulations des Grandes Echelles sont réalisées pour évaluer la robustesse des observations à grands nombres de ReynoldsAxisymmetric turbulence is a two-dimensional three-component flow. The investigation of this type of turbulence is motivated by the fact that it represents the asymptotic limit of anisotropic flows and since it has been the subject of theoretical investigations in the past. In the present manuscript such a flow is investigated in wall-bounded cylindrical geometry using spectral and pseudo-spectral numerical simulations.Previous results on the generation of coherent structures, obtained for freely decaying flow, are here assessed in the context of statistically steady flow, where the energy is supplied by either a spectrally localized forcing, or by moving top and bottom plates of the cylinder. It is shown that the observed structures are consistent with theoretical predictions.When an anisotropic forcing protocol is used, a bifurcation is observed from a non-swirling (two-dimensional two-component, 2D2C) flow to a swirling (two-dimensional three-component 2D3C) turbulent flow. This transition is modelled by a system of two ordinary differential equations (ODE), and it is shown that this model retains the essential physics of the transition.The transition of the axisymmetric flow to three-dimensional (3D3C) flow is then studied using non-integer dimension, by smoothly introducing azimuthal variation into the system. It is shown that the 2D2C limit is singular and that small azimuthal variation allows a redistribution of energy over the different energy components. The ODE model is adapted for this system and it is shown that for the considered flow the pressure-strain correlation is responsible for a swirl-level approximately proportional to the non-integer dimension. Large-Eddy Simulations are carried out to assess the robustness of the observations at higher Reynolds number
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Teichmann, Jakob. "Stochastic modeling of Brownian and turbulent coagulation." Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2017. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-220625.
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Als Beitrag zu einer verbesserten Filtration von Metallschmelzen werden stochastische Modelle für den essentiellen Mechanismus der Koagulation von Brownschen Partikeln und Partikeln in turbulenten Strömungen entwickelt und untersucht. Formeln für die zeitliche Entwicklung der Partikelkonzentration in diesen Systemen erlauben die Bestimmung von physikalischen Parametern, welche die Koagulation und somit die Filtration begünstigen. Um wichtige Resultate im Zusammenhang mit der traditionellen Herangehensweise für Brownsche Partikel zu berichtigen und zu erweitern, wird ein neuer Ansatz in Form zweier Modelle entwickelt. Für beide werden Formeln für die Partikelkonzentration, auf Basis einer neuartigen Verallgemeinerung der Matérn Hard-Core-Punktprozesse, abgeleitet. Um im Hinblick auf die Koagulationsgleichung der fraktalartigen Gestalt der Agglomerate besser Rechnung zu tragen, wird deren Morphologie anhand zweier neuer Modelle quantifiziert. Die Arbeit wird durch Anwendung der Modelle und numerische Simulationen von Koagulation und Abscheidung in turbulenten Strömungen abgerundet.
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Qin, Zecong. "Transitions in Axisymmetric Turbulence." Electronic Thesis or Diss., Lyon, 2019. http://www.theses.fr/2019LYSEC023.
