Spatial modulations of kinetic energy in the roughness sublayer

Autor: Romain Mathis, Jérémy Basley, Laurent Perret
Přispěvatelé: Laboratoire de recherche en Hydrodynamique, Énergétique et Environnement Atmosphérique (LHEEA), École Centrale de Nantes (ECN)-Centre National de la Recherche Scientifique (CNRS), Imperial College London, Institut de mécanique des fluides de Toulouse (IMFT), Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université Fédérale Toulouse Midi-Pyrénées, Centre National de la Recherche Scientifique - CNRS (FRANCE), Ecole Centrale de Nantes (FRANCE), Institut National Polytechnique de Toulouse - Toulouse INP (FRANCE), Université Toulouse III - Paul Sabatier - UT3 (FRANCE), Imperial College London (UNITED KINGDOM), Laboratoire de recherche en Hydrodynamique, Energétique et Environnement Atmosphérique - LHEEA (Nantes, France), Institut National Polytechnique de Toulouse - INPT (FRANCE)
Jazyk: angličtina
Rok vydání: 2018
Předmět:
Zdroj: Journal of Fluid Mechanics
Journal of Fluid Mechanics, Cambridge University Press (CUP), 2018, 850, pp.584-610. ⟨10.1017/jfm.2018.458⟩
ISSN: 0022-1120
1469-7645
DOI: 10.1017/jfm.2018.458⟩
Popis: International audience; High-Reynolds-number experiments are conducted in the roughness sublayer of a turbulent boundary-layer developing over a cubical canopy. Stereoscopic particle image velocimetry is performed in a wall-parallel plane to evidence a high degree of spatial modulation of the small-scale turbulence around the footprint of large-scale motions, despite the suppression of the inner layer by the high roughness elements. Both Fourier and wavelets analyses show that the near-wall cycle observed in smooth-wall-bounded flows is severely disrupted by the canopy, whose wake in the roughness sublayer generates a new range of scales, closer to that of the outer-layer large-scale motions. This restricts significantly scale separation, hence a diagnostic method is developed to divide carefully and rationally the fluctuating velocity fields into large- and small-scale components. Our analysis across all turbulent kinetic energy terms sheds light on the spatial imprint of the modulation mechanism, revealing a very different signature on each velocity component. The roughness sublayer shows a preferential arrangement of the modulated scales similar to what is observed in the outer-layer of smooth-wall-bounded flows – small-scale turbulence is enhanced near the front of high momentum regions and damped at the front of low-momentum regions. More importantly, accessing spanwise correlations reveals that modulation intensifies the most along the flanks of the large-scale motions.
Databáze: OpenAIRE
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