Download or read book Transition vers la turbulence via intermittence spatio temporelle written by Hugues Chaté and published by . This book was released on 1989 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Cette thèse regroupe des travaux analytiques et numériques sur le problème de la transition vers la turbulence des systèmes a grand rapport d'aspect pouvant présenter des régimes dynamiques ou coexistent et évoluent, dans le temps et l'espace, des régions ordonnées (laminaires) et désordonnées (turbulentes). Nous développons, pour ces régimes d'intermittence spatio-temporelle, une méthode d'analyse montrant que les transitions sont en général bien décrites en termes de transition de phase, ce qui constitue une irruption nouvelle de la mécanique statistique dans le champ de l'hydrodynamique. La première partie est consacrée a l'étude d'équations aux dérivées partielles non intégrables similaires au modèle de kuramoto-sivashinsky, qui peuvent être vues comme des modèles unidimensionnels de la convection de rayleigh-benard. La seconde partie traite de réseaux d'itérations couplées et présente les transitions d'un modèle minimal dans des espaces de dimension un a quatre. Cette étude montre que la transition vers la turbulence via intermittence spatio-temporelle n'est pas universelle au sens des classes d'universalité des phénomènes critiques. Dans la troisième partie, nous étudions des automates cellulaires relies au problème de la transition vers la turbulence via intermittence spatio-temporelle et proposons une explication de la non-universalité de la transition

Download or read book STRUCTURES COHERENTES ET TRANSITION VERS LA TURBULENCE PAR INTERMITTENCE SPATIO TEMPORELLE DANS L ECOULEMENT DE COUETTE PLAN written by SABINE.. BOTTIN and published by . This book was released on 1998 with total page 240 pages. Available in PDF, EPUB and Kindle. Book excerpt: CETTE THESE CONCERNE L'ETUDE EXPERIMENTALE DE LA TRANSITION VERS LA TURBULENCE DANS LE CAS DE L'ECOULEMENT DE COUETTE PLAN. CET ECOULEMENT EST LINEAIREMENT STABLE POUR TOUT NOMBRE DE REYNOLDS ET, LORSQU'IL EST PERTURBE, UNE COEXISTENCE ENTRE L'ETAT LAMINAIRE ET L'ETAT TURBULENT PEUT ETRE OBSERVEE. NOUS MONTRONS A L'AIDE D'UNE PERTURBATION LOCALISEE ET PERMANENTE -UN FIL PERPENDICULAIRE A L'ECOULEMENT- QUE LES STRUCTURES COHERENTES DE ROULEAUX LONGITUDINAUX CONTRA-ROTATIFS PRESENTES AUTOUR DU FIL SONT IDENTIQUES A CELLES OBSERVEES EN BORDURE DE SPOTS, ET QUE CE SONT DES SOLUTIONS D'AMPLITUDES FINIES DANS LA LIMITE DE L'ECOULEMENT DE COUETTE PLAN NON MODIFIE. UN GEL SPATIAL DE LA DYNAMIQUE DE CES ROULEAUX A ETE REALISE A L'AIDE D'UN PETIT OBSTACLE -UNE PERLE- INSTALLE AU CENTRE DE L'ECOULEMENT. LE COMPORTEMENT INTERMITTENT OBSERVE EST REVELATEUR D'UNE DYNAMIQUE SOUS-JACENTE DE CHAOS SPATIO-TEMPOREL POUR LE SYSTEME NON PERTURBE. POUR ETUDIER LA TRANSITION, NOUS UTILISONS DES PERTURBATIONS INSTANTANEES D'AMPLITUDE VARIABLE ET DES TREMPES EN R. NOUS OBSERVONS UN REGIME D'INTERMITTENCE SPATIO-TEMPORELLE (IST) ET CARACTERISONS UN NOMBRE DE REYNOLDS CRITIQUE, R#C, AU DESSUS DUQUEL L'IST EST PERSISTANTE ET LA FRACTION TURBULENTE MOYENNE BIEN DEFINIE CROIT AVEC R. UN ATTRACTEUR TURBULENT UNIQUE COEXISTE AVEC L'ECOULEMENT LAMINAIRE, ET UNE DEFINITION PROPRE D'UNE COURBE D'AMPLITUDE CRITIQUE EST DONNEE. EN DESSOUS DE R#C, IL EXISTE DES TRANSITOIRES LONGS QUI RELAXENT VERS L'ETAT LAMINAIRE ; L'ATTRACTEUR EST TRANSFORME EN UN REPULSEUR CHAOTIQUE. CETTE ETUDE A ETE ENTREPRISE D'UN POINT DE VUE STATISTIQUE ET GUIDEE PAR L'ETUDE PARALLELE D'UN MODELE NUMERIQUE SIMPLE DE RESEAU D'ITERATIONS COUPLES POUR L'IST. CETTE TRANSITION VERS L'IST EST IDENTIFIEE COMME DISCONTINUE.

