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Etude théorique et experimentale d'un écoulement tournant dans une conduite.

Abstract : This thesis is a contribution to the study of rotating flow dynamics at high Reynolds number. It aims at explaining the destabilization, for a sufficiently high swirl number, of a uniformly rotating flow developing in a cylindrical duct of constant cross-section followed by a contraction, and exhausting as a swirling jet. The first part of the thesis focuses on the corresponding turbulence that is observed in the jet exit plane. Hot-wire anemometry measurements, performed for different contraction ratios of the final duct portion, confirm that the origin of the turbulence has to be mainly sought in the duct flow and not in the jet. The second part thus investigates this flow through a bibliographic and theoretical study. It is first shown that the contraction may strongly affect the flow upstream of it when it is subcritical with respect to inertial (or Kelvin) axisymmetric waves. Using an inviscid axisymmetric model, we then study the in! fluence on the flow of the contraction ratio and of the upstream boundary conditions in the transcritical regime. A wall recirculation is seen to occur inside the contraction near the critical swirl. In the third part the duct flow is investigated by stereoscopic PIV. Comparison of these measurements with a numerical simulation of axisymmetric flow at a moderate Reynolds number reveals a new kind of transition towards subcritical flow. The contraction is seen to suppress vortex breakdown in favor of large-amplitude standing axisymmetric inertial waves. Finally, small-scale centrifugal instabilities and a global axisymmetric instability are identified as possible sources of turbulence.
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Submitted on : Wednesday, July 28, 2010 - 2:46:28 PM
Last modification on : Tuesday, March 16, 2021 - 3:44:45 PM
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  • HAL Id : pastel-00002408, version 1



Benjamin Leclaire. Etude théorique et experimentale d'un écoulement tournant dans une conduite.. Sciences de l'ingénieur [physics]. Ecole Polytechnique X, 2006. Français. ⟨pastel-00002408⟩



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