Abstract
A large-eddy simulation (LES) of a laboratory-scale horizontal axis tidal stream turbine operating over an irregular bathymetry in the form of dunes is performed. The Reynolds number based on the approach velocity and the chord length of the turbine blades is approximately 60,000. The simulated turbine is a 1:30 scale model of a full-scale prototype and both turbines operate at very similar tip-speed ratio of λ ≈ 3. The simulations provide quantitative evidence of the effect of seabed-induced turbulence on the instantaneous performance and structural loadings of the turbine revealing how large-scale, energetic turbulence structures affect turbine performance and bending moments of the rotor blades. The data analysis shows that wake recovery is notably enhanced in comparison to the same turbine operating above a flat-bed and this is due to the higher turbulence levels generated by the dune. The results demonstrate the need for studying in detail the flow and turbulence characteristics at potential tidal turbine deployment sites and to incorporate observed large-scale velocity and pressure fluctuations into the structural design of the turbines.
Highlights
Tidal stream energy has been identified by the European Commission [1, 2] as one of the five most promising renewable energy resources
This paper presents a Large-Eddy Simulation (LES) of a Horizontal Axis Tidal Turbine (HATT) operating in nature-like turbulent flow conditions with the aim of quantifying the impact of bathymetry-induced turbulence on the performance and structural loadings of the turbine
A horizontal axis tidal turbine operating over an irregular bathymetry has been simulated with the goal to study the impact of realistic turbulent flow conditions on the performance and loadings of the device
Summary
Tidal stream energy has been identified by the European Commission [1, 2] as one of the five most promising renewable energy resources. Main drawbacks of tidal turbines are: (i) relatively high costs that makes extremely difficult to test turbine arrays as large facilities are required [26]; (ii) hydraulic flumes, featuring smooth flat beds which do not represent the conditions found at typical marine deployment locations and the limited width of laboratory flumes which induces a blockage effect that alters the turbine’s performance and wake recovery behaviour if compared with boundless environments (e.g. estuaries or sea) [17, 27]; and (iii) the experimental data is usually not detailed enough to provide a full understanding of the complex flow-turbine interaction [11, 12].
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