Wake characterization of an undulating membrane tidal energy converter

Abstract

Most of the research done on tidal energy focuses on marine current turbines. Therefore, tidal turbine's wake is well-documented. The tidal energy converter studied here is based on the fluid-structure interactions that occur between a flexible membrane and an axial flow, resulting in an undulating motion that can be used to harvest energy. This device's performance had been studied but it is the first time its wake is experimentally characterized from two-dimensional Particle Image Velocimetry (PIV) measurements. PIV is synchronized with a motion tracking system that gives information on trajectory and power conversion. Wake measurement gives access to velocity deficit, turbulence intensity and vorticity. Three configurations are tested in order to identify the influence of the main adjustment parameters. Pre-stress increases the membrane vertical speed, leading to a more important vertical expansion of the wake. The power extraction slows down the membrane's motion, thus limiting the wake's length and intensity. The flume tank measurements suggest that the best location for a downstream device in a tidal farm would be in the same horizontal position, at 5 membrane's length. In the open sea, the membrane interaction effects should not predominant. Highlights► Undulating membrane first wake characterization from PIV measurements, ► Phase-averaged velocity deficit and vorticity are measured and presented, ► Vorticity dissipation rate result can be used to calibrate numerical model.

Numerical modelling of an undulating membrane tidal energy converter

“…Between these areas, the flow is decelerated. This is consistent with the experimental results presented in [19] for a similar, but different configuration.…”

“…B is the transformation matrix calculated by Eq. (19). c and s respectively refer to cos(β) and sin(β), δ is the differential operator.…”

“…Sampling frequency is f s = 100 Hz and measurement time is ∆t = 80s. A PIV wake characterisation has also been carried out and presented in [19]. The membrane motion obtained with these parameters is plotted in Fig.…”