Download or read book IUTAM Symposium on Laminar Turbulent Transition and Finite Amplitude Solutions written by Tom Mullin and published by Springer Science & Business Media. This book was released on 2005-12-28 with total page 335 pages. Available in PDF, EPUB and Kindle. Book excerpt: An exciting new direction in hydrodynamic stability theory and the transition to turbulence is concerned with the role of disconnected states or finite amplitude solutions in the evolution of disorder in fluid flows. This volume contains refereed papers presented at the IUTAM/LMS sponsored symposium on "Non-Uniqueness of Solutions to the Navier-Stokes equations and their Connection with Laminar-Turbulent Transition" held in Bristol 2004. Theoreticians and experimentalists gathered to discuss developments in understanding both the onset and collapse of disordered motion in shear flows such as those found in pipes and channels. The central objective of the symposium was to discuss the increasing amount of experimental and numerical evidence for finite amplitude solutions to the Navier-Stokes equations and to set the work into a modern theoretical context. The participants included many of the leading authorities in the subject and this volume captures much of the flavour of the resulting stimulating and lively discussions.

Download or read book Transition to Turbulence Via Spatio Temporal Intermittency written by Paul Manneville and published by . This book was released on 1987 with total page 18 pages. Available in PDF, EPUB and Kindle. Book excerpt: This lecture presented a scenario of transition to turbulence specific to large aspect ratio systems. Starting with simulations on a model chosen for its relevance to the field of convective instabilities we characterized the spatio-temporal intermittent 'phase'. Then we examined the transition process having recourse to simpler systems: coupled maps lattices. This process appeared to involve the propagation of an information, laminar/turbulent which seemed stochastic though it was generated by a deterministic dynamics. Concepts first introduced in the statistical physics of critical phenomena applied to directed percolation allowed us to account for most features of spatio-temporal intermittency, and especially the change of behavior at what turned out to be a true threshold. The implications of this approach are important because, in large aspect ratio systems, we have to face the possibility that what we think is turbulence may be simply a finite life-time but very long turbulent transient. If the percolation analogy is valid, then a threshold exists above which the turbulent state percolates through the system and turbulence has virtually no chance to decay.

Download or read book Sixth IUTAM Symposium on Laminar Turbulent Transition written by Rama Govindarajan and published by Springer Science & Business Media. This book was released on 2006-01-18 with total page 466 pages. Available in PDF, EPUB and Kindle. Book excerpt: The dynamics of transition from laminar to turbulent flow remains to this day a major challenge in theoretical and applied mechanics. A series of IUTAM symposia held over the last twenty five years at well-known Centres of research in the subject - Novosibirsk, Stuttgart, Toulouse, Sendai and Sedona (Arizona) - has proved to be a great catalyst which has given a boost to research and our understanding of the field. At this point of time, the field is changing significantly with several emerging directions. The sixth IUTAM meeting in the series, which was held at the Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore, India, focused on the progress after the fifth meeting held at Sedona in 1999. The s- posium, which adhered to the IUTAM format of a single session, included seven invited lectures, fifty oral presentations and eight posters. During the course of the symposium, the following became evident. The area of laminar-turbulent transition has progressed considerably since 1999. Better theoretical tools, for handling nonlinearities as well as transient behaviour are now available. This is accompanied by an en- mous increase in the level of sophistication of both experiments and direct numerical simulations. The result has been that our understanding of the early stages of the transition process is now on much firmer footing and we are now able to study many aspects of the later stages of the transition process.

