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Étude des instabilités d'un jet plan à masse volumique variable

Abstract : We study the influence of density variation on the development of primary instabilitiesof a plane jet by direct numerical simulation of the incompressible Navier-Stokes equations.Each numerical method and the structure of the program are presented in detail with aspecial focus on the way boundary conditions are set. To validate the overall numericalsimulation, we develop a linear analysis which provides results for a wide range of densityratio. Thanks to our non linear code, we study the convective/absolute transition of thevaricose mode when density is decreased for several profiles, including Bickley and top-hatlike, and prove that the linear marginal stability criterion is not su_cient to explain theobserved dynamics of the jet. For a top-hat like profile and values of the density ratioclose to unity, we observe dumped global modes. An hypothesis is proposed to explain thisphenomenon. A short experimental study ends this work: we insist on the used methodsand give information about the characteristic frequencies of the jet deduced from velocityand density measurements.
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Submitted on : Tuesday, February 21, 2006 - 1:57:29 PM
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Stéphane Ravier. Étude des instabilités d'un jet plan à masse volumique variable. Dynamique des Fluides [physics.flu-dyn]. Université de la Méditerranée - Aix-Marseille II, 2004. Français. ⟨tel-00011653⟩

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