Página 1 dos resultados de 451 itens digitais encontrados em 0.214 segundos

‣ Estudo comparativo entre os modelos LES e DES para simulação de escoamento compressível turbulento.; A comparative study using les and des models for turbulent compressible flow simulation.

Pedrão, Nelson
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 25/05/2010 Português
Relevância na Pesquisa
78.95775%
Neste trabalho foi realizado um estudo utilizando os modelos de turbulência Simulação das Grandes Escalas, Large Eddy Simulation (LES), e Simulação dos Vórtices Desprendidos, Detached Eddy Simulation (DES), para simular o escoamento compressível interno em um duto contendo válvulas controladoras na saída dos gases de combustão de um reator de craqueamento catalítico fluido, com o objetivo de comparar o desempenho numérico e computacional de ambas as técnicas. Para isso foi utilizado um programa comercial de dinâmica dos fluidos computacional, Computational Fluid Dynamics (CFD), que possui em seu código os dois modelos de turbulência.; In the present work a study was conducted using Large Eddy Simulation (LES) and Detached Eddy Simulation (DES) turbulence models in order to simulate the internal compressible flow in a duct containing the flue gas discharge control valves of a fluid catalytic cracking reactor so as to compare the numerical and computational behavior of both techniques. A commercial Computational Fluid Dynamics (CFD) software, which includes these turbulence models in its code, was used.

‣ Análise numérica na Engenharia do Vento Computacional empregando computação de alto desempenho e simulação de grandes escalas; Numerical analysis in the computational wind engineering employng high-performance programming and large eddy simulation

Piccoli, Guilherme Luiz
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Dissertação Formato: application/pdf
Português
Relevância na Pesquisa
98.59831%
O presente trabalho tem como objetivo o desenvolvimento de um sistema voltado à solução de problemas relacionados à Engenharia do Vento Computacional. Para o tratamento das estruturas turbulentas, a Simulação das Grandes Escalas é empregada. Esta metodologia resolve diretamente as estruturas que governam a dinâmica local do escoamento (grandes escalas) e utiliza modelos para resolver as escalas com características mais universais (pequenas escalas). Neste estudo, os efeitos sub-malha são obtidos a partir do modelo clássico de Smagorinsky. Na análise numérica, o método dos elementos finitos é avaliado a partir da utilização de elementos hexaédricos e uma formulação baseada nas equações governantes de escoamentos quase-incompressíveis. Para reduzir o requerimento de memória computacional, esquemas explícitos para solução de sistemas de equações são empregados. O primeiro aspecto a ser abordado para o desenvolvimento do sistema proposto é a redução do tempo de processamento. Partindo do algoritmo desenvolvido por [Petry, 2002], desenvolvese um estudo a cerca de técnicas computacionais de alto desempenho visando acelerar o processamento dos problemas. Assim, apresenta-se um comparativo entre alocações estática e dinâmica de vetores e matrizes...

‣ Large eddy simulation of three-dimensional turbulent flows by the finite element method

Petry, Adriane Prisco; Awruch, Armando Miguel
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Artigo de Revista Científica Formato: application/pdf
Português
Relevância na Pesquisa
98.59823%
The main objectives of this work are the formulation, implementation and applications of a numerical algorithm to simulate turbulent, incompressible, isothermal flows. The transient three-dimensional flow is analyzed using an explicit Taylor-Galerkin scheme and the finite element method with hexahedrical eight-node element. Turbulence is simulated using Large Eddy Simulation. For sub-grid scales two models were implemented, the classical Smagorinsky´s model and the dynamic eddy viscosity model. For the second filtration, which is necessary in the dynamic model, a new method was developed based on independent finite elements that involve each node in the original mesh. The implemented scheme is efficient and good results with low additional computational cost were obtained. Results for two classical problems, the driven cavity and the backward facing step are presented. Comments about the model applicability for flows with high Reynolds numbers are also presented.

