Relevant bibliographies by topics / Bifurcation turbulente

Contents

  1. Journal articles
  2. Dissertations / Theses
  3. Books
  4. Book chapters
  5. Conference papers

Academic literature on the topic 'Bifurcation turbulente'

Author: Grafiati
Published: 4 June 2021
Last updated: 1 February 2022

Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles

Select a source type:

Consult the lists of relevant articles, books, theses, conference reports, and other scholarly sources on the topic 'Bifurcation turbulente.'

Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.

You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.

Journal articles on the topic "Bifurcation turbulente"

1

MELLIBOVSKY, F., and B. ECKHARDT. "Takens–Bogdanov bifurcation of travelling-wave solutions in pipe flow." Journal of Fluid Mechanics 670 (January 25, 2011): 96–129. http://dx.doi.org/10.1017/s0022112010005239.

Full text
Abstract:
The appearance of travelling-wave-type solutions in pipe Poiseuille flow that are disconnected from the basic parabolic profile is numerically studied in detail. We focus on solutions in the twofold azimuthally-periodic subspace because of their special stability properties, but relate our findings to other solutions as well. Using time-stepping, an adapted Krylov–Newton method and Arnoldi iteration for the computation and stability analysis of relative equilibria, and a robust pseudo-arclength continuation scheme, we unfold a double-zero (Takens–Bogdanov) bifurcating scenario as a function of Reynolds number (Re) and wavenumber (κ). This scenario is extended, by the inclusion of higher-order terms in the normal form, to account for the appearance of supercritical modulated waves emanating from the upper branch of solutions at a degenerate Hopf bifurcation. We provide evidence that these modulated waves undergo a fold-of-cycles and compute some solutions on the unstable branch. These waves are shown to disappear in saddle-loop bifurcations upon collision with lower-branch solutions, in accordance with the bifurcation scenario proposed. The travelling-wave upper-branch solutions are stable within the subspace of twofold periodic flows, and their subsequent secondary bifurcations could contribute to the formation of the phase space structures that are required for turbulent dynamics at higher Re.
APA, Harvard, Vancouver, ISO, and other styles
2

Riols, A., F. Rincon, C. Cossu, G. Lesur, P. Y. Longaretti, G. I. Ogilvie, and J. Herault. "Global bifurcations to subcritical magnetorotational dynamo action in Keplerian shear flow." Journal of Fluid Mechanics 731 (August 14, 2013): 1–45. http://dx.doi.org/10.1017/jfm.2013.317.

Full text
Abstract:
AbstractMagnetorotational dynamo action in Keplerian shear flow is a three-dimensional nonlinear magnetohydrodynamic process, the study of which is relevant to the understanding of accretion processes and magnetic field generation in astrophysics. Transition to this form of dynamo action is subcritical and shares many characteristics with transition to turbulence in non-rotating hydrodynamic shear flows. This suggests that these different fluid systems become active through similar generic bifurcation mechanisms, which in both cases have eluded detailed understanding so far. In this paper, we build on recent work on the two problems to investigate numerically the bifurcation mechanisms at work in the incompressible Keplerian magnetorotational dynamo problem in the shearing box framework. Using numerical techniques imported from dynamical systems research, we show that the onset of chaotic dynamo action at magnetic Prandtl numbers larger than unity is primarily associated with global homoclinic and heteroclinic bifurcations of nonlinear magnetorotational dynamo cycles born out of saddle-node bifurcations. These global bifurcations are found to be supplemented by local bifurcations of cycles marking the beginning of period-doubling cascades. The results suggest that nonlinear magnetorotational dynamo cycles provide the pathway to injection of both kinetic and magnetic energy for the problem of transition to turbulence and dynamo action in incompressible magnetohydrodynamic Keplerian shear flow in the absence of an externally imposed magnetic field. Studying the nonlinear physics and bifurcations of these cycles in different regimes and configurations may subsequently help to understand better the physical conditions of excitation of magnetohydrodynamic turbulence and instability-driven dynamos in a variety of astrophysical systems and laboratory experiments. The detailed characterization of global bifurcations provided for this three-dimensional subcritical fluid dynamics problem may also prove useful for the problem of transition to turbulence in hydrodynamic shear flows.
APA, Harvard, Vancouver, ISO, and other styles
3

Banks, J., and N. W. Bressloff. "Turbulence Modeling in Three-Dimensional Stenosed Arterial Bifurcations." Journal of Biomechanical Engineering 129, no. 1 (July 28, 2006): 40–50. http://dx.doi.org/10.1115/1.2401182.

Full text
Abstract:
Under normal healthy conditions, blood flow in the carotid artery bifurcation is laminar. However, in the presence of a stenosis, the flow can become turbulent at the higher Reynolds numbers during systole. There is growing consensus that the transitional k−ω model is the best suited Reynolds averaged turbulence model for such flows. Further confirmation of this opinion is presented here by a comparison with the RNG k−ϵ model for the flow through a straight, nonbifurcating tube. Unlike similar validation studies elsewhere, no assumptions are made about the inlet profile since the full length of the experimental tube is simulated. Additionally, variations in the inflow turbulence quantities are shown to have no noticeable affect on downstream turbulence intensity, turbulent viscosity, or velocity in the k−ϵ model, whereas the velocity profiles in the transitional k−ω model show some differences due to large variations in the downstream turbulence quantities. Following this validation study, the transitional k−ω model is applied in a three-dimensional parametrically defined computer model of the carotid artery bifurcation in which the sinus bulb is manipulated to produce mild, moderate, and severe stenosis. The parametric geometry definition facilitates a powerful means for investigating the effect of local shape variation while keeping the global shape fixed. While turbulence levels are generally low in all cases considered, the mild stenosis model produces higher levels of turbulent viscosity and this is linked to relatively high values of turbulent kinetic energy and low values of the specific dissipation rate. The severe stenosis model displays stronger recirculation in the flow field with higher values of vorticity, helicity, and negative wall shear stress. The mild and moderate stenosis configurations produce similar lower levels of vorticity and helicity.
APA, Harvard, Vancouver, ISO, and other styles
4

Lopez, Juan M., and Francisco Marques. "Instability of plumes driven by localized heating." Journal of Fluid Mechanics 736 (November 13, 2013): 616–40. http://dx.doi.org/10.1017/jfm.2013.537.

