TY - JOUR

T1 - Turbulence and Coherent Structure Characterisation in a Tidally Energetic Channel

AU - Lucas, Natasha

AU - Austin, Martin

AU - Rippeth, Tom

AU - Powell, Ben

AU - Wakonigg, Pablo

N1 - This project was supported by Knowledge Economy Skills Scholarship (KESS 2, 80815/BUK2108) led by Bangor University on behalf of the Welsh higher education sector through funding from the Welsh European Funding Office (WEFO), the European Social Fund (ESF) and the company partner Nortek-AS, Norway

PY - 2022/7

Y1 - 2022/7

N2 - Understanding the temporal and spatial characteristics of turbulent coherentstructures is of interest to the emergent sector of marine renewable energy forpower generation from tidal stream turbines as loading due to these vortexstructures has resulted in costly device failure. Here methods for characteris-ing these coherent structures are developed using an off the shelf broadbandacoustic Doppler current profiler (ADCP) vertical beam with the metrics fastFourier transforms and a wavelet element model. Results indicate length-scales fall in the range 2.5 to 51 m. Focused study on a 30-minute windowfinds the 5 most powerful features have a median lengthscale of 13.2 m andthe strongest signal lies at ∼6.8 m, which scale to 0.9 and 0.4 times the waterdepth respectively, these features have a periodicity of ∼127 s. Methods us-ing variance across ADCP beams are common for turbulence characterisationwithin the tidal energy sector, with turbulence intensity being appropriatedfrom the wind energy sector. However, turbulence intensity is found to be a poor predictor water column turbulence in the presence of coherent struc-tures.Keywords: Hydrodynamics, Tidal stream turbines, Coherent Structures,Tidal Power, Variance Method, Alternative Energy Site Assessment

AB - Understanding the temporal and spatial characteristics of turbulent coherentstructures is of interest to the emergent sector of marine renewable energy forpower generation from tidal stream turbines as loading due to these vortexstructures has resulted in costly device failure. Here methods for characteris-ing these coherent structures are developed using an off the shelf broadbandacoustic Doppler current profiler (ADCP) vertical beam with the metrics fastFourier transforms and a wavelet element model. Results indicate length-scales fall in the range 2.5 to 51 m. Focused study on a 30-minute windowfinds the 5 most powerful features have a median lengthscale of 13.2 m andthe strongest signal lies at ∼6.8 m, which scale to 0.9 and 0.4 times the waterdepth respectively, these features have a periodicity of ∼127 s. Methods us-ing variance across ADCP beams are common for turbulence characterisationwithin the tidal energy sector, with turbulence intensity being appropriatedfrom the wind energy sector. However, turbulence intensity is found to be a poor predictor water column turbulence in the presence of coherent struc-tures.Keywords: Hydrodynamics, Tidal stream turbines, Coherent Structures,Tidal Power, Variance Method, Alternative Energy Site Assessment

KW - Hydrodynamics

KW - tidal stream turbines

KW - Coherent structures

KW - Variance method

KW - Alternative energy site assessment

U2 - 10.1016/j.renene.2022.05.044

DO - 10.1016/j.renene.2022.05.044

M3 - Article

VL - 194

SP - 259

EP - 272

JO - Renewable Energy

JF - Renewable Energy

SN - 0960-1481

ER -