Готові списки джерел за темами / Turbulence

Добірка наукової літератури з теми "Turbulence"

Автор: Grafiati
Опубліковано: 4 червня 2021
Оновлено: 20 квітня 2024

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Статті в журналах з теми "Turbulence":

1

Atac, Omer Faruk, Hyunsu Lee, and Seoksu Moon. "Detecting ultrafast turbulent oscillations in near-nozzle discharged liquid jet using x-ray phase-contrast imaging with MHz frequency." Physics of Fluids 35, no. 4 (April 2023): 045102. http://dx.doi.org/10.1063/5.0143351.

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Characteristics of a discharged liquid jet in near-nozzle are determined by the in-flow turbulences generated by the evolution of inflow vortices and cavitation. High-fidelity simulations have indicated that such physical processes can generate ultrafast turbulent fluctuations (in the range of MHz) originating from the nature of turbulence by the interaction between the large and small-scale turbulence in the flow. Detecting ultrafast turbulent oscillations while resolving small-scale turbulences in the optically dense near-nozzle liquid jet has not been observed through experimental methods so far. In this study, therefore, ultrafast x-ray phase-contrast imaging, which can provide a clear image in the near-field using a high-energy x-ray source, was applied to observe the fluctuation of flow velocity in the near-field to obtain the ultrafast turbulent oscillations at the discharged jet. To capture the ultrafast variance of flow velocity originating from the nature of turbulence, the high imaging frequency was applied up to 1.2 MHz. With the implemented methodology, turbulence intensity distributions of discharged liquid jets were measured for various injection pressures and nozzle geometries. Such turbulence intensity results were also correlated with the initial dispersion angle of the spray. In addition, the turbulence length scales, which can be detected through the current methodology, were estimated and discussed considering standard-length scales. The results showed that the current experimental method introduced in this study can provide important insights into the turbulence characteristics of spray by resolving Taylor scale turbulences and can provide valuable validation data and boundary conditions for reliable spray simulations.
2

Souza, José Francisco Almeida de, José Luiz Lima de Azevedo, Leopoldo Rota de Oliveira, Ivan Dias Soares, and Maurício Magalhães Mata. "TURBULENCE MODELING IN GEOPHYSICAL FLOWS – PART I – FIRST-ORDER TURBULENT CLOSURE MODELING." Revista Brasileira de Geofísica 32, no. 1 (March 1, 2014): 31. http://dx.doi.org/10.22564/rbgf.v32i1.395.

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ABSTRACT. The usage of so-called turbulence closure models within hydrodynamic circulation models comes from the need to adequately describe vertical mixing processes. Even among the classical turbulence models; that is, those based on the Reynolds decomposition technique (Reynolds Averaged Navier-Stokes – RANS), there is a variety of approaches that can be followed for the modeling of turbulent flows (second moment) of momentum, heat, salinity, and other properties. Essentially, these approaches are divided into those which use the concept of turbulent viscosity/diffusivity in the modeling of the second moment, and those which do not use it. In this work we present and discuss the models that employ this concept, in which the viscosity can be considered constant or variable. In this latter scenario, besides those that use the concepts of mixture length, the models that use one or two differential transport equations for determining the viscosity are presented. The fact that two transport equations are used – one for the turbulent kinetic energy and the other for the turbulent length scale – make these latter ones the most complete turbulent closure models in this category. Keywords: turbulence modeling, turbulence models, first-order models, first-order turbulent closure. RESUMO. A descrição adequada dos processos de mistura vertical nos modelos de circulação hidrodinâmica é o objetivo dos chamados modelos de turbulência, os quais são acoplados aos primeiros. Mesmo entre os modelos clássicos de turbulência, isto é, aqueles que se baseiam na técnica de decomposição de Reynolds (Reynolds Averaged Navier-Stokes – RANS), existe uma variedade de abordagens que podem ser seguidas na modelagem dos fluxos turbulentos (segundos momentos) de momentum, calor, salinidade e outras propriedades. Fundamentalmente estas abordagens dividem-se entre aquelas que utilizam o conceito de viscosidade/ difusividade turbulenta na modelagem dos segundos momentos, e aquelas que não o utilizam. Nesse trabalho são apresentados e discutidos os modelos que empregam este conceito, onde a viscosidade pode ser considerada constante ou variável. No caso variável, além daqueles que utilizam o conceito de comprimento de mistura, são ainda apresentados os modelos que utilizam uma ou duas equações diferenciais de transporte para a determinação da viscosidade. O fato de empregar duas equações de transporte, uma para a energia cinética turbulenta e outra para a escala de comprimento turbulento, fazem destes últimos os mais completos modelos de fechamento turbulento desta categoria. Palavras-chave: modelagem da turbulência, modelos de turbulência, modelos de primeira ordem, fechamento turbulento de primeira orde
3

Bašták Ďurán, Ivan, and Pascal Marquet. "Les travaux sur la turbulence : les origines, Toucans, Cost-ES0905 et influence de l'entropie." La Météorologie, no. 112 (2021): 079. http://dx.doi.org/10.37053/lameteorologie-2021-0023.