‣ Dynamics of coherent vortices in mixing layers using direct numerical and large-eddy simulations

Silvestrini,Jorge H.
Fonte: The Brazilian Society of Mechanical Sciences Publicador: The Brazilian Society of Mechanical Sciences
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2000 Português
Relevância na Pesquisa
88.54546%
Coherent vortices in turbulent mixing layers are investigated by means of Direct Numerical Simulation (DNS) and Large-Eddy Simulation (LES). Subgrid-scale models defined in spectral and physical spaces are reviewed. The new "spectral-dynamic viscosity model", that allows to account for non-developed turbulence in the subgrid-scales, is discussed. Pseudo-spectral methods, combined with sixth-order compact finite differences schemes (when periodic boundary conditions cannot be established), are used to solve the Navier- Stokes equations. Simulations in temporal and spatial mixing layers show two types of pairing of primary Kelvin-Helmholtz (KH) vortices depending on initial conditions (or upstream conditions): quasi-2D and helical pairings. In both cases, secondary streamwise vortices are stretched in between the KH vortices at an angle of 45° with the horizontal plane. These streamwise vortices are not only identified in the early transitional stage of the mixing layer but also in self-similar turbulence conditions. The Re dependence of the "diameter" of these vortices is analyzed. Results obtained in spatial growing mixing layers show some evidences of pairing of secondary vortices; after a pairing of the primary Kelvin-Helmholtz (KH) vortices...

‣ Simulação de grandes escalas e simulação híbrida RANS/LES do escoamento sobre o degrau com condições de contorno turbulentas; Large-eddy simulation and hybrid RANS/LES simulation of the backwardfacing step flow with turbulent boundary conditions

Spode, Cleber
Fonte: Universidade Federal de Uberlândia Publicador: Universidade Federal de Uberlândia
Tipo: Dissertação
Português
Relevância na Pesquisa
99.11428%
A simulação numérica de escoamentos turbulentos através da hipótese de Boussinesq é representada, atualmente, por duas grandes metodologias distintas, a Simulação de Grandes Escalas (LES – Large-Eddy Simulation) e as Equações Médias de Reynolds (RANS – Reynolds Averaged Navier-Stokes). Uma nova metodologia, chamada de Híbrida RANS/LES, está em desenvolvimento, tirando proveito das potencialidades das metodologias tradicionais LES e RANS através de um único modelo. O presente trabalho trata da avaliação das três metodologias, LES, RANS e Híbrida RANS/LES de modelagem da turbulência através da simulação numérica do escoamento turbulento sobre um degrau. Os modelos são avaliados através deste escoamento, que apesar de simples geometricamente, é capaz de gerar um escoamento complexo, com regiões de escoamento parietal e cisalhante livre. Juntamente com a modelagem da turbulência, um estudo de imposição de condições de contorno turbulentas na entrada do domínio utilizado revelou que tão importante quanto o modelo de turbulência, as condições de contorno empregadas modificam substancialmente os resultados obtidos. Foi implementado um modelo de geração de contorno baseado no escalonamento de informações internas do escoamento de forma a satisfazer estatística e topologicamente o caráter turbulento da condição de contorno na entrada. Resultados para as três metodologias revelam que a Simulação de Grandes Escalas e métodos Híbridos RANS/LES apresentam descrições muito semelhantes para o escoamento turbulento sobre o degrau...

‣ Simulação de grandes escalas de jatos periódicos temporais utilizando a metodologia psedo-espectral de Fourier; Large eddy simulation of periodic temporal jets using the Fourier pseudo-spectral method

