Abstract
The deployment of tidal turbine arrays entails a comprehensive understanding of the flow at tidal energy sites. Among the parameters critical to a tidal energy site characterization, inflow turbulence and related scales are vital as they profoundly affect the load on turbine blades and are also known to affect the downstream wake. Previous studies from our group have focused on studying the interaction of inflow turbulence with a tidal turbine operating at optimal efficiency. However, due to periodicity in the inflow, the turbine may also operate at sub-optimal conditions at tip speed ratios (TSRs) below or greater than the peak efficiency point. In the present study, an active grid turbulence generator in the Tidal Turbine Testing Facility (T3F) at Lehigh University was used to generate turbulence inflow conditions that mimic the highly energetic open water tidal sites. Two flow conditions were generated and compared; the benchmark case is named the quasi-laminar flow with a turbulence intensity of ~ 2.2%; the second case is called the elevated-Ti case with a turbulence intensity of ~ 12.6%. For the current study, a 1:20 scaled tidal turbine model was used to measure performance at three tip speed ratios [2.5, 4.5 (optimal), and 6.0]. It was observed that although the mean performance was not affected by elevated inflow turbulence, the load fluctuations increased considerably by a factor of ~4 at the highest TSR. An Acoustic Doppler Velocimeter (ADV) was used to help give insights into the wake recovery process up to four diameters downstream. Detailed analysis of the wake deficit, turbulence kinetic energy, and Reynolds stresses will be presented to help illustrate the wake evolution processes. We will discuss the inflow-flow-turbine interactions and highlight the impact of turbulence on the loads and wake flows of tidal turbines.