Abstract
To fully understand the performance of tidal stream turbines for the development of ocean renewable energy, a range of computational models is required. We review and compare results from several models of horizontal axis turbines at different spatial scales. Models under review include blade element momentum theory (BEMT), blade element actuator disk, Reynolds averaged Navier Stokes (RANS) CFD (BEM-CFD), blade-resolved moving reference frame and coastal models based on the shallow water equations. To evaluate the BEMT, a comparison is made to experiments with three different rotors. We demonstrate that, apart from the near-field wake, there are similarities in the results between the BEM-CFD approach and a coastal area model using a simplified turbine fence at a headland case.
Highlights
The attempt to fully understand the mechanics of extraction of energy from tidal currents is a challenging engineering problem
The results show that the wake shape for the BEM-CFD method is symmetric, while the blade-resolved geometry (BRG)
The results show that blade element momentum theory (BEMT) under-predicts power in comparison to BEM-CFD
Summary
The attempt to fully understand the mechanics of extraction of energy from tidal currents is a challenging engineering problem. Computationally-efficient schemes, such as the BEMT and BEM-CFD approaches, rely on pre-determined lift and drag data and, can only capture the effects of changes in sectional properties (e.g., as a result of biofouling or pitting) if these data are altered. As a result of the sparse data and the interpolation, the BEMT results contain many small discontinuities, since in many cases, a relatively small change in inflow angle results in a large jump in the lift and drag properties of the foil This is noticeable in the BEMT work carried out at Manchester, as can be seen in the studies that report their experimental results [10]. Note that an earlier numerical investigation by Batten et al [15] treated drag in a similar fashion, but did not consider the effects of roughness on lift These results are presented graphically, along with experimental data for the IFREMER and Manchester turbines. The agreement between BEMT predictions and experimental results allows us to be confident in our numerical model
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