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Le schéma de turbulence Toucans est utilisé dans la configuration opérationnelle Alaro du modèle Aladin depuis début 2015. Son développement a été initié, guidé et en grande partie conçu par Jean-François Geleyn. Ce développement a commencé avec le prédécesseur du schéma Toucans, le schéma « pseudo-pronostique » en énergie cinétique turbulente, lui-même basé sur l'ancien schéma de turbulence de Louis, mais étendu dans Toucans à un schéma pronostique. Le schéma Toucans a pour objectif de traiter de manière cohérente les fonctions qui dépendent de la stabilité verticale de l'atmosphère, de l'influence de l'humidité et des échelles de longueur de la turbulence (de mélange et de dissipation). De plus, de nouvelles caractéristiques ont été ajoutées : une représentation améliorée pour les stratifications très stables (absence de nombre de Richardson critique), une meilleure représentation de l'anisotropie, un paramétrage unifié de la turbulence et des nuages par l'ajout d'une deuxième énergie turbulente pronostique et la paramétrisation des moments du troisième ordre. The Toucans turbulence scheme is a turbulence scheme that is used in the operational Alaro configuration of the Aladin model since early 2015. Its development was initiated, guided and to a large extend authored by Jean-François Geleyn. The development started with the predecessor of the Toucans scheme, the "pseudo-prognostic" turbulent kinetic energy scheme which itself was built on the "Louis" turbulence scheme, but extended to a prognostic scheme. The Toucans scheme aims for a consistent treatment of stability dependency functions, influence of moisture, and turbulence length scales. Additionally, new features were added to the turbulence scheme: improved representation of turbulence in very stable stratification (absence of critical gradient Richardson number), better representation of anisotropy, unified parameterization of turbulence and clouds via addition of second prognostic turbulence energy, and parameterization of third order moments.
4

Liu, Xianlong, Fei Wang, Minghui Zhang, and Yangjian Cai. "Effects of Atmospheric Turbulence on Lensless Ghost Imaging with Partially Coherent Light." Applied Sciences 8, no. 9 (August 28, 2018): 1479. http://dx.doi.org/10.3390/app8091479.

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Ghost imaging with partially coherent light through two kinds of atmospheric turbulences: monostatic turbulence and bistatic turbulence, is studied, both theoretically and experimentally. Based on the optical coherence theory and the extended Huygens–Fresnel integral, the analytical imaging formulae in two kinds of turbulence have been derived with the help of a tensor method. The visibility and quality of the ghost image in two different atmospheric turbulences are discussed in detail. Our results reveal that in bistatic turbulence, the visibility and quality of the image decrease with the increase of the turbulence strength, while in monostatic turbulence, the image quality remains invariant when turbulence strength changes in a certain range, only the visibility decreases with the increase of the strength of turbulence. Furthermore, we carry out experimental demonstration of lensless ghost imaging through monostatic and bistatic turbulences in the laboratory, respectively. The experiment results agree well with the theoretical predictions. Our results solve the controversy about the influence of atmospheric turbulence on ghost imaging.
5

Marxen, Olaf, and Tamer A. Zaki. "Turbulence in intermittent transitional boundary layers and in turbulence spots." Journal of Fluid Mechanics 860 (December 5, 2018): 350–83. http://dx.doi.org/10.1017/jfm.2018.822.

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Direct numerical simulation data of bypass transition in flat-plate boundary layers are analysed to examine the characteristics of turbulence in the transitional regime. When intermittency is 50 % or less, the flow features a juxtaposition of turbulence spots surrounded by streaky laminar regions. Conditionally averaged turbulence statistics are evaluated within the spots, and are compared to standard time averaging in both the transition region and in fully turbulent boundary layers. The turbulent-conditioned root-mean-square levels of the streamwise velocity perturbations are notably elevated in the early transitional boundary layer, while the wall-normal and spanwise components are closer to the levels typical for fully turbulent flow. The analysis is also extended to include ensemble averaging of the spots. When the patches of turbulence are sufficiently large, they develop a core region with similar statistics to fully turbulent boundary layers. Within the tip and the wings of the spots, however, the Reynolds stresses and terms in the turbulence kinetic energy budget are elevated. The enhanced turbulence production in the transition zone, which exceeds the levels from fully turbulent boundary layers, contributes to the higher skin-friction coefficient in that region. Qualitatively, the same observations hold for different spot sizes and levels of free-stream turbulence, except for young spots which do not yet have a core region of developed turbulence.
6

Baumert, H. Z., and H. Peters. "Turbulence closure: turbulence, waves and the wave-turbulence transition – Part 1: Vanishing mean shear." Ocean Science Discussions 5, no. 4 (November 14, 2008): 545–80. http://dx.doi.org/10.5194/osd-5-545-2008.

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Abstract. A new two-equation, closure-like turbulence model for stably stratified flows is introduced which uses the turbulent kinetic energy (K) and the turbulent enstrophy (Ω) as primary variables. It accounts for mean shear – and internal wave-driven mixing in the two limits of mean shear and no waves and waves but no mean shear, respectively. The traditional TKE balance is augmented by an explicit energy transfer from internal waves to turbulence. A modification of the Ω-equation accounts for the effect of the waves on the turbulence time and space scales. The latter is based on the assumption of a non-zero constant flux Richardson number in the limit of vanishing mean-flow shear when turbulence is produced exclusively by internal waves. The new model reproduces the wave-turbulence transition analyzed by D'Asaro and Lien (2000). At small energy density E of the internal wave field, the turbulent dissipation rate (ε) scales like ε~E2. This is what is observed in the deep sea. With increasing E, after the wave-turbulence transition has been passed, the scaling changes to ε~E1. This is observed, for example, in the swift tidal flow near a sill in Knight Inlet. The new model further exhibits a turbulent length scale proportional to the Ozmidov scale, as observed in the ocean, and predicts the ratio between the turbulent Thorpe and Ozmidov length scales well within the range observed in the ocean.
7

Baumert, H. Z., and H. Peters. "Turbulence closure: turbulence, waves and the wave-turbulence transition – Part 1: Vanishing mean shear." Ocean Science 5, no. 1 (March 6, 2009): 47–58. http://dx.doi.org/10.5194/os-5-47-2009.

