An experimental investigation simulating flow effects in first generation marine current energy converter arrays

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 highlight 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. This will lead to a synergistic effect whereby an array of devices can generate more power than an equivalent number of isolated machines.