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Статті в журналах з теми "Modèle URANS":
1
Maïzi, Mohamed, Rabah Dizène, and Ouahiba Guerri. "Simulation instationnaire de l’écoulement autour d’un rotor éolien à axe horizontal." Journal of Renewable Energies 15, no. 4 (October 25, 2023): 599–608. http://dx.doi.org/10.54966/jreen.v15i4.349.
Анотація:
Les pales d’une éolienne sont soumises à des chargements aérodynamiques, génèrent des écoulements extrêmement complexes. Nous nous intéressons à la dynamique des écoulements autour des pales d’éolienne à axe horizontal en rotation. Ce papier présente une méthode de simulation numérique pour la prédiction de l’écoulement autour d’une éolienne à axe horizontal opérant en régime instationnaire, tridimensionnel turbulent utilisant l’approche basée sur les équations de Navier-Stokes moyennées (URANS) en utilisant le code ‘CFX’.Un maillage structuré a été adopté en utilisant la technique des interfaces (interface frozen rotor) entre le corps mobile (la pale) et le corps fixe (l’entourage). Le modèle de turbulence SST a été utilisé pour décrire l’écoulement turbulent. Les résultats de simulation ont été comparés avec les résultats expérimentaux, pour les conditions de rotation. En général, des bonnes concordances ont été notées. Une attention spéciale est portée sur les effets instationnaires, conséquents de rotation du rotor qui est mise en évidence par le calcul des pressions fluctuantes sur l’interface entre les parties fixes et mobiles en aval et en amont de la machine. Une analyse fréquentielle de ces signaux en utilisant une transformée de Fourier discrète (FFT) afin d’analyser le comportement instationnaire de la pale.
2
Stalewski, Wieńczysław, and Katarzyna Surmacz. "Helicopter Flight Simulation based on URANS Solver and Virtual Blade Model." Journal of KONES 26, no. 3 (September 1, 2019): 211–17. http://dx.doi.org/10.2478/kones-2019-0075.
Анотація:
Abstract The methodology of simulation of a rotorcraft flight has been developed and applied to simulate several stages of flight of light helicopter. The methodology is based on coupling of several computational models of Computational Fluid Dynamics, Flight Dynamic. The essence of the methodology consists in calculation of aerodynamic forces acting on the flying rotorcraft by solving during the simulation the Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations. In this approach, the rotorcraft is flying inside the computational 3D mesh modelling the space filled with the air. The flight simulation procedure is completely embedded in the URANS solver ANSYS FLUENT. Flow effects caused by rotating blades of main or tail rotor are modelled by application of the developed Virtual Blade Model (VBM). In this approach, real rotors are replaced by volume discs influencing the flow field similarly as rotating blades. Time-averaged aerodynamic effects of rotating blades are modelled using momentum source terms placed inside the volume-disc zones. The momentum sources are evaluated based on the Blade Element Theory, which associates local flow parameters in the blade sections with databases of 2D-aerodynamic characteristics of these sections. Apart of the VBM module, two additional UDF modules support the simulation of helicopter flight: the module responsible for modelling of all kinematic aspects of the flight and the module gathering the momentary aerodynamic loads and solves 6 DOF-Equations describing a motion of the helicopter seen as solid body. Exemplary simulation of helicopter flight, starting from a hover, through an acceleration and fast flight until a deceleration and steep descent, has been discussed.
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Castellani, Francesco, Abdelgalil Eltayesh, Francesco Natili, Tommaso Tocci, Matteo Becchetti, Lorenzo Capponi, Davide Astolfi, and Gianluca Rossi. "Wind Flow Characterisation over a PV Module through URANS Simulations and Wind Tunnel Optical Flow Methods." Energies 14, no. 20 (October 12, 2021): 6546. http://dx.doi.org/10.3390/en14206546.
Анотація:
Despite their simplicity, photovoltaic (PV) modules are often arranged in structures that can be affected by severe and complex wind loads: in this context, the wind flow and the dynamic excitation induced by vortex shedding can introduce unexpected aeroelastic responses. This work introduces a novel wind tunnel application of experimental techniques to address this issue by the use of flow visualisation and video postprocessing, through the optical flow algorithm. Numerical simulations based on unsteady Reynolds-averaged Navier–Stokes (RANS) models are performed and compared against the experimental wind tunnel tests on a PV panel that was also instrumented with pressure taps. A setup with a 65∘ tilt angle was examined because, based on preliminary analyses, it was considered interesting for the free flow–wake transition associated with the dynamic response of the PV panel. The comparison of the experimental and numerical average wind fields supported that the proposed optical flow method was appropriate for characterising the wake of the panel, because there was enough seeding to perform the video postprocessing. Experiments and numerical predictions were compared as regards the average pressure distribution on the panel surfaces, and the average percentage was in the error of 7%; this supports that the URANS method was capable of reproducing the average behaviour of the panel, as well as for the selected configuration, which is particularly challenging. Furthermore, the simulated and measured power spectral densities of the wind speed were compared, and this resulted in the numerical model quite faithfully reproducing the frequency of the peak at 5 m/s, while the error was in the order of 20% for the 10 m/s case; this supports that, despite the URANS approach being affected by well-known critical points regarding the simulation of instantaneous quantities, it can be employed to elaborate information that can be particularly useful for the structural design of the panel. This kind of result can be considered as a first step, obtained with simplified and affordable methods, towards a characterisation of the dynamic behaviour of a PV panel in a real-world setup.
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Mitrofanov, S. V., D. K. Baykasenov, and A. U. Nemaltsev. "Operational experience of a Solar Power Plant with a Dual-Axis Solar Tracking System in the conditions of the Southern Urals." E3S Web of Conferences 124 (2019): 01022. http://dx.doi.org/10.1051/e3sconf/201912401022.
Анотація:
The paper substantiates the need for the introduction of solar tracking systems for photovoltaic plants and presents a brief review of the scientific and technical literature on the development of solar trackers. Principal scheme of a heliostation with a dual-axis solar tracker of Orenburg State University has been designed. A comparative analysis of the generated electricity by a statically located solar module and a solar module with the dual-axis solar tracker is represented. Data for analysis have been obtained in Orenburg (Russia) using the developed automated system for remote diagnostics and monitoring of photovoltaic system parameters and a wireless weather station HP2000. The use of a dual-axis heliotracker for the solar plant in the conditions of the Southern Urals has allowed to increase the generation of electricity by 34.7% compared to a statically located PV panel.
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Paktovskiy, Yu G., and A. G. Popov. "Devonian diamond reservoir of the Urals." LITHOSPHERE (Russia) 23, no. 4 (September 7, 2023): 683–700. http://dx.doi.org/10.24930/1681-9004-2023-23-4-683-700.
Анотація:
Research subject. The Takata formation of the Emsian tier of the Lower Devonian (D1tk) in the Urals is a reservoir of Devonian diamonds. Aim. Confirmation and determination of the diamond-bearing conditions of the reservoir. Materials and Methods. Generalization of primary and interpreted geological information. Lithofacial analysis. Historical and geological reconstruction. Cartographic analysis and geological and cartographic modeling in the ArcMapESRY GIS environment using the ModelBuilder module. Results. The Takata formation is part of the Emsian tier of the Lower Devonian. Tectonically, the Takata formation is located in the West Ural Folded Zone. The diamond content in the Urals is spatially related to the outputs of the Takata formation. The industrial diamond-bearing capacity and the highest density of diamond placers are located in the Vishersky, Chykmansky and Chusovskoy diamond-bearing regions of the Northern and Middle Urals within the Perm Krai. In the early Devonian, the Takata Sea existed in the Vishera diamond-bearing area; a large river with a delta flowed in the direction from northwest to southeast. The sediments of the formation comprise the facies cycle: flood-plain - channel alluvium - delta sediments - underwater-delta - marine sediments. Diamonds are concentrated in the thickness of coarse-grained alluvium, small-pebble basal conglomerates that formed on the land-sea boundary of the paleocontinent of the Russian Plate. Three facies types of the Takata formation section are distinguished: continental, coastal-marine and marine. Its diamond-bearing capacity is associated with the continental and coastal-marine sediments of the formation within the Perm Region. To the north and south of the diamond-bearing areas of the Perm Krai, the Takata formation is represented by marine sediments. According to the geodynamic model based on the geological section of the Northern Urals, the alluvial and coastal-marine Takata diamond placers were formed in the early Devonian as a result of the demolition of material from the Russian Plate. The sources of destruction were rocks of the Precambrian, Ordovician and Silurian. The main spatial-geomorphological criterion for searching for diamond-bearing conglomerates of the Takata formation is the maximum distance of demolition from these conglomerations to placers, equal to 500 m.
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Diartika, Eka Imbia Agus. "Efektivitas Modul Pencemaran Sampah dengan Model Argument-Driven Inquiry (ADI) untuk Meningkatkan Keterampilan Berpikir Kritis Mahasiswa Biologi." Indo-MathEdu Intellectuals Journal 5, no. 2 (May 10, 2024): 2090–102. http://dx.doi.org/10.54373/imeij.v5i2.983.