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Abstract. This paper extends a turbulence closure-like model for stably stratified flows into a new dynamic domain in which turbulence is generated by internal gravity waves rather than mean shear. The model turbulent kinetic energy (TKE, K) balance, its first equation, incorporates a term for the energy transfer from internal waves to turbulence. This energy source is in addition to the traditional shear production. The second variable of the new two-equation model is the turbulent enstrophy (Ω). Compared to the traditional shear-only case, the Ω-equation is modified to account for the effect of the waves on the turbulence time and space scales. This modification is based on the assumption of a non-zero constant flux Richardson number in the limit of vanishing mean shear when turbulence is produced exclusively by internal waves. This paper is part 1 of a continuing theoretical development. It accounts for mean shear- and internal wave-driven mixing only in the two limits of mean shear and no waves and waves but no mean shear, respectively. The new model reproduces the wave-turbulence transition analyzed by D'Asaro and Lien (2000b). At small energy density E of the internal wave field, the turbulent dissipation rate (ε) scales like ε~E2. This is what is observed in the deep sea. With increasing E, after the wave-turbulence transition has been passed, the scaling changes to ε~E1. This is observed, for example, in the highly energetic tidal flow near a sill in Knight Inlet. The new model further exhibits a turbulent length scale proportional to the Ozmidov scale, as observed in the ocean, and predicts the ratio between the turbulent Thorpe and Ozmidov length scales well within the range observed in the ocean.
8

Donnelly, Russell J., and Charles E. Swanson. "Quantum turbulence." Journal of Fluid Mechanics 173 (December 1986): 387–429. http://dx.doi.org/10.1017/s0022112086001210.

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We present a review of quantum turbulence, that is, the turbulent motion of quantized vortex lines in superfluid helium. Our discussion concentrates on the turbulence produced by steady, uniform heat flow in a pipe, but touches on other turbulent flows as well. We have attempted to motivate the study of quantum turbulence and discuss briefly its connection with classical turbulence. We include background on the two-fluid model and mutual friction theory, examples of modern experimental techniques, and a brief survey of the phenomenology. We discuss the important recent insights that vortex dynamics has provided to the understanding of quantum turbulence, from simple scaling arguments to detailed numerical simulations. We conclude with a discussion of open questions in this field.
9

MIYAUCHI, Toshio. "Turbulence and Turbulent Combustion." TRENDS IN THE SCIENCES 19, no. 4 (2014): 4_44–4_48. http://dx.doi.org/10.5363/tits.19.4_44.

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10

Wang, B. B., G. P. Zank, L. Adhikari, and L. L. Zhao. "On the Conservation of Turbulence Energy in Turbulence Transport Models." Astrophysical Journal 928, no. 2 (April 1, 2022): 176. http://dx.doi.org/10.3847/1538-4357/ac596e.

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Abstract Zank et al. developed models describing the transport of low-frequency incompressible and nearly incompressible turbulence in inhomogeneous flows. The formalism was based on expressing the fluctuating variables in terms of the Elsässar variables and then taking “moments” subject to various closure hypotheses. The turbulence transport models are different according to whether the plasma beta regime is large, of order unity, or small. Here, we show explicitly that the three sets of turbulence transport models admit a conservation representation that resembles the well-known WKB transport equation for Alfvén wave energy density after introducing appropriate definitions of the “pressure” associated with the turbulent fluctuations. This includes introducing a distinct turbulent pressure tensor for 3D incompressible turbulence (the large plasma beta limit) and pressure tensors for quasi-2D and slab turbulence (the plasma beta order-unity or small regimes) that generalize the form of the WKB pressure tensor. Various limits of the different turbulent pressure tensors are discussed. However, the analogy between the conservation form of the turbulence transport models and the WKB model is not close for multiple reasons, including that the turbulence models express fully nonlinear physical processes unlike the strictly linear WKB description. The analysis presented here both serves as a check on the validity and correctness of the turbulence transport models and also provides greater transparency of the energy dissipation term and the “turbulent pressure” in our models, which is important for many practical applications.
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Статті в журналах Дисертації Книги

Дисертації з теми "Turbulence":

1

PARET, JEROME. "Turbulence bidimensionnelle et dispersion turbulente : etude experimentale." Paris 6, 1999. http://www.theses.fr/1999PA066384.

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Nous presentons une etude experimentale approfondie de la turbulence bidimensionnelle entretenue. Les experiences sont realisees dans de minces couches de fluides stratifiees et les champs de vitesse sont determines a l'aide d'une technique de velocimetrie par suivi de particules. Les conjectures de kraichnan sur la cascade inverse d'energie et la cascade directe d'enstrophie sont confirmees, notamment les lois de puissance pour les spectres d'energie. Nous etudions la cascade inverse de maniere plus detaillee. Nous trouvons que, en fonction de la dissipation d'energie aux grandes echelles, le regime de cascade inverse classique ou le regime condense sont obtenus comme etats statistiquement stationnaires. Les proprietes statistiques des tourbillons coherents tendent a montrer que la dynamique de la cascade est regie par un mecanisme d'agregation des tourbillons de meme signe plutot que par une succession de fusions creant des tourbillons de taille de plus en plus grande. De plus, en net contraste par rapport au cas tridimensionnel, nous trouvons que la cascade d'energie ne presente pas d'intermittence, avec des statistiques quasiment gaussiennes et des exposants de fonctions de structures indiscernables des valeurs de kolmogorov. Ce comportement non intermittent est egalement observe pour la cascade d'enstrophie. Nous etudions la dispersion relative de paires de particules passives dans des ecoulements presentant une cascade inverse d'energie. Les proprietes statistiques de ce processus sont determinees en integrant numeriquement les trajectoires lagrangiennes des particules a partir des champs de vitesse experimentaux. La loi hyperdiffusive de richardson est observee et un comportement fortement non-gaussien est obtenu pour les distributions des separations des paires. Nous montrons que le processus est temporellement auto-similaire et que de fortes correlations temporelles sont presentes. Ces observations compromettent l'approche en terme de vols de levy.
2

Sung, Kyung-Sub. "Turbulent dispersion in strongly stratified turbulence." Thesis, Imperial College London, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.582577.

