Abstract
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.
Highlights
Reducing the reliance on high-carbon fuels is an important issue for governments
A comparison of results among the methods is shown in Tab.1. Overall these results indicate the importance of Computational Fluid Dynamic (CFD) models for their wake capacity; RANS models would benefit from further refinement for predicting the near wake zone
To develop a comprehensive overview of this issue, the blade element momentum (BEM) method may increase in complexity, by incorporating the dynamic wake, stall, and the added mass effects and wave loads on turbine and support structure [126], [127]
Summary
Reducing the reliance on high-carbon fuels is an important issue for governments. Quite recently, the kinetic energy of tidal streams has been converted into electricity through. To fulfil the envisioned tidal stream potential, it is crucial to establish steps committed to the financial success of electricity-delivering tidal stream systems These include the development of cost-effective foundations and understanding of turbine performance in site conditions, requiring the characterization of the marine currents and flow past the turbine. A primary concern of the tidal farms is to maximize profits in a small-invasive ecological manner [37] In many cases, it may be associated with the resulting, disturbed rotating flow behind a single turbine, named the wake; since the changes in onset flow are known to have a serious effect in the turbine’s production of electricity [38]. With the recent trends in climate change action and proliferation of farm project proposals, more knowledge will become available from field trials and prototypes, corroborating the above findings
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