Анотація:
Critical thinking skills are a crucial aspect of the 21st century, playing a fundamental role in various areas of life, yet they are still not optimally developed in classrooms. This research aims to develop critical thinking skills through the Argument Driven Inquiry (ADI) module for biology students. This study uses a nonrandomized control-group pretest-posttest design experiment involving three classes as the experimental group, positive control, and negative control. This research sample consisted of 67 biology students from Universitas Negeri Malang across three classes. Data collection techniques employed pretest and posttest questions on critical thinking skills. Data analysis was performed using ANCOVA. The results of the ANCOVA test on the biology students' critical thinking revealed a significance of learning at 0.036 (less than 0.05), thus it can be concluded that the research hypothesis is accepted, indicating a difference in critical thinking between students using the ADI module, ADI model, and PowerPoint. The ADI module proved effective in enhancing the critical thinking skills of biology students, with significantly higher posttest results compared to other learning models. The development of this module also included the integration of interactive videos about the conditions of garbage mountains and leachate water pollution at the Supit Urang Malang landfill, providing a more realistic context for the students
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Maslennikova, Anna V., Valerii N. Udachin, Vladimir V. Deryagin, and Mikhail V. Shtenberg. "Reconstruction of Turgoyak lake (the Southern Urals) ecosystem changes in holocene." LITOSFERA, no. 6 (December 28, 2018): 914–27. http://dx.doi.org/10.24930/1681-9004-2018-18-6-914-927.
Анотація:
Object. Multi-proxy analysis of 265 cm long sediments core of Lake Turgoyak, one of the deepest lakes of the Southern Urals, is presented. Materials and methods. The lake ecosystem changes was reconstructed based on diatom, radiocarbon dating and geochemical analysis. Statistical treatment of the surface sediments composition and hydrochemistry data of 56 lakes from Southern and Middle Urals lakes database allowed to obtain geochemical indexes for reconstruction of water parameters: index of organic matter content (ОМ = LOI550ºС/(Al2O3 + TiO2 + Na2O + K2O)) and index of salinity (ММ = LOI950ºC/LOI550ºС). Results. Radiocarbon dating shows that sedimentation in Lake Turgoyak was began more than 12 cal kyr BP ago. Each of six lithological units of sediments core is characterized by its own geochemical features and associated with global (11.8, 11.2, 8.2 cal kyr BP) and regional (12, 10.3 cal kyr BP) climate events of the Northern Hemisphere. Four main stages of Lake ecosystem development were identified: 1) the beginning of lake sedimentation (>12.1 cal kyr BP); 2) the stage of a subsaline shallow-water lake (12.1–11.2 cal kyr BP); 3) the stage of a freshwater lake with increased water-level (11.2–8.0 cal kyr BP); 4) the stage of water organic matter increase (<8.0 cal kyr BP). Conclusions. High content of mesohalobic diatoms and salinity module values showed significant increase of lake water salinity as response to Early Holocene climate warming (11.8–11.2 cal kyr BP). Pantle-Buck’s Saprobity Index and OM values pointed to the lake water organic matter increase due to the next climate warming since 9–8 cal kyr BP. Thus, Lake Turgoyak water parameters were reapeatedly changed during the Holocene. However the response of lake ecosystem was different in different periods of its development.
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Bugała, Pamela, Janusz Sznajder, and Adam Sieradzki. "Numerical Modelling of Static Aeroelastic Deformations of Slender Wing in Aerodynamic Design." Transactions on Aerospace Research 2023, no. 4 (December 1, 2023): 52–70. http://dx.doi.org/10.2478/tar-2023-0023.
Анотація:
Abstract The article presents the validation of two methods for analyzing the aerodynamic properties of the aircraft wing concerning aeroelastic effects. The first method is based on low-cost computational models (Euler–Bernoulli Beam Model and Vortex Lattice Method [VLM]). Its primary objective is to estimate the wing’s deformation early in the design stages and during the automatic optimization process. The second one is a method that uses solutions of unsteady Navier–Stokes equations (URANS). This method suits early design, particularly for unconventional designs or flight conditions exceeding lowfidelity method limits. The coupling of the flow and structural models was done by Radial Basis Functions implemented as a user-defined module in the ANSYS Fluent solver. The structural model has variants for linear and nonlinear wing deformations. Features enhancing applicability for real-life applications, such as the definition of deformable and nondeformable mesh zones with smooth transition between them, have been included in this method. A rectangular wing of a high-altitude long-endurance (HALE) aeroplane, built based on the NACA 0012 profile, was used to validate both methods. The resulting deflections and twists of the wing have been compared with reference data for the linear and nonlinear variants of the model.
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Zakirova, Natalia Nikolaevna, Vera Nikolaevna Martyanova, Olga Yuryevna Ovchenkova, Svetlana Leonidovna Skopkareva, and Yanina Alexandrovna Chigovskaya-Nazarova. "Regional component in the main curriculum of secondary general education." SHS Web of Conferences 121 (2021): 02009. http://dx.doi.org/10.1051/shsconf/202112102009.
Анотація:
The article is devoted to the development of a programme (built-in module) on literature based on the involvement of a regional component in the content of literary education of students of general education and specialized schools of the Udmurt Republic, as well as other national schools of the Volga region and the Urals. Knowledge of their national literature, literature of neighbouring peoples, and familiarization with the treasury of the spiritual culture of their people contribute to the patriotic education of the younger generation. The content of the module consists of sections devoted to the work of the most significant representatives of the literature of Udmurtia and Russian writers who influenced the formation of the cultural code of the region (V. Korolenko, M. Khudyakov, K. Mitrey, K. Gerd, M. Petrov, G. Krasilnikov, V. Ar-Sergi, V. Vladykin and many others). The programme module can be implemented both within the framework of the work curriculum for literature, and at the profile level in the form of an elective course. In accordance with the requirements of the federal state educational standard of secondary general education the course realizes innovative approaches, such as: system-activity, competence, personality-oriented contributing to the creation of an innovative learning space. Productive techniques and technologies (technologies of thoughtful reading, reading and writing for the development of critical thinking, research and project activities, ICT technologies, etc.), and the widespread use of Internet resources contribute to the formation of both subject and metasubject competencies. In addition to theoretical knowledge, students will acquire and improve practical skills in research, work with various sources, analysis and comparison of various texts including in the national language.
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Osipov, Mikhail, and Mikhail Sokolnikov. "Previous Malignancy as a Risk Factor for the Second Solid Cancer in a Cohort of Nuclear Workers." SciMedicine Journal 3, no. 1 (March 1, 2021): 8–15. http://dx.doi.org/10.28991/scimedj-2021-0301-2.
Анотація:
This paper describes the results of epidemiological analysis of a cohort of nuclear workers hired at the main facilities of “Mayak” Production Association located in the city of Ozyorsk in Southern Urals of the Russian Federation. Previous malignancy as a risk factor for second cancer in a cohort of 22,373 workers occupationally exposed to ionizing radiation has been analyzed in a retrospective study with more than 60 years of follow-up. Information on main radiation and non-radiation risk factors (attained age, sex, tobacco smoking), as well as the dose of exposure to occupational ionizing radiation has been obtained for the analysis using the data from cancer register as well as other main population registries created in Epidemiological Laboratory of Southern Urals Biophysics Institute. Poisson’s regression realized in the “Amfit” module of “Epicure” statistical package has been applied for risk analysis. Excess relative risk per 1 Gy of absorbed dose of external gamma radiation and internal alpha radiation has been calculated using linear model. Among the 2,471 cancer cases accumulated in the study cohort to the end of follow-up 6.4% of second cancer cases have been diagnosed among workers occupationally exposed to protracted external gamma- and internal alpha radiation. The relative risk of second cancer (except for non-melanoma skin cancer) among nuclear workers with previously diagnosed cancer was about 4 times higher after a decade compared with those cancer patients who had single cancer only. The results showed that previous malignancy along with main non-radiation factors is statistically significant carcinogenic risk factor among nuclear workers exposed to protracted occupational radiation. Doi: 10.28991/SciMedJ-2021-0301-2 Full Text: PDF
Дисертації з теми "Modèle URANS":
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Charrière, Boris. "Modélisation et simulation d'écoulements turbulents cavitants avec un modèle de transport de taux de vide." Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAI108/document.