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The first part is the derivation of one-particle vertical diffusion for stably stratified turbulence with or without rapid rotation. Nicolleau & Vassilicos (2000) have analytically calculated vertical one-particle diffusion in stably stratified turbulence without rotation. One-particle vertical diffusion for turbulence with stable stratification and with or without rapid rotation has been derived here analytically using the solutions of the linearized equations of motions. The second part is an attempt to explain the depletion of horizontal pair diffusion in strongly stratified turbulence. "Recently, Nicolleau et al. (2005) have shown that in their Kinematic Simulations (KS) of vertically stably and strongly stratified homogeneous turbulence (Froude number smaller than 1). horizontal pair diffusion is significantly depleted by comparison to unstratified isotropic and homogeneous two- and three-dimensional turbulence. We have seeked to explain this depletion of horizontal pair diffusion by vertical stratification in terms of the probability density function of the horizontal divergence of the velocity field and the statistics of stagnation points following the recent approach to Richardson pair diffusion by Davila & Vassilicos (2003), Goto & Vassilicos (2004), Goto et al. (2005) and Osborne et al. (2005). We measure the number density of stagnation points in the KS of three-dimensional strongly stratified turbulence and find that it is virtually identical to what it is in KS of three-dimensional isotropic turbulence The third part is a study of the vertical motions of small, spherical inertial particles in strongly stratified turbulence.
3

Le, Roy Pascal. "Cascade inverse et dispersion turbulente en turbulence bidimensionnelle." Phd thesis, Ecole Nationale des Ponts et Chaussées, 1988. http://tel.archives-ouvertes.fr/tel-00529772.

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Cette thèse étudie la turbulence bidimensionnelle au moyen de simulations numériques. La turbulence bidimensionnelle intéresse surtout les météorologues et les océanographes car elle constitue une première approximation de leurs écoulements. Mon travail sur le modèle de turbulence bidimensionnelle du Laboratoire de Météorologie Dynamique a consisté à la fois en l'amélioration du modèle et la réalisation de diverses expériences sur ce modèle. La principale amélioration apportée au modèle est la mise au point d'une bonne modélisation de la cascade inverse d'énergie, i.e. une simulation plus réaliste des plus grandes échelles de l'écoulement. Les expériences réalisées sur ce modèle amélioré concernent la dispersion (absolue ou relative), i.e. nous simulons l'advection de flotteurs lagrangiens par l'écoulement. Les résultats obtenus diffèrent sensiblement des conjectures théoriques et nous obligent à envisager une approche différente de la dispersion turbulente. J'ai ajouté le travail d'une année, réalisé comme scientifique du contingent à l'Institut de Mécanique de Grenoble, sur les instabilités qui se développent dans une couche de mélange bidimensionnelle.
4

Alves, Portela Felipe. "Turbulence cascade in an inhomogeneous turbulent flow." Thesis, Imperial College London, 2017. http://hdl.handle.net/10044/1/63233.

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The inhomogeneous, anisotropic turbulence downstream of a square prism is investigated by means of direct numerical simulations (DNS) and two-point statistics. As noted by Moffatt (2002) “it now seems that the intense preoccupation [...] with the problem of homogeneous isotropic turbulence was perhaps misguided” acknowledging there is now a revived interest in studying inhomogeneous turbulence. The full description of the turbulence cascade requires a two-point analysis which re- volves around the recently derived Kármán-Howarth-Monin-Hill equation (KHMH). This equation is the inhomogeneous/anisotropic analogue to the so-called Kolmogorov equation (or Kármán-Howarth equation) used in Kolmogorov’s 1941 seminal papers (K41) which are the foundation to the most successful turbulence theory to date. Particular focus is placed on the near wake region where the turbulence is anticipated to be highly inhomogeneous and anisotropic. Because DNS gives direct access to all ve- locity components and their derivatives, all terms of the KHMH can be computed directly without resorting to any simplifications. Computation of the term associated with the non-linear inter-scale transfer of energy (Π) revealed that this rate is roughly constant over a range of scales which increases (within the bounds of our database) with distance to the wake generator, provided that the orientations of the pairs of points are averaged-out on the plane of the wake. This observation appears in tandem with a near −5/3 power law in the spectra of fluctuating velocities which deteriorates as the constancy of Π improves. The constant non-linear inter-scale transfer plays a major role in K41 and is required for deriving the 2/3-law (which is real space equivalent of the −5/3). We extend our analysis to a triple decomposition where the organised motion associ- ated with the vortex shedding is disentangled from the stochastic motions which do not display a distinct time signature. The imprint of the shedding-associated motion upon the stochastic component is observed to contribute to the small-scale anisotropy of the stochastic motion. Even though the dynamics of the shedding-associated motion differs drastically from that of the stochastic one, we find that both contributions are required in order to preserve the constant inter-scale transfer of energy. We further find that the inter- scale fluxes resulting from this decomposition display local (in scale-space) combinations of direct and inverse cascades. While the inter-scale fluxes associated with the coherent motion can be explained on the basis of simple geometrical arguments, the stochastic motion shows a persistent inverse cascade at orientations normal to the centreline despite its energy appearing to be roughly isotropically distributed.
5

Ahmed, Umair. "Flame turbulence interaction in premixed turbulent combustion." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/flame-turbulence-interaction-in-premixed-turbulent-combustion(f23c7263-df3d-41fa-90ed-41735fcaa34a).html.

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6

Tanaka, Dan. "Chemical turbulence equivalent to Nikolaevskii turbulence." 京都大学 (Kyoto University), 2005. http://hdl.handle.net/2433/145070.

