Analysis of array spacing on tidal stream turbine farm performance using Large-Eddy Simulation

Ouro, Pablo; Ramírez, Luis; Harrold, Magnus

doi:10.1016/j.jfluidstructs.2019.102732

Cited by 62 publications

(30 citation statements)

References 59 publications

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“…Thus, we now investigate how the theoretical predictions of the performance of infinitely large tidal arrays compare to high-fidelity numerical predictions using LES. We adopt the well-validated in-house LES code digital offshore farms simulator (DOFAS) in which turbine blades are represented using an actuator line method (ALM) (Ouro et al 2019c) and the flow solver is fully parallelised using the message passing interface (MPI), providing a great computational scalability and performance (Ouro et al 2019a). Details of the flow solver are provided in Appendix A.…”

Section: Large-eddy Simulation Set-upmentioning

confidence: 99%

“…Many existing studies looking into tidal array optimisation have adopted low-fidelity flow models, such as two-dimensional shallow water models (Culley et al 2018), analytical wake models, e.g. Gaussian models (Stansby & Stallard 2015) and aforementioned theoretical models based on the LMADT (Nishino & Willden 2013;Draper & Nishino 2014), while high-fidelity simulations have been restricted to relatively small arrays with a limited number of configurations, due to their large computational expense (Afgan et al 2013;Chawdhary et al 2017;Ouro, Ramírez & Harrold 2019c). However, as the performance of tidal devices in arrays is driven by wake-turbine interactions as well as bathymetry-induced turbulence (Stallard et al 2013;, turbulence-resolving approaches such as large-eddy simulation (LES) are valuable to yield reliable hydrodynamics results as well as to build more accurate low-order models that can improve array optimisation tools.…”

Section: Introductionmentioning

confidence: 99%

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Performance and wake characteristics of tidal turbines in an infinitely large array

Ouro

Nishino

2021

J. Fluid Mech.

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The efficiency of tidal stream turbines in a large array depends on the balance between negative effects of turbine-wake interactions and positive effects of bypass-flow acceleration due to local blockage, both of which are functions of the layout of turbines. In this study we investigate the hydrodynamics of turbines in an infinitely large array with aligned or staggered layouts for a range of streamwise and lateral turbine spacing. First, we present a theoretical analysis based on an extension of the linear momentum actuator disc theory for perfectly aligned and staggered layouts, employing a hybrid inviscid-viscous approach to account for the local blockage effect within each row of turbines and the viscous (turbulent) wake mixing behind each row in a coupled manner. We then perform large-eddy simulation (LES) of open-channel flow for 28 layouts of tidal turbines using an actuator line method with doubly periodic boundary conditions. Both theoretical and LES results show that the efficiency of turbines (or the power of turbines for a given bulk velocity) in an aligned array decreases as we reduce the streamwise turbine spacing, whereas that in a staggered array remains high and may even increase due to the positive local blockage effect (causing the local flow velocity upstream of each turbine to exceed the bulk velocity) if the lateral turbine spacing is sufficiently small. The LES results further reveal that the amplitude of wake meandering tends to decrease as we reduce the lateral turbine spacing, which leads to a lower wake recovery rate in the near-wake region. These results will help to understand and improve the efficiency of tidal turbines in future large arrays, even though the performance of real tidal arrays may depend not only on turbine-to-turbine interactions within the array but also on macro-scale interactions between the array and natural tidal currents, the latter of which are outside the scope of this study.

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Section: Large-eddy Simulation Set-upmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Performance and wake characteristics of tidal turbines in an infinitely large array

Ouro

Nishino

2021

J. Fluid Mech.

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“…An alternative approach for the local and global hydrodynamics may be undertaken using higher-fidelity models such as those that utilise three-dimensional Reynolds-averaged Navier-Stokes (RANS) (Abolghasemi et al, 2016;Deskos et al, 2017) or large-eddy simulation (LES) methods (Churchfield et al, 2013;Ouro et al, 2019) which inherently allow for greater insight and accuracy in the near-wake region by allowing both horizontal and vertical wake dispersion through scale-resolving simulations. Such simulations emphasise how wake avoidance is not only critical for maximum exploitation of the channel potential, but also in reducing turbulence onto downstream turbines which may compromise the devices' lifetime due to fatigue (Thiébaut et al, 2020).…”