Download or read book Experimental Study And Characterization Of Chaos A Collection Of Reviews And Lecture Notes written by Bailin Hao and published by World Scientific. This book was released on 1990-05-01 with total page 476 pages. Available in PDF, EPUB and Kindle. Book excerpt: This is a continuation of the previous two volumes of review papers on chaotic dynamics and related topics, published in 1987 and 1988 respectively. In addition to a few reviews written by active researchers specially for the volume, it also contains several reviews based on lectures delivered at the Spring School on Experimental Study of Chaotic Phenomena, held in Tianjing, China, in May 1989, and at the session on Nonlinear Dynamics during the Workshop on Condensed Matter, Molecular and Atomic Physics, held in June - August, 1989, at the International Centre for Theoretical Physics at Trieste, Italy. The emphasis has been made on multifractals, applied symbolic dynamics, the role of unstable orbits and transient chaos. This volume would be useful to graduate students and researchers in physical sciences and engineering.

Download or read book Introduction to Nonlinear Science written by G. Nicolis and published by Cambridge University Press. This book was released on 1995-06-22 with total page 274 pages. Available in PDF, EPUB and Kindle. Book excerpt: The aim of this book is to develop a unified approach to nonlinear science, which does justice to its multiple facets and to the diversity and richness of the concepts and tools developed in this field over the years. Nonlinear science emerged in its present form following a series of closely related and decisive analytic, numerical and experimental developments that took place over the past three decades. It appeals to an extremely large variety of subject areas, but, at the same time, introduces into science a new way of thinking based on a subtle interplay between qualitative and quantitative techniques, topological and metric considerations and deterministic and statistical views. Special effort has been made throughout the book to illustrate both the development of the subject and the mathematical techniques, by reference to simple models. Each chapter concludes with a set of problems. This book will be of great value to graduate students in physics, applied mathematics, chemistry, engineering and biology taking courses in nonlinear science and its applications.

Download or read book PROPRIETES SPATIO TEMPORELLES ET TRANSITION VERS LA TURBULENCE EN CONVECTION DE RAYLEIGH BENARD A 1 ET 2 DIMENSIONS written by FRANCOIS.. DAVIAUD and published by . This book was released on 1990 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: NOUS ETUDIONS LES PROPRIETES SPATIO-TEMPORELLES ET LA TRANSITION A LA TURBULENCE DANS DES SYSTEMES D'ECOULEMENTS CONVECTIFS DE RAYLEIGH-BENARD POSSEDANT UNE OU DEUX DIMENSIONS D'ESPACE. LA PREMIERE PARTIE EST CONSACREE A L'ETUDE DE SYSTEMES CONVECTIFS UNIDIMENSIONNELS. ELLE REVELE L'EXISTENCE DE COMPORTEMENTS DYNAMIQUES COLLECTIFS, PUIS UNE TRANSITION VERS LA TURBULENCE VIA UN PHENOMENE D'INTERMITTENCE SPATIO-TEMPOREL CARACTERISE PAR LA COEXISTENCE DE REGIONS ORDONNEES (LAMINAIRES) ET DESORDONNEES (TURBULENTES), QUI EVOLUENT DANS LE TEMPS ET DANS L'ESPACE. NOUS MONTRONS PAR UNE ETUDE STATISTIQUE QUE CETTE EVOLUTION PEUT ETRE DECRITE EN TERMES DE TRANSITION DE PHASE ET QU'ELLE EST SIMILAIRE A LA TRANSITION OBSERVEE DANS CERTAINS MODELES NUMERIQUES, NOTAMMENT EN PERCOLATION DIRIGEE. LA SECONDE PARTIE CONCERNE L'ETUDE DES ROUTES VERS LA TURBULENCE QUI SONT OBSERVEES DANS DES GEOMETRIES ETENDUES ET A FAIBLE NOMBRE DE PRANDTL. LES RESULTATS EXPERIMENTAUX SONT PRESENTES PUIS INTERPRETES DANS LE CADRE D'UN FORMALISME UTILISANT LES EQUATIONS DE PHASE. ILS MONTRENT L'INTERACTION EXISTANT ENTRE LES COURANTS A GRANDE ECHELLE ET LES ECOULEMENTS CONVECTIFS, ET METTENT EN EVIDENCE L'INFLUENCE DES CONDITIONS AUX LIMITES SUR L'EVOLUTION DES STRUCTURES CONVECTIVES