Moreira, Leonardo de Queiroz
Fonte: Universidade Federal de Uberlândia Publicador: Universidade Federal de Uberlândia
Tipo: Dissertação
Português
Relevância na Pesquisa
98.465%
A turbulência nos fluídos é um dos problemas mais desafiadores da atualidade, em especial no que se refere às aplicações industriais que envolvem processos de mistura de componentes, transferência de calor, lubrificação e degelo, injeção de combustível em câmaras de combustão, sistemas de propulsão de aviões e aeronaves. Diante de considerável interesse, no presente trabalho objetivou-se a análise da transição a turbulência de jatos em desenvolvimento temporal a números de Reynolds moderados utilizando a metodologia LES. Primeiramente desenvolveu-se um código computacional ESPC3D, com alta ordem de resolução para simulação de escoamentos do tipo jatos em desenvolvimento temporal em transição e/ou turbulentos. O código foi desenvolvido no Laboratório de Transferência de Calor e Massa e Dinâmica dos Fluidos (LTCM). Resultados consistentes foram obtidos do ponto de vista da análise física utilizando o código ESPC3D, com o qual realizou-se simulações de grandes escalas empregando o método pseudo-espectral de Fourier. Os resultados das simulações permitem verificar a transição a turbulência bem como suas estruturas típicas. Foi possível também verificar a influência da modelagem da turbulência utilizando a metodologia LES...

‣ Estimativa da constante de Kolmogorov (C0) para a camada limite est??vel usando simula????o dos grandes turbilh??es; Estimation of the Kolmogorov constant (C0) for the stable boundary layer by large-eddy simulation

LOVATO, Rodrigo Gularte
Fonte: Universidade Federal de Pelotas; Meteorologia; Programa de P??s-gradua????o em Meteorologia; UFPel; BR Publicador: Universidade Federal de Pelotas; Meteorologia; Programa de P??s-gradua????o em Meteorologia; UFPel; BR
Tipo: Dissertação Formato: application/pdf; application/zip
Português
Relevância na Pesquisa
98.465%
Neste trabalho, n??s estimamos a constante de Kolmogorov, C01 atrav??s da determina????o de um conjunto de trajet??rias Lagrangeanas em uma Camada Limite Est??vel simulada pelo modelo de simula????o dos grandes turbilh??es (Large-Eddy Simulation model). A partir do conjunto de trajet??rias, a forma da fun????o de estrutura da velocidade Lagrangeana no subintervalo inercial ?? avaliada, permitindo a determina????o de C0. O valor de C0 encontrado ?? 3,70.

‣ Large eddy simulation of the near wake of a circular cylinder at sub-critical Reynolds number

Doolan, C.
Fonte: Hong Kong Polytechnic University Publicador: Hong Kong Polytechnic University
Tipo: Artigo de Revista Científica
Publicado em //2010 Português
Relevância na Pesquisa
98.465%
This paper investigates the unsteady, near wake of a circular cylinder in cross flow at a Reynolds number of 5.5 x 10(3) using Large Eddy Simulation (LES). The near and intermediate wake velocity fields and unsteady aerodynamic forces compare well against available experimental data. Flow visualisation results show the presence of intermittent Kelvin Helmholtz (KH) instabilities in the very near wake. An empirical relation is presented for the spanwise length scales associated with KH instability that compares favourably with LES data. A wavelet analysis technique is used to investigate the frequency content of near wake. This analysis shows the existence of vortex pairing and breakdown in the near wake, providing further evidence that the near wake shear layer behaves in a similar manner to a mixing layer.; C. J. Doolan

‣ Large eddy simulation of sediment-laden turbulent flow in an open channel

Wan, Z.; Sun, Z.; You, Z.; Zhang, Q.
Fonte: World Scientific Publ Co Pte Ltd Publicador: World Scientific Publ Co Pte Ltd
Tipo: Artigo de Revista Científica
Publicado em //2008 Português
Relevância na Pesquisa
98.465%
Sediment transport in fully developed turbulent open channel flow has been investigated using large eddy simulation (LES) of the incompressible Navier–Stokes equations. The scalar transport equation of the sediments concentration, which is based on the continuous-phase approach, is adopted. The settling process is taken into account with a modified settling velocity appearing in the sediment concentration equation. A Smagorinsky model allowing for the interaction between the fluid flow and the suspended sediment is used to simulate the unresolved, subgrid scale terms. The LES results are compared with the experimental data, and good general agreement is achieved.; Zhanhong Wan, Zhilin Sun, Zhenjiang You, Qiyan Zhang

‣ Turbulent wake study of the NREL phase VI wind turbine in a virtual wind tunnel using Large Eddy Simulation