Full text
Abstract:
AbstractPlumes due to localized buoyancy sources are of wide interest owing to their prevalence in many situations. This study investigates the transition from laminar to turbulent dynamics. Several experiments have reported that this transition is sensitive to external perturbations. As such, a well-controlled set-up has been chosen for our numerical study, consisting of a localized heat source at the bottom of an enclosed cylinder whose walls are all maintained at a fixed uniform temperature, except for the localized heat source. At moderate Rayleigh numbers $\mathit{Ra}$, the flow consists of a steady, axisymmetric purely poloidal plume. On increasing $\mathit{Ra}$, the flow undergoes a supercritical Hopf bifurcation to an axisymmetric ‘puffing’ plume, where a vortex ring is periodically emitted from the localized heater. At higher $\mathit{Ra}$, this state becomes unstable to a sequence of symmetry-breaking bifurcations, going through a quasi-periodic ‘fluttering’ stage where the axisymmetric rings are tilted, and other states in which the sequence of tilted rings interact with each other. The sequence of symmetry-breaking bifurcations in the transition to turbulence culminates in a torus breakup event in which all the spatial and spatio-temporal symmetries of the system are broken.
APA, Harvard, Vancouver, ISO, and other styles
5

Swanson, L. W., and I. Catton. "Enhanced Heat Transfer Due to Secondary Flows in Mixed Turbulent Convection." Journal of Heat Transfer 109, no. 4 (November 1, 1987): 943–46. http://dx.doi.org/10.1115/1.3248207.

Full text
Abstract:
An experimental study of the fluid flow and heat transfer phenomena associated with opposing mixed turbulent convection in vertical ducts has been conducted. The duct considered had vertical and horizontal aspect ratios of 24.4 and 9.7, respectively. The working fluid was Freon-113, providing a Prandtl number of approximately 6.5. The results showed that a number of flow bifurcations occurred as GrDh/ReDh2 was increased. The first bifurcation observed was from parallel turbulent mean flow to a large single flow cell in the x−z plane. This occurred in the neighborhood of GrDh/ReDh2 = 2. Further bifurcations to multiple cells and eventually pure large-scale chaos were also observed. A correlation for the enhanced heat transfer was found to be NuDh/NuDh,0 = 1.0 + 0.9[ln(GrDh/ReDh2 + 1)]1.39, where NuDh,0 is the Petukhov–Virillov correlation for pure forced turbulent convection.
APA, Harvard, Vancouver, ISO, and other styles
6

Howard, L. N., and R. Krishnamurti. "Large-scale flow in turbulent convection: a mathematical model." Journal of Fluid Mechanics 170 (September 1986): 385–410. http://dx.doi.org/10.1017/s0022112086000940.

Full text
Abstract:
A mathematical model of convection, obtained by truncation from the two-dimensional Boussinesq equations, is shown to exhibit a bifurcation from symmetrical cells to tilted non-symmetrical ones. A subsequent bifurcation leads to time-dependent flow with similarly tilted transient plumes and a large-scale Lagrangian mean flow. This change of symmetry is similar to that occurring with the advent of a large-scale flow and transient tilted plumes seen in laboratory experiments on turbulent convection at high Rayleigh number. Though not intended as a description of turbulent convection, the model does bring out in a theoretically tractable context the possibility of the spontaneous change of symmetry suggested by the experiments.Further bifurcations of the model lead to stable chaotic phenomena as well. These are numerically found to occur in association with heteroclinic orbits. Some mathematical results clarifying this association are also presented.
APA, Harvard, Vancouver, ISO, and other styles
7

Bakas, Nikolaos A., and Petros J. Ioannou. "Is spontaneous generation of coherent baroclinic flows possible?" Journal of Fluid Mechanics 862 (January 15, 2019): 889–923. http://dx.doi.org/10.1017/jfm.2018.928.

Full text
Abstract:
Geophysical turbulence is observed to self-organize into large-scale flows such as zonal jets and coherent vortices. Previous studies of barotropic $\unicode[STIX]{x1D6FD}$-plane turbulence have shown that coherent flows emerge from a background of homogeneous turbulence as a bifurcation when the turbulence intensity increases. The emergence of large-scale flows has been attributed to a new type of collective, symmetry-breaking instability of the statistical state dynamics of the turbulent flow. In this work, we extend the analysis to stratified flows and investigate turbulent self-organization in a two-layer fluid without any imposed mean north–south thermal gradient and with turbulence supported by an external random stirring. We use a second-order closure of the statistical state dynamics, that is termed S3T, with an appropriate averaging ansatz that allows the identification of statistical turbulent equilibria and their structural stability. The bifurcation of the statistically homogeneous equilibrium state to inhomogeneous equilibrium states comprising zonal jets and/or large-scale waves when the energy input rate of the excitation passes a critical threshold is analytically studied. Our theory predicts that there is a large bias towards the emergence of barotropic flows. If the scale of excitation is of the order of (or larger than) the deformation radius, the large-scale structures are barotropic. Mixed barotropic–baroclinic states with jets and/or waves arise when the excitation is at scales shorter than the deformation radius with the baroclinic component of the flow being subdominant for low energy input rates and insignificant for higher energy input rates. The predictions of the S3T theory are compared with nonlinear simulations. The theory is found to accurately predict both the critical transition parameters and the scales of the emergent structures but underestimates their amplitude.
APA, Harvard, Vancouver, ISO, and other styles
8

Deepti, K., and M. Aditya. "Importance of Proximal Angle in Generation of Abnormal Plaque at Coronary Bifurcation Lesions." Indian Journal of Cardiovascular Disease in Women WINCARS 01, no. 01 (March 2016): 008–13. http://dx.doi.org/10.1055/s-0038-1656469.

Full text
Abstract:
AbstractBACKGROUND: Changing of linear blood flow to turbulence at branching points predisposes to development of obstructive coronary lesions. We hypothesize that in addition to bifurcation angle (BA), proximal (PA) and third angle (TA) of branching site are important in generating more vertices of blood flow.METHODS: 65 normal and 36 significantly diseased LAD – D1, 72 normal and 27 significantly diseased LCX – OM, 73 normal and 16 significantly diseased RCA – PDA – PLV and 34 normal and 14 significantly diseased LMCA – LAD – LCX bifurcations were analyzed with QCA.RESULTS: In LAD – D1 normal vs. significantly diseased bifurcations BA and PA were 78.2±13.2 vs. 65.1±11.3 (p <0.000) and 122.7±13.8 vs. 131.6.36±12.5 (p <0.001) respectively. In LCX – OM normal vs. significantly diseased bifurcations BA and PA were 76.8±13.6 vs. 60.7±13.8 (p=0.000) and 125.1±13.5 vs. 137.8±12.8 (p <0.000) respectively. In RCA - PDA – PLV normal vs. significantly diseased bifurcations BA, PA and TA were 91.1±13.8 vs. 71.5±15.9 (p 0.004), 113.0±14.1 vs. 128.4±20.2 (p=0.000), 118.2±21.7 vs. 133.8±12.4 (p=0.007) respectively. In LMCA –LAD – LCX normal vs. significantly diseased bifurcations BA, PA and TA were 84.0±39.1 vs. 73.0±17.6 (p >0. 32), 123.2±26.3 vs. 115.3±30.4 (p > 0.38), 130.3±27.3 vs. 137.5±33.5 (p >0.45) respectively. There was a significant difference but no correlation between the angles in normal and diseased bifurcation segment. We derived logistic regression equations for predicting the disease in different coronary bifurcations.CONCLUSION: In LAD - D1, LCX – OM and RCA – PDA – PLV bifurcations lesser the BA, greater the PA, were more likely to develop significant lesion, which was not true in LMCA – LAD – LCX bifurcation.
APA, Harvard, Vancouver, ISO, and other styles
9

Nowakowski, Mirosław, Krzysztof Sibilski, Anna Sibilska-Mroziewicz, and Andrzej Żyluk. "Bifurcation Flight Dynamic Analysis of a Strake-Wing Micro Aerial Vehicle." Applied Sciences 11, no. 4 (February 8, 2021): 1524. http://dx.doi.org/10.3390/app11041524.