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Kyoto University (京都大学)
0048
新制・課程博士
博士(理学)
甲第11301号
理博第2859号
新制||理||1427(附属図書館)
22944
UT51-2005-D52
京都大学大学院理学研究科物理学･宇宙物理学専攻
(主査)助教授 篠本 滋, 教授 小貫 明, 助教授 早川 尚男
学位規則第4条第1項該当
7

Sanderson, V. E. "Turbulence modelling of turbulent buoyant jets and compartment fires." Thesis, Cranfield University, 2001. http://hdl.handle.net/1826/137.

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Turbulent buoyant jets are a major feature in fire hazards. The solution of the Reynolds Averaged Navier-Stokes (RANS) equations through computational fluid dynamic (CFD) techniques allow such flows to be simulated. The use of Reynolds averaging requires an empirical model to close the set of equations, this is known as the turbulence model. This thesis undertakes to investigate linear and nonlinear approaches to turbulence modelling and to apply the knowledge gained to the simulation of compartment fires. The principle contribution of this work is the reanalysis of the standard k- ε turbulence model and the implementation and application of more sophisticated models as applied to thermal plumes. Validation in this work, of the standard k- ε model against the most recent experimental data, counters the established view that the model is inadequate for the simulation of buoyant flows. Examination of previous experimental data suggests that the measurements were not taken in the self-similar region resulting in misleading comparisons with published numerical solutions. This is a significant conclusion that impacts of the general approach taken to modelling turbulence in this field. A number of methods for modelling the Reynolds stresses and the turbulent scalar fluxes have been considered and, in some cases for the first time, are applied to nonisothermal flows. The relative influence of each model has been assessed enabling its performance to be gauged. The results from this have made a valuable contribution to the knowledge in the field and have enabled the acquired experience to be applied to the simulation of compartment fires. The overall conclusion drawn from this thesis is that for the simulation of compartment fires, the most appropriate approach with current computational resources, is still the buoyancy corrected standard k- ε model. However, the turbulence scalar flux should be modelled by the generalised gradient diffusion hypothesis (GGDH) rather than the eddy-diffusivity assumption.
8

Khorsandi, Babak. "Effect of background turbulence on an axisymmetric turbulent jet." Thesis, McGill University, 2011. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=104661.

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The effect of background turbulence on a turbulent jet was investigated experimentally. The primary objective of this work was to study the effect of different levels of the background turbulence on the dynamics and mixing of an axisymmetric turbulent jet at different Reynolds numbers. The secondary objective, which arose during the experiments, was to improve the acoustic Doppler velocimetry measurements which were found to be inaccurate when measuring turbulence statistics. In addition to acoustic Doppler velocimetry (ADV), flying hot-film anemometry was employed in this study. To move the hot-film probe at constant speeds, a high precision traversing mechanism was designed and built. A data acquisition system and LabVIEW programs were also developed to acquire data and control the traversing mechanism. The experiments started by benchmarking the two measurement techniques in an axisymmetric turbulent jet. Comparing the results with those of the other studies validated the use of flying hot-film anemometry to estimate the mean and the root-mean square (RMS) velocities. The experiments also validated the use of ADV for measurement of the mean velocities (measured in three Cartesian directions) and the RMS velocity (measured in the z-direction only). RMS velocities measured by the ADV along the x- and y-direction of the probe were overestimated.Attempts to improve the turbulence statistics measured by the ADV using the post-processing and noise-reduction methods presented in the literature were undertaken. However, the RMS velocities remained higher than the accepted values. In addition, a noise-reduction method was presented in this study which reduced the RMS velocities down to the accepted values. It was also attempted to relate Doppler noise to current velocity, and thus improve the results by subtracting the Doppler noise from the measured RMS velocities in the jet. However, no relationship was found between the Doppler noise and the mean velocity. The effect of different levels of background turbulence on the dynamics and mixing of an axisymmetric turbulent jet at different Reynolds numbers was then investigated. The background turbulence was generated by a random jet array. To confirm that the turbulence is approximately homogeneous and isotropic and has a low mean flow, the background flow was first characterized. Velocity measurements in an axisymmetric jet issuing into two different levels of background turbulence were then conducted. Three different jet Reynolds numbers were tested (Re = UJD/ν, where UJ is the jet exit velocity, D is the exit diameter of the jet, and ν is the kinematic viscosity). The results showed that (compared to the jet in a quiescent ambient) the mean axial velocities decay faster in the presence of background turbulence, while the mean radial velocities increase, especially close to the edges of the jet. At lower Reynolds numbers, the jet structure was destroyed in the near-field of the jet. The increase in the level of the background turbulence resulted in a faster decay of the mean axial velocities. The RMS velocity of the jet issuing into the turbulent background also increased, indicating that the level of turbulence in the jet increases. In addition, the jet's width increased in the presence of the background turbulence. The mass flow rate of the jet decreased in the presence of the background turbulence from which it can be inferred that the entrainment into the jet is reduced. The effect of background turbulence on entrainment mechanisms – large-scale engulfment and small-scale nibbling – is discussed. It is concluded that in the presence of background turbulence, engulfment is expected to be the main entrainment mechanism.
L'effet de la turbulence ambiante sur l'évolution d'un jet turbulent est étudié dans le cadre de cette recherche expérimentale. L'objectif primaire de ce travail est l'étude de l'effet de l'intensité de la turbulence ambiante sur l'évolution d'un jet turbulent, à trois nombres de Reynolds différents. L'objectif secondaire est l'amélioration des mesures de vélocimétrie acoustique Doppler qui se sont avérées inexactes au cours de ce travail. Un dispositif à anémométrie à fil chaud volant a aussi été développé pour effectuer des mesures dans le cadre de cette étude. A cette fin, un mécanisme de translation a été conçu pour déplacer la sonde à vitesse constante. Un système d'acquisition de données et des programmes LabVIEW ont été développés pour enregistrer les données et contrôler le mécanisme. De premières expériences (dans un jet turbulent axisymétrique en milieu tranquille) ont prouvé le bien-fondé i) des mesures de vitesses moyenne et moyenne quadratique par anémométrie à fil chaud volant, et ii) des mesures de vitesse moyenne (dans tous le sens) et de vitesse moyenne quadratique (dans le sens z) par vélocimétrie acoustique Doppler. Les mesures par vélocimétrie acoustique Doppler dans les sens x et y étaient surestimées. L'amélioration des mesures de vitesse moyenne quadratique par vélocimétrie acoustique Doppler a été tentée par moyen de techniques de réduction de bruit existantes. Néanmoins, les vitesses moyennes quadratiques restaient surestimées. Une nouvelle technique de réduction de bruit (qui avait pour résultat des vitesses moyennes quadratiques précises) a été proposée dans le cadre de cette étude. En outre, des expériences ayant pour but de quantifier le rapport entre le bruit Doppler et la vitesse de l'écoulement ont été entreprises (pour pouvoir soustraire le bruit Doppler des mesures de vitesses moyennes quadratiques). Cependant, celles-ci n'ont trouvé aucun rapport entre ces deux quantités. Par la suite, l'effet de l'intensité de la turbulence ambiante sur l'évolution d'un jet turbulent axisymétrique, à trois nombres de Reynolds différents, a été étudié. La turbulence ambiante a été produite par moyen d'une maille de jets aléatoires. La turbulence ambiante s'est avérée, par moyen de mesures d'anémométrie à fil chaud volant et de vélocimétrie acoustique Doppler, homogène est isotrope. L'évolution d'un jet turbulent (à trois nombres de Reynolds) émis en milieux turbulents (de deux intensités différentes) a ensuite été étudiée. Les mesures ont démontré que la turbulence ambiante i) réduisait la vitesse axiale moyenne du jet (en augmentant le taux de décroissance), et ii) augmentait la vitesse radiale moyenne du jet (surtout prés du bord du jet). Pour les jets à nombre de Reynolds bas, la structure du jet a été détruite dans le champ proche du jet. Les vitesses moyennes quadratiques du jet émis en milieu turbulent étaient plus grandes, indiquant une croissance du niveau de turbulence dans le jet. En outre, la demi-largeur du jet augmentait en milieu turbulent. Par contre, en environnement turbulent, le débit massique du jet émis a diminué, ce qui implique que le taux d'entraînement du jet est aussi réduit. L'effet de la turbulence ambiante sur les mécanismes de l'entraînement (par engloutissement à grande échelle ou par grignotage) est examiné. Il est conclu que, en environnement turbulent, l'engloutissement est le mécanisme d'entraînement principal.
9

