Abstract
This paper investigates the influence of wake interaction and blockage on the performance of individual turbines in a staggered configuration in a tidal stream farm using the CFD based Immersed Body Force turbine modelling method. The inflow condition to each turbine is unknown in advance making it difficult to apply the correct loading to individual devices. In such cases, it is necessary to establish an appropriate range of operating points by varying the loading or body forces in order to understand the influence of wake interaction and blockage on the performance of the individual devices. The performance of the downstream turbines was heavily affected by the wake interaction from the upstream turbines, though there were accelerated regions within the farm which could be potentially used to increase the overall power extraction from the farm. Laterally closely packed turbines can improve the performance of those turbines due to the blockage effect, but this could also affect the performance of downstream turbines. Thus balancing both the effect of blockage and wake interaction continues to be a huge challenge for optimising the performance of devices in a tidal stream farm.
Highlights
The study of turbine to turbine interaction is crucial to understand how energy shadowing of an array of devices influences energy extraction by the individual devices
A model of a small (7 turbine) tidal stream farm was constructed to investigate the influence of wake interaction on the performance of individual devices
This study has provided valuable information on how to identify the maximum operating points of turbines in cases where the inlet flow conditions to each turbine is unknown in advance
Summary
The study of turbine to turbine interaction is crucial to understand how energy shadowing of an array of devices influences energy extraction by the individual devices. Simple turbine to turbine interactions can be investigated using small scale experiments on two or three turbines, but the feasibility of experimental studies with multiple devices in a tidal stream farm is challenging due to the practical and cost implications of an experiment involving tens of devices within a sufficiently large flow domain. For single turbine simulations either in wind or tidal turbines, it is possible to employ detailed modelling techniques such as tracking the individual blade motions with current computational resources. As the number of devices increases, such as in the study of arrays of devices, the computational cost spirals and detailed blade modelling becomes impractical. In such cases we must investigate lower cost turbine modelling such as actuator disk methods
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