Ethan Lust

Hydrodynamic performance of a horizontal axis tidal turbine under steady flow conditions

Performance characteristics are presented for a two-bladed horizontal axis tidal turbine, representing a 1/25th scale operational turbine. The tests were conducted in a 116 m long tow tank facility at the United States Naval Academy. The performance characteristics of power and thrust coefficient are measured for the turbine for a range of tip speed ratios. The results of the model test are applicable to full scale due to Re number independence of the rotor blades for the tested conditions. A full uncertainty analysis is performed and major sources of uncertainty are identified. Uncertainty levels are 4% and 1% for power and thrust coefficient respectively, and 3% for the tip speed ratio.

Near wake flow field measurements of a marine current turbine: Preliminary results

More advanced simulation tools are required to predict the loads experienced by a turbine in situ due to the surrounding environment including the effects of inflow turbulence, the impact of turbines operating upstream, the effect of the free surface, and the impact of surface waves, to name a few. These advanced models require detailed data sets for validation. At this time, few studies have focused on the near wake in an effort to provide such detailed data. It is critical to understand this region because it is where much of the high-energy phenomena occur that is most likely to impact turbine performance and reliability. To this end, a towing-tank particle image velocimetry (PIV) system was designed, built, and used to provide measurements of the flow in the near wake of a scale-independent marine current turbine. Included are preliminary results including a representative case and turbulent statistics for an ensemble of realizations.

Effects of waves on BEM theory in a marine tidal turbine environment

Blade Element Momentum (BEM) theory is a well understood and proven method for modeling blade loads and determining steady state performance characteristics of wind turbines. Recently this theory has successfully been applied to horizontal axis marine current turbines when incorporating modifications that lead to better predictions of turbine performance for a range of operating conditions. Relatively little work exists in the implementation of BEM theory in a marine environment with surface gravity waves. A better understanding of the effects of waves on tidal turbines is necessary to predict fatigue loading that can eventually lead to blade failure. This paper presents a BEM numerical model that incorporates the unsteady velocities due to the presence of waves and assesses the effects of waves on tidal turbine performance. Numerical results of the coefficient of power (CP) and coefficient of thrust (CT) match closely with experimental results for the mean Cp and CT for a range of tip speed ratios. The model is also able to predict the instantaneous amplitudes of the performance characteristics as compared with the measured values except for the BEM calculated thrust which shows a 20% reduction in amplitude.