Choudhry, A.; Mo, J.; Arjomandi, M.; Lee, Y.H.
Fonte: Engineers Australia; CDROM / DVDROM Publicador: Engineers Australia; CDROM / DVDROM
Tipo: Conference paper
Publicado em //2012 Português
Relevância na Pesquisa
98.465%
The objective of the current investigation is to achieve a better understanding of the turbulent wake characteristics behind a wind turbine for the purpose of the improvement of the overall wind farm efficiency and a better prediction of the fatigue loads on tandem wind turbines. Large Eddy Simulation was performed at a low wind speed of 7m/s in a numerical wind tunnel model with dimensions similar to the NASA Ames Wind Tunnel (24.4 m x 36.6 m). An ANSYS CFD Fluent solver based on the dynamic Smagorinsky-Lilly model was employed to simulate the flow surrounding the wind turbine placed inside the numerical wind tunnel. For validation purposes, the aerodynamic characteristics of the blade were compared with the published experimental data of the NREL Phase VI. A good agreement was found between the experimental and the numerical results for the surface pressure distributions along the blade. It was observed that in the near-wake the turbulence intensity was a maximum of 12.12% at a distance of three rotor diameters downstream, after which a gradual decrease in the turbulence intensity was observed due to the wake instability. In the far-wake region, the turbulence intensity showed a tendency to increase, due to the presence of counter-rotating helical vortices determining the dynamics of far-wake. The system of vortices in the near-wake becomes unstable and breaks down due to the wake instability at a distance of approximately five rotor diameters downstream of the wind turbine. The vortex breakdown was used to define the boundary between the near and far-wake regions. The collapsed spiral wake was found to spread in all directions in the far-wake resulting in the formation of the two counter-rotating vortices which caused the gradual increase of turbulent intensity. The results and related discussion of the turbulent wake characteristics are presented in the current article.; Amanullah Choudhry...

‣ Large-eddy simulation and modelling of dissolved oxygen transport and depletion in water bodies

Scalo, CARLO
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado
Português
Relevância na Pesquisa
98.465%
In the present doctoral work we have developed and tested a model for dissolved oxygen (DO) transfer from water to underlying flat and cohesive sediment beds populated with DO-absorbing bacteria. The model couples Large-Eddy Simulation (LES) of turbulent transport in the water-column, a biogeochemical model for DO transport and consumption in the sediment, and Darcy’s Law for the pore water-driven solute dispersion and advection. The model’s predictions compare well against experimental data for low friction-Reynolds numbers (Re). The disagreement for higher Re is investigated by progressively increasing the complexity of the model. A sensitivity analysis shows that the sediment-oxygen uptake (or demand, SOD) is approximately proportional to the bacterial content of the sediment layer, and varies with respect to fluid dynamics conditions, in accordance to classic high-Schmidt-number mass-transfer laws. The non- linear transport dynamics responsible for sustaining a statistically steady SOD are investigated by temporal- and-spatial correlations and with the aid of instantaneous visualizations: the near-wall coherent structures modulate the diffusive sublayer, which exhibits complex spatial and temporal filtering behaviours; its slow and quasi-periodic regeneration cycle determines the streaky structure of the DO field at the sediment-water interface (SWI)...

‣ Large eddy simulation of three-dimensional turbulent flows by the finite element method

Petry,Adriane P.; Awruch,Armando M.
Fonte: Associação Brasileira de Engenharia e Ciências Mecânicas - ABCM Publicador: Associação Brasileira de Engenharia e Ciências Mecânicas - ABCM
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2006 Português
Relevância na Pesquisa
98.59823%
The main objectives of this work are the formulation, implementation and applications of a numerical algorithm to simulate turbulent, incompressible, isothermal flows. The transient three-dimensional flow is analyzed using an explicit Taylor-Galerkin scheme and the finite element method with hexahedrical eight-node element. Turbulence is simulated using Large Eddy Simulation. For sub-grid scales two models were implemented, the classical Smagorinsky's model and the dynamic eddy viscosity model. For the second filtration, which is necessary in the dynamic model, a new method was developed based on independent finite elements that involve each node in the original mesh. The implemented scheme is efficient and good results with low additional computational cost were obtained. Results for two classical problems, the driven cavity and the backward facing step are presented. Comments about the model applicability for flows with high Reynolds numbers are also presented.