Download or read book Instabilities and Nonequilibrium Structures VI written by E. Tirapegui and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 404 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book contains two introductory papers on important topics of nonlinear physics. The first one, by M. San Miguel et al., refers to the effect of noise in nonequilibrium systems. The second, by M.E. Brachet, is a modern introduction to turbulence in fluids. The material can be very useful for short courses and is presented accordingly. The authors have made their texts self-contained. The volume also contains a selection of the invited seminars given at the Sixth International Workshop on Instabilities and Nonequilibrium Structures. Audience: This book should be of interest to graduate students and scientists interested in the fascinating problems of nonlinear physics.

Download or read book Transition to Turbulence written by Tapan K. Sengupta and published by Cambridge University Press. This book was released on 2021-09-30 with total page 643 pages. Available in PDF, EPUB and Kindle. Book excerpt: "Present understanding of transition to turbulence has now been studied over one hundred and fifty years. The path the studies have taken posed it as a modal eigenvalue problem. Some researchers have suggested alternative models without being specific. First-principle based approach of receptivity is the route to build bridges among ideas for solving the Navier-Stokes equation for specific canonical problems. This book highlights the mathematical physics, scientific computing, and new ideas and theories for nonlinear analyses of fluid flows, for which vorticity dynamics remain central. This book is a blend of classic with distinctly new ideas, which establish different dynamics of flows, from genesis to evolution of disturbance fields with rigorously developed methods to tracing coherent structures amidst the seemingly random and chaotic fluid dynamics of transitional and turbulent flows"--

Download or read book Intermittence en turbulence pleinement d velopp e et en dynamique non lin aire written by Aurore Naso and published by . This book was released on 2005 with total page 182 pages. Available in PDF, EPUB and Kindle. Book excerpt: Cette thèse se compose de deux parties. Dans la première est étudié un modèle de turbulence hydrodynamique se présentant sous la forme d’un système d’équations différentielles stochastiques. On présente dans un premier temps les solutions de ce système calculées dans l’approximation semi-classique, puis celles obtenues par une méthode de type Monte-Carlo adaptée au problème, dans le cas où le forçage est supposé statistiquement homogène et isotrope. Ces solutions présentent un bon accord avec des résultats d’expériences et de simulations numériques directes de l’équation de Navier-Stokes. Dans un second temps sont présentées les solutions du système lorsqu’un cisaillement est appliqué à l’écoulement. La seconde partie est consacrée à l’étude de la transition au chaos spatio-temporel par intermittence dans un système hydrodynamique. Cette transition est d’abord étudiée quantitativement, puis un modèle d’intermittence spatio-temporelle est appliqué aux conditions aux limites de l’expérience. Comme le système réel, les solutions de ce modèle présentent pour certaines valeurs des paramètres dont dépend un régime de bistabilité, près du seuil, entre l’intermittence spatio-temporelle et un régime où le désordre n’est présent que sur les bords.