Анотація:
La simulation numérique des écoulements turbulents cavitants revêt de nombreuses difficultés tant dans la modélisation des phénomènes physiques que dans le développement de méthodes numériques robustes. En effet de tels écoulements sont caractérisés par un changement de phase associé à des gradients de la masse volumique, des variations du nombre de Mach causées par une chute de la vitesse du son, des zones de turbulence diphasique et la présence d'instationnarités.Les travaux de la présente thèse s'inscrivent dans la continuité des études expérimentales et numériques menées au sein du Laboratoire des Ecoulements Géophysiques et Industriels (LEGI),qui visent à améliorer la compréhension et la modélisation d'écoulements cavitants. Les simulations s'appuient sur un code compressible associé à une technique de pré-contionnement bas-Mach qui permet de traiter les zones incompressibles. Les écoulements diphasiques sont reproduits à l'aide d'un modèle de mélange homogène 1-fluide avec discrétisation implicite en pas de temps dual. Enfin la résolution adopte l'approche moyennée RANS qui couple le système des équations de conservation avec des modèles de turbulence du premier ordre basés sur la notion de viscosité turbulente.Dans les zones diphasiques, le calcul des variables thermodynamiques nécessite l'introduction d'équations d'état. La pression au sein du mélange est ainsi reliée aux grandeurs conservatives soit à partir d'une équation d'état de mélange des gaz raides, soit par une relation sinusoïdale incorporant la fraction volumique de vapeur (le taux de vide). La valeur ajoutée de ces travaux de thèse repose sur l'introduction d'une équation de transport pour le calcul du taux de vide. Celle-ci incorpore un terme source dont le transfert de masse entre les phases est fermé grâce à une hypothèse de proportionnalité à la divergence du champ de vitesse. Outre l'amélioration des phénomènes de convection, de dilatation et de collapse, cette équation supplémentaire permet de relaxer l'équilibre thermodynamique local et d'introduire un état métastable pour la phase vapeur.Les simulations 2D et 3D sont réalisées sur des géométries de type Venturi caractérisées par le développement de poches de cavitation partielle instables. L'objectif consiste à reproduire les instationnarités inhérentes à chaque profil telles que la formation d'un jet rentrant liquide à proximité de la paroi ou la production de nuages de vapeur convectés par l'écoulement principal.Les résultats numériques mettent en avant une variation de la fréquence des instationnarités en fonction du calcul de la vitesse du son en zone de mélange. D'autre part, la prise en compte de déséquilibre de la phase vapeur amplifie les phénomènes de propagation d'ondes de pression générées par le collapse des structures cavitantes et participe à la déstabilisation de la poche. Enfin, l'influence de l'équation de transport de taux de vide est analysée en confrontant les résultats des simulations à ceux obtenus ultérieurement à partir d'un modèle à seulement trois équations de conservationThe computation of turbulent cavitating flows involves many difficulties both in modeling the physical phenomena and in the development of robust numerical methods. Indeed such flows are characterized by phase transitions and large density gradients, Mach number variation due to speed of sound decrease, two-phase turbulent areas and unsteadiness.This thesis follows experimental and numerical studies led at the Laboratoire des Ecoulements Géophysiques et Industriels which aim to improve the understanding and modeling of cavitating flows. Simulations are based on a compressible code coupled with a pre-conditionning technique which handles low-Mach number areas. The two-phase flows are reproduced using a one-fluid homogeneous model and temporal discretisation is performed using an implicit dual-time stepping method . The resolution is based on the RANS approach that couples conservation equations with firts-order closure models to compute eddy viscosity.In two-phase flows areas, the computation of thermodynamic quantities requires to close the system with equations of state (EOS). Thus, two formulations are investigated to determine the pressure in the mixture. The stiffened gas EOS is written with conservative quantities while a sinusoidal law deduces the pressure from the volume fraction of vapor (the void fraction). The present study improves the homogeneous equilibrium models by including a transport equation for the void ratio. The mass transfer between phases is assumed to be proportional to the divergence of the velocity. In addition to a better modeling of convection, expansion and collapse phenomenon, this added transport equation allows to relax the local thermodynamic equilibrium and to introduce a mestastable state to the vapor phase.2D and 3D simulations are performed on Venturi type geometries characterized by the development of unstable partial cavitation pockets. The goal is to reproduce unsteadiness linked to each profile such as the formation of a re-entrant jet or the quasi-periodic vapor clouds shedding. Numerical results highlight frequency variations of unsteadiness depending on the speed of sound computation. Moreover, the simulation conducted with a relaxed vapor density increase the pressure wave propagation magnitude generated by the collapse of cavitating structures. It contributes to the destabilization of the pocket. Finally, the role of the void ratio equation is analyzed by comparing the simulation results to those obtained subsequently from a model involving only three conservation equations
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Alam, Boulos. "Modélisation numérique de la turbulence et de la dispersion atmosphérique par faibles vents en milieu urbain." Electronic Thesis or Diss., université Paris-Saclay, 2023. https://www.biblio.univ-evry.fr/theses/2023/interne/2023UPAST179.pdf.
Анотація:
Cette thèse se situe dans le contexte de la modélisation de la dispersion atmosphérique, en particulier en présence de vents faibles. Les sources de pollution atmosphérique, souvent situées près du sol et influencées par des obstacles complexes, engendrent des concentrations élevées de polluants à proximité, ce qui se traduit par des fluctuations significatives de ces concentrations. Les vents faibles, généralement associés à des conditions atmosphériques stables, posent un défi particulier en matière de modélisation de la dispersion des polluants, nécessitant une analyse approfondie des donnéesmétéorologiques et une adaptation des modèles de prédiction. Afin de relever ce défi complexe, l'utilisation de la Dynamique des Fluides Numérique (CFD) est incontournable, même si des recherches supplémentaires sont nécessaires pour valider son efficacité dans le champ proche des sources et en présence de vents faibles. Le logiciel Code_Saturne® (EDF R&D) est sélectionné en raison de sonefficacité avérée dans la simulation de la dispersion de polluants atmosphériques. Cette thèse se décompose en trois phases distinctes : la première phase se concentre sur les fondements de la dispersion atmosphérique, en explorant l'impact de différents paramètres tels que la structure de la couche limite atmosphérique, la turbulence atmosphérique et la stabilité de l'atmosphère. Ces éléments jouent un rôle crucial dans la manière dont les polluants se dispersent dans l'air. La deuxièmephase détaille la méthodologie utilisée dans Code_Saturne pour effectuer les simulations, notamment les modèles de turbulence utilisés et les critères d'évaluation de ces modèles. En plus des modèles isotropes classiques, cette recherche se penche sur l'utilisation de modèles de turbulence anisotropes pour étudier la dispersion dans divers contextes. La troisième phase de la thèse se concentre sur l'évaluation de différents modèles de turbulence et de corrélations vitesse-scalaire à l'aide d'observations effectuées en milieu urbain dans des conditions atmosphériques neutres et stables.Enfin, la dernière phase de la recherche explore les conditions de vent faible et stable, caractérisées généralement par des vitesses de vent inférieures à 2 m/s et des variations aléatoires du vent. Cette phase examine les méandres dans la dispersion des polluants et évalue les limites des modèles analytiques et CFD pour prédire la concentration dans de telles condi- tions. À cet effet, un modèle URANS est développé et évalué. Enfin, une méthode gaussienne segmentée est élaborée pour comparer les résultats aux prédictions CFD et aux observations sur le terrainThis thesis is situated in the context of atmospheric dispersion modeling, particularly in the presence of low winds. Atmospheric pollution sources, often located near the ground and influenced by complex obstacles, generate high concentrations of pollutants nearby, resulting in significant concentration fluctuations. Low winds, typically associated with stable atmospheric conditions, pose a specific challenge in modeling pollutant dispersion, requiring a thorough analysis of meteorological data and adaptation of prediction models. To address this complex challenge, the use of Computational Fluid Dynamics (CFD) is necessary, although further research is needed to validate its effectiveness in the near-field and in the presence of low winds. The Code_Saturne® software (EDF R&D) is selected due to its proven efficiency in simulating atmospheric pollutant dispersion. This thesis is divided into three distinct phases : the first phase focuses on the fundamentals of atmospheric dispersion, exploring the impact of various parameters such as the atmospheric boundary layer structure, atmospheric turbulence, and atmospheric stability. These elements play a crucial role in how pollutants disperse in the air. The second phase details the methodology used in Code_Saturne for conducting simulations, including the turbulence models employed and the criteria for evaluating these models. In addition to traditional isotropic models, this research investigates the use of anisotropic turbulence models to study dispersion in various contexts. The third phase of the thesis concentrates on the evaluation of different turbulence models and velocity-scalar correlations using observations conducted in urban environments under neutral and stable atmospheric conditions. Finally, the last phase of the research explores conditions of low and stable winds, typically characterized by wind speeds below 2 m/s and random wind variations. This phase examines the meandering patterns in pollutant dispersion and assesses the limitations of analytical and CFD models in predicting concentration in such conditions. To this end, a URANS model is developed and evaluated. Ultimately, a segmented Gaussian method is devised to compare the results with CFD predictions and field observations
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Fadai-Ghotbi, Atabak. "Modélisation de la turbulence en situation instationnaire par approches URANS et hybride RANS-LES : prise en compte des effets de paroi par pondération elliptique." Phd thesis, Université de Poitiers, 2007. http://tel.archives-ouvertes.fr/tel-00163592.