‣ Towards Robust Unstructured Turbomachinery Large Eddy Simulation

Watson, R. A.; Tucker, P. G.; Wang, Z.-N.; Yuan, X.
Fonte: Elsevier Publicador: Elsevier
Tipo: Article; published version
Português
Relevância na Pesquisa
98.73154%
This is the final version of the article. It first appeared from Elsevier via http://dx.doi.org/10.1016/j.compfluid.2015.06.017; Industrial legacy codes usually have had long pedigrees within companies, and are deeply embedded into design processes. As the affordability and availability of computing power has increased, these codes have found themselves pushed into service as large eddy simulation solvers. The approximate Riemann solver of Roe, which is frequently used as the core method in such legacy codes, is shown to need much user care when adopted as the discretisation scheme for large eddy simulation. A kinetic energy preserving (KEP) scheme?which retains the same advantageous stencil and communications halo as the original Roe scheme?is instead implemented and tested. The adaptations of code required to switch between the two schemes were found to be extremely straightforward. As the KEP scheme intrinsically bounds the growth of the kinetic energy, it is significantly more stable than the classical non-dissipative schemes. This means that the expensive smoothing terms of the Roe scheme are not always necessary. Instead, an explicit subgrid scale turbulence model can be sensibly applied. As such, a range of mixed linear?non-linear turbulence models are tested. The performance of the KEP scheme is then tested against that of the Roe for canonical flows and engine-realistic turbine blade cutback trailing edge cases. The new KEP scheme is found to perform better than the original in all cases. A range of mesh topologies: hexahedral; prismatic; and tetrahedral; are also tested with both schemes...

‣ Large Eddy Simulations of extinction

Ayache, S.; Garmory, A.; Tyliszczak, A.; Mastorakos, E.
Fonte: Universidade de Cambridge Publicador: Universidade de Cambridge
Tipo: Vídeo
Português
Relevância na Pesquisa
88.77714%
Large Eddy Simulations, with the Conditional Moment Closure as the combustion sub-model, have been used to capture localised extinction, flame lift-off, and whole flame blow-off for simple geometries like jet flames (Movies 1 and 2 below), swirl-stabilised recirculating flames of natural gas (Movies 3-6), and spray flames (Paper "Spray_LESCMC_PalermoSept2012.pdf". The work is described fully in the following papers: (i) Garmory, A. and Mastorakos, E. (2011) Capturing localised extinction in Sandia Flame F with LES-CMC. Proceedings of the Combustion Institute 33, 1673-1680. doi:10.1016/j.proci.2010.06.065; (ii) Ayache, S. & Mastorakos, E. (2012) Conditional Moment Closure / Large Eddy Simulation of the Delft-III natural gas non-premixed jet flame. Flow, Turbulence and Combustion 88, 207-231. doi: 10.1007/s10494-011-9368-6; (iii) Tyliszczak, A. & Mastorakos, E. (2012) LES/CMC of blow-off in a liquid fuelled swirl burner. To be presented at the THMT7, Palermo, 24-27 September 2012; (iv) Ayache, S. & Mastorakos, E. (2012) Investigation of the ?TECFLAM? non-premixed flame using Large Eddy Simulation and Proper Orthogonal Decomposition. Submitted to Flow, Turbulence and Combustion; (iv) S. Ayache, PhD thesis, University of Cambridge, 2012.

