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

卷:204

Article

Mercier, Philippe¹  Ikhennicheu, Maria²  Guillou, Sylvain¹  Germain, Gregory²  Poizot, Emmanuel¹  Grondeau, Mikael¹  Thiebot, Jerome¹  Druault, Philippe³ 

[1] Normandie Univ, UNICAEN LUSAC, EA 4253, 60 Rue Max Pol Fouchet,CS 20082, Cherbourg En Cotentin 50130, France

[2] IFREMER, Marine Struct Lab, 150 Quai Gambetta, Boulogne Sur Mer 62200, France

[3] Sorbonne Univ, Inst Jean Le Rond dAlembert, CNRS, UMR 7190, F-75005 Paris, France

关键词: Turbulence;    Coherent flow structure;    Numerical simulation;    Lattice Boltzmann Method;    Large Eddy Simulation;    Wall-mounted obstacles;   

DOI  :  10.1016/j.oceaneng.2020.107274

来源: Elsevier

【 摘 要 】

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.

【 授权许可】

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