Анотація:
L'objectif de ce travail est de prendre en compte les instationnarités naturelles à grande échelle dans les écoulements décollés et à un coût plus faible que la LES, tout en s'intéressant à la modélisation des effets de paroi par des modèles statistiques au second ordre. S'inspirant des approches de Durbin, le modèle à pondération elliptique EB-RSM reproduit l'effet non-local de blocage, en résolvant une équation différentielle sur le terme de pression. La limite à deux composantes de la turbulence est bien prédite en canal. Ce modèle est appliqué à la marche descendante, dans une approche URANS. Nous avons montré que les erreurs numériques peuvent être suffisantes pour exciter le mode le plus instable de la couche cisaillée, et aboutir à une solution instationnaire. La solution est stationnaire quand on raffine le maillage, rendant l'URANS peu fiable. Récemment, Schiestel \& Dejoan ont proposé le modèle hybride non-zonal PITM. Le coefficient $C_{\e_2}$ de l'équation de la dissipation devient fonction de la coupure dans le spectre, et la valeur $C_{\e_1}=3/2$ est déduite par ces auteurs. Nous avons donné une formulation plus générale où la valeur de $C_{\e_1}$ est quelconque. Pour offrir un formalisme plus cohérent aux modèles hybrides non-zonaux dans les écoulements de paroi, une approche basée sur un filtrage temporel est proposée. Enfin, l'adaptation du modèle EB-RSM dans un cadre hybride a été réalisée. Les résultats en canal sont encourageants : la transition continue d'un modèle RANS en proche paroi à une LES au centre du canal est mise en évidence. Le transfert d'énergie des échelles modélisées vers celles résolues est bien reproduit quand on raffine le maillage.
4
Grondin, Julissa. "Analyse des instabilités et de la restabilisation d'un rouet centrifuge à régime partiel." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSEC019.
Анотація:
Ce manuscrit présente une étude numérique des instabilités aérodynamiques dans le compresseur centrifuge Turbocel, actuellement en essais au LMFA. L’étude vise à mieux comprendre les mécanismes des instabilités tournantes et de la restabilisation à bas débit observées dans le compresseur à régime partiel. L’étude est restreinte au rouet seul sans prendre en compte les autres composants de l’étage (Roue Directrice d’Entrée et diffuseur radial), au moyen de simulations RANS et URANS d'un seul canal (conditions de périodicité aux frontières latérales), à une iso-vitesse à régime partiel. Le code utilisé est le code elsA.Les simulations RANS sont capables de reproduire la forte augmentation du taux de pression du rouet observée à bas débit en essais. D’après les simulations ce comportement résulte d’une forte augmentation du travail transmis par les pales au fluide, coïncidant avec le développement d’un écoulement de retour en tête dans l’inducteur du rouet. Celui-ci s’initie entre le bord d’attaque des pales principales et celui des pales intercalaires, peu avant le pic de la caractéristique de taux de pression du rouet. Il commence par l’inversion du fluide issu du décollement au bord d’attaque des pales principales, après sa remontée jusqu’au carter et son transport par le jeu. La zone de recirculation s’étend lorsque le débit diminue, à la fois vers le moyeu et au-delà des plans d’entrée et de sortie du rouet. Les simulations URANS permettent ensuite de caractériser l’écoulement instationnaire dans le rouet. Bien que restreintes à un unique canal, elles captent l’apparition de structures tournantes dans l’inducteur du rouet, dans la zone à pente positive de la caractéristique de taux de pression issue des calculs RANS. Dans les deux zones à pente négative en revanche les champs restent stationnaires, identiques à la solution RANS. Les structures observées diffèrent du décollement tournant dans son acceptation classique car leur propagation n'est pas due à un effet de répartition du débit d’un canal à l’autre (puisqu’il n’y a qu’un seul canal), mais à la propagation d’une structure tourbillonnaire lâchée par un décollement au bord d’attaque et convectée par l’écoulement de jeu autour de la circonférence. La comparaison avec les résultats expérimentaux montre que ces structures reflètent correctement les cellules observées en essais. Les simulations mono-canal sont en outre validées par une comparaison à une simulation 360° sur un point de fonctionnement pour lequel l’instabilité est pleinement développée. En l’absence de perturbation extérieure et sans les autres composants de l’étage, le résultat du calcul 360° reste identique au calcul mono-canal sur le temps de calcul simulé, avec autant de structures tournantes que d’aubes. Dans les calculs la présence de ces structures tournantes coïncide avec des oscillations de débit importantes dans tout le domaine. Ces oscillations sont attribuées au fait que le nombre de cellules est égal au nombre d’aubes du rouet, de manière similaire à une interaction rotor-stator entre un rotor et un stator de même nombre d’aubes. D'autre part les performances moyennes sont supérieures aux performances obtenues en RANS. Pour tenter de comprendre pourquoi, des résultats illustratifs avec le modèle analytique de pompage et de décollement tournant de Moore-Greitzer sont présentés pour un cas axial. Ce modèle prédit des performances moyennes supérieures à la caractéristique dite sous-jacente du compresseur, ce qui fournit une piste d'explication. Enfin, le modèle de Moore-Greitzer ne capte pas les oscillations de débit observées dans les calculs. Cela suggère qu'il serait intéressant d'intégrer dans le modèle un mécanisme d'interaction rotor-stator entre les cellules de décollement tournant et les aubesThis work presents a numerical investigation of the aerodynamic instabilities occurring in the centrifugal compressor Turbocel, which is currently tested at the LMFA laboratory. The study aims at better understanding the mechanisms of these instabilities, as well as the mechanisms of the restabilization which is observed in the compressor at low mass flow rates and partial regime. The computational domain is restricted to the isolated impeller without the other components of the stage (Inlet Guide Vane and radial diffuser). RANS and URANS simulations are carried out on a single channel of the impeller, with the elsA solver. RANS simulations are able to capture the strong increase in impeller pressure ratio, which is observed in the tests at low flow rate. The simulations show that this increase results from a strong rise in the work transferred to the flow by the blades. This coincides with the initiation of a reversed flow zone in the impeller inducer, in the zone between the main blades and the splitter blades leading edges. The first flow particles to reverse are those coming from a stall zone on the main blade leading edge, after they have gone up to the shroud and have been transported by the tip clearance flow. This recirculation zone extends towards both the hub and the inlet when the mass flow decreases. Secondly, URANS simulations are used to characterize the unsteady flow in the impeller. Albeit restricted to a single channel, these simulations capture the existence of rotating structures in the impeller inducer, at mass flow rates which correspond to the positively-sloped part of the pressure ratio performance curve obtained from RANS results. On the other hand, in the two negatively-sloped parts of the characteristic, the field remains steady and equal to the corresponding RANS solution. The simulated rotating structures differ from classical rotating stall because their propagation is due to a convection effect by the tip flow around the circumference, rather than a mass flow repartition between the different channels. The numerical results are then validated against experimental results, and against a full-annulus simulation as well. Without external perturbation, the results of the full-annulus and isolated channel simulations remain identical during the simulated time. In the computations the presence of such rotating instabilities coincides with mass flow rate oscillations in the whole computational domain. The latter are attributed to a mechanism of rotor-stator interaction between the blades and the stall cells, due to the fact that the number of blades and the number of stall cells are equal. Moreover, when these stall cells are observed in the simulations, the average performance of the impeller is higher than the RANS performance. Illustrative results with the analytical model of Moore-Greitzer for surge and rotating stall are presented in an axial configuration. They also result in a performance which stands above the steady, underlying characteristic of the compressor. Finally, the Moore-Greitzer model proves to be unable to capture the mass flow rate oscillations which are observed in the simulations. As an outlook, this suggests to integrate the rotor-stator interaction between the rotating stall cells and the blades in the analytical model, in order to improve the fast prediction of aerodynamic instabilities in the future
5
Dominguez, Bermudez Favio Enrique. "Simulation numérique de parcs d'hydroliennes à axe vertical carénées par une approche de type cylindre actif." Thesis, Université Grenoble Alpes (ComUE), 2016. http://www.theses.fr/2016GREAI020.
Анотація:
La récupération, grâce aux hydroliennes, de l’énergie cinétique de courants marins et fluviaux constitue une source d’énergie renouvelable considérable et prédictible. La simulation fine, par une description statistique instationnaire de type URANS, de l’écoulement autour d’une hydrolienne isolée à axe vertical, bi-rotor et munie d’un carénage (hydrolienne de type HARVEST) donne accès à une estimation précise de la puissance produite. Cependant, le coût élevé de cette approche URANS la rend inadaptée à la simulation d’un parc de machines. Une analyse de la littérature conduit à retenir un modèle basse-fidélité de type Blade Element Momentum (BEM) pour décrire à moindre coût l’effet du rotor de la turbine sur l’écoulement, dans le contexte d’une description 2D (coupe horizontale). La performance de l’hydrolienne est alors prédite par un calcul RANS incluant des termes sources distribués dans un anneau rotor virtuel et conservant le maillage des parties fixes (carénage). Ces termes sources sont construits grâce à une procédure originale exploitant les conditions locales de l’écoulement en amont des cellules du rotor virtuel et le débit de l’écoulement traversant l’hydrolienne. Les coefficients hydrodynamiques utilisés pour le calcul des termes sources BEM-RANS sont construits une fois pour toutes en exploitant une série de simulations URANS préliminaires ; ils intègrent les effets du carénage et le fonctionnement de chaque rotor à une vitesse de rotation optimale (maximisant la puissance produite) grâce au système de régulation de l’hydrolienne. Le modèle BEM-RANS développé est validé par comparaison avec des simulations URANS de référence : il fournit une estimation fiable de la puissance produite (erreur de quelques % par rapport à l’approche URANS) pour un coût réduit de plusieurs ordres de grandeur. Ce modèle est appliqué à l'analyse de la puissance produite par une rangée d’hydroliennes HARVEST dans un canal pour différents facteurs de blocage et d’espacement latéral ainsi qu’à une ferme marine composée de trois hydroliennesThe capture, thanks to hydrokinetic turbines, of the kinetic energy generated by sea and river currents provides a significant and predictable source of renewable energy. The detailed simulation, using an unsteady statistical description of URANS type, of the flow around an isolated water turbine of HARVEST type (cross flow vertical axis ducted water turbine) provides an accurate estimate of the power output. However, the cost of the URANS approach is much too expensive to be applied to a farm of several turbines. A review of the literature leads to select a low-fidelity model of Blade Element Momentum (BEM) type to describe at a reduced cost the rotor effect on the flow, in a 2D context (horizontal cross-section). The turbine performance is then predicted using a steady RANS simulation including source terms distributed within a virtual rotor ring and preserving the mesh of the turbine fixed parts (duct). These source terms are derived using an original procedure which exploits both the local flow conditions upstream of the virtual rotor cells and the flow rate through the turbine. The hydrodynamic coefficients used to compute the BEM-RANS source terms are built once for all from a series of preliminary URANS simulations; they include the effects of the duct on the flow and the rotor operating at optimal rotational speed (maximizing the power output) thanks to the turbine regulation system. The BEM-RANS model is validated against reference URANS simulations: it provides a reliable prediction for the power output (within a few % of the URANS results) at a computational cost which is lowered by several orders of magnitude. This model is applied to the analysis of the power produced by a row of Vertical Axis Water Turbines in a channel for various values of the blockage ratio and lateral spacing as well as to a 3-machine sea farm
6
Junior, Silvio Rodrigues de Faria. "Genotipagem de poliplóides: um modelo de urnas e bolas." Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/45/45133/tde-08092013-214551/.