‣ Investigation of two industrial developmental injectors using Large Eddy Simulation and ProperOrthogonal Decomposition; Complement to the PhD thesis entitled "Simulations of turbulent swirl combustors"

Ayache, Simon
Fonte: Universidade de Cambridge Publicador: Universidade de Cambridge
Tipo: Report; not applicable
Português
Relevância na Pesquisa
98.51785%
This report is a complement to the PhD thesis entitled "Simulations of turbulent swirl combustors". This work extends the application of the Large Eddy Simulation/ Conditional Moment Closure approach developed in the thesis to flows of industrial level of geometric complexity. It has been carried out during a secondment to work at Rolls-Royce plc with the aim of sharing fundamental and applied research developments. In the PhD thesis, Proper Orthogonal Decomposition (POD) has been systematically used in order to analyze further the physics underlying the large numerical datasets obtained during the simulations. The work presented here applies these analytical methods developed in the PhD work for the academic TECFLAM burner to two lean-burn industrial injectors. POD identifies the different PVCs generated by the different swirlers composing the injector and it associates a frequency to each of them. The LES/POD analysis of industrial injectors gives results that are very consistent with the ones obtained for the TECFLAM academic burner in the PhD thesis.; This work was supported by the European Commission through the Marie Curie Project MYPLANET and was carried out at Rolls-Royce plc in Derby (United-Kingdom) during the PhD.

‣ Towards robust unstructured turbomachinery large eddy simulation

Watson, R. A.; Tucker, P. G.; Wang, Z.-N.; Yuan, X.
Fonte: Elsevier Publicador: Elsevier
Tipo: Article; published version
Português
Relevância na Pesquisa
98.73154%
This is the final version of the article. It first appeared from Elsevier via http://dx.doi.org/10.1016/j.compfluid.2015.06.017; Industrial legacy codes usually have had long pedigrees within companies, and are deeply embedded into design processes. As the affordability and availability of computing power has increased, these codes have found themselves pushed into service as large eddy simulation solvers. The approximate Riemann solver of Roe, which is frequently used as the core method in such legacy codes, is shown to need much user care when adopted as the discretisation scheme for large eddy simulation. A kinetic energy preserving (KEP) scheme?which retains the same advantageous stencil and communications halo as the original Roe scheme?is instead implemented and tested. The adaptations of code required to switch between the two schemes were found to be extremely straightforward. As the KEP scheme intrinsically bounds the growth of the kinetic energy, it is significantly more stable than the classical non-dissipative schemes. This means that the expensive smoothing terms of the Roe scheme are not always necessary. Instead, an explicit subgrid scale turbulence model can be sensibly applied. As such, a range of mixed linear?non-linear turbulence models are tested. The performance of the KEP scheme is then tested against that of the Roe for canonical flows and engine-realistic turbine blade cutback trailing edge cases. The new KEP scheme is found to perform better than the original in all cases. A range of mesh topologies: hexahedral; prismatic; and tetrahedral; are also tested with both schemes...

‣ Large-Eddy Simulation of Pulverized Coal Jet Flame -Effect of Oxygen Concentration on NOx formation

Muto, Masaya; Watanabe, Hiroaki; Kurose, Ryoichi; Komori, Satoru; Balusamy, Saravanan; Hochgreb, Simone
Fonte: Elsevier Publicador: Elsevier
Tipo: Article; published version
Português
Relevância na Pesquisa
98.65108%
This is the final version of the article. It was first published by Elsevier at http://www.sciencedirect.com/science/article/pii/S0016236114010643; Large-eddy simulation is applied to a laboratory-scale open-type pulverized coal flame generated by a triple stream burner, and the NO production and reduction in oxy- fuel condition are investigated for the first time. Pulverized Cerrejon coal which is classified as bituminous coal is used as a fuel. The results show that regardless of the equivalence ratio, as the O2 concentration increases from 21% to 40%, O2 consumption becomes marked because gas temperature rises and oxidation reaction is enhanced by the higher concentration of O2. Also, NO is formed rapidly due to the oxidation reaction of nitrogen from volatile matter of coal, and its concentration reaches a few hundred ppm further downstream. After the rapid formation, in the case of equivalence ratio larger than unity, NO decreases, because the reducing atmosphere becomes dominant due to the lack of O2. The trend becomes signi cant as the O2 concentration in the carrier gas increases from 21% to 40%. In the case of equivalence ratio less than unity, on the other hand, NO does not decrease clearly, because the oxidizing atmosphere contributes to the further formation of NO. Present study shows the usefulness of the large-eddy simulations for predicting the characteristics of pulverized coal flames.; This research was partially supported by \Strategic Programs for Innovative Research (SPIRE) - Field No. 4: Industrial Innovations" from MEXT (Ministry of Education...

