Evaluating the performance of turbulence closure models for tidal stream resource characterization

Abstract

Harvesting tidal stream energy from the ocean for electricity generation has been considered as an energy resource alternative to fossil fuels for mitigating the negative impact of climate change and enhancing energy security and coastal resilience. Numerical models have been used extensively to characterize and assess tidal resources at potential tidal energy development sites. Turbulence plays an important role in site selection and tidal turbine farm deployment. However, most of the numerical modeling studies for tidal energy resource characterization do not include turbulence characteristics because of the limitation of Reynolds averaged Navier–Stokes coastal ocean model in resolving the inertial sub-range turbulence scales. However, studies also demonstrated that turbulence properties, such as turbulence intensity and turbulence kinetic energy, simulated by the coastal ocean models based on turbulence closures can be useful in assisting tidal resource characterization at tidal energy sites. In this study, we evaluated four General Ocean Turbulence Model (GOTM)  turbulence closure models implemented in a tidal hydrodynamic model –Finite Volume Community Ocean Model (FVCOM)  to characterize the tidal energy resource in the Western Passage, Maine, USA – a top ranked tidal energy site. The four turbulence closure models used in this analysis are k–kl (Mellor–Yamada Level 2.5), k-ε, k–ω, and a generic model. Model sensitivities showed that the MY2.5 model performed the best in comparison with the field measurements. In particular, the simulated time series of turbulence intensity and kinetic energy matched the observed data very well in the Western Passage. Detailed analysis was conducted to characterize turbulence properties on the horizontal plane and at selective cross-sections. This study demonstrated that turbulence properties simulated by a coastal ocean model, along with tidal hydrodynamic properties, can be very informative for tidal energy resource characterization and project site selection, as recommended by the International Electrotechnical Commission (IEC) technical specifications (IEC TS 62600-201).