Experimental analysis of the floor inclination effect on the turbulent wake developing behind a wall mounted cube

Type Article
Date 2018-11
Language English
Author(s) Ikhennicheu Maria1, Gaurier BenoitORCID1, Druault Philippe2, Germain GregoryORCID1
Affiliation(s) 1 : IFREMER, Marine Struct Lab, 150 Quai Gambetta, F-62200 Boulogne Sur Mer, France.
2 : UPMC Univ Paris 06, Sorbonne Univ, Inst Jean Rond dAlembert, CNRS,UMR 7190, F-75005 Paris, France.
Source European Journal Of Mechanics B-fluids (0997-7546) (Elsevier Science Bv), 2018-11 , Vol. 72 , P. 340-352
DOI 10.1016/j.euromechflu.2018.07.003
WOS© Times Cited 3
Keyword(s) Turbulence, Experimental trials, Wall-mounted obstacles, PIV, POD, Quadrant method
Abstract

The present study aims at investigating turbulence characteristics in high flow velocity areas like those suitable for marine energy application. The Reynolds number, based on the rugosity height and mean flow velocity, is rather high: . For that purpose, experiments are carried out in a flume tank with as high as achievable in Froude similitude (in the tank: and ). Obstacles are canonical wall-mounted elements chosen to be representative of averaged bathymetric variations: a cube and a cube followed by an inclined floor. First, the wake topology past a canonical wall-mounted cube is illustrated from PIV measurements. Results show a flow behaviour already observed in the literature but for different upstream conditions ( and turbulence intensity). Second, the impact of the addition of an inclined floor is studied. It is shown that the inclination causes a squeezing of the cube wake that strongly impacts the shape and intensity of the shear layer (up to 10% more intense with the inclined floor). To fully grasp the turbulence organization in the wake for both test cases, an analysis using both complementary Proper Orthogonal Decomposition and quadrant method is performed. POD acts as a turbulent noise filter and quadrant method decomposes turbulent events. Results show the predominance of ejection (Q2) and sweep (Q4) events in the flow Reynolds shear stress. Q2 events are more energetic although Q4 events prevail. It is observed that the inclined floor causes a persistence of Q2 and Q4 events higher into the water column, more than the impulsion given by the floor altitude variations. The rise of the cube wake due to the inclined floor is thus illustrated using Q4 predominance area.

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