Анотація:
Desde os primórdios da agricultura e pecuária, o homem seleciona indivíduos com características desejáveis para reprodução e aumento da proporção de novos indivíduos com tais qualidades. Com o conhecimento da estrutura de DNA e o advento da engenharia genética, a identificação e caracterização de espécies e indivíduos conta com novas tecnologias para auxiliar no desenvolvimento de novas variedades de plantas e animais para diversos fins. Tais tecnologias envolvem procedimentos bioquímicos e físicos cada vez mais apurados que produzem medidas cada vez mais precisas, um exemplo disso são as técnicas que empregam a espectometria de massa para comparar polimorfismos de base única (SNPs). Nas plantas é comum a ocorrência de poliploidia, que consiste na presença de mais de dois cromossomos num mesmo grupo de homologia. A determinação do nível de ploidia é fundamental para a correta genotipagem e por consequência maior eficiência no estudo e aprimoramento genético de plantas. Neste trabalho caracterizamos o fenômeno da poliploidia com modelos probabilísticos de urnas e bolas, propondo um método eficiente e adequado de simulação, assim como uma técnica simples para inferir níveis de ploidia e classificar amostras bialélicas aproveitando características geométricas do problema. Análises de dados simulados e reais provenientes de um experimento de cana-de-açúcar foram realizadas com diferentes medidas de separação entre agrupamentos e diferentes condições experimentais. Para os dados reais, métodos gráficos descritivos evidenciam a corretude e coerência do método proposto, que pode ser generalizado para a genotipagem de locos multialélicos poliplóides. Encerramos o trabalho comparando nossos resultados com a abordagem SuperMASSA [Serang2012] que trouxe excelentes resultados ao problema. Todo código desenvolvido em linguagem R está disponibilizado com o texto.Since the beginnings of agriculture and livestock, the man selects individuals with desirable characteristics to breed and increase the proportion of new individuals with such qualities. With knowledge of the DNA structure and the advent of genetic engineering, the identification and characterization of individual species can make use of new technologies to help develop new varieties of plants and animals for many purposes. These technologies involve complex biochemical and physical procedures that produce even more accurated measures, like techniques that employ mass spectrometry to compare single nucleotide polymorphisms (SNPs). In plants it is common the occurrence of polyploidy, which is the presence of more than two chromosomes in the same group of homology. The determination of polyploidy level is essential for correct SNPs genotype calling and therefore greater efficiency in the study and genetic improvement of plants. In this work we characterize the phenomenon of poliploidy with probabilistic urns and balls models, proposing an efficient and appropriate method of simulation, as well as a simple technique to infer ploydy levels and classify biallelic samples accurately taking advantage of geometrical characteristics of the problem. Analysis of simulated and real data from an experiment of sugarcane were conducted with different measures of separation between groups and different experimental conditions. For the actual data, descriptive graphical methods show the correctness and consistency of the proposed method, which can be generalized to multi-allelic loci genotyping polyploid. We end our work comparing our results with the SuperMASSA [Serang2012] approach that brought excellent results to the problem. All code developed in language R were provided with the text.
7
Oliveira, Paulo Roberto de. "Modelos de urnas e loterias." Universidade Federal de Goiás, 2014. http://repositorio.bc.ufg.br/tede/handle/tede/3960.
Анотація:
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES
Many monthly, others weekly play in lottery games ignoring the randomness of the results, believing in luck or strategies that are sold to them in books about games. This monograph aims to show some concepts of probability and statistics unexplored in high school and also day to day situations that contain mathematical concepts of probability more accessible to this level of education showing some mathematical theories applied in practice games. Concepts will be discussed here: some probability distributions, their hope and variance, as well as lottery games and their probability calculations. Probability distributions will be calculated and listed in situations created from models of urns with two colors of balls, always having green as the color whose extraction will be considered successful and the red, whose extraction will be considered a failure. Now extractions with replacement balls will be made and sometimes extractions will be done without replacing them. Also, there is the case where new balls are added to both colors or one color.
Muitos jogam mensalmente, outros semanalmente, em jogos de loterias desconhecendo a aleatoriedade dos seus resultados, acreditando na sorte ou em estratégias que lhes são vendidas em livros sobre jogos. A presente monogra a tem como objetivo mostrar alguns conceitos da Probabilidade e Estatística não explorados no Ensino Médio e também situações do dia a dia que contenham conceitos matemáticos sobre Probabilidade mais acessíveis a este nível de ensino, mostrando um pouco de teorias matemáticas aplicadas na prática de jogos. Serão conceitos aqui discutidos: algumas distribuições de probabilidade, sua esperan ça e variância, além de jogos de loterias e seus cálculos de probabilidade. As distribuições de probabilidade serão enunciadas e calculadas em situações criadas a partir de modelos de urnas com duas cores de bolas, tendo sempre o verde como a cor cuja extração será considerada sucesso e, o vermelho, cuja extração será considerada insucesso. Ora serão feitas extrações com reposições das bolas e ora serão feitas extrações sem a reposição das mesmas. Também, há o caso em que serão adicionadas novas bolas de ambas as cores ou uma cor apenas.
8
Benyoucef, Farid. "Amélioration de la prévision des écoulements turbulents par une approche URANS avancée." Thesis, Toulouse, ISAE, 2013. http://www.theses.fr/2013ESAE0014/document.
Анотація:
Ces travaux de recherche ont pour but d’évaluer la méthode dite de la "Simulation auxEchelles Adaptées" (SAS pour Scale-Adaptive Simulation). Cette approche coïncide avec uneapproche RANS classique dans les zones pariétales attachées et adapte le niveau de viscositéturbulente dans les zones décollées pour y permettre une résolution partielle des structures turbulentes.Dans une première partie, une analyse théorique du modèle SAS original a été menéeet a permis de développer une correction visant à favoriser l’adaptation du niveau de viscositéturbulente dans les zones sièges d’instabilités de type Kelvin-Helmholtz. Le modèle ainsi corrigéest nommé SAS-αL. Les modèles SAS et SAS-αL ont été implantés dans le code de calculNavier-Stokes elsA de l’ONERA. À l’issue de cette étape, trois cas académiques d’écoulementsturbulents instationnaires, cylindre à grand nombre de Reynolds, marche descendante et cavitétranssonique, ont été simulés grâce aux trois modèles de turbulence SST, SAS et SAS-αL. Outreune comparaison aux bases de données expérimentales disponibles, une attention particulièrea été portée à l’influence de paramètres numériques tels que des schémas numériques d’ordreélevé. Enfin, afin d’étudier la viabilité de l’approche SAS dans un contexte industriel, les troismodèles de turbulence ont été testés sur une configuration issue de l’industrie aéronautique etcorrespondant à la sortie d’air chaud d’un système de dégivrage des nacelles d’avion. La comparaisondes prévisions obtenues avec les modèles SST, SAS et SAS-αL aux données expérimentalesobtenues à l’ONERA a permis de montrer un gain de précision grâce à l’emploi de l’approcheSAS et ce pour un coût de calcul compatible avec un cycle de conception industrielleThis research work is meant to assess an upgraded URANS approach, namely the Scale-Adaptive Simulation (SAS). This method is similar to a conventional RANS approach (namelythe SSTmodel) in attached areas and is able to adapt the eddy-viscosity level in detached areas toensure the resolution, at least partially, of the turbulent structures. In a first part of this researchwork, an improvement of the SAS approach is suggestedto allowa better sensitivity of themodelto instabilities such as Kelvin-Helmholtz ones. This "improved" model is referred to as SAS-αLmodel. Both SAS and SAS-αL models were implemented in the ONERA Navier-Stokes solverelsA and both of themaswell as the SSTmodelwere tested on academic test cases : a cylinder in acrossflowat a high Reynolds number, a backward-facing step flowcorresponding to theDriver&Seegmiller experiment and the transonic flow over the M219 cavity experimentally investigatedby de Henshaw. The influence of the numerical parameters was deeply investigated and particularattention was paid to the high-order space-discretization schemes effects. The reliabilityof the SAS approach in an industrial framework was assessed on an aeronautic configurationnamely a nacelle de-icing device. Comparisons between the threemodels (SST, SAS and SAS-αL)and an experimental database available at ONERA - The French Aerospace Lab have shown thebetter accuracy of the SAS approach as well as the high potential of the SAS-αL model
9
Thiery, Mylène. "Modélisation numérique du tremblement sur profil d'aile supercritique." Toulouse, ENSAE, 2005. http://www.theses.fr/2005ESAE0022.
