Measurements of Turbulence at Two Tidal Energy Sites in Puget Sound, WA

TLDR

Field measurements of turbulence are presented from two sites in Puget Sound, WA, that are proposed for electrical power generation using tidal current turbines. The study analyzes time‑series data from multiple acoustic Doppler instruments to quantify fluctuations in tidal current magnitude and direction, examines turbulence length and time scales, and addresses data quality and Doppler noise removal. Turbulence intensities at turbine hub heights are about 10 %, with large‑scale anisotropic eddies dominating the spectra—likely from headland proximity—while a small‑scale isotropic cascade balances shear production, informing turbine performance and fatigue estimates.

Abstract

Field measurements of turbulence are presented from two sites in Puget Sound, WA, that are proposed for electrical power generation using tidal current turbines. Time series data from multiple acoustic Doppler instruments are analyzed to obtain statistical measures of fluctuations in both the magnitude and direction of the tidal currents. The resulting turbulence intensities (i.e., the turbulent velocity fluctuations normalized by the deterministic tidal currents) are typically 10% at the hub heights (i.e., the relevant depth) of the proposed turbines. Length and time scales of the turbulence are also analyzed. Large-scale, anisotropic eddies dominate the turbulent kinetic energy (TKE) spectra, which may be the result of proximity to headlands at each site. At small scales, an isotropic turbulent cascade is observed and used to estimate the dissipation rate of TKE, which is shown to balance with shear production. Data quality and sampling parameters are discussed, with an emphasis on the removal of Doppler noise from turbulence statistics. The results are relevant to estimating the performance and fatigue of tidal turbines.