Full textAbstract:
La turbulence axisymétrique est un écoulement bidimensionnel trois-composantes. L’étude de ce type de turbulence est motivée par le fait que celle-ci représente la limite asymptotique des écoulements anisotropes, et qu’elle a été le sujet des investigations théoriques dans le passé. Dans ce manuscrit, la turbulence axisymétrique a étudié en géométrie fermée en utilisant des simulations numériques spectrales et pseudo-spectrales.Études antérieures concernant la génération des structures cohérentes, obtenues dans les écoulements en déclin libre, sont considérées ici dans le contexte des écoulements statistiquement stationnaires, où l’énergie est injectée soit par un forçage spectralement localisé ou par une rotation des disques en haut et en bas du cylindre. On montre que les structures observées sont conformes aux prédictions théoriques.Lorsqu’un protocole de forçage anisotrope est utilisé, une bifurcation est observée entre un état non-tourbillonnant (bidimensionnel deux-composantes, 2D2C) et un écoulement tourbillonnant turbulent (bidimensionnel trois-composante, 2D3C). Cette transition est modélisée à travers un système de deux équations différentielles ordinaires (ODE), et on montre que ce modèle retient la physique essentielle de cette transition. La transition de l’écoulement axisymétrique à un écoulement tridimensionnel (3D3C) est ensuite étudiée à l’aide d’une dimension non-entière, en introduisant de façon continue la variation azimutale dans le système. On montre que la limite 2D2C est singulière et qu’une petite variation azimutale permet une redistribution d’énergie sur les différentes composante énergétiques. Le modèle ODE est adapté pour ce système et on montre que pour l’écoulement considéré la corrélation pression-déformation est responsable d'un niveau approximativement proportionnel à la dimension non-entière. Des Simulations des Grandes Echelles sont réalisées pour évaluer la robustesse des observations à grands nombres de ReynoldsAxisymmetric turbulence is a two-dimensional three-component flow. The investigation of this type of turbulence is motivated by the fact that it represents the asymptotic limit of anisotropic flows and since it has been the subject of theoretical investigations in the past. In the present manuscript such a flow is investigated in wall-bounded cylindrical geometry using spectral and pseudo-spectral numerical simulations.Previous results on the generation of coherent structures, obtained for freely decaying flow, are here assessed in the context of statistically steady flow, where the energy is supplied by either a spectrally localized forcing, or by moving top and bottom plates of the cylinder. It is shown that the observed structures are consistent with theoretical predictions.When an anisotropic forcing protocol is used, a bifurcation is observed from a non-swirling (two-dimensional two-component, 2D2C) flow to a swirling (two-dimensional three-component 2D3C) turbulent flow. This transition is modelled by a system of two ordinary differential equations (ODE), and it is shown that this model retains the essential physics of the transition.The transition of the axisymmetric flow to three-dimensional (3D3C) flow is then studied using non-integer dimension, by smoothly introducing azimuthal variation into the system. It is shown that the 2D2C limit is singular and that small azimuthal variation allows a redistribution of energy over the different energy components. The ODE model is adapted for this system and it is shown that for the considered flow the pressure-strain correlation is responsible for a swirl-level approximately proportional to the non-integer dimension. Large-Eddy Simulations are carried out to assess the robustness of the observations at higher Reynolds number
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Fang, Le Bertoglio Jean-Pierre. "Applying the Kolmogorov equation to the problem of subgrid modeling for Large-Eddy Simulation of turbulence." [S.l.] : [s.n.], 2009. http://bibli.ec-lyon.fr/exl-doc/lfang.pdf.
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Wu, Xuemei. "Monte-Carlo modeling of turbulent dispersion of small particles in channels." Diss., Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/17389.
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Bærland, Tarjei. "Release and Spreading of Dense Gases : Turbulence modeling with Kameleon FireEx." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for energi- og prosessteknikk, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-13688.
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A dense gas released into the atmosphere will have a flow development that can be described by a large range of physical scales and quantities. An instantaneous release will slump towards the ground unaffcted by the wind, before it is gradually and increasingly diluted by the turbulence in the surrounding flow. Therefore, when the gas is far from the release point, its movement is determined by that of the wind.The wind's turbulence characteristics varies with the atmospheric stability. An unstably stratified boundary layer will have turbulence production by negative density gradients, regardless of free stream velocity. A stable stratification, however, requires a wind velocity and shear to produce turbulence. The wind profile's velocity and turbulence characteristics can be described by similarity models, which may further be used as initial and boundary conditions in a turbulence model.The ke~model is a second order turbulence closure that has proved succesful in describing several turbulent flow scenarios. The version of the model used in the software package Kameleon FireEx has here been tested for dense gas releases, with a focus on far field development. Wind modeling is an area where the standard k-[epsilon] model is known to have problems, as it gives an unrealistic, inhomogoneous flow field.Three alterations to the k-[epsilon] model were tested in the work on this thesis. The first was a model constant varying with the local turbulence parameters, the second was a modification to the turbulence Schmidt number and, finally, a correctional production was added to the transport equations for k and [epsilon]. Of the three approaches, the last one gave the most encouraging results.There are still problems left regarding the k-[epsilon] model's handling of buoyancy-affected diffusivity. The Schmidt number modification dampens the dense gas' ability to diffuse also in the lateral directions, not only in the vertical, an effect that should be investigated further.
