EXPERIMENTAL CHARACTERISATION OF THE WAKE OF A BOTTOM-MOUNTED TWO TANDEM OF CYLINDERS PLACED IN A HIGH VELOCITY AREA

Abstract

Following the development of renewable marine energies, the characterization of areas with strong marine currents has become necessary. The Normandy coasts (France) are among the sites suitable for the installation of tidal turbine parks because they have significant energy potential. Projects to install machines in these sites raise questions about various factors affecting the performance of the turbines that would be placed there.

We are currently working on the understanding of the mechanisms leading to the generation of ambient flow turbulence on the seabed. More particularly, we are interested in the impact of the complexity of the bathymetry on the organization of the wake generated. To simplify the modeling of the bathymetry of the seabed, we use generic cylindrical obstacles of rectangular section. The obstacles are placed on the bottom of the study area of ​​the Hydrodynamic Tunnel of the LUSAC laboratory and occupy its entire width. Measurements are made using Particle Image Velocimetry (PIV-2D) for a velocity flow of 3 m/s.

In a first time, in a previous contribution, was evaluated the impact of the ratio between the Height and the Width (H/W) of the cross section of the cylinder on the organization of the near wake. Indeed, the average velocity fields obtained for six different obstacles, highlighted the modification of the organization of the flow topology. The variation of this ratio H/W leads to the modification of the length of the average vortex formation zone, implies the presence of two or even three average recirculation zones in the near wake of the cylinder and leads to the possible presence of a recirculation zone average placed upstream of the cylinder.

Nevertheless, in the seabed the structures are not isolated. In the contrary, on the seabed we can observe successions of structures anchored on the funds, leading to the interaction of a structure with the wake generated upstream by another one structure. The experimental study  with the characterization of the flow around a tandem of “long” cylindrical obstacles of square section (side H). The distance between these two cylinders is equal to 2H.

As expected, in the present study, it can be observed the modifications of the topology of the mean flow and the distribution of the turbulent kinetic energy. Indeed, the interaction between the mean recirculation, generated downstream each cylinder, is shown.