Abstract
A novel method for modelling tidal-stream energy capture at the regional scale is used to evaluate the performance of two marine turbine arrays configured as a fence and a partial fence. These configurations were used to study bounded and unbounded flow scenarios, respectively. The method implemented uses turbine operating conditions (TOC) and the parametrisation of changes produced by power extraction within the turbine near-field to compute a non-constant thrust coefficient, and it is referred to as a momentum sink TOC. Additionally, the effects of using a shock-capture capability to evaluate the resource are studied by comparing the performance of a gradually varying flow (GVF) and a rapidly varying flow (RVF) solver. Tidal-stream energy assessment of bounded flow scenarios through a full fence configuration is better performed using a GVF solver, because the head drop is more accurately simulated; however, the solver underestimates velocity reductions due to power extraction. On the other hand, assessment of unbounded flow scenarios through a partial fence was better performed by the RVF solver. This scheme approximated the head drop and velocity reduction more accurately, thus suggesting that resource assessment with realistic turbine configurations requires the correct solution of the discontinuities produced in the tidal-stream by power extraction.
Highlights
Resource characterisation is the initial step of any tidal energy project
Analysis of an actuator disc within a finite flow unveiled the importance of turbine bypass flow, blockage ratio (B), and the turbine downstream mixing region; where B indicates the fraction of a channel cross-sectional area occupied by the turbine
Momentum sink turbine operating conditions (TOC) was implemented in two numerical hydrodynamic models based on the depth integrated velocity and solute transport (DIVAST) model [28]
Summary
Resource characterisation is the initial step of any tidal energy project. conventional methodologies to assess tidal-stream power are based on infinite extent flow and the representation of a turbine as actuator disc [1,2,3,4,5,6]. The model uses a low-order scheme to simulate the regions where strong gradients exist and spurious numerical solutions are likely to appear This solver constitutes an efficient approach for simulating energy capture in rapidly varying flows because the scheme is not required to solve the Riemann problem at each grid, where an array of turbines are defined, to compute the discontinuities produced in the flow due to power removal. Analytical models provide an understanding of the physics involved in tidal-stream power extraction; numerical simulations are required to provide a more complete analysis of the effects of tidal energy extraction In this context, the two-dimensional approach, the line sink of momentum was developed to assess tidal-stream resource with a long partial fence, through the solution of shallow water equations. The methodology proposed will enable the identification of a less computationally expensive numerical tool that provides a reliable evaluation of the resource in realistic scenarios
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