Wake Recovery of a Horizontal Axis Tidal Turbine under Elevated Turbulent Inflow

Tidal stream turbines have been widely deployed at tidal energy sites with high turbulence intensity levels. The harsh environment can significantly affect the wake dynamics, which in turn affects the overall efficiency of tidal turbine arrays/farms. Current studies have demonstrated faster wake recovery and increased fatigue loads perceived by rotors due to incoming turbulence. However, the dynamics of wakes and the recovery mechanism in turbulence were not fully understood. In this talk, we will discuss a detailed analysis of the near-wake characteristics of a three-bladed, horizontal-axis tidal turbine. The results revealed a strong correlation between the wake recovery process and the instability of the tip vortex. Specifically, the onset of instability was greatly accelerated by incoming turbulence, which in turn sped up wake expansion, shear layer development, and the production of turbulence kinetic energy. The momentum recovery process was further quantified using the streamwise momentum equation, which manifests the important role of turbulence transport and vertical advection in the near wake region. The entire measurements and analysis provided a comprehensive insight into the wake recovery process of axial-flow hydrokinetic turbines, especially in turbulent environments.