Characterization of turbulence anisotropy, coherence, and intermittency at a prospective tidal energy site: Observational data analysis

Abstract

a b s t r a c tAs interest in marine renewable energy increases, observations are crucial for understanding the environments that prospective turbines will encounter. Data from an acoustic Doppler velocimeter in Puget Sound, WA are used to perform a detailed characterization of the turbulent flow encountered by a turbine in a tidal strait. Metrics such as turbulence intensity, structure functions, probability density functions, intermittency, coherent turbulence kinetic energy, anisotropy invariants, and a new scalar measure of anisotropy are used to characterize the turbulence. The results indicate that the scalar anisotropy magnitude can be used to identify and parameterize coherent, turbulent events in the flow. An analysis of the anisotropy characteristics leads to a physical description of turbulent stresses as being primarily one-or two-dimensional, in contrast to isotropic, three-dimensional turbulence. A new measure of the anisotropy magnitude is introduced to quantify the level of anisotropic, coherent turbulence in a coordinate-independent way. These diagnostics and results will be useful for improved realism in modeling the performance and loading of turbines in realistic ocean environments.

Wave-Turbulence Decomposition Methods Applied to Tidal Energy Site Assessment

“…The integral time scale can then be obtained by integrating ρ(τ) until the first zero-crossing point. By assuming Taylor's frozen field hypothesis, the integral length scale can be calculated by multiplying the integral time scale by the average velocity [11]. Here, this analysis is performed over 5-min periods.…”

“…Observation of low and high frequency variations at turbine loadings indicated the presence of a variety of length scales and led to the conclusion that quantifying turbulence parameters is important to guarantee the device's long-term functionality. These results highlight the need to obtain accurate site-specific estimates of turbulence characteristics to ensure the optimum performance of tidal turbines and avoid unnecessary conservativeness and premature fatigue [10][11][12][13][14].…”

Engineering analysis of turbulent flow measurements near Kuchinoshima Island

“…Turbulence intensity is a standard metric used in the wind turbine industry [13,14] and is commonly used in the tidal power research field [15]. It is given by Here n 2 is the noise-induced variance 2 noise associated with ADCP instruments as described above.…”

Multiscale anisotropic fluctuations in sheared turbulence with multiple states

“…The notion that all turbulent flows attain universal properties at small scales, regardless of the macroscopic details, has been an enduring and yet unproved concept in turbulence research [1][2][3]. The energy containing scales in many flows such as shear, rotation, natural convection, thick layers, atmospheric boundary layer and magneto-hydrodynamic flows, are all strongly affected by anisotropic (and non-homogeneous) effects of the extrinsic stirring and boundary conditions, resulting in seemingly different flow configurations [4][5][6][7][8][9][10][11][12][13]. As such, anisotropic fluctuations are always connected to some degree of non-universality, i.e.…”