Download or read book Instabilit s et transition vers la turbulence faible spatio temporelle dans une exp rience de plasma written by Alex Madon and published by . This book was released on 1996 with total page 322 pages. Available in PDF, EPUB and Kindle. Book excerpt: LE PROBLEME ABORDE DANS CE TRAVAIL EST DE FOURNIR DES MODELES POUR LA ROUTE VERS LA TURBULENCE OBSERVEE DANS UN SYSTEME EXPERIMENTAL. LE SYSTEME CONSIDERE EST UN PLASMA DE DECHARGE CONFINE MAGNETIQUEMENT. UN DIAGNOSTIC SPATIO-TEMPOREL EST ASSURE PAR UNE COURONNE DE 64 SONDES DE LANGMUIR. LORSQU'UN DES PARAMETRES DE CONTROLE DE L'EXPERIENCE (UNE TENSION) AUGMENTE, ON OBSERVE DIFFERENTS REGIMES, DU PLASMA STABLE A L'ETAT DE TURBULENCE FAIBLE SPATIO-TEMPORELLE. UNE METHODE D'ANALYSE DES DONNEES EST PROPOSEE. ELLE S'APPUIE SUR LA DECOMPOSITION BI-ORTHOGONALE ET CONSISTE A IDENTIFIER DANS LES SIGNAUX DES ONDES MODULEES. LA DESCRIPTION DU COMPORTEMENT DU SYSTEME EN TERMES D'ONDES MODULEES PERMET DE DETECTER DES BIFURCATIONS QUI N'AVAIENT PAS ETE OBSERVEES PAR LES METHODES CLASSIQUES. UN MODELE POUR LE PHENOMENE DE DOUBLEMENT DE VITESSE OBSERVE DANS LES SIGNAUX EXPERIMENTAUX EST PROPOSE. IL EST BASE SUR DES MODULATIONS PUREMENT SPATIALES. UN DEUXIEME MODELE EST PROPOSE AFIN DE DECRIRE LA ROUTE COMPLETE VERS LA TURBULENCE. PLUS PRECISEMENT, NOUS DONNONS UN SYSTEME DYNAMIQUE QUI DECRIT L'EVOLUTION TEMPORELLE DES AMPLITUDES DES ONDES MODULEES ET QUI PEUT ETRE CONSIDERE COMME UNE FORME NORMALE POUR LA SEQUENCE DE BIFURCATIONS OBSERVEES: 1) APPARITION D'UNE ONDE MODULEE 2) UN ETAT QUASI-PERIODIQUE A QUATRE ONDES MODULEES 3) UN ETAT D'ACCROCHAGE DE FREQUENCE A QUATRE ONDES MODULEES 4) L'ETAT TURBULENT. CE MODELE, CONSTRUIT DE MANIERE HEURISTIQUE, EST ENSUITE JUSTIFIE PAR DES CALCULS ANALYTIQUES ET PAR DES SIMULATIONS NUMERIQUES. ENFIN, EN ANNEXE, LE MODELE EST RELIE AUX EQUATIONS FLUIDES DES PLASMAS

Download or read book Instability Transition and Turbulence written by M.Y. Hussaini and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 626 pages. Available in PDF, EPUB and Kindle. Book excerpt: This volume contains the proceedings of the Workshop on In stability, Transition and Turbulence, sponsored by the Institute for Computer Applications in Science and Engineering (ICASE) and the NASA Langley Research Center (LaRC), during July 8 to August 2, 1991. This is the second workshop in the series on the subject. The first was held in 1989, and its proceedings were published by Springer-Verlag under the title "Instability and Transition" edited by M. Y. Hussaini and R. G. Voigt. The objectives of these work shops are to i) expose the academic community to current technologically im portant issues of transition and turbulence in shear flows over the entire speed range, ii) acquaint the academic community with the unique combination of theoretical, computational and experimental capabilities at LaRC and foster interaction with these capabilities, and iii) accelerate progress in elucidating the fundamental phenomena of transition and turbulence, leading to improved transition and turbulence modeling in design methodologies. The research areas covered in these proceedings include receptiv ity and roughness, nonlinear theories of transition, numerical simu lation of spatially evolving flows, modelling of transitional and fully turbulent flows as well as some experiments on instability and tran sition. In addition a one-day mini-symposium was held to discuss 1 recent and planned experiments on turbulent flow over a backward facing step.

