Cette thèse, composée de quatre chapitres, aborde sur quelques exemples le problème de l'existence de solutions aux équations de Navier-Stokes pour le modèle de l'écoulement isentropique d'un gaz parfait. Le premier chapitre regroupe les théorèmes classiques utilisés pour étudier les équations de Navier-Stokes. Nous y avons ajouté quelques résultats, spécifiquement développés pour ce travail, qui concernent l'équation de conservation de la masse. Dans le second chapitre, nous nous intéressons à un écoulement bidimensionnel entre deux parois parallèles. Le domaine sur lequel sont étudiées les équations est alors un rectangle et le système d'équations est complété par des conditions initiales et des conditions limites portant sur la densité et la vitesse du gaz. Nous fournissons alors une preuve de l'existence d'une solution à ce problème en nous appuyant sur une extension convenable des conditions de bord. Dans le troisième chapitre, en nous inspirant des idées exploitées au chapitre précédent, nous développons l'étude de deux nouveaux exemples. Le premier concerne un problème d'écoulement autour d'une aile d'avion et le second exemple reprend le modèle du chapitre deux en modifiant la vitesse sur le bord du domaine. Le quatrième et dernier chapitre traite de l'existence d'une solution aux équations de Navier-Stokes linéarisées au voisinage d'une solution stationnaire. Nous prouvons un tel résultat dans le cas d'un écoulement semblable à celui étudié au chapitre deux. Enfin, nous terminons ce chapitre en démontrant le caractère exponentiellement stable du système étudié dans le cas monodimensionnel.

Contents: A New Approach to the Helmholtz Decomposition and the Neumann Problem in Lq-Spaces for Bounded and Exterior Domains (C G Simader & H Sohr)On the Energy Equation and on the Uniqueness for D-Solutions to Steady Navier-Stokes Equations in Exterior Domains (G P Galdi)On the Asymptotic Structure of D-Solutions to Steady Navier-Stokes Equations in Exterior Domains (G P Galdi)On the Solvability of an Evolution Free Boundary Problem for the Navier-Stokes Equation in Hölder Spaces of Functions (I S Mogilevskii & V A Solonnikov) Readership: Applied mathematicians.

The book presents the modern state of the art in the mathematical theory of compressible Navier-Stokes equations, with particular emphasis on the applications to aerodynamics. The topics covered include: modeling of compressible viscous flows; modern mathematical theory of nonhomogeneous boundary value problems for viscous gas dynamics equations; applications to optimal shape design in aerodynamics; kinetic theory for equations with oscillating data; new approach to the boundary value problems for transport equations. The monograph offers a comprehensive and self-contained introduction to recent mathematical tools designed to handle the problems arising in the theory.

Originally published in 1977, the book is devoted to the theory and numerical analysis of the Navier-Stokes equations for viscous incompressible fluid. On the theoretical side, results related to the existence, the uniqueness, and, in some cases, the regularity of solutions are presented. On the numerical side, various approaches to the approximation of Navier-Stokes problems by discretization are considered, such as the finite dereference method, the finite element method, and the fractional steps method. The problems of stability and convergence for numerical methods are treated as completely as possible. The new material in the present book (as compared to the preceding 1984 edition) is an appendix reproducing a survey article written in 1998. This appendix touches upon a few aspects not addressed in the earlier editions, in particular a short derivation of the Navier-Stokes equations from the basic conservation principles in continuum mechanics, further historical perspectives, and indications on new developments in the area. The appendix also surveys some aspects of the related Euler equations and the compressible Navier-Stokes equations. The book is written in the style of a textbook and the author has attempted to make the treatment self-contained. It can be used as a textbook or a reference book for researchers. Prerequisites for reading the book include some familiarity with the Navier-Stokes equations and some knowledge of functional analysis and Sololev spaces.

This volume consists of five research articles, each dedicated to a significant topic in the mathematical theory of the Navier-Stokes equations, for compressible and incompressible fluids, and to related questions. All results given here are new and represent a noticeable contribution to the subject. One of the most famous predictions of the Kolmogorov theory of turbulence is the so-called Kolmogorov-obukhov five-thirds law. As is known, this law is heuristic and, to date, there is no rigorous justification. The article of A. Biryuk deals with the Cauchy problem for a multi-dimensional Burgers equation with periodic boundary conditions. Estimates in suitable norms for the corresponding solutions are derived for "large" Reynolds numbers, and their relation with the Kolmogorov-Obukhov law are discussed. Similar estimates are also obtained for the Navier-Stokes equation. In the late sixties J. L. Lions introduced a "perturbation" of the Navier Stokes equations in which he added in the linear momentum equation the hyper dissipative term (-Ll),Bu, f3 ~ 5/4, where Ll is the Laplace operator. This term is referred to as an "artificial" viscosity. Even though it is not physically moti vated, artificial viscosity has proved a useful device in numerical simulations of the Navier-Stokes equations at high Reynolds numbers. The paper of of D. Chae and J. Lee investigates the global well-posedness of a modification of the Navier Stokes equation similar to that introduced by Lions, but where now the original dissipative term -Llu is replaced by (-Ll)O:u, 0 S Ct

This book presents the mathematical theory of turbulence to engineers and physicists, and the physical theory of turbulence to mathematicians. The mathematical technicalities are kept to a minimum within the book, enabling the language to be at a level understood by a broad audience.