Full text
Abstract:
Non-linear phenomena are particularly important in -flight dynamics of micro-class unmanned aerial vehicles. Susceptibility to atmospheric turbulence and high manoeuvrability of such aircraft under critical flight conditions cover non-linear aerodynamics and inertia coupling. The theory of dynamical systems provides methodology for studying systems of non-linear ordinary differential equations. The bifurcation theory forms part of this theory and deals with stability changes leading to qualitatively different system responses. These changes are called bifurcations. There is a number of papers, the authors of which applied the bifurcation theory for analysing aircraft flight dynamics. This article analyses the dynamics of critical micro aerial vehicle flight regimes. The flight dynamics under such conditions is highly non-linear, therefore the bifurcation theory can be applied in the course of the analysis. The application of the theory of dynamical systems enabled predicting the nature of micro aerial vehicle motion instability caused by bifurcations and analysing the post-bifurcation microdrone motion. This article presents the application of bifurcation analysis, complemented with time-domain simulations, to understand the open-loop dynamics of strake-wing micro aerial vehicle model by identifying the attractors of the dynamic system that manages upset behaviour. A number of factors have been identified to cause potential critical states, including non-oscillating spirals and oscillatory spins. The analysis shows that these spirals and spins are connected in a one-parameter space and that due to improper operation of the autopilot on the spiral, it is possible to enter the oscillatory spin.
APA, Harvard, Vancouver, ISO, and other styles
10

Yang, K. T. "Transitions and Bifurcations in Laminar Buoyant Flows in Confined Enclosures." Journal of Heat Transfer 110, no. 4b (November 1, 1988): 1191–204. http://dx.doi.org/10.1115/1.3250620.

Full text
Abstract:
Recent advances in experimental and numerical studies of flow instability, bifurcation, and transition to turbulence for buoyant flow in three-dimensional rectangular enclosures heated from below and from the sides are reviewed, with emphasis on the physical causes of various instabilities and bifurcations as well as the observed and calculated routes to chaotic motions. Also discussed are the current successes and shortcomings of numerical simulations of experimental data and observations. Finally, unresolved critical issues and needs for future research are also addressed.
APA, Harvard, Vancouver, ISO, and other styles
More sources

Dissertations / Theses on the topic "Bifurcation turbulente"

1

Lefort, Eric. "Caractérisation des bifurcations et de la dynamique d'une lentille thermique par analyse spectrale." Rouen, 1987. http://www.theses.fr/1987ROUES019.

Full text
Abstract:
Un faisceau laser est focalisé sur la face d'entrée d'une cuve transparente remplie d'un liquide absorbant. Une lentille thermique est formée; les oscillations de la lentille sont la manifestation visible d'oscillations hydrodynamiques du liquide dans la cuve. Le système présente un comportement de transition laminaire turbulente, un certain nombre de bifurcations ayant été observées. Analyse spectrale du signal temporel
APA, Harvard, Vancouver, ISO, and other styles
2

Coiret, Alex. "Mise en évidence et étude expérimentale d'une bifurcation turbulente réductrice des bruits auto-entretenus dans les écoulements." La Rochelle, 1999. http://www.theses.fr/1999LAROS038.

Full text
Abstract:
Le sujet est lié à l'interaction entre une onde acoustique et une surface fluide instable. Un processus d'auto-entretien peut se créer dans une cavité, aboutissant à la génération de bruits auto-entretenus, qui peuvent être intenses. L’objectif est la réduction des bruits de ce type créés par les écoulements. Le processus peut, qualitativement, être décrit en termes simples: un premier obstacle engendre un détachement de tourbillons. Ceux-ci, en venant frapper un deuxième obstacle à l'aval, engendrent des ondes acoustiques qui remontent l'écoulement. Ces ondes peuvent alors commander le détachement tourbillonnaire amont: une énergie, et donc une nuisance sonore considérable peut alors être engendrée par ce phénomène d'auto-entretien. La réduction de bruit est classiquement traitée, aux basses fréquences par des méthodes de contrôle actif, aux fréquences plus élevées par des méthodes passives (matériaux absorbants par exemple). Nous proposons une méthode alternative nouvelle qui utilise les propriétés aérodynamiques d'écoulements auxiliaires venant inhiber le processus de bouclage aéroacoustique. Le résultat le plus remarquable est la mise en évidence expérimentale d'un chemin stable d'une bifurcation turbulente qui a la propriété de réduire le niveau sonore des bruits auto entretenus dans un écoulement. Des modifications géométriques mineures et localisées sont utilisées, sans mettre en cause la fonction principale de l'installation. Les secteurs d'application concernés relèvent aussi bien du domaine du transport, des machines industrielles, que du domaine des faibles vitesses dans les ambiances habitables.
APA, Harvard, Vancouver, ISO, and other styles
3

Persillon, Hélène. "Analyse physique par simulation numérique bi- et tri-dimensionnelle de la transition laminaire-turbulente dans l'écoulement autour d'un cylindre." Toulouse, INPT, 1995. http://www.theses.fr/1995INPT100H.

Full text
Abstract:
Les equations de navier-stokes tridimensionnelles ont ete resolues pour predeterminer l'ecoulement derriere un cylindre circulaire. Les caracteristiques dynamiques de cette simulation ont ete comparees a celles issues du calcul bidimensionnel et ont permis de faire apparaitre la bifurcation tridimensionnelle ainsi que des nouvelles structures (tourbillons longitudinaux et transversaux). Les discontinuites observees experimentalement dans la relation du nombre de strouhal en fonction du nombre de reynolds ont ete simulees et expliquees. L'etude spectrale du sillage et l'evolution spatiale de l'instabilite de von karman ont egalement ete examinees dans cette etude
APA, Harvard, Vancouver, ISO, and other styles
4

Le, Quéré Patrick. "Etude de la transition à l'instationnarité des écoulements de convection naturelle en cavité verticale différentiellement chauffée par méthodes spectrales chebyshev." Poitiers, 1987. http://www.theses.fr/1987POIT2003.