Section: On the Characterisation Of Array Hydrodynamicsmentioning

confidence: 99%

Combining shallow-water and analytical wake models for tidal array micro-siting

Jordan¹,

Dundovic²,

Fragkou³

et al. 2022

Preprint

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Array optimisation is critical for improving power performance and reducing infrastructure costs thereby helping enable tidal-stream energy to become a competitive renewable energy source. However, ascertaining an optimal array layout is a highly complex problem, subject to the specific site hydrodynamics characterisation and multiple inter-disciplinary constrains. In this work, we present a novel optimisation approach that combines an analytical-based wake model, FLORIS, with an ocean model, Thetis. The approach is demonstrated with applications of increasing complexity. By utilising the method of analytical wake superposition, the addition or alteration of turbine position does not require re-calculation of the entire flow field, thus allowing the use of simple heuristic techniques to perform optimisation at a fraction of the computational cost of more sophisticated methods. Using a custom condition-based placement algorithm, this methodology is applied to the Pentland Firth for 24 turbines with a rated speed of 3.05 m/s, demonstrating practical implications whilst also considering the temporal variability of the tide. Micro-siting using this technique generated an array 12% more productive on average than a staggered layout, despite flow speeds regularly exceeding the rated value. Performance was further evaluated through assessment of the optimised layout within the ocean model that represents the turbines through a discrete turbine representation.Used iteratively, this methodology could be applied to deliver improved array configurations in a manner that accounts for local hydrodynamic effects.

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“…For example, Harrison [98] reports inconsistencies between the actuator BEM and actuator disk's predictions of power of in-line turbines, using an array of 10 turbines with infinite transverse rows: 7D and 2D, downstream and lateral offset, respectively. In comparison, results using the actuator line have been promising, although at a high cost, for predicting power and flow properties in a turbine array [82], [93], [94].…”

Section: Numerical Simulation Of Turbine Performance and Wake Amentioning

confidence: 99%

A Review on Numerical Development of Tidal Stream Turbine Performance and Wake Prediction

et al. 2020

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Recently, the output of Computational Fluid Dynamic (CFD) prediction on tidal stream turbine systems has been receiving great attention owing to the vast and untapped tidal stream potential. For several years, many publications have documented the accuracy of CFD methods for steady flows, but not for unsteady flows. A challenging area persisting in the computational field is its dependence on large computing resources, and the unsteady nature of usual tidal streams. To overcome this problem, researchers have proposed modelling simpler, representative devices or combined CFD with alternative predictive methods. Nevertheless, the turbulent modelling has been a critical issue in the CFD methods and great effort has been devoted to the study of turbulence and wave effect on the wake and functioning of the turbine. The present paper is a review of CFD application on tidal stream turbine performance in both steady and unsteady flows. The performance of the turbine predicted by actuator and blade resolved methods, has been in accordance with laboratory observations. Findings of the wake have been both consistent and inconsistent with measurements, arising from interpretation of the blade force, fluid-solving method and onset flow model, and downstream range distance. With regards to arrays, preliminary work shows turbine arrangement can have profound effects in the onset flow, and in consequence, the performance of adjacent turbine rows. The results reported appear to support the wind similarity assumption, such as wake Gaussian velocity distributions and fluctuating turbine output in unsteady flows. Under the influence of surface waves, the wake recovers faster than steady flow condition due to the flow's convective acceleration, but the mean performance stays almost equal. The findings in this paper give a critical review and insight of important implications for future turbine research, such as experimental validation of the turbine prediction output in small and large arrays. INDEX TERMS Computational fluid dynamic, tidal stream turbine, unsteady flow, turbine performance, wake characteristics.

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Analysis of array spacing on tidal stream turbine farm performance using Large-Eddy Simulation

Cited by 62 publications

References 59 publications

Performance and wake characteristics of tidal turbines in an infinitely large array

Performance and wake characteristics of tidal turbines in an infinitely large array

Combining shallow-water and analytical wake models for tidal array micro-siting

A Review on Numerical Development of Tidal Stream Turbine Performance and Wake Prediction

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