Experimental study of the wall-mounted cylinder wake effects on a tidal turbine behaviour compared to free stream turbulence

Abstract

International audienceTurbulence impacts significantly the performance and fatigue of tidal turbines. In this study, two cases of turbulence inflows are considered. At laboratory scale, in the wave and current circulating tank of Ifremer, experimental conditions are chosen to be representative of in-situ characteristics at a 1:20 scale, in Froude similitude (Fr = 0.23 and Re ∼ 10 5). The first inflow case is seabed variations, experimentally represented with a wall-mounted cylinder. Recent experiments have shown that a large aspect ratio bottom-mounted obstacle produces a very extended wake, with large velocity fluctuations. The second inflow case is a 14% ambient turbulence intensity flow. The main objective of this study is to characterize the effect of the turbulence present in the two inflow cases on a 3-bladed horizontal turbine. The turbine is positioned within the obstacle wake at a distance of 16H from the obstacle or within the ambient turbulent flow. To monitor the velocity fluctuations reaching the turbine, two types of measurement are performed in synchronisation with the turbine parameters: Particle Image Velocimetry (PIV) and Laser Doppler Velocimetry (LDV). Measurements are performed far upstream and close to the turbine. In this work, both inflow conditions will be spatially and temporally described. Then, a full temporal and spectral analysis will be achieved on the turbine performance, in terms of thrust and torque. Finally, a comparison will be proposed, between the perturbation effects on the turbine induced by both inflow cases