Experimental investigation of the turbulent wake past real seabed elements for velocity variations characterization in the water column.

Type Article
Date 2019-08
Language English
Author(s) Ikhennicheu Maria1, Germain GregoryORCID1, Druault Philippe2, Gaurier BenoitORCID1
Affiliation(s) 1 : Ifremer, Marine Structure Laboratory, 150 Quai Gambetta Boulogne sur Mer 62200, France
2 : Sorbonne Université, UPMC Univ Paris 06, CNRS, UMR 7190, Institut Jean Le Rond d’Alembert, Paris F-75005, France
Source International Journal Of Heat And Fluid Flow (0142-727X) (Elsevier BV), 2019-08 , Vol. 78 , P. 108426 (14p.)
DOI 10.1016/j.ijheatfluidflow.2019.108426
WOS© Times Cited 17
Keyword(s) Turbulence, Experimental trials, Wall-mounted obstacles, PIV, LDV, Marine energy

In high flow velocity areas like those suitable for marine energy application, bathymetry variations create strong velocity fluctuations in the water column. It is therefore essential to characterize the turbulence evolution in the wake of seabed elements which may impact the loads on tidal turbines. For that purpose, experiments are carried out in a flume tank with Re as high as achievable in Froude similitude, with bathymetry variations experimentally represented with various wall-mounted square elements of height H: a cylinder or a cube as unitary obstacles and combinations of these elements followed by an inclined floor to resemble smooth bathymetry changes. The onset flow is a simple boundary layer profile with height 1.3 H and a low turbulence intensity. PIV and LDV measurements are used to investigate the wake past all test cases in order to distinguish high floor elevation cases (unitary obstacles) from mean roughness effect (obstacle combinations). Results show that the obstacle combinations produce a wake less extended than for a single wide cylinder that produces an extended wake and very energetic turbulent events. With a single cube, no downstream development of large turbulent events exist and the wake reduces by a factor of 3 compared to the wake cylinder case. An inclined floor downstream of a single wall-mounted obstacle reduces its wake length but does not alter the turbulent structures shed. Turbulent velocity profiles extracted from every wake topology investigated are also compared. The general conclusion is that: for small aspect ratio cases, the obstacle will not affect the water column. On the contrary, strong energetic turbulent events are emitted from large aspect ratio obstacles. Combinations cases stand in-between.

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