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Etude de la dynamique auto-entretenue des bandes turbulentes et de la turbulence pleinement développée dans un écoulement de canal

Abstract : This thesis aims at studying the main mechanisms involved in transitional and turbulent channel flows. Concerning the transitional channel flow, there is a range of Reynolds numbers for which turbulent oblique bands plunged in the laminar flow are observed. In this thesis, the main mechanisms involved in the origin and growth of these turbulent bands are investigated using linear and nonlinear optimization techniques. First, in a large-sized channel, it is shown that the minimal-energy perturbation able to generate turbulent bands has a spot-like structure characterized by small- and large-scale structures. Depending on the Reynolds number, this minimal seed evolves in time with two different mechanisms: for Re < 1200 an isolated oblique band is created; whereas, for Re > 1200, a quasi spanwise-symmetric evolution is observed, giving rise to two distinct bands. Then, reducing the problem complexity to a tilted domain, it is found that two main elements are necessary to induce transition towards turbulent bands: i) a linear energy growth mechanism such as the lift-up for generating streaks inside the turbulent bands; ii) large-scale vortices ensuring spatial localisation.In the last part of this thesis, in order to investigate the coherent structures usually observed in turbulent flows, the nonlinear optimization technique is extended to the turbulent channel flow and a 'new' mathematical framework for the computation of statistically-invariant coherent solutions is proposed. In both techniques, the unsteady Reynolds-Averaged Navier-Stokes equations written in a perturbative form with respect to the turbulent mean flow are used and solutions with structures at multiple turbulent scales are found.
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Submitted on : Tuesday, May 31, 2022 - 3:37:12 PM
Last modification on : Wednesday, September 28, 2022 - 5:53:33 AM

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  • HAL Id : tel-03683350, version 1

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Enza Parente. Etude de la dynamique auto-entretenue des bandes turbulentes et de la turbulence pleinement développée dans un écoulement de canal. Mécanique des matériaux [physics.class-ph]. HESAM Université; Politecnico di Bari. Dipartimento di Ingegneria Meccanica e Gestionale (Italia), 2021. Français. ⟨NNT : 2021HESAE057⟩. ⟨tel-03683350⟩

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