Irvine, Mark Rankin. "Turbulence and turbulent transport above and within coniferous forests." Thesis, University of Liverpool, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240324.

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10

Mergheni, Mohamed Ali. "Interactions particules - turbulence dans un jet axisymétrique diphasique turbulent." Rouen, 2008. http://www.theses.fr/2008ROUES067.

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Ce travail de thèse s'inscrit dans le cadre des études sur les écoulements turbulents gaz-solide et porte sur une étude numérique et une étude expérimentale de jets ronds coaxiaux diphasiques où le rapport des vitesses entre les jets externe et interne est supérieur et inférieur à un. Le but est de contribuer à la caractérisation des interactions entre la phase porteuse gazeuse et la phase dispersée et leur effet sur la modification de l'écoulement porteur. Le premier travail s'appuie sur une simulation de type Eulérienne / Lagrangienne qui résout les équations moyennées de Navier Stokes par la méthode des volumes finis. La turbulence du fluide est traitée par le modèle k-E standard. Le traitement de la phase dispersée consiste à un suivi Lagrangien de particules au sein de l'écoulement d'air. Le chargement en particules est suffisamment important pour que les particules influent sur la phase gazeuse (couplage) mais suffisamment faible pour pouvoir négliger les collisions interparticulaires. Le second travail consiste à réaliser un dispositif expérimental de jet gazeux ensemencé de particules solides (dp=100-212γm) issu d'un injecteur coaxial. L'écoulement diphasique est obtenu en utilisant un système d'ensemencement de particules assurant une injection régulière et homogène des particules dans le jet central. L'originalité de l'expérience consiste à mesurer simultanément les vitesses des particules et du fluide par une méthode optique non intrusive afin d'analyser le couplage entre deux phases. Ces résultats ont été obtenus à l'aide d'une chaîne de mesures optique PDA (Phase Doppler Anémométrie). L'analyse des caractéristiques dynamiques du fluide diphasique dans la zone proche de l'injecteur coaxial met en évidence que la vitesse de l'écoulement chargé est inférieure à la vitesse du fluide sans particules et que la présence des particules amplifie la turbulence du fluide lorsque la vitesse du jet centrale est supérieure à la vitesse du jet annulaire (ru>1). Ainsi, on note un décalage du pic de turbulence vers l'intérieur du jet central. Plus loin la vitesse moyenne du fluide en présence de particules devient supérieure à celle du jet monophasique à cause des transferts de quantité de mouvement des particules vers le fluide et on remarque une atténuation de la turbulence. Par contre, lorsque la vitesse du jet annulaire est supérieure à la vitesse du jet central (ru<1) on remarque une atténuation de la turbulence par la présence des particules et un décalage du pic de turbulence vers l'extérieur du jet central. On peut dire que la présence de particules solides permet à la turbulence de s'installer plus rapidement au sein du fluide pour ru>1. Lorsque ru<1, les particules ont tendance à calmer l'écoulement. Pour examiner l'approche numérique, les comparaisons avec mes travaux expérimentaux ont été réalisés. Les effets observés dans la partie expérimentale ont été reproduits dans deux cas différents (ru>1 et ru<1).
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Книги з теми "Turbulence":

1

Stanišić, M. M. The mathematical theory of turbulence. New York: Springer-Verlag, 1985.

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2

Nance, John J. Turbulence. New York: Jove Books, 2003.

