The merging of Kelvin–Helmholtz vortices into large coherent flow structures in a high Reynolds number flow past a wall-mounted square cylinder

Type Article
Date 2020-05
Language English
Author(s) Mercier Philippe1, Ikhennicheu Maria2, Guillou Sylvain1, Germain GregoryORCID2, Poizot Emmanuel1, Grondeau Mikaël1, Thiébot Jérôme1, Druault Philippe3
Affiliation(s) 1 : Normandie Université, UNICAEN LUSAC, EA 4253, 60 rue Max Pol Fouchet, CS 20082, 50130 Cherbourg-en-Cotentin, France
2 : Ifremer, Marine Structure Laboratory, 150 Quai Gambetta 62200 Boulogne sur Mer, France
3 : Sorbonne Université, CNRS, UMR 7190, Institut Jean Le Rond d’Alembert, F-75005 Paris, France
Source Ocean Engineering (0029-8018) (Elsevier BV), 2020-05 , Vol. 204 , P. 107274 (13p.)
DOI 10.1016/j.oceaneng.2020.107274
WOS© Times Cited 6
Keyword(s) Turbulence, Coherent flow structure, Numerical simulation, Lattice Boltzmann Method, Large Eddy Simulation, Wall-mounted obstacles

Flows at tidal-stream energy sites are characterised by high turbulence intensities and by the occurrence of highly energetic large and coherent flow structures. The interaction of the flow with seabed roughness is suspected to play a major role in the generation of such coherent flow structures. The problem is introduced with canonical wall-mounted square obstacles representing abrupt changes of bathymetry, with high Reynolds number flow (Re = 250000). Two methods are used: a numerical model, based on the LBM (Lattice Boltzmann Method) combined with LES (Large Eddy Simulation) and an experimental set-up in a circulating tank. The numerical model is validated by comparison with experimental data. In the case of a wall-mounted square cylinder, large-scale turbulent structures are identified in experiments where boils at the free surface can be observed. LBM simulation allows their three-dimensional characterisation. The dynamic of such large-scale events is investigated by temporal, spatial and spectral numerical analysis. Results show that periodical Kelvin–Helmholtz vortices are emitted in the cylinder wake. Then, they merge to form larger and more coherent structures that rise up to the surface. A wavelet study shows that the emission frequency of the Kelvin–Helmholtz vortices is not constant over time.

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Mercier Philippe, Ikhennicheu Maria, Guillou Sylvain, Germain Gregory, Poizot Emmanuel, Grondeau Mikaël, Thiébot Jérôme, Druault Philippe (2020). The merging of Kelvin–Helmholtz vortices into large coherent flow structures in a high Reynolds number flow past a wall-mounted square cylinder. Ocean Engineering, 204, 107274 (13p.). Publisher's official version : , Open Access version :