Full text
Abstract:
On developpe un algorithme d'integration des equations bidimensionnelles instationnaires de navier-stokes d'un fluide de bomussinesq qui couple une discretisation spatiale des variables dependantes par approximation spectrale de chebyshev a une discretisation temporelle de type differences-finies du second ordre. Les cavites etudiees ont des rapports de forme de 1 a 10. Suivant le rapport de forme et les conditions aux limites thermiques, il existe trois mecanismes differents de transition a l'instationnarite qui correspondent a des bifurcations de hopf supercritiques
APA, Harvard, Vancouver, ISO, and other styles
5

Boronski, Piotr. "Méthode des potentiels poloïdal-toroïdal appliquée à l'écoulement de von Kármán en cylindre fini." Phd thesis, Ecole Polytechnique X, 2005. http://tel.archives-ouvertes.fr/tel-00162594.

Full text
Abstract:
Ce travail est motivé par l'effort international actuel de créer expérimentalement une dynamo fluide auto-entretenue. L'effet dynamo, dont l'existence a été prevu par Larmor au début du XXème siècle, est considéré comme étant responsable de la production du champ matnétique terrestre et d'autres objets célestes par l'intermédiaire de l'écoulement d'un fluide conducteur. Afin d'étudier numériquement l'écoulement de von Kármán, qui modélise la configuration d'une expérience dynamo mise en place à Cadarache, nous avons développé une approche numérique originale permettant la résolution des équations magnétohydrodynamiques dans une géométrie dylindrique en formulation potentielle. La décomposition en potentiels poloïdal et toroïdal a été utilisée pour garantir la nature solénoïdale des champs de vitesse et magnétique. Nous utilisons la technique de la matrice d'influence pour satisfaire aux conditions aux limites et aux conditions de continuité du champ magnétique à la paroi du cylindre. La grande puissance de calcul, résultant de la parallélisation MPI du code, a presmis de l'appliquer deux problèmes concernant la turbulence dans la géométrie cylindrique : la turbulence axisymétrique et une bifurcation entre états turbulents.
APA, Harvard, Vancouver, ISO, and other styles
6

Busquet, Denis. "Study of a high Reynolds number flow around a two dimensional airfoil at stall : an approach coupling a RANS framework and bifurcation theory." Thesis, Institut polytechnique de Paris, 2020. http://www.theses.fr/2020IPPAX027.

Full text
Abstract:
Le phénomène de décrochage est souvent décrit comme une chute soudaine de portance lorsque l'angle d'incidence augmente. Ce phénomène est préjudiciable aux avions et aux hélicoptères et limite leur enveloppe de vol. Plusieurs études numériques et expérimentales, particulièrement centrées sur le décrochage statique (i.e. pour des ailes fixes), ont révélé des phénomènes apparaissant proche de l'angle de décrochage : des oscillations basses fréquences et une hystérésis des coefficients aérodynamiques. Le premier phénomène se traduit par une oscillation de la portance entre une valeur maximale et une valeur minimale obtenues quand l'écoulement est respectivement attaché ou détaché. Le nombre de Strouhal associé (St ~ 0.02) est habituellement un ordre de grandeur plus faible que le nombre de Strouhal (St ~ 0.2) du lâcher tourbillonnaire qui apparaît pour de plus grandes incidences. Le second phénomène est caractérisé par l'existence de solutions moyennées en temps autour de l'angle de décrochage qui diffèrent selon que l'angle d'attaque est augmenté ou diminué.L'objectif de cette thèse est d'avoir une meilleure compréhension de l'origine du décrochage et de ces deux phénomènes grâce à des simulations numériques d'écoulements turbulents modélisés par une approche RANS (Reynolds-Averaged Navier-Stokes). Une combinaison de diverses approches numériques et théoriques (simulations instationnaires, continuation de solutions stationnaires, stabilité linéaire et analyse de bifurcation) est développée et appliquée dans le cas du décrochage d'un profil 2D de pale d'hélicoptère, le OA209, à bas nombre de Mach (M~0.2) et haut nombre de Reynolds (Re~1.8x10^6).Des solutions stationnaires sont calculées pour différents angles d'attaques en considérant le modèle de turbulence de Spalart-Allmaras et en utilisant des méthodes de continuation (continuation naïve et méthode du pseudo-arclength). Les résultats mettent en évidence une branche supérieure (à haute portance), une branche inférieure (à basse portance) et, entre les deux, une branche du milieu. Pour un même angle d'attaque, des solutions coexistent proche de l’angle de décrochage sur chacune des branches, ce qui est caractéristique d’un phénomène d'hystérésis. Des analyses de stabilité linéaire réalisées autour de ces états d'équilibres révèlent l'existence d'un mode instable basse fréquence associé au décrochage. L'évolution des valeurs propres associées à ce mode le long des branches stationnaires nous permet d'établir une première version du diagramme de bifurcation. Afin de le compléter, des calculs RANS instationnaires sont réalisés et des cycles limites basse fréquence sont identifiés sur une plage réduite d'angles d'attaque proches du décrochage. Ces solutions périodiques sont caractérisées par des valeurs de portance maximales et minimales plus grandes et plus petites que celles des solutions stationnaires à haute et basse portance associées, respectivement. Pour clarifier la formation et la disparition de ce cycle limite basse fréquence et permettre une meilleure compréhension du scénario de bifurcation, un modèle à une équation reproduisant les caractéristiques linéaires du phénomène est proposé. Ce modèle non-linéaire du décrochage statique est calibré sur les états stationnaires et leur comportement linéaire obtenus par calculs RANS. Une étude du comportement non-linéaire de ce modèle révèle un scenario possible qui pourrait conduire à l'apparition et à la disparition du cycle limite basse fréquence. Finalement, le cas d'un NACA0012 à nombre de Reynolds Re~1.0x10^6 est considéré pour valider la robustesse du scenario identifié
Airfoil stall is commonly described as a sudden drop of lift when increasing the angle of attack. This phenomenon is detrimental to aircrafts and helicopters, since it strongly limits their flight envelope. Past experimental and numerical investigations, specifically dedicated to static stall (i.e. for rigid wings), have clearly identified two phenomena which appear close to the stall angle: low-frequency oscillations and hysteresis of the lift coefficient. The first one is an oscillation of the lift between maximal and minimal values obtained when the instantaneous flow is attached and fully separated, respectively. The corresponding Strouhal number (St ~ 0.02) is usually an order of magnitude lower than the Strouhal number (St ~ 0.2) of the vortex-shedding that may appear for larger angles of attack. The second phenomenon is characterized by the existence of different time-averaged solutions around the stall angle depending on whether the angle of attack is increased or decreased.The objective of this thesis is to better understand the origin of stall and of these two phenomena using numerical simulations of turbulent flows modelled in the RANS (Reynolds-Averaged Navier-Stokes) framework. A combination of various numerical and theoretical approaches (unsteady simulations, continuation of steady solutions, linear stability and bifurcation analyses) have been developed and applied to the stall of a 2D helicopter blade airfoil OA209 at low Mach number (M~0.2) and high Reynolds number (Re~1.8x10^6).Steady RANS computations are performed using Spalart-Allmaras model to obtain steady states for several angles of attack taking advantage of continuation methods (naive continuation and pseudo-arclength method). The results highlight one upper branch (of high lift), one lower branch (of low lift) and, in between, a middle branch. Close to stall, for a same angle of attack, solutions coexist on each branch, characterizing a hysteresis phenomenon. Linear stability analyses performed around these equilibrium states reveal the existence of a low-frequency unstable mode associated to stall. The evolution of the corresponding eigenvalues along the branches of steady solutions allows us to establish a first sketch of the bifurcation scenario. Unsteady RANS computations are carried out to complete it. Low-frequency limit-cycle solutions have been identified in a narrow range of angles of attack close stall. These periodic solutions are characterized by maximal and minimal instantaneous values of the lift that are larger and lower than the associated high-lift and low-lift steady solutions, respectively. To clarify the formation and disappearance of this low-frequency limit cycle, and thus improve our knowledge about the bifurcation scenario, a one-equation model reproducing the linear characteristics of the phenomenon is proposed. This nonlinear static-stall model is calibrated on the steady states and their linear behavior obtained with RANS computations. A study of the nonlinear behavior of this model then reveals a possible scenario leading to the appearance and collapsing of the low frequency limit cycle. Finally, the case of a NACA0012 at Re~1.0x10^6 is considered to check the robustness of the scenario identified
APA, Harvard, Vancouver, ISO, and other styles
7

