Marine Hydrokinetic Turbine Array Performance and Wake Characteristics

Abstract

Three scale model horizontal axis MHK turbines (1:45) were tested in a flume at various array spacings. The scale rotors are based on the full-scale Department of Energy Reference Model 1, modified to reproduce the hydrodynamic performance of the full-scale turbine (20 m diameter) at the reduced experimental Reynolds number (10^5 vs 10^6, based on chord length). Flow incident on the turbines and in the wakes was characterized by Particle Image Velocimetry (PIV) and Acoustic Doppler Velocimetry (ADV) measurements. Tip speed ratio (TSR) similarity of the turbines is achieved by controlling the torque applied by magnetic particle brakes. Single turbines were characterized over a range of mean freestream velocities to explore the effect of Reynolds number on turbine performance. Measured turbine efficiencies of approximately 40% are similar to efficiencies predicted from full-scale simulations, indicating similar power extraction efficiency at scale. Wake characteristics and turbine efficiencies have been investigated at a range of TSR's, with the goal of determining array spacing and operating conditions that maximize overall array efficiency.