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3

Aliabadi, Amir A. Turbulence. Cham: Springer International Publishing, 2022. http://dx.doi.org/10.1007/978-3-030-95411-6.

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4

Tabeling, P., and O. Cardoso, eds. Turbulence. Boston, MA: Springer US, 1994. http://dx.doi.org/10.1007/978-1-4615-2586-8.

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5

Nieuwstadt, Frans T. M., Jerry Westerweel, and Bendiks J. Boersma. Turbulence. Cham: Springer International Publishing, 2016. http://dx.doi.org/10.1007/978-3-319-31599-7.

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6

Bailly, Christophe, and Geneviève Comte-Bellot. Turbulence. Cham: Springer International Publishing, 2015. http://dx.doi.org/10.1007/978-3-319-16160-0.

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7

Dooley, Maura. Turbulence. Clapham, Lancaster: Giant Steps, 1988.

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8

Nance, John J. Turbulence. London: Pan, 2002.

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9

Joris, Pierre. Turbulence. Rhinebeck, NY: St. Lazaire Press, 1991.

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10

Rahim, Ali. Turbulence. New Haven, Conn: Yale School of Architecture, 2011.

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Частини книг з теми "Turbulence":

1

Deville, Michel O. "Turbulence." In An Introduction to the Mechanics of Incompressible Fluids, 211–56. Cham: Springer International Publishing, 2022. http://dx.doi.org/10.1007/978-3-031-04683-4_9.

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AbstractThe Reynolds decomposition and statistical averaging of velocity and pressure generate the Reynolds averaged Navier–Stokes (RANS) equations. The closure problem is solved by the introduction of a turbulence constitutive equation. Several linear turbulence models are presented in the RANS framework: $$K-\varepsilon , K-\omega $$ K - ε , K - ω . The solution of the RANS equations for the turbulent channel flow is elaborated giving the celebrated logarithmic profile. Non-linear models are built on the anisotropy tensor and the incorporation of the concept of integrity bases. The chapter ends with the theory of large eddy simulations with a few up-to-date models: dynamic model, approximate deconvolution method.
2

Smoot, L. Douglas, and Philip J. Smith. "Turbulence." In Coal Combustion and Gasification, 245–65. Boston, MA: Springer US, 1985. http://dx.doi.org/10.1007/978-1-4757-9721-3_10.

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3

Ivancevic, Vladimir G., and Tijana T. Ivancevic. "Turbulence." In High-Dimensional Chaotic and Attractor Systems, 529–616. Dordrecht: Springer Netherlands, 2007. http://dx.doi.org/10.1007/978-1-4020-5456-3_8.

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4

von Windheim, Jesko. "Turbulence." In The Startup, 1–11. Cham: Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-45078-6_1.

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5

Argyris, John, Gunter Faust, Maria Haase, and Rudolf Friedrich. "Turbulence." In An Exploration of Dynamical Systems and Chaos, 593–676. Berlin, Heidelberg: Springer Berlin Heidelberg, 2015. http://dx.doi.org/10.1007/978-3-662-46042-9_9.

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6

Herring, Jackson R. "Turbulence." In Handbook of Weather, Climate, and Water, 69–81. Hoboken, NJ, USA: John Wiley & Sons, Inc., 2004. http://dx.doi.org/10.1002/0471721603.ch6.

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7

Cuvelier, C., A. Segal, and A. A. van Steenhoven. "Turbulence." In Finite Element Methods and Navier-Stokes Equations, 442–51. Dordrecht: Springer Netherlands, 1986. http://dx.doi.org/10.1007/978-94-010-9333-0_17.

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8

Marchioro, Carlo, and Mario Pulvirenti. "Turbulence." In Applied Mathematical Sciences, 230–71. New York, NY: Springer New York, 1994. http://dx.doi.org/10.1007/978-1-4612-4284-0_7.

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9

Block, Louis Stuart, and William Andrew Coppel. "Turbulence." In Lecture Notes in Mathematics, 25–46. Berlin, Heidelberg: Springer Berlin Heidelberg, 1992. http://dx.doi.org/10.1007/bfb0084765.

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10

Westerhof, Nicolaas, Nikolaos Stergiopulos, and Mark I. M. Noble. "Turbulence." In Snapshots of Hemodynamics, 21–23. Boston, MA: Springer US, 2010. http://dx.doi.org/10.1007/978-1-4419-6363-5_4.

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Тези доповідей конференцій з теми "Turbulence":

1

MURTHY, S., and S. HONG. "Turbulent boundary layer with free stream turbulence." In 21st Fluid Dynamics, Plasma Dynamics and Lasers Conference. Reston, Virigina: American Institute of Aeronautics and Astronautics, 1990. http://dx.doi.org/10.2514/6.1990-1503.

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2

Nakabayashi, Koichi, Osami Kitoh, and Yoshitaka Katou. "TURBULENCE CHARACTERISTICS OF COUETTE-POISEUILLE TURBULENT FLOWS." In Second Symposium on Turbulence and Shear Flow Phenomena. Connecticut: Begellhouse, 2001. http://dx.doi.org/10.1615/tsfp2.80.

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3

Nishiki, Shinnosuke, Tatsuya Hasegawa, and Ryutaro Himeno. "ANISOTROPIC TURBULENCE GENERATION IN TURBULENT PREMIXED FLAMES." In Second Symposium on Turbulence and Shear Flow Phenomena. Connecticut: Begellhouse, 2001. http://dx.doi.org/10.1615/tsfp2.240.

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4

Montazeri, Hanif, Siamak Kazemzadeh Hannani, and Bijan Farhanieh. "Turbulent Flow Using a Modified V2f Turbulence Model." In ASME 2004 International Mechanical Engineering Congress and Exposition. ASMEDC, 2004. http://dx.doi.org/10.1115/imece2004-60342.

