Experimental study of coherent flow structures past a wall-mounted square cylinder

Type Article
Date 2019-06
Language English
Author(s) Ikhennicheu Maria1, Germain GregoryORCID1, Druault Philippe2, Gaurier BenoitORCID1
Affiliation(s) 1 : Ifremer, Marine Structure Laboratory, 150 Quai Gambetta 62200 Boulogne sur Mer, France
2 : Sorbonne Université, UPMC Univ Paris 06, CNRS, UMR 7190, Institut Jean Le Rond d’Alembert, F-75005, Paris, France
Source Ocean Engineering (0029-8018) (Elsevier BV), 2019-06 , Vol. 182 , P. 137-146
DOI 10.1016/j.oceaneng.2019.04.043
WOS© Times Cited 9
Keyword(s) Turbulence, Experimental trials, Wall-mounted cylinder, PIV, LDV, POD, Lamb-Oseen
Abstract

In high flow velocity areas like those suitable for tidal applications, turbulence intensity is high and flow variations may have a major impact on tidal turbines behaviour. Large boils that can be observed at the sea surface are emitted from the sea floor and may interact with the tidal turbines. These boils have then to be characterized. The Reynolds number, based on the rugosity height and the mean flow velocity, is rather high in this context: Re ¼ 2:5 107. For that purpose, experiments are carried out in a flume tank with Re as high as achievable in Froude similitude (in the tank: Re ¼ 2:5  105 and Fr ¼ 0:23) in order to study coherent flow structures emitted behind seabed obstacles. The obstacle is here a canonical square wall-mounted cylinder chosen to be representative of specific in-situ bathymetric variations. Using PIV and LDV measurements, the flow past the cylinder is investigated. Using a POD filter, large coherent structures are identified and their trajectories are analysed. By means of a Lamb-Oseen profile approximation, properties of these structures are determined. The formation mechanism of such structures is discussed in this paper and their behaviour is characterized. It is assumed that vortices periodically shed from the obstacle interact and generate hairpin structures.

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