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Weng, Chenyang. "Modeling of sound-turbulence interaction in low-Mach-number duct flows." Licentiate thesis, KTH, MWL Strömningsakustik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-129319.
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When sound waves propagate in a duct in the presence of turbulent flow, tur- bulent mixing can cause extra attenuation of the sound waves in addition to that caused by the viscothermal eects. Experiments show that compared to the vis- cothermal eects, turbulent absorption becomes the dominant contribution to the sound attenuation at suciently low frequencies. The mechanism of this turbulent absorption is attributed to the turbulent stress and the turbulent heat transfer act- ing on the coherent perturbations (including to sound waves) near the duct wall, i.e. sound-turbulence interaction. The purpose of the current investigation is to understand the mechanism of the sound-turbulence interaction in low-Mach-number internal flows by means of theoretical modeling and numerical simulation. The turbulence absorption can be modeled through perturbation turbulent Reynolds stresses and perturbation turbu- lent heat flux in the linearized perturbation equations. In this thesis, the linearized perturbation equations are reviewed, and dierent models for the turbulent absorp- tion of the sound waves are investigated. In addition, a new non-equilibrium model for the perturbation turbulent Reynolds stress is proposed. The proposed model is validated by comparing the computed perturbation fields with experimental data from turbulent pipe flow measurements, and large eddy simulations (LES) of turbu- lent channel flow. Good agreements are observed. Besides the theoretical modeling, LES is also carried out as a numerical investi- gation of the sound-turbulence interaction. Some preliminary results from the LES are presented.Vid ljudutbredning i kanaler med turbulent flöde kan diusion som orsakas av turbulens ge extra dämpning av ljudvågor utöver den som orsakas av viskoter- miska eekter. Experiment visar att vid låga frekvenser ger denna absorption det dominerande bidraget till ljuddämpning. Mekanismen för denna absorption är tur- bulensens inverkan på koherenta störningar, bland annat ljudvågor, dvs ljud - tur- bulensinteraktion. Syftet med denna undersökning är att förstå mekanismen för ljud - turbulensin- teraktion i internströmning vid låga Machtal med hjälp av teoretisk modellering och numeriska simuleringar. Ljudabsorption pga turbulens kan modelleras via mod- ellering av störningar av de turbulenta Reynoldska spänningarna och störningar i den turbulenta värmetransporten i de linjäriserade störningsekvationerna. I denna avhandling går vi igenom de linjäriserade störningsekvationerna, och olika modeller för turbulent absorption av ljudvågor utreds. Dessutom presenteras en ny icke- jämviktsmodell för små störningar av de turbulenta Reynoldska spänningarna. Den föreslagna modellen utvärderas genom att de beräknade störningsfältet jämförs med experimentella data från mätningar i rör med turbulent strömning, samt med Large Eddy Simulations (LES) av turbulent strömning. God överensstämmelse kan visas. Förutom teoretisk modellering, kommer LES också att användas för att numeriskt undersöka ljud - turbulensinteraktion. Några preliminära resultat från LES presen- teras.
QC 20130927
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Michelen, Strofer Carlos Alejandro. "Machine Learning and Field Inversion approaches to Data-Driven Turbulence Modeling." Diss., Virginia Tech, 2021. http://hdl.handle.net/10919/103155.