Ravelet, Florent. "Bifurcations globales hydrodynamiques et magnetohydrodynamiques dans un ecoulement de von Karman turbulent." Phd thesis, Ecole Polytechnique X, 2005. http://tel.archives-ouvertes.fr/tel-00011016.

Full text
Abstract:
Nous étudions ici expérimentalement l'écoulement de von Kármán, produit dans un cylindre entre deux turbines coaxiales. Nous nous plaçons plus particulièrement en régime de turbulence pleinement développée, pour un écoulement contrarotatif forcé inertiellement. Nous étudions dans un premier temps la transition à la turbulence de cet écoulement fermé, depuis les régimes laminaires. Nous insistons sur le rôle des grandes échelles lentement variables
de la couche de mélange. Nous étudions alors la stabilité de l'écoulement moyen et mettons en évidence une bifurcation des grandes échelles en régime turbulent. Nous étudions statistiquement le rôle des fluctuations sur le déclenchement des transitions. Ces transitions peuvent également avoir une dynamique intermittente à temps long.
Dans un deuxième temps, nous étudions la possibilité d'un effet dynamo pour le champ de vitesse moyenné dans le temps. L'effet dynamo est une instabilité du champ magnétique dans un fluide conducteur en écoulement. Nous définissons ainsi la configuration de l'expérience VKS2, en sodium liquide, et discutons enfin les premiers résultats de l'expérience. Nous y retrouvons la trace des instationnarités des grandes échelles de l'écoulement.
APA, Harvard, Vancouver, ISO, and other styles
8

Ravelet, Florent. "Bifurcations globales hydrodynamiques et magnétohydrodynamiques dans un écoulement de von Karman turbulent." Palaiseau, Ecole polytechnique, 2005. http://www.theses.fr/2005EPXX0016.

Full text
APA, Harvard, Vancouver, ISO, and other styles
9

Cao, Norman Ming-Chen. "Characterization of a turbulence bifurcation underlying L-mode confinement transitions on Alcator C-Mod." Thesis, Massachusetts Institute of Technology, 2020. https://hdl.handle.net/1721.1/127313.

Full text
Abstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2020
Cataloged from the official PDF of thesis.
Includes bibliographical references (pages 153-164).
Empirical energy confinement scalings play a crucial role in the design of tokamak fusion reactors, measuring how quickly energy is transported by turbulence from the fusion-producing core to conduction loss at the edge. Unfortunately, experiments often exhibit discontinuous changes in scaling behavior as the plasma parameters are varied, termed confinement transitions. Navigating these transitions requires an understanding of the physical origin and limits of confinement scalings, and is crucial for retiring the physics risk of extrapolating empirical results to future reactors. This thesis explores the connection between two universally observed transitions in tokamak transport: the Linear to Saturated Ohmic Confinement (LOC/SOC) transition and the concomitant intrinsic rotation reversal. Analysis and modeling of rotation reversal hysteresis experiments show that a single turbulent bifurcation underlies both transitions on Alcator C-Mod.
Plasmas on either side of the reversal exhibit different toroidal rotation profiles and therefore different turbulence characteristics despite profiles of density and temperature which are indistinguishable within measurement uncertainty. Elements of this bifurcation are also shown to persist for auxiliary heated L-modes. Within a reduced quasilinear transport model, the deactivation of subdominant (in linear growth rate and contribution to heat transport) ion temperature gradient (ITG) and trapped electron mode (TEM) instabilities is identified as the only possible change in turbulence across the reversal which is consistent with the measured profiles and inferred heat and particle fluxes. Experimental constraints on a possible change from strong to weak turbulence, outside the description of the quasilinear model, are also discussed.
These results indicate an explanation for the LOC/SOC transition that provides a mechanism for the hysteresis through the dynamics of subdominant modes and changes in their relative populations, and does not involve a change in the most linearly unstable ion-scale drift-wave instability. This work highlights the importance of considering the dynamics of the entire mode spectrum, and not just the dominant modes, in making predictions about transport and confinement regimes.
by Norman Ming-Chen Cao.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Nuclear Science and Engineering
APA, Harvard, Vancouver, ISO, and other styles
10

Thiruvengadam, Magesh. "Three-dimensional laminar and turbulent convection in separated flow." Diss., Rolla, Mo. : Missouri University of Science and Technology, 2008. http://scholarsmine.mst.edu/thesis/pdf/Thiruvengadam_09007dcc80557d79.pdf.

Full text
Abstract:
Thesis (Ph. D.)--Missouri University of Science and Technology, 2008.
Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed August 21, 2008) Includes bibliographical references.
APA, Harvard, Vancouver, ISO, and other styles
More sources

Books on the topic "Bifurcation turbulente"

1

Invariant manifold theory for hydrodynamic transition. Harlow, Essex, England: Longman Scientific & Technical, 1990.