Анотація:
Cette thèse est consacrée à la modélisation numérique de l'oscillation de choc sur un profil d’aile supercritique, en liaison avec la prévision du phénomène de tremblement. L'étude s’appuie sur la base de données expérimentale générée par l'ONERA, à la soufflerie S3 de Chalais Meudon, sur le profil OAT15A. La démarche est de modéliser progressivement les contraintes géométriques de la veine d’essais pour assurer une évaluation objective des modèles de turbulence de type RSAM, à l’aide du logiciel eIsA. Elle débute par l’étude d’une configuration simple, sans oscillation de choc, en utilisant une approche RANS 2D en atmosphère illimitée. Les prévisions des modèles de turbulence sont très satisfaisantes excepté sur le positionnement du choc. Les fermetures non linéaires influencent principalement la recompression. Ensuite, la simulation de l'oscillation de choc est abordée en évaluant les effets : (i) de confinement 2D avec une approche URANS, (ii) d’envergure avec deux types de modélisation URANS et DES et (iii) de confinement 3D avec une approche URANS. Ce dernier calcul est considéré comme pionnier car seules des études stationnaires 3D sont publiées à ce jour. Quelle que soit la stratégie numérique, le modèle de Menter avec correction SST fournit les meilleures prévisions. Le confinement 2D accroît le niveau global d'instationnarité sur le profil alors que le confinement 3D compense quasi-totalement cette augmentation. Pour notre cas d’étude, l'approche URANS 2D en atmosphère illimitée s’avère suffisante pour reproduire l'écoulement expérimental, les fluctuations de pression observées à l'intrados du profil et sur les parois haute et basse étant suffisamment faibles.
10
Ammour, Dalila. "Highly resolved LES and tests of the effectiveness of different URANS models for the computation of challenging natural convection cases." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/highly-resolved-les-and-tests-of-the-effectiveness-of-different-urans-models-for-the-computation-of-challenging-natural-convection-cases(bc3e7813-b1b0-4d5b-9f27-4e50180dff59).html.
Анотація:
In the present thesis turbulent natural convection of air within different challenging test cases are investigated numerically by means of an unstructured finite volume code, Code_Saturne. First, flow within both two-dimensional vertical and inclined differentially heated rectangular cavities at 60° and 15° to the horizontal for an aspect ratio of H/L=28.6 and Rayleigh number of 0.86×10e6 is computed using several high and low-Re models. Here the effectiveness of the RANS models in Code_Saturne is assessed through comparisons with a range of available experimental data. After some tests of thermal field inside vertical cavity, the “two-velocity-scale wall function” is chosen to be used with high-Re models. In both vertical and inclined cases the overall flow pattern appears similar, with a single circulation cell, and a boundary layer at the wall. The levels of turbulence energy are generally slightly lower in the inclined case. Most models give a reasonable prediction of measured Nusselt number, with the two low-Re approaches generally being closer to the data than the schemes employing wall functions. For the 15° inclined cavity, a multi cellular motion is shown by the high-Re models. Nevertheless, all the model predictions disagree with experimental data due to the presence in real flow of 3-D unsteady structures as found in Benard convection problems. These cannot, definitely, be reproduced using a 2-D geometry. Both highly resolved LES and unsteady RANS computations are then conducted, for turbulent natural convection of air inside 15° unstably and stably stratified cavities. In accordance with recent experimental data, the LES computations for both enclosures returned three-dimensional time-averaged flow fields. In the case of the unstably stratified enclosure, the flow is highly unsteady with coherent turbulent structures in the core of the enclosure. Results of LES computations show close agreement with the measured data. Subsequent comparisons of different URANS schemes with the present LES are used in order to explore to what extent these models are able to reproduce the large-scale unsteady flow structures. All URANS schemes have been found to be able to reproduce the 3-D unsteady flow features present in the 15° unstable cavity. However, the low-Re model tested as well as requiring a high resolution near-wall grid, also needed a finer grid in the core region than the high-Re models, thus making it computationally very expensive. Flow within the 15° stable cavity also shows some 3-D features, although it is significantly less unsteady, and the URANS models tested here have been less successful in reproducing this flow pattern. Finally, natural convection of CO2 inside a horizontal annular penetration enclosure, which can be found in AGR's, has been performed using a highly resolved LES and a set of RANS models. The Rayleigh number is 1.5×10e9. RANS models agree with the present LES on the fact that the flow is unsteady and there are large-scale oscillations present which decrease in amplitude as one moves from the open towards the closed end of the annular enclosure. Overall heat transfer and thermal quantitative and dynamic results show that RANS schemes are in close agreement with the current LES data except some discrepancies shown by the high-Re model which can be returned to the limitation of the simple wall function used to predict such complex flow.
Книги з теми "Modèle URANS":
1
United States. National Aeronautics and Space Administration., ed. Voyager radio occultation by the Uranian rings: Structure, dynamics, and particle sizes. Standford, CA: Center for Radar Astronomy, Stanford Electronics Laboratories, Stanford University, 1990.
2
Shen, Xiuzhong. KUR teinōshuku uran shirisaido nenryō roshin no anzen kaiseki. Ōsaka-fu Sennan-gun Kumatori-chō: Kyōto Daigaku Genshiro Jikkenjo, 2010.
3
Maldonado, Marta Fraile. Cuando la economía entra en las urnas: El voto económico en España, 1979-1996. Madrid: Centro de Investigaciones Sociológicas, 2005.
4
J, Gierasch Peter, Leroy Stephen S, and United States. National Aeronautics and Space Administration., eds. Temperature and circulation in the stratospheres of the outer planets. [Washington, DC: National Aeronautics and Space Administration, 1989.
5
Sarotte, Mary Elise. Heroic Aspirations in 1990. Princeton University Press, 2017. http://dx.doi.org/10.23943/princeton/9780691163710.003.0004.
Анотація:
This chapter discusses former Secretary General Mikhail Gorbachev's challenge to his own original plan: a heroic model of multinationalism. Gorbachev dropped the restoration concept entirely and instead proposed to build a vast new edifice from the Atlantic to the Urals: the fulfillment of his desire to create a common European home of many rooms. States under this model would retain their own political orders, but cooperate via international economic and military institutions. Ironically, former East German dissident movements proposed a similar model. They wanted new construction as well, though of a more limited expanse. Their goal was the construction of an improved socialism in East Germany, with a curiously prescient kind of “property pluralism” that would allow both private property and state intervention in times of economic crisis.
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Maldonado, Marta Fraile. Cuando La Economia Entra En Las Urnas: El Voto Economico En Espa~na, 1979-1996. Centro de Investigaciones Sociologicas, 2005.
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Fandiño Bohórquez, Andrés. Participación de las víctimas en la Jurisdicción Especial para la Paz (JEP) ¿Verdadera participación? Universidad Libre Sede Principal, 2017. http://dx.doi.org/10.18041/978-958-5466-80-7.