Download or read book TRANSITION SOUS CRITIQUE VERS LA TURBULENCE CAS DE L ECOULEMENT DE COUETTE PLAN written by OLIVIER.. DAUCHOT and published by . This book was released on 1995 with total page 259 pages. Available in PDF, EPUB and Kindle. Book excerpt: CETTE THESE S'INTERESSE A L'ETUDE EXPERIMENTALE DE LA DESTABILISATION PAR DES PERTURBATIONS D'AMPLITUDE FINIE DE L'ECOULEMENT DE COUETTE PLAN, LINEAIREMENT STABLE POUR TOUTE VALEUR DU NOMBRE DE REYNOLDS. DEUX FAMILLES DE PERTURBATIONS LOCALISEES SONT IMPOSEES A L'ECOULEMENT. LA PREMIERE, INSTANTANEE, EST APPORTEE PAR UN JET TRANSVERSE ET LA SECONDE, PERMANENTE, EST OBTENUE PAR L'INTRODUCTION D'UN FIL DANS LE PLAN CENTRAL DE L'ECOULEMENT. DANS LE CAS OU LA PERTURBATION EST INSTANTANNEE, NOUS METTONS EN EVIDENCE UNE AMPLITUDE CRITIQUE DE PERTURBATION ET SA DEPENDANCE SELON LE NOMBRE DE REYNOLDS, AINSI QU'UNE VALEUR SEUIL DE CE DERNIER SOUS LAQUELLE AUCUNE PERTURBATION NE PEUT MODIFIER L'ECOULEMENT DE FACON DURABLE. LORSQUE LA PERTURBATION EST EFFICACE, UN SPOT TURBULENT, DONT NOUS ANALYSONS LES MECANISMES DE CROISSANCE, SE DEVELOPPE. DANS LE CAS OU LA PERTURBATION EST PERMANENTE, NOUS OBSERVONS LA FORMATION DE VORTEX LONGITUDINAUX, QUE NOUS CARACTERISONS. UN MECANISME DE FORMATION DE CES VORTEX EST PROPOSE. NOUS ETUDIONS AUSSI LES ETATS ASYMPTOTIQUES AUXQUELLES CONDUISENT CES PERTURBATIONS, LORSQUE LE NOMBRE DE REYNOLDS AUTORISE LE DEVELOPPEMENT DE TURBULENCE. INDEPENDANTS DU MODE DE PERTURBATION CHOISI, ILS SE CARACTERISENT PAR LA COEXISTENCE DE DOMAINES LAMINAIRES ET TURBULENTS. ENFIN NOUS DISCUTONS D'UNE PART DES MECANISMES DE TRANSITIONS VERS LA TURBULENCE, D'AUTRE PART DE LA MODELISATION DES ETATS ASYMPTOTIQUES. C'EST POUR NOUS L'OCCASION DE MONTRER LE CARACTERE NECESSAIREMENT NON LINEAIRE DE LA TRANSITION, ET DE TESTER LA POSSIBILITE D'UNE DESCRIPTION EN TERME D'INTERMITTENCE SPATIOTEMPORELLE