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There still is a practical need for improved closure models for the Reynolds-averaged Navier-Stokes (RANS) equations. This dissertation explores two different approaches for using experimental data to provide improved closure for the Reynolds stress tensor field. The first approach uses machine learning to learn a general closure model from data. A novel framework is developed to train deep neural networks using experimental velocity and pressure measurements. The sensitivity of the RANS equations to the Reynolds stress, required for gradient-based training, is obtained by means of both variational and ensemble methods. The second approach is to infer the Reynolds stress field for a flow of interest from limited velocity or pressure measurements of the same flow. Here, this field inversion is done using a Monte Carlo Bayesian procedure and the focus is on improving the inference by enforcing known physical constraints on the inferred Reynolds stress field. To this end, a method for enforcing boundary conditions on the inferred field is presented. The two data-driven approaches explored and improved upon here demonstrate the potential for improved practical RANS predictions.Doctor of Philosophy
The Reynolds-averaged Navier-Stokes (RANS) equations are widely used to simulate fluid flows in engineering applications despite their known inaccuracy in many flows of practical interest. The uncertainty in the RANS equations is known to stem from the Reynolds stress tensor for which no universally applicable turbulence model exists. The computational cost of more accurate methods for fluid flow simulation, however, means RANS simulations will likely continue to be a major tool in engineering applications and there is still a need for improved RANS turbulence modeling. This dissertation explores two different approaches to use available experimental data to improve RANS predictions by improving the uncertain Reynolds stress tensor field. The first approach is using machine learning to learn a data-driven turbulence model from a set of training data. This model can then be applied to predict new flows in place of traditional turbulence models. To this end, this dissertation presents a novel framework for training deep neural networks using experimental measurements of velocity and pressure. When using velocity and pressure data, gradient-based training of the neural network requires the sensitivity of the RANS equations to the learned Reynolds stress. Two different methods, the continuous adjoint and ensemble approximation, are used to obtain the required sensitivity. The second approach explored in this dissertation is field inversion, whereby available data for a flow of interest is used to infer a Reynolds stress field that leads to improved RANS solutions for that same flow. Here, the field inversion is done via the ensemble Kalman inversion (EKI), a Monte Carlo Bayesian procedure, and the focus is on improving the inference by enforcing known physical constraints on the inferred Reynolds stress field. To this end, a method for enforcing boundary conditions on the inferred field is presented. While further development is needed, the two data-driven approaches explored and improved upon here demonstrate the potential for improved practical RANS predictions.
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Wu, Jinlong. "Predictive Turbulence Modeling with Bayesian Inference and Physics-Informed Machine Learning." Diss., Virginia Tech, 2018. http://hdl.handle.net/10919/85129.
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Reynolds-Averaged Navier-Stokes (RANS) simulations are widely used for engineering design and analysis involving turbulent flows. In RANS simulations, the Reynolds stress needs closure models and the existing models have large model-form uncertainties. Therefore, the RANS simulations are known to be unreliable in many flows of engineering relevance, including flows with three-dimensional structures, swirl, pressure gradients, or curvature. This lack of accuracy in complex flows has diminished the utility of RANS simulations as a predictive tool for engineering design, analysis, optimization, and reliability assessments. Recently, data-driven methods have emerged as a promising alternative to develop the model of Reynolds stress for RANS simulations. In this dissertation I explore two physics-informed, data-driven frameworks to improve RANS modeled Reynolds stresses. First, a Bayesian inference framework is proposed to quantify and reduce the model-form uncertainty of RANS modeled Reynolds stress by leveraging online sparse measurement data with empirical prior knowledge. Second, a machine-learning-assisted framework is proposed to utilize offline high-fidelity simulation databases. Numerical results show that the data-driven RANS models have better prediction of Reynolds stress and other quantities of interest for several canonical flows. Two metrics are also presented for an a priori assessment of the prediction confidence for the machine-learning-assisted RANS model. The proposed data-driven methods are also applicable to the computational study of other physical systems whose governing equations have some unresolved physics to be modeled.Ph. D.
Reynolds-Averaged Navier–Stokes (RANS) simulations are widely used for engineering design and analysis involving turbulent flows. In RANS simulations, the Reynolds stress needs closure models and the existing models have large model-form uncertainties. Therefore, the RANS simulations are known to be unreliable in many flows of engineering relevance, including flows with three-dimensional structures, swirl, pressure gradients, or curvature. This lack of accuracy in complex flows has diminished the utility of RANS simulations as a predictive tool for engineering design, analysis, optimization, and reliability assessments. Recently, data-driven methods have emerged as a promising alternative to develop the model of Reynolds stress for RANS simulations. In this dissertation I explore two physics-informed, data-driven frameworks to improve RANS modeled Reynolds stresses. First, a Bayesian inference framework is proposed to quantify and reduce the model-form uncertainty of RANS modeled Reynolds stress by leveraging online sparse measurement data with empirical prior knowledge. Second, a machine-learning-assisted framework is proposed to utilize offline high fidelity simulation databases. Numerical results show that the data-driven RANS models have better prediction of Reynolds stress and other quantities of interest for several canonical flows. Two metrics are also presented for an a priori assessment of the prediction confidence for the machine-learning-assisted RANS model. The proposed data-driven methods are also applicable to the computational study of other physical systems whose governing equations have some unresolved physics to be modeled.
