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Etude de la dynamique d`un écoulement à cisaillements croisés : interaction couche de mélange - sillage

type de publication      thèse de doctorat
date de publication 12-12-2003
auteur(s) Braud Caroline
jury G. Arroyo; J.P. Bonnet; J. Delville; P. Givone; M. Provensal; M. Stanislas
  
pages 1 – 235
résumé The aim of this study is to understand the dynamics of a complex flow: a mixing layer - wake interaction. This flow, 3D and inhomogeneous in all three directions, is first analyzed with hot wire and wall pressure measurements. From those data, the Reynolds number, the aspect ratio and the shear parameter influence have been analyzed on the Strouhal number, the base pressure coefficient and the vortex-formation length. In particular, analyses show that, above the impact area of the mixing layer (the low velocity side), the spectral analysis systematically shows at least two cells of different frequency. The main organization is then analyzed by means of PIV (Particle Image Velocimetry) and of POD (Proper Orthogonal Decomposition). First POD modes, which are representative of the energetically dominant coherent structures, clearly show the presence of oblique structures on each side of the mixing layer impact area. In the high velocity zone, where flow is three-dimensional, the higher POD modes show linkages of structures, longitudinal structures and dislocation of structures, close to those found at the time of the wake three-dimensionalisation (both by their intrinsic nature or by perturbations along the span of the cylinder). In addition, a LODS (Low Order Dynamical System) is constructed using a Galerkin projection in the plane behind the cylinder axis. The analyze reveals the existence of a low beating frequency of an ``injecting`` flow on the high velocity side. Lastly, low Reynolds number simulated data comfort experimental results on the characteristic behavior for this flow configuration.
mots clés Fluid dynamics, Turbulence, free shear flow, wake, mixing layer
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