Turbulence measurements at three potential tidal energy sites in the Salish Sea

Abstract

Understanding turbulence is critical for the robust design of current energy converters. Subsurface moorings were deployed in the Salish Sea, WA to characterize the turbulence statistics at three potential tidal energy sites: Bellingham Channel, Rosario Strait, and Tacoma Narrows. Measurements were made over two days during spring tides with a combination of acoustic Doppler velocimeters and current profilers in order to analyze the turbulence intensity, integral length scales and turbulent kinetic energy balance. For the four full tidal cycles collected at each site, water velocity peaks at 2.0, 2.8, and 2.5 m/s with average turbulence intensities of 12%, 9%, and 10% for Bellingham Channel, Rosario Strait, and Tacoma Narrows, respectively. The majority of turbulent energy is contained in horizontal anisotropic structures, consistent with the integral length scales observed, and turbulent energy production and dissipation are roughly balanced at the observed sites. Additionally, these channels have significant transverse shear stresses and should not be approximated as wall-bounded flows. This study shows the successful use of buoy-mounted ADVs to gain mid-water column turbulence measurements pertinent to the tidal energy industry, and results from this deployment are important for future work improving a numerical resource characterization model for the Salish Sea.