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Coherent dynamics of large scale turbulent motions

Rawat, Subhandu. Coherent dynamics of large scale turbulent motions. PhD, Institut National Polytechnique de Toulouse, 2014

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Official URL: http://ethesis.inp-toulouse.fr/archive/00003011/

Abstract

My thesis work focused on ‘dynamical systems’ understanding of the large-scale dynamics in fully developed turbulent shear flow. In plane Couette flow, large-eddy simulation (L.E.S) is used to model small scale motions and to only resolve large-scale motions in order to compute nonlinear traveling waves (NTW) and relative periodic orbits (RPO). Artificial over-damping has been used to quench an increasing range of small-scale motions and prove that the motions in large-scale are self-sustained. The lower-branch traveling wave solutions that lie on laminar-turbulent basin boundary are obtained for these over-damped simulation and further continued in parameter space to upper branch solutions. This approach would not have been possible if, as conjectured in some previous investigations, large-scale motions in wall bounded shear flows are forced by mechanism based on the existence of active structures at smaller scales. In Poseuille flow, relative periodic orbits with shift-reflection symmetry on the laminar-turbulent basin boundary are computed using DNS. We show that the found RPO are connected to the pair of traveling wave (TW) solution via global bifurcation (saddle-node-infinite period bifurcation). The lower branch of this TW solution evolve into a spanwise localized state when the spanwise domain is increased. The upper branch solution develops multiple streaks with spanwise spacing consistent with large-scale motions in turbulent regime.

Item Type:PhD Thesis
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Institution:Université de Toulouse > Institut National Polytechnique de Toulouse - INPT (FRANCE)
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Research Director:
Cossu, Carlo and Rincon, François
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Deposited On:02 Mar 2015 22:58

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