‣ Large eddy simulation/conditional moment closure modeling of swirl-stabilized non-premixed flames with local extinction

Zhang, Huangwei; Garmory, Andrew; Cavaliere, Davide E.; Mastorakos, Epaminondas
Fonte: Elsevier Publicador: Elsevier
Tipo: Article; accepted version
Português
Relevância na Pesquisa
98.51785%
This is the accepted manuscript. The final version is available from Elsevier at http://www.sciencedirect.com/science/article/pii/S1540748914000558.; The Large Eddy Simulation (LES)/three-dimensional Conditional Moment Closure (3D-CMC) model with detailed chemistry and finite-volume formulation is employed to simulate a swirl-stabilized nonpremixed flame with local extinction. The results demonstrate generally good agreement with the measurements concerning velocity, flame shape, and statistics of flame lift-off, but the penetration of fuel jet into the recirculation zone is under-predicted possibly due to the over-predicted swirl velocities in the chamber. Localized extinctions are seen in the LES, in agreement with experiment. The local extinction event is shown by very low heat release rate and hydroxyl mass fraction and reduced temperature, and is accompanied by relatively high scalar dissipation. In mixture fraction space, CMC cells with strong turbulence-chemistry interaction and local extinction show relatively large fluctuations between fully burning and intermediate distributions. The probability density functions of conditional reactedness, which shows how far the conditionally-filtered scalars are from reference fully burning profiles...

‣ PRELIMINARY RESULTS OF LARGE EDDY SIMULATIONS OF A HYDROCYCLONE

Souza, F. J.; Silveira Neto, A.
Fonte: UFPR Publicador: UFPR
Tipo: info:eu-repo/semantics/article; info:eu-repo/semantics/publishedVersion; Peer-reviewed Article Formato: application/pdf
Publicado em 08/03/2005 Português
Relevância na Pesquisa
88.33426%
Subgrid-scale modeling, which characterizes Large Eddy Simulation (LES), has been used to predict the behavior of a water-fed hydrocyclone operating without an air core. The governing equations were solved by a fractional step method on a staggered grid. The Smagorinsky subgrid-scale model was employed to account for turbulent effects. Numerical results actually capture the main features of the flow pattern and agree reasonably well with experiments, suggesting that LES represents an interesting alternative to classical turbulence models when applied to the numerical solution of fluid flows within hydrocyclones.

‣ LARGE EDDY SIMULATION OF TURBULENT INCOMPRESSIBLE FLUID FLOWS BY A NINE-NODES CONTROL VOLUME-FINITE ELEMENT METHOD

Silva, J. B. C.; Mansur, S. S.; Lima, R. C.
Fonte: UFPR Publicador: UFPR
Tipo: info:eu-repo/semantics/article; info:eu-repo/semantics/publishedVersion; Peer-reviewed Article Formato: application/pdf
Publicado em 05/07/2006 Português
Relevância na Pesquisa
98.73154%
The main purpose of this work is the numerical computation of turbulent incompressible fluid flows by a nine-node control volume finite element method (CVFEM) using the methodology of large-eddy simulation.. The domain is discretized using nine nodes finite elements and the equations are integrated into control volumes around the nodes of the finite elements. The Navier?Stokes equations are filtered for simulation of the large scales variables and the sub-grid scales stress appearing due to the filtering process are modeled through the eddy viscosity model of Smagorinsky. The two-dimensional benchmark problem of the lid-driven cavity flow is solved to validate the numerical code and preliminary results for the horizontal and vertical velocity profiles at the centerlines of the cavity and the stream functions are presented and compared with available results from the literature.