Find full text
APA, Harvard, Vancouver, ISO, and other styles
2

Murray, Tobak, and Ames Research Center, eds. Observations, theoretical ideas, and modeling of turbulent flows - past, present, and future. Moffett Field, Calif: National Aeronautics and Space Administration, Ames Research Center, 1985.

Find full text
APA, Harvard, Vancouver, ISO, and other styles
3

Archibald, Robert B. The Evolutionary Future. Oxford University Press, 2017. http://dx.doi.org/10.1093/acprof:oso/9780190251918.003.0010.

Full text
Abstract:
The higher education system is resilient. Disruption is not around the corner. Yet the future is not secure. There has been a growing bifurcation of the system into a set of well-resourced institutions that serve families with means and a group of underresourced institutions that serve the bulk of the nation’s underprivileged students. The schools most at risk are nonselective public institutions and financially weaker small private colleges. This chapter describes how the turbulence buffeting the higher education system is likely to play out among our diverse higher education institutions, and how this may affect social mobility in the future.
APA, Harvard, Vancouver, ISO, and other styles

Book chapters on the topic "Bifurcation turbulente"

1

Lukaschuk, S. N., V. S. L’vov, A. A. Predtechensky, and A. I. Chernykh. "First Bifurcations in Circular Couette Flow: Laboratory and Numerical Experiments." In Laminar-Turbulent Transition, 653–58. Berlin, Heidelberg: Springer Berlin Heidelberg, 1985. http://dx.doi.org/10.1007/978-3-642-82462-3_80.

Full text
APA, Harvard, Vancouver, ISO, and other styles
2

Christov, C. I., and V. P. Nartov. "On a Bifurcation and Emerging of a Stochastic Solution in a Variational Problem for Poiseuille Flows." In Laminar-Turbulent Transition, 227–32. Berlin, Heidelberg: Springer Berlin Heidelberg, 1985. http://dx.doi.org/10.1007/978-3-642-82462-3_28.

Full text
APA, Harvard, Vancouver, ISO, and other styles
3

Busse, F. H., and R. M. Clever. "Higher Bifurcations in Fluid Flows and Coherent Structures in the Turbulent State." In Advances in Turbulence VI, 309–12. Dordrecht: Springer Netherlands, 1996. http://dx.doi.org/10.1007/978-94-009-0297-8_87.

Full text
APA, Harvard, Vancouver, ISO, and other styles
4

Moloney, J. V. "Global Bifurcations and Turbulence in a Passive Optical Resonator." In Instabilities and Chaos in Quantum Optics, 139–73. Berlin, Heidelberg: Springer Berlin Heidelberg, 1987. http://dx.doi.org/10.1007/978-3-642-71708-6_7.

Full text
APA, Harvard, Vancouver, ISO, and other styles
5

Aubry, N., and S. Sanghi. "Bifurcations and bursting of streaks in the turbulent wall layer." In Fluid Mechanics and Its Applications, 227–51. Dordrecht: Springer Netherlands, 1991. http://dx.doi.org/10.1007/978-94-015-7904-9_15.

Full text
APA, Harvard, Vancouver, ISO, and other styles
6

Minea, Gheorghe. "Loss of Stability of the Globally Unique Steady-State Equilibrium and the Bifurcation of Closed Orbits in a Class of Navier-Stokes Type Dynamical Systems." In Turbulence in Fluid Flows, 101–22. New York, NY: Springer New York, 1993. http://dx.doi.org/10.1007/978-1-4612-4346-5_7.

Full text
APA, Harvard, Vancouver, ISO, and other styles
7

Busse, F. H., and R. M. Clever. "Higher Order Bifurcations in Fluid Systems and Coherent Structures in Turbulence." In Nonlinear Coherent Structures in Physics and Biology, 405–16. Boston, MA: Springer US, 1994. http://dx.doi.org/10.1007/978-1-4899-1343-2_65.

Full text
APA, Harvard, Vancouver, ISO, and other styles
8

Vasanta Ram, Venkatesa I., and Burkhard Müller. "Bifurcation characteristics of the channel flow on a rotating system undergoing transition under the influence of the Coriolis force." In Seventh IUTAM Symposium on Laminar-Turbulent Transition, 597–600. Dordrecht: Springer Netherlands, 2009. http://dx.doi.org/10.1007/978-90-481-3723-7_109.

Full text
APA, Harvard, Vancouver, ISO, and other styles
9

Arecchi(a), F., R. Meucci, G. Puccioni, and J. Tredicce. "Experimental Evidence of Subharmonic Bifurcations, Multistabilìty, and Turbulence in a Q-Switched Gas Laser." In Universality in Chaos, 170–73. CRC Press Taylor & Francis Group 6000 Broken Sound Parkway NW, Suite 300 Boca Raton, FL 33487-2742: CRC Press, 2017. http://dx.doi.org/10.1201/9780203734636-16.

Full text
APA, Harvard, Vancouver, ISO, and other styles
10

Radhakrishnan, H., and S. Kassinos. "Numerical Modeling of Turbulent Airflow and Particle Deposition in a Bifurcating Airway Model." In IFMBE Proceedings, 2089–92. Berlin, Heidelberg: Springer Berlin Heidelberg, 2009. http://dx.doi.org/10.1007/978-3-642-03882-2_554.

Full text
APA, Harvard, Vancouver, ISO, and other styles

Conference papers on the topic "Bifurcation turbulente"

1

Mofakham, Amir A., Lin Tian, and Goodarz Ahmadi. "Near Wall Turbulence Effects on Particle Transport and Deposition in Human Tracheobronchial Multi-Level Bifurcation Model." In ASME/JSME/KSME 2015 Joint Fluids Engineering Conference. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/ajkfluids2015-26336.

Full text
Abstract:
Transport and deposition of micro and nano-particles in the upper tracheobronchial tree were analyzed using a multi-level asymmetric lung bifurcation model. The multi-level lung model is flexible and computationally efficient by fusing sequence of individual bifurcations with proper boundary conditions. Trachea and the first two generations of the tracheobronchial airway were included in the analysis. In these regions, the airflow is in turbulent regime due to the disturbances induced by the laryngeal jet. Anisotropic Reynolds stress transport turbulence model (RSTM) was used for mean the flow simulation, together with the enhanced two-layer model boundary conditions. Particular attention is given to evaluate the importance of the “quadratic variation of the turbulent fluctuations perpendicular to the wall” on particle deposition in the upper tracheobroncial airways.
APA, Harvard, Vancouver, ISO, and other styles
2

Xu, Qihang, and Ramesh K. Agarwal. "Blood Flow Simulations of Particle Trapping in Models of Arterial Bifurcations." In ASME 2020 Fluids Engineering Division Summer Meeting collocated with the ASME 2020 Heat Transfer Summer Conference and the ASME 2020 18th International Conference on Nanochannels, Microchannels, and Minichannels. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/fedsm2020-20042.

