PNNL

Abstract

There has been an increasing interest in harvesting tidal stream energy because it is clean and renewable, highly predictable, stable, and abundant in locations close to coastal communities. Numerical models combined with field measurements are regularly used to assess and characterize tidal energy resources at potential energetic tidal sites following International Electrotechnical Commission (IEC) technical specifications (IEC TS 62600-201). However, most of the existing works only focus on the tidal hydrodynamic characteristics, and turbulence parameters are often not reported because of the lack of high-quality turbulence measurements and the limitations of numerical models in resolving micro-scale turbulent eddies. In this study, we implemented a 3D Reynolds-averaged Navier–Stokes model - Finite Volume Community Ocean Model (FVCOM) to characterize the tidal energy resource in the Western Passage - a highly energetic tidal channel between New Brunswick, Canada, and the state of Maine in the United States - by taking care of the essential macro-scale turbulence properties, such as turbulence intensity and kinetic energy. IEC technical specifications were followed during model development and simulations, and field measurements of water level, tidal current, and turbulence were used for model validation. We observed excellent model performance in simulating turbulence intensity and kinetic energy using the Mellow-Yamada turbulence length-scale model (MY2.5). Estimating along- and across-channel vertical variation of the turbulent kinetic energy and intensity added a new perspective to the resource site ranking approach. In addition, we conducted a sensitivity analysis to investigate the role of channel geometry and bathymetry, such as headlands and underwater sills, on turbulence production. The sensitivity analysis illustrated that the momentum ratio between tributary and main channel and underwater sills near headlands can significantly enhance the sheared flow and turbulent eddies. Ultimately, this study demonstrated that incorporating tidal turbulence in resource characterization can be useful to the marine renewable energy community worldwide.