An experimental and numerical assessment of tidal stream turbine behavior under seabed bathymetry proximity and blockage ratio effect

The combination of waves, currents, and seabed bathymetry can result in large hydrodynamic loads that can lead to excessive loading, tidal turbine fatigue and power fluctuations. In this work, a 1:50 scaled tidal stream turbine model is utilized to further the fundamental understanding of tidal turbine behavior with present of seabed bathymetry. The influence of seabed bathymetry proximity on tidal turbines power and loading fluctuations are assessed in terms of spectral density. In the spectral domain of power coefficient, the presence of seabed bathymetry effectively reduces the energy cascade. For thrust coefficient, the frequency decay depicted peaks nearly at the harmonics along the rotor's rotational (fr). The coupled effects of seabed bathymetry and blockage ratio were also examined by a transient numerical analysis. The implication of blockage effects is not only to increase the hydrodynamic performance but also shifting the optimum performance TSR to a higher value. The presence of seabed bathymetry resulted in skewed wake flows and the seabed element obstruction is the primary mechanism for reduced performance at close proximity. The results of this study provide recommendations for turbine positioning and fatigue analysis in such flows.