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Horne, Jimmy D. "Modeling optical turbulence with coamps during two observation periods at Vandenberg AFB /." Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2004. http://library.nps.navy.mil/uhtbin/hyperion/04Mar%5FHorne.pdf.
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Thesis (M.S. in Meteorology and Physical Oceanography)--Naval Postgraduate School, March 2004.Thesis advisor(s): Douglas Miller. Includes bibliographical references (p. 67-70). Also available online.
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Li, Zhaorui. "Modeling and simulation of turbulent multiphase flows." Diss., Connect to online resource - MSU authorized users, 2008.
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EREK, ERMAN. "k-ε turbulence modeling for a wind turbine : Comparison of RANS simulations with ECN wind turbine test site Wieringermeer (EWTW) measurements." Thesis, KTH, Kraft- och värmeteknologi, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-111532.
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In this report we discuss the use of k-ε RANS (Reynolds-averaged Navier-Stokes equations) turbulence model for wind turbine applications. This model has been implemented in the new wind turbine wake CFD code that is being developed at ECN. Simulations of the wind turbine test site EWTW are compared with measurements conducted between 2005 and 2009 and with FarmFlow, ECN's current wind turbine wake code. Based on the results the uncertainties in the current approach are highlighted and areas for possible improvement are discussed.
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Sala, Kyle. "Analysis of Stochastic Methods for Predicting Particle Dispersion in Turbulent Flows." ScholarWorks @ UVM, 2013. http://scholarworks.uvm.edu/graddis/207.
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The current research seeks to develop a computational model that accurately describes particle dispersion in turbulent ow. Current particle dispersion models do not accurately predict the small-scale clumping of particles in turbulent ow that occurs due to interaction with turbulent eddies. A new stochastic vortex structure (SVS) model was developed and compared with current stochastic Lagrangian models (SLM) for turbulent ows. To examine what characteristics of the uid ow eld that lead to dispersion of particles, a number of non trivial measures were used. A discrete-element model is used to transport particle locations for cases with and without adhesive forces. Direct numerical simulations (DNS) are used as a baseline for comparison between the two models. Initial results show that the SVS model matches the spatial structure of the ow eld of DNS reasonably well, while the SLMs do not. Investigation of particle collision rate suggest that while SVS matches the large length scales of ow, it omits the smaller scales of the ow.
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Tsau, Fang-Hei. "The analytical modeling of a turbulent diffusion flame behind a backward facing step." Diss., Georgia Institute of Technology, 1988. http://hdl.handle.net/1853/12493.
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Zhao, Ming. "Unsteady pipe friction : formulation of efficient models and investigation of existing modeling assumptions /." View abstract or full-text, 2004. http://library.ust.hk/cgi/db/thesis.pl?CIVL%202004%20ZHAO.
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Thesis (Ph. D.)--Hong Kong University of Science and Technology, 2004.Includes bibliographical references (leaves 175-184). Also available in electronic version. Access restricted to campus users.
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Meakin, Casey Adam. "Hydrodynamic Modeling of Massive Star Interiors." Diss., The University of Arizona, 2006. http://hdl.handle.net/10150/194035.
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In this thesis, the hydrodynamics of massive star interiors are explored. Our primary theoretical tool is multi-dimensional hydrodynamic simulation using realistic initial conditions calculated with the one-dimensional stellar evolution code, TYCHO. The convective shells accompanying oxygen and carbon burning are examined, including models with single as well as multiple, simultaneously burning shells. A convective core during hydrogen burning is also studied in order to test the generality of the flow characteristics. Two and three dimensional models are calculated. We analyze the properties of turbulent convection, the generation of internal waves in stably stratified layers, and the rate and character of compositional mixing at convective boundaries.