Full text
Abstract:
Abstract This paper describes the particle trapping mechanism in blood flow in different arterial bifurcation models. For validation of CFD calculations, a T-junction model and a Y-junction model are analyzed. In both the models, there is one inlet pipe with two outlet pipes creating a symmetric bifurcation at some angle from the centerline of the inlet pipe. Naiver-Stokes (RANS) equations are solved for single phase laminar flow using the commercial CFD software ANSYS Fluent. After validation, Eulerian simulations are performed by using the Discrete Phase Model (DPM) for two-phase flow with particles injected in different bifurcation models with bifurcation angle of an outlet pipe varying from 80° to 100° w.r.t the centerline of the inlet pipe (90° being the bifurcation angle of T-junction). By changing the average Reynolds number of the flow and the injected particle diameters, the mechanism of particle trapping is investigated in laminar flow. The contours of velocity magnitude, pressure and wall shear stress are also obtained and analyzed. It is found that the particle trapping increases as the bifurcation angle decreases from 90° and becomes negligible as the bifurcation angle increases from 90°. This is a very important result which has never been reported in the previous literature. In addition, turbulent flow computations for T-junction flow are performed using the SST k-ω and Wray-Agarwal turbulence models. Finally, the influence of stenosis in Y-junction is studied and analyzed. The results have implications in understanding the hemodynamic flows in arterial bifurcations without and with stenosis.
APA, Harvard, Vancouver, ISO, and other styles
3

Radulescu, Victorita. "Experimental and Numerical Modeling of Viscous Fluid Flow in Bifurcated Long Pipes for Oil Transport." In ASME 2020 Fluids Engineering Division Summer Meeting collocated with the ASME 2020 Heat Transfer Summer Conference and the ASME 2020 18th International Conference on Nanochannels, Microchannels, and Minichannels. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/fedsm2020-20447.

Full text
Abstract:
Abstract The present paper presents some experimental and numerical modeling of the Newtonian and viscoelastic flows in bifurcated configurations of pipes, for stationary and non-permanent regimes. The main purpose of this study is to select an optimal design of the pipes ramifications, for minimizing the local pressure losses and to improve the efficiency of fluid transportation. The method is based on the transformation of the flow field obtained with particle image visualization technique, for different Reynolds numbers. Based on experimental results will be established optimum geometry of the ramifications. The results will be used as the boundary conditions for numerical modeling. The experimental measurements were performed into a closed circuit of pipes, with different diameters, consisting of a centrifugal pump supplied by a tank, sensors for estimating the pressure losses and devices for measuring the flow rate. It is detailed presented in a dedicated paragraph. The main pipe is connected to a transparent bifurcation with branches at different angles from the main pipe axis. The measurements illustrate that the flow has different aspects, depending on the bifurcation’s angle. The numerical simulations are performed with Fluent CFD based on the volume numerical method, to obtain the Navier-Stokes solutions for the Newtonian model in the laminar or turbulent flow conditions. A pre-processor has been used to create the geometry of the bifurcation and to generate the mesh. The 3D-flow domain contains 944390 volumes, tetrahedral hybrid. It was obtained the numerical solutions of the fluid flow in branching pipes for the Reynolds numbers from 1000 up to 40000. The governing equations were assumed from the k-ε model for turbulence flow, the equation of continuity, equation of fluid motion, and the transport equation. Finally, some conclusions and references are presented.
APA, Harvard, Vancouver, ISO, and other styles
4

Guzma´n, Amador M., and Fernando A. Villar. "Flow Bifurcations and Heat Transfer Enhancement in Asymmetric Grooved Channels." In ASME 2005 Summer Heat Transfer Conference collocated with the ASME 2005 Pacific Rim Technical Conference and Exhibition on Integration and Packaging of MEMS, NEMS, and Electronic Systems. ASMEDC, 2005. http://dx.doi.org/10.1115/ht2005-72314.

Full text
Abstract:
Numerical investigations of the flow bifurcations, transition scenario and heat transfer enhancement in asymmetric grooved channels are performed by direct numerical simulations of the mass, momentum and energy equations. The governing equations are solved for laminar and time-dependent transitional flow regimes by the spectral element method in a periodic computational domain with appropriated boundary conditions. Numerical results show a flow transition scenario with two Hopf bifurcations B1 and B2, occurring in critical Reynolds numbers Rec1 y Rec2, respectively. Fundamental frequencies ω1 and ω2, and super harmonic combinations of both develop as the Reynolds number increases from a laminar to higher transitional flow regime. Numerical calculations demonstrate that the time-average mean Nusselt number (the non-dimensional heat transfer rate), increases significantly as the flow passes from a laminar to a periodic—and then to a quasi-periodic flow regime. This increase is accompanied by a reasonable increase in both the friction factor and the pumping power. The obtained behavior is comparable to other geometries and configurations as well as to previously reported numerical results for the studied geometry. This numerical investigation shows a transition scenario at the onset of turbulence, similar to the Ruelle-Takens-Newhouse scenario, which has not been found or reported by other researchers using this geometry. The numerical simulation results also show the existence of a bifurcation scenario that develops a path-dependent flow and heat transport behavior. In the vicinity of the first Hopf flow bifurcation (and consequently, the critical Reynolds number Rec1), the resulting stable time periodic flow depends on both the initial flow conditions and the way in which the incremental process to higher flow regimes is carried out.
APA, Harvard, Vancouver, ISO, and other styles
5

Singh, Samarjeet, Amitesh Roy, K. V. Reeja, Asalatha Nair, Swetaprovo Chaudhuri, and R. I. Sujith. "Intermittency, Secondary Bifurcation and Mixed-Mode Oscillations in a Swirl-Stabilized Annular Combustor: Experiments and Modeling." In ASME Turbo Expo 2020: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/gt2020-15356.

