Actuator discs may be used as a simple method for simulating horizontal axis tidal turbines, both in experiments and CFD models. They produce a similar far wake to a real turbine, but eliminate some of the scaling issues which occur in experiments, and reduce the mesh density required in CFD simulations. This paper examines methods for applying a simple actuator disc in a commercial CFD code, Ansys CFX, and compares the wake produced with experimental results for similar values of disk thrust coefficient (C T). The results show that the CFD model gives reasonable agreement with the experimental results. The main factors affecting the wake structure are the initial C T value, the ambient turbulence levels, and potentially the disc induced turbulence. The main differences between the models and experiments were in terms of the turbulence levels throughout the model. With further development, it is considered that the CFD actuator disc could be an accurate and validated method for numerically modelling tidal turbines.

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+0044 (0)23 8059 3940 L.E. Myers@soton.ac.uk www.energy.soton.ac.uk At present a small number of full-scale marine current energy converters are undergoing sea trials to demonstrate commercial viability of the technology. In order to provide meaningful quantities of electrical power to the grid, the next phase in the development of the technology will be the installation and operation of farms or arrays composed of multiple devices. As most tidal current sites are bi-directional and with bathymetry constraints, array layouts will necessarily take the form of highly optimized geometric configurations with reduced lateral inter-device spacing. This work discusses the concept of array layouts and proposes an appropriate and clear classification that can aid developers in understanding how arrays operate. This classification is supported by experimental studies conducted using several arrangements of multiple actuator disks to simulate early generation marine current energy converter arrays. The work presents quantification of the flow field around a 2-row array, device/device interaction as well as a study of the structure of the far wake region where subsequent devices could be installed. The results highlighted an optimal lateral spacing between devices where, under certain conditions flow can be accelerated between a pair of rotor disks. For the work presented here this accelerated region of flow possessed 22% more kinetic energy than the flow far upstream with no measurable negative effect upon the 2 actuator disks. This enhanced flow speed gives rise to the counterintuitive notion of a downstream row of devices producing more power than the upstream row.

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