Download or read book Strong resonances of a field of oscillators and defect bifurcation written by Kjartan Emilsson and published by Kjartan Emilsson. This book was released on 1994-06-01 with total page 92 pages. Available in PDF, EPUB and Kindle. Book excerpt: There are two subjects in this thesis. In the first part, a qualitative method to classify and predict the structure of defects in reaction-diffusion systems is introduced. This qualitative approach makes it easier to analyze the behavior of defects in complex systems. It also gives us information about the inner structure of the defect, and from that point of view, it makes it possible to approach the concept of defect bifurcation in a novel manner. In the second part, we study the normal form governing the evolution of a spatially extended homogeneous temporal instability, in the presence of a temporal forcing. This is equivalent to studying strong resonances of a field of nonlinear oscillators. A detailed analysis of the phase space of this normal form reveals a rich dynamical structure, which gives rise to a variety of spatial structures. These include excitable pulses, excitable spirals, fronts and spatially periodic structures. These structures are studied and their possible bifurcations are analyzed from a qualitative point of view.

Download or read book Instability Transition and Turbulence written by M.Y. Hussaini and published by Springer. This book was released on 1992-09-23 with total page 620 pages. Available in PDF, EPUB and Kindle. Book excerpt: This volume contains the proceedings of the Workshop on In stability, Transition and Turbulence, sponsored by the Institute for Computer Applications in Science and Engineering (ICASE) and the NASA Langley Research Center (LaRC), during July 8 to August 2, 1991. This is the second workshop in the series on the subject. The first was held in 1989, and its proceedings were published by Springer-Verlag under the title "Instability and Transition" edited by M. Y. Hussaini and R. G. Voigt. The objectives of these work shops are to i) expose the academic community to current technologically im portant issues of transition and turbulence in shear flows over the entire speed range, ii) acquaint the academic community with the unique combination of theoretical, computational and experimental capabilities at LaRC and foster interaction with these capabilities, and iii) accelerate progress in elucidating the fundamental phenomena of transition and turbulence, leading to improved transition and turbulence modeling in design methodologies. The research areas covered in these proceedings include receptiv ity and roughness, nonlinear theories of transition, numerical simu lation of spatially evolving flows, modelling of transitional and fully turbulent flows as well as some experiments on instability and tran sition. In addition a one-day mini-symposium was held to discuss 1 recent and planned experiments on turbulent flow over a backward facing step.

Download or read book Etude de la transition vers la turbulence d un coulement de disque tournant written by Anne Cros and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Cette étude expérimentale porte sur la caractérisation de différents processus de transition vers la turbulence d'un écoulement d'eau entre un disque fixe et un disque tournant à la vitesse W.Lorsque les deux disques sont suffisamment proches, l'écoulement de base est de type "Couette de torsion" : les couches limites sont jointes. Lorsque W est augmenté, l'écoulement se déstabilise et un réseau de spirales périodiques se développe. Pour des valeurs plus grandes de W, des défauts apparaissent dans le réseau. L'acquisition de diagrammes spatiotemporels sur un rayon permet 'analyser statistiquement le régime de turbulence de défauts qui se développe ; et un processus de type poissonien pour l'avènement des défauts est mis en évidence au seuil de ce régime. Pour des valeurs plus importantes de W, la distance séparant deux défauts diminue et des spirales turbulentes issent dans l'écoulement. Celles-ci génèrent un régime d'intermittence spatiotemporelle, analysé dans le cadre des transitions critiques. Bien que ces spirales disparaissent au-delà d'une certaine vitesse, des exposants critiques égaux à ceux obtenus dans d'autres expériences sont mesurés sur la partie croissante de la fraction turbulente. Pour de plus grandes valeurs de W, de nouvelles structures très localisées envahissent l'écoulement. Lorsque les deux disques sont suffisamment espacés, l'écoulement de base est de type Batchelor, c'est-à-dire à couches limites séparées. Dans cette configuration, deux réseaux de spirales interagissent non linéairement et l'écoulement devient de plus en plus désordonné quand W augmente. L'analyse des trajectoires dans l'espace des phases généré par des modes propres de la décomposition biorthogonale des signaux spatiotemporels permet de mettre en évidence une bifurcation par doublement de tore.