Анотація:
A dos años del Acuerdo Colón (24 de noviembre de 2016), la incertidumbre y las esperanzas afloran en materia de implementación del Acuerdo suscrito entre el gobierno colombiano y el exgrupo guerrillero FARC. No es para menos, la lectura de vaso medio lleno o medio vacío no se hace esperar. Más de cuatro complejos años de negociación para la construcción de un documento histórico, leído de forma positiva por la Comunidad Internacional y los expertos en terminación de conflictos en el mundo, pero seriamente cuestionado en el marco interno por aquellos que aún veían en la guerra una opción para Colombia. Entre otras consecuencias, fruto de la firma del Acuerdo, hoy podemos destacar: el fin de la guerra, la entrega de armas, el cierre de la “fábrica de víctimas”, la construcción de proyectos de vida de los viejos excombatientes, la reconstrucción de territorios y las esperanzas de millones de víctimas y de colombianos en la creación de las condiciones del “nunca jamás”. Y aunque han surgido muchas limitaciones a la hora de implementar la tamaña empresa de la paz, el solo Acuerdo y el fin de la guerra ya son un triunfo. Un triunfo que aún huele a pólvora, lágrimas y abandono del Estado y de una sociedad que se enamora gradualmente de la paz. Es evidente que la consolidación de este proceso y el cumplimiento de lo pactado apenas avanza en un país que construye de forma lenta una nueva historia política desligada de la violencia y las armas. Qué difícil vernos sin armas, sin guerra, sin conflicto armado. De la noche a la mañana desnudos, “sin fierros”, sin enemigos eternos, sin “terroristas”, sin emboscadas, sin muertos, sin motivos para continuar matándonos. El Acuerdo Colón, aunque seriamente intervenido a partir del triunfo del “No” en las urnas, constituye además de una gran hoja de ruta, un modelo a seguir en materia de transición. Es un documento único, es un proceso histórico, es una de las mejores noticias del siglo XXI para Colombia, la historia le dará su digno lugar. Es el reflejo de una exguerrilla cuyo origen campesino y liberal cifró en la tierra y el campo parte de sus originales reivindicaciones, lastimosamente afectadas por el mundo del narcotráfico en los años 80 y la pauperización de sus ideales políticos. También el Acuerdo es el fiel ejemplo de la intervención de las víctimas en la construcción de una nueva historia. Es un documento escrito a mil manos, millones de espíritus, millones de esperanzas. Así, leer el Acuerdo de Paz es observar la historia de Colombia y de su conflicto armado con esta antiquísima guerrilla: tierra, reforma rural integral, participación polí
Частини книг з теми "Modèle URANS":
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Jacobs, Bart. "Drawing from an Urn is Isometric." In Lecture Notes in Computer Science, 101–20. Cham: Springer Nature Switzerland, 2024. http://dx.doi.org/10.1007/978-3-031-57228-9_6.
Анотація:
AbstractDrawing (a multiset of) coloured balls from an urn is one of the most basic models in discrete probability theory. Three modes of drawing are commonly distinguished: multinomial (draw-replace), hypergeometric (draw-delete), and Pólya (draw-add). These drawing operations are represented as maps from urns to distributions over multisets of draws. The set of urns is a metric space via the Wasserstein distance. The set of distributions over draws is also a metric space, using Wasserstein-over-Wasserstein. The main result of this paper is that the three draw operations are all isometries, that is, they preserve the Wasserstein distances.
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Layton, W., and M. McLaughlin. "On URANS Congruity with Time Averaging: Analytical Laws Suggest Improved Models." In Mathematical Analysis With Applications, 85–108. Cham: Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-42176-2_10.
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Barklage, Alexander, and Rolf Radespiel. "Interaction of Wake and Propulsive Jet Flow of a Generic Space Launcher." In Notes on Numerical Fluid Mechanics and Multidisciplinary Design, 129–43. Cham: Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-53847-7_8.
Анотація:
Abstract This work investigates the interaction of the afterbody flow with the propulsive jet flow on a generic space launcher equipped with two alternative nozzle concepts and different afterbody geometries. The flow phenomena are characterized by experimental measurements and numerical URANS and LES simulations. Investigations concern a configuration with a conventional truncated ideal contour nozzle and a configuration with an unconventional dual-bell nozzle. In order to attenuate the dynamic loads on the nozzle fairing, passive flow control devices at the base of the launcher main body are investigated on the configuration with TIC nozzle. The nozzle Reynolds number and the afterbody geometry are varied for the configuration with dual-bell nozzle. The results for integrated nozzles show a shift of the nozzle pressure ratio for transition from sea-level to altitude mode to significant lower levels. The afterbody geometry is varied including a reattaching and non-reattaching outer flow on the nozzle fairing. Investigations are performed at supersonic outer flow conditions with a Mach number of $$Ma_\infty =3$$. It turns out, that a reattachment of the outer flow on the nozzle fairing leads to an unstable nozzle operation.
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Gomez, I., M. Chavez, J. de Vicente, and E. Valero. "Numerical Evaluation of URANS/Zonal-DES Models in the Acoustic Prediction of a High Reynolds Compressible Open Cavity Flow." In Progress in Hybrid RANS-LES Modelling, 291–302. Berlin, Heidelberg: Springer Berlin Heidelberg, 2012. http://dx.doi.org/10.1007/978-3-642-31818-4_25.
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PODOLAK, M., W. B. HUBBARD, and D. J. STEVENSON. "MODELS OF URANUS’ INTERIOR AND MAGNETIC FIELD." In Uranus, 29–62. University of Arizona Press, 1991. http://dx.doi.org/10.2307/j.ctv1v7zdtq.6.
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"Analytic Urns." In Polya Urn Models, 133–50. Chapman and Hall/CRC, 2008. http://dx.doi.org/10.1201/9781420059847-11.
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"Analytic Urns." In Polya Urn Models, 117–33. Chapman and Hall/CRC, 2008. http://dx.doi.org/10.1201/9781420059847.ch7.
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"URANOS." In Designing for Human-Machine Symbiosis Using the URANOS Model, 28–71. IGI Global, 2017. http://dx.doi.org/10.4018/978-1-5225-1888-4.ch002.
Анотація:
This chapter presents a generic system model called URANOS, that allows to design complex human-centered systems. It is not aligned to any particular discipline. Rather, it helps to build integral systems in different domains of science and engineering, even though it was originally intended to participate in the design of complex human-centered systems in the framework of ICT. URANOS aims at encouraging interdisciplinary work and reinforces the understanding of complex systems in general. It combines different epistemological standpoints and their corresponding realities into a wholeness. Concretely, the three fundamental standpoints of objectivism, subjectivism and holism are used to holistically handle all relevant entities such as humans, animals, machines and environments. This chapter also addresses systemic features like consciousness, collaboration and symbiosis providing a generic and abstract understanding of them.
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"Urns Evolving by Multiple Drawing." In Polya Urn Models, 221–38. Chapman and Hall/CRC, 2008. http://dx.doi.org/10.1201/9781420059847-14.
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"Urns Evolving by Multiple Drawing." In Polya Urn Models, 205–22. Chapman and Hall/CRC, 2008. http://dx.doi.org/10.1201/9781420059847.ch10.
Тези доповідей конференцій з теми "Modèle URANS":
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Gopalan, Harish, Peifeng Ma, Haihua Xu, Ankit Choudhary, Anis Hussain, and Rajeev K. Jaiman. "Hybrid RANS-LES Formulations for Wake Interference Physics in Tandem Cylinders and Multi-Column Floaters." In ASME 2015 34th International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/omae2015-41145.
Анотація:
Accurate prediction of hydrodynamic forces on tandem bluff bodies at high Reynolds numbers is of interest in many fields of offshore engineering. The most commonly used turbulence modeling strategy for studying these flows is unsteady Reynolds-averaged Navier-Stokes methods (URANS) due to its speed. However, the accuracy of URANS results are problem dependent and usually poor for bluff bodies flow separation predictions. To overcome this deficiency, two different modeling methods have been considered: (i) large eddy simulation (LES) and (ii) non-linear URANS. LES are accurate and computationally feasible for low to moderate Reynolds number flows. However, the cost of LES makes it infeasible at high Reynolds numbers. On the other hand, non-linear URANS methods are fast like URANS, and its accuracy is comparable to LES for certain flows. It is usually not known in advance if the simulations using non-linear methods are accurate. Hybrid models have been proposed in the literature as an alternative to existing methods. They employ a URANS model in the near-body region and LES in the near and far wake regions. Simulations performed using hybrid models are computationally cheaper than LES and more accurate than URANS. Most hybrid models developed in the literature employ linear URANS models. The use of non-linear URANS models in the hybrid context has not received significant attention. In this study, we propose the use of a hybrid model based on a non-linear URANS model. Flow past tandem cylinders, with different spacing ratio, at sub-critical Reynolds number regime, is chosen as the test case. Simulations are also performed using URANS and linear hybrid models for comparison. It is shown that the non-linear hybrid models provides the best agreement to measurement data in the literature. Non-linear URANS models will be shown to provide acceptable prediction of hydrodynamic forces. The models are finally used to predict the current load on a generic multi-column floater.
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Elkhoury, M., J. Najem, and Z. Nakad. "URANS Modeling of Three Airfoils With Different Stall Mechanisms." In ASME 2008 Fluids Engineering Division Summer Meeting collocated with the Heat Transfer, Energy Sustainability, and 3rd Energy Nanotechnology Conferences. ASMEDC, 2008. http://dx.doi.org/10.1115/fedsm2008-55023.
Анотація:
Capability of recently developed Menter (ME) and Modified Menter (MME) one-equation models in predicting prestall and poststall characteristics of three airfoils that exhibit different stall onset mechanisms is investigated. The Spalart-Allmaras (SA) turbulence model is also included to form a baseline against which both the ME and the MME models are assessed. The effects of subiteration, grid size, and time stepping on the predictive accuracy of the numerical scheme are addressed. However, transition effect is not accounted for and hence, all test cases are run fully turbulent. Significant differences in the flow predictions of all models are noticed in regions with massively flow separation.
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Pedro, H. T. C., K. W. Leung, M. H. Kobayashi, and H. R. Riggs. "Numerical Study of the Wave Impact on a Square Column Using Large Eddy Simulation." In ASME 2007 26th International Conference on Offshore Mechanics and Arctic Engineering. ASMEDC, 2007. http://dx.doi.org/10.1115/omae2007-29729.