Full text
Abstract:
Abstract We experimentally study thermoacoustic transitions in an annular combustor consisting of sixteen premixed, swirl-stabilized turbulent flames. We show the changes in the characteristics of bifurcations leading to the state of longitudinal thermoacoustic instability (TAI) when equivalence ratio and bulk velocity are systematically varied. Depending upon the bulk velocity, we observe different states of combustor operation when the equivalence ratio is varied. These states include combustion noise, intermittency, low-amplitude TAI, mixed-mode oscillations (MMO), and high-amplitude TAI. We closely examine the special case of MMO that is encountered during the transition from low-amplitude TAI to high-amplitude TAI. We also discuss the global and local flame dynamics observed during the state of MMO. We find that during epochs of low-amplitude oscillations of MMO, all the flames are partially synchronized, while during epochs of high-amplitude oscillations, all the flames are perfectly synchronized. Finally, we replicate the criticalities of bifurcation of the annular combustor in a phenomenological model containing sixth-order nonlinearities.
APA, Harvard, Vancouver, ISO, and other styles
6

Jacob, Chinthaka, David Tingay, and Justin Leontini. "Conditional turbulence in the reciprocating flow in a bifurcating pipe." In 22nd Australasian Fluid Mechanics Conference AFMC2020. Brisbane, Australia: The University of Queensland, 2020. http://dx.doi.org/10.14264/5e62bd1.

Full text
APA, Harvard, Vancouver, ISO, and other styles
7

Kovinskaya, Svetlana I., and Eduard L. Amromin. "Bifurcation in Rotating Flow Due to Boundary Oscillation." In ASME 2003 International Mechanical Engineering Congress and Exposition. ASMEDC, 2003. http://dx.doi.org/10.1115/imece2003-41725.

Full text
Abstract:
Numerical analysis of viscous flow in narrow gaps between rotating disks gives several solutions for the same value of the Reynolds number. The non-uniqueness of solution can be considered as indication of the flow instability and close laminar-turbulent transition. Although the obtained solutions have the same boundary values of velocity components and their first derivatives, these solutions differ by the second derivative of the axial velocity. This second derivative is generally proportional to the axial component of the boundary acceleration. Consequently, the mentioned difference can be associated with disk oscillation/vibration and can exhibit the minimum stimulating acceleration as function of Reynolds number. Although the flow bifurcation can be associated with the laminar-turbulent transition, such analysis of viscous flow gives no information on principal flow modes that may appear due to this stimulation. These principal modes can be found in the framework of potential theory. According to many experimental and numerical researches, the flow between rotating disks is composed from a quite thin boundary layer and the practically inviscid core. The Reynolds-dependent time-averaged circumferential velocity in this core is smaller than the disk rotation speed. Possible modes of flow oscillations and their frequencies depend on the ratio of this circumferential velocity to the rotation speed.
APA, Harvard, Vancouver, ISO, and other styles
8

Stratton, Zachary T., and Tom I.-P. Shih. "Effects of Density and Blowing Ratios on the Turbulent Structure and Effectiveness of Film-Cooling." In ASME Turbo Expo 2018: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/gt2018-76170.

Full text
Abstract:
Large eddy simulations (LES) were performed to investigate film cooling of a flat plate, where the cooling jets issued from a plenum through one row of circular holes of diameter D and length 4.7D that are inclined at 35° relative to the plate. The focus is on understanding the turbulent structure of the film-cooling jet and the film-cooling effectiveness. Parameters studied include blowing ratio (BR = 0.5 and 1.0) and density ratio (DR = 1.1 and 1.6). Also, two different boundary layers (BL) upstream of the film-cooling hole were investigated — one in which a laminar BL was tripped to become turbulent from near the leading edge of the flat plate, and another in which a mean turbulent BL is prescribed directly. The wall-resolved LES solutions generated were validated by comparing its time-averaged values with data from PIV and thermal measurements. Results obtained show that having an upstream BL that does not have turbulent fluctuations enhances the cooling effectiveness significantly at low velocity ratios (VR) when compared to an upstream BL that resolved the turbulent fluctuations. However, these differences diminish at higher VRs. Instantaneous flow reveals a bifurcation in the jet vorticity as it exits the hole at low VRs, one branch forming the shear-layer vortex, while the other forms the counter-rotating vortex pair. At higher VRs, the shear layer vorticity is found to reverse direction, changing the nature of the turbulence and the heat transfer. Results obtained also show the strength and structure of the turbulence in the film-cooling jet to be strongly correlated to VR.
APA, Harvard, Vancouver, ISO, and other styles
9

Handy, Tim A., Evan C. Lemley, Dimitrios V. Papavassiliou, and Henry J. Neeman. "Simulations to Determine Laminar Loss Coefficients for Flow in Circular Ducts With Arbitrary Planar Bifurcation Geometries." 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/fedsm2008-55181.

Full text
Abstract:
The goal of this study was to determine laminar stagnation pressure loss coefficients for circular ducts in which flow encounters a planar bifurcation. Flow conditions and pressure losses in these laminar bifurcations are of interest in microfluidic devices, in porous media, and in other networks of small ducts or pores. Until recently, bifurcation geometries had been studied almost exclusively for turbulent flow, which is often found in fluid supply and drain systems. Recently, pressure loss coefficients from simulations of a few arbitrary bifurcation geometries in two-dimensions have been published — the present study describes the extension of these two-dimensional simulations to three-dimensional circular ducts. The pressure loss coefficients determined in this study are intended to allow realistic simulation of existing laminar flow networks or the design of these networks. This study focused on a single inlet duct with two outlet ducts, which were allowed to vary in diameter, flow fraction, and angle — all relative to the inlet duct. All ducts considered in this study were circular with their axes in a common plane. Laminar stagnation pressure loss coefficients were determined by simulating incompressible flow through 475 different geometries and flow condition combinations. In all cases, the flow was laminar in the inlet and outlet ducts with a Reynolds number of 15 in the inlet duct. Simulations of the dividing flow geometries were done using FLUENT and a custom written computer code, which automated the process of creating the three-dimensional flow geometries. The outputs, pressure and velocity distributions at the inlet and outlets, were averaged over the circular ducts and then used to calculate pressure loss coefficients for each of the geometries and flow fraction scenarios simulated. The results for loss coefficient for the geometries considered ranged from 2.0 to 70. The loss coefficient for any geometry increased significantly as the outlet flow fraction increased. A consistent increase in loss coefficient was also observed as a function of decreasing outlet duct diameter. Less significant variation of the loss coefficient was observed as a function of the angles of the outlet ducts.
APA, Harvard, Vancouver, ISO, and other styles
10

Senoo, T., K. Deguchi, and M. Nagata. "Bifurcation of flows of a fluid with internal heat sources in a vertical pipe." In THMT-12. Proceedings of the Seventh International Symposium On Turbulence, Heat and Mass Transfer Palermo, Italy, 24-27 September, 2012. Connecticut: Begellhouse, 2012. http://dx.doi.org/10.1615/ichmt.2012.procsevintsympturbheattransfpal.2250.

Full text
APA, Harvard, Vancouver, ISO, and other styles
You might also be interested in the extended bibliographies on the topic 'Bifurcation turbulente' for particular source types:
Journal articles Dissertations / Theses
We offer discounts on all premium plans for authors whose works are included in thematic literature selections. Contact us to get a unique promo code!

To the bibliography