Abstract
In the long-term, tidal turbines will most likely be deployed in farms/arrays where energy extraction by one turbine may significantly affect the energy available to another turbine. Given the prohibitive cost of experimental and/or field investigations of such turbine interactions, numerical models can play a significant role in determining the optimum layout of tidal turbine arrays with respect to energy capture. In the present research, a low-cost modelling solution for optimising turbine array layouts is presented and assessed. Nesting is used in a far-field model to telescope spatial resolution down to the scale of the turbines within the turbine array, allowing simulation of the interactions between adjacent turbines as well as the hydrodynamic impacts of individual turbines. The turbines are incorporated as momentum sinks. The results show that the model can compute turbine wakes with similar far-field spatial extents and velocity deficits to those measured in published experimental studies. The results show that optimum spacings for multi-row arrays with regard to power yield are 3–4 rotor diameters (RD) across-stream and 1–4 RD along-stream, and that turbines in downstream rows should be staggered to avoid wake effects of upstream turbines and to make use of the accelerated flows induced by adjacent upstream turbines.
Highlights
Turbines placed in a fluid flow will alter the prevailing hydrodynamics
Unlike wind turbines, which only occupy a small fraction of the air column within which they sit, tidal turbines can occupy a large proportion of the limited water depth available in a channel
In order to realize a significant fraction of a channel’s potential to produce power, it is recommended that tidal turbines should occupy a large fraction of a channel’s water depth [2]
Summary
An area of reduced velocity, the wake, is created behind a turbine, primarily as a result of the thrust exerted by the turbine on the flow. In order to realize a significant fraction of a channel’s potential to produce power, it is recommended that tidal turbines should occupy a large fraction of a channel’s water depth [2]. The resulting blockage of flow due to the turbine's presence can lead to acceleration of the flow around the turbine (due to continuity). Structural drag will lead to reductions in current velocities in the vicinity of the turbine due to frictional losses. Accurate calculations of the expected power output from a turbine must account for wake, blockage and drag effects
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