Анотація:
This work concerns the numerical investigation of the impact of a wave on a square column. The wave is generated by a dam break in a wave tank. Two turbulence models were used: Large Eddy Simulations (LES) and Unsteady Reynolds Averaged Navier-Stokes (URANS). The numerical simulations were carried out using a finite volume approximation and the SIMPLE algorithm for the solution of the governing equations. Turbulence was modeled with the standard Smagorinsky-Lilly subgrid-model for the LES and the standard κ-ε model for the URANS. The results are validated against experimental data for the wave impact on a square column facing the flow. The results, especially for LES, show very good agreement between the predictions and experimental results. The overall accuracy of the LES, as expected, is superior to the URANS. However, if computational resources are limited, URANS can still provide satisfactory results for structural design.
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Israel, Daniel. "URANS and VLES: Using Conventional RANS Models for Time Dependent Flows." In 36th AIAA Fluid Dynamics Conference and Exhibit. Reston, Virigina: American Institute of Aeronautics and Astronautics, 2006. http://dx.doi.org/10.2514/6.2006-3908.
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Ridluan, A., and A. Tokuhiro. "SRANS and URANS CFD Simulations of Turbulent VHTR Lower Plenum Flow." In ASME 2007 International Mechanical Engineering Congress and Exposition. ASMEDC, 2007. http://dx.doi.org/10.1115/imece2007-42474.
Анотація:
Time-dependent and time-independent CFD simulations of the flow through a staggered tube bundle were performed. This flow configuration partially simulates the anticipated flow in the lower plenum of a Very High Temperature Reactor (VHTR) design. To design a nuclear reactor with confidence, one needs strict benchmarking as part of a validation and verification exercise for any and all commercial CFD codes. Thus CFD simulations (FLUENT) of isothermal (at present), periodic flow through a tube bundle using both Steady Reynolds Averaged Navier-Stokes (SRANS) and Unsteady Reynolds Averaged Navier-Stokes (URANS) equations were investigated. Selected turbulence models for a single tube diameter and inlet velocity based Re-number, Re ∼ 1.8 × 104, were investigated. The first-order turbulence models were: a standard k-ε turbulence model, a Renormalized Group (RNG) k-ε model, and lastly, a Shear Stress Transport (SST) k-ε model; the second-order model was a Reynolds Stress Model (RSM). Comparison of CFD simulations against experimental results of Simonin and Barcouda was undertaken at five stations (x, y) locations. Under the SRANS, we found the ability of the models to predict the turbulence stresses (u′u′, v′v′, u′v′) generally marginal to poor. However, upon adapting a concept from Large Eddy Simulation (LES), our URANS simulation with RSM revealed a spatiotemporal, oscillating flow structures in the wake. In contrast, it appears that the URANS with (even a) RNG k-ε model is unable to simulate this flow phenomena. In fact, the data suggests that the RNG k-ε model is too spatiotemporally dissipative. Some aspects of the SRANS versus URANS and using the aforementioned turbulence models will be presented.
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Zou, Lu, and Zao-jian Zou. "URANS Simulations of a Cruise Ship in Crabbing Motion." In ASME 2021 40th International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2021. http://dx.doi.org/10.1115/omae2021-62741.
Анотація:
Abstract In ship manoeuvrability, the crabbing test is critical to evaluate the hydrodynamic quantities for the guidance of an efficient and safe berthing or unberthing manoeuvres. In the present study, the crabbing performance of a cruise ship is investigated by an unsteady Reynolds-averaged Navier-Stokes (URANS) method considering the instantaneous relative motion between the ship and the quay. In the numerical simulations, the cruise ship is approaching the quay wall at a constant lateral speed. The crabbing motion with five degrees of freedom is modeled by the dynamic overset mesh technique, while the free surface elevation is simulated by the Volume of Fluid method. For reliable predictions of the crabbing performances, the timestep dependency study is conducted and a suitable time step is determined. From the computations, the hydrodynamic performances of the cruise ship, including forces and moments, as well as the surge, sinkage, roll, trim and yaw motions are predicted. The numerical results indicate variations of the hydrodynamic quantities under the impacts of ship speed and blockage effects by the quay wall. The present results can be used to evaluate the crabbing ability of the cruise ship and to provide guidance for estimating and designing the crabbing model test in further investigations.
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Kok, Zhen, Yuting Jin, Shuhong Chai, Shaun Denehy, and Jonathan Duffy. "URANS Prediction of Berthed Ship–Passing Ship Interactions." In ASME 2017 36th International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/omae2017-61738.
Анотація:
In this paper, the unsteady Reynolds-Averaged Navier-Stokes computational method has been employed for investigating the hydrodynamic interactions between berthed and passing ships. Initially, simulations in model-scale were performed for validating the numerical modelling technique using available benchmark experimental test cases. A formal study of verification and validation was carried out for quantifying the numerical uncertainties. Based on the validated numerical setup, systematic computations were conducted for further investigations on the influence of varying passing ship speeds and lateral separations on the interaction forces and moments. The same conditions were repeated in full scale to quantify possible scale effects. The numerical results demonstrate that the interaction forces and moments are proportional to the square of the passing ship speed and inversely proportional to the lateral separation between the two ships, which agrees well with the findings by Remery (1974) and Kriebel (1995) respectively. In addition, when comparing model and full scale results, the overall differences are not very significant and are within the simulation uncertainty for most cases.
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Tangermann, Eike, and Michael Pfitzner. "Numerical Investigation of Flame Flashback Into Swirling Flow." In ASME Turbo Expo 2008: Power for Land, Sea, and Air. ASMEDC, 2008. http://dx.doi.org/10.1115/gt2008-51081.
Анотація:
A lean premixed swirl burner configuration has been investigated numerically regarding its vulnerability with respect to flame flashback caused by combustion induced vortex breakdown (CIVB). The flashback phenomenon has been simulated using a simplified quasi two-dimensional URANS method to cover a large range of operational conditions and using Large-Eddy-Simulation to achieve a detailed view of the processes involved. The Lindsted-Vaos turbulent premixed combustion model supplemented with quenching models has been used in URANS simulations. In the LES the combustion has been modeled with a thickened flame model using a one-step reaction mechanism. The isothermal flow and the stable flame were validated and flashback limits for different operational conditions were determined.
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Burden, Shaun, John W. Chew, Feng Gao, and Olaf Marxen. "Effects of Turbine Conditions on Rim Seal Performance and Prediction." In ASME Turbo Expo 2022: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2022. http://dx.doi.org/10.1115/gt2022-83194.
Анотація:
Abstract Predicting the degree of hot gas ingestion into turbine disc cavities is a challenge for computational fluid dynamics due to the complex unsteady flow dynamics in turbine rim seals and sensitivity to operating condition and seal geometry. This paper reports research aimed at clarifying the effect of operating conditions on seal performance and turbulence modelling requirements. A systematic study of sealing performance for an axial rim seal is reported, comparing an unsteady Reynolds-averaged Navier-Stokes (URANS) model and wall-modelled large-eddy simulation (WMLES). The conditions considered are classed as rotation-driven ingestion, pressure-driven ingestion, and combined mechanism ingestion. WMLES and URANS results showed similar ingestion levels and seal flows within the pressure-driven regime. For the rotationally-driven condition URANS displays larger, more coherent vortical flow structures than the WMLES. The larger vortices in the URANS drive ingress into the wheel-space resulting in higher levels of ingestion than indicated by the WMLES. For the combined ingestion condition, WMLES shows higher levels of ingestion and flow unsteadiness than URANS. The present results give some explanation for the mixed results reported for the performance of URANS models in previous studies.
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Gopalan, Harish, Dominic Denver John Chandar, Narasimha Rao Pillamarri, Guan Mengzhao, Rajeev K. Jaiman, Peifeng Ma, Haihua Xu, Ankit Choudhary, and Anis Hussain. "Numerical Investigation of Flow Interference Effects in Fixed and Vibrating Tandem Square Columns Using Hybrid RANS-LES Models." In ASME 2015 34th International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/omae2015-41659.
Анотація:
Investigation of flow past tandem and side-by-side circular and square columns is of interest in offshore engineering. Flow past fixed and vibrating circular columns has received a lot of focus in the literature. However, the studies focused on square columns, especially at high Reynolds numbers are very limited due to the computational cost of large eddy simulation (LES). Unsteady Reynolds-averaged Navier-Stokes (URANS) methods are limited by their accuracy, especially for tandem columns in the wake interference regime (spacing to diameter ratio: L=D ∼ 3:0). Hybrid URANS-LES models (URANS near the solid-wall and LES away from the wall) can overcome the drawbacks of the traditional URANS methods and can provide a reasonable prediction of the flow physics at a fraction of the cost of LES without significantly sacrificing numerical accuracy. Arbitrary Lagrangian-Eulerian (ALE) methods fails when vibrating tandem bodies are in close proximity to each other or vibrate at high reduced velocities. Remeshing the domain can be expensive, especially at high Reynolds numbers (Re). Alternate strategies are necessary to efficiently simulation this problems. This study proposes the use of a non-linear URANS-LES model, coupled with an overset mesh method (for vibrating columns), for studying flow past tandem square columns. Simulations are performed at sub-critical Re to match the experimental Re. The initial results are encouraging for further investigation of fixed and vibrating tandem square column flow interference at high Reynolds numbers.