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On the self-sustained nature of large-scale motions in turbulent Couette flow

Rawat, Subhandu and Cossu, Carlo and Hwang, Yongyun and Rincon, François On the self-sustained nature of large-scale motions in turbulent Couette flow. (2015) Journal of Fluid Mechanics, 782. 515-540. ISSN 0022-1120

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Official URL: http://dx.doi.org/10.1017/jfm.2015.550

Abstract

Large-scale motions in wall-bounded turbulent flows are frequently interpreted as resulting from an aggregation process of smaller-scale structures. Here, we explore the alternative possibility that such large-scale motions are themselves self-sustained and do not draw their energy from smaller-scale turbulent motions activated in buffer layers. To this end, it is first shown that large-scale motions in turbulent Couette flow at Re 2150 self-sustain, even when active processes at smaller scales are artificially quenched by increasing the Smagorinsky constant Cs in large-eddy simulations (LES). These results are in agreement with earlier results on pressure-driven turbulent channel flows. We further investigate the nature of the large-scale coherent motions by computing upper- and lower-branch nonlinear steady solutions of the filtered (LES) equations with a Newton–Krylov solver, and find that they are connected by a saddle–node bifurcation at large values of Cs . Upper-branch solutions for the filtered large-scale motions are computed for Reynolds numbers up to Re = 2187 using specific paths in the Re–Cs parameter plane and compared to large-scale coherent motions. Continuation to Cs = 0 reveals that these large-scale steady solutions of the filtered equations are connected to the Nagata–Clever–Busse–Waleffe branch of steady solutions of the Navier–Stokes equations. In contrast, we find it impossible to connect the latter to buffer-layer motions through a continuation to higher Reynolds numbers in minimal flow units.

Item Type:Article
Additional Information:Thanks to Cambridge University Press. The definitive version is available at http://journals.cambridge.org/ The original PDF of the article can be found at http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9996770&fileId=S0022112015005509
Audience (journal):International peer-reviewed journal
Uncontrolled Keywords:
Institution:French research institutions > Centre National de la Recherche Scientifique - CNRS (FRANCE)
Université de Toulouse > Institut National Polytechnique de Toulouse - INPT (FRANCE)
Université de Toulouse > Université Toulouse III - Paul Sabatier - UPS (FRANCE)
Other partners > Imperial College London (UNITED KINGDOM)
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Deposited By: Carlo COSSU
Deposited On:17 May 2016 08:43

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