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An improved version of the V2f turbulence model has been examined in this paper. The objective was to overcome the convergence problem encountered in the original V2f model. The convergence problem is due to the commonly-used wall boundary condition, which therefore has been modified in the proposed model. To test the soundness of the new model, several two-dimensional cases such as Poiseuille flow, channel flow, and backward-step flow has been analyzed and the results are compared with the standard k-ε model, DNS, and in case of the backward flow problem, also with the original V2f model. Based on the comparison, the new model presents a promising approach both with respect to convergence as well as the accuracy of results.
5

Holmes, Marlin, Eric J. DeMillard, and Jonathan W. Naughton. "Turbulence Structure of the Swirling Axisymmetric Turbulent Wake." In 35th Wind Energy Symposium. Reston, Virginia: American Institute of Aeronautics and Astronautics, 2017. http://dx.doi.org/10.2514/6.2017-0919.

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6

NARAYAN, J., and S. GIRIMAJI. "Turbulent reacting flow computations including turbulence-chemistry interactions." In 30th Aerospace Sciences Meeting and Exhibit. Reston, Virigina: American Institute of Aeronautics and Astronautics, 1992. http://dx.doi.org/10.2514/6.1992-342.

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7

Redford, John A., and Gary N. Coleman. "NUMERICAL STUDY OF TURBULENT WAKES IN BACKGROUND TURBULENCE." In Fifth International Symposium on Turbulence and Shear Flow Phenomena. Connecticut: Begellhouse, 2007. http://dx.doi.org/10.1615/tsfp5.860.

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8

Pal, Anikesh, and Sutanu Sarkar. "EFFECT OF EXTERNAL TURBULENCE ON A TURBULENT WAKE." In Ninth International Symposium on Turbulence and Shear Flow Phenomena. Connecticut: Begellhouse, 2015. http://dx.doi.org/10.1615/tsfp9.180.

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9

Taylor, Travis S., Don A. Gregory, Peter S. Erbach, and T. Michelle Eckstein. "Turbulence simulation and optical processing through turbulent media." In AeroSense '97, edited by David P. Casasent and Tien-Hsin Chao. SPIE, 1997. http://dx.doi.org/10.1117/12.270389.

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10

He, Renjie, Zhiyong Wang, Yangyu Fan, and David Fengg. "Atmospheric turbulence mitigation based on turbulence extraction." In 2016 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP). IEEE, 2016. http://dx.doi.org/10.1109/icassp.2016.7471915.

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Звіти організацій з теми "Turbulence":

1

Sreenivasan, K. R. Turbulence, Turbulence Control, and Drag Reduction. Fort Belvoir, VA: Defense Technical Information Center, August 1987. http://dx.doi.org/10.21236/ada185643.

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2

Sreenivasan, K. R. Studies in Turbulence and Turbulence Control. Fort Belvoir, VA: Defense Technical Information Center, June 1993. http://dx.doi.org/10.21236/ada266318.

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3

Moum, James N. Turbulence Fluxes. Fort Belvoir, VA: Defense Technical Information Center, January 1996. http://dx.doi.org/10.21236/ada329288.

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4

Laganelli, A. L., and S. M. Dash. Turbulence Modeling. Fort Belvoir, VA: Defense Technical Information Center, October 1991. http://dx.doi.org/10.21236/ada415956.

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5

Horton, W., and G. Hu. Plasma turbulence. Office of Scientific and Technical Information (OSTI), July 1998. http://dx.doi.org/10.2172/661635.

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6

Hart, Carl, and Gregory Lyons. A tutorial on the rapid distortion theory model for unidirectional, plane shearing of homogeneous turbulence. Engineer Research and Development Center (U.S.), July 2022. http://dx.doi.org/10.21079/11681/44766.

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The theory of near-surface atmospheric wind noise is largely predicated on assuming turbulence is homogeneous and isotropic. For high turbulent wavenumbers, this is a fairly reasonable approximation, though it can introduce non-negligible errors in shear flows. Recent near-surface measurements of atmospheric turbulence suggest that anisotropic turbulence can be adequately modeled by rapid-distortion theory (RDT), which can serve as a natural extension of wind noise theory. Here, a solution for the RDT equations of unidirectional plane shearing of homogeneous turbulence is reproduced. It is assumed that the time-varying velocity spectral tensor can be made stationary by substituting an eddy-lifetime parameter in place of time. General and particular RDT evolution equations for stochastic increments are derived in detail. Analytical solutions for the RDT evolution equation, with and without an effective eddy viscosity, are given. An alternative expression for the eddy-lifetime parameter is shown. The turbulence kinetic energy budget is examined for RDT. Predictions by RDT are shown for velocity (co)variances, one-dimensional streamwise spectra, length scales, and the second invariant of the anisotropy tensor of the moments of velocity. The RDT prediction of the second invariant for the velocity anisotropy tensor is shown to agree better with direct numerical simulations than previously reported.
7

Clark, T. T., Shi-Yi Chen, L. Turner, and C. Zemach. Turbulence and turbulence spectra in complex fluid flows. Office of Scientific and Technical Information (OSTI), November 1997. http://dx.doi.org/10.2172/544691.

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8

Trowbridge, J. H. Testing Turbulence Closure Models against Oceanic Turbulence Measurements. Fort Belvoir, VA: Defense Technical Information Center, September 2001. http://dx.doi.org/10.21236/ada625214.

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9

Trowbridge, J. H. Testing Turbulence Closure Models Against Oceanic Turbulence Measurements. Fort Belvoir, VA: Defense Technical Information Center, August 2002. http://dx.doi.org/10.21236/ada626861.

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10

Raymond, William H., and Roland B. Stull. CAT (Clear Air Turbulence) Forecasting Using Transilient Turbulence Theory. Fort Belvoir, VA: Defense Technical Information Center, February 1988. http://dx.doi.org/10.21236/ada198768.

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