Tidal currents are one of the most promising sources of power within the renewable energy sector, especially for countries with suitable marine conditions. The United Kingdom has the edge over the rest of countries in this type of renewable energy and leads the innovation race in order to keep the UK economy competitive in future years. Following these reasons, several types of marine turbines are currently being developed and tested. Nevertheless, one of the key issues, in the future development of marine hydrokinetic power generation systems, is to properly understand their prospective performance, not only for each power generation device alone but also for an array of devices as a whole. Recent theoretical studies have suggested that a dense cross-stream array of turbines (so-called turbine fence) is a promising way to extract power from marine currents; however, its optimal intraturbine spacing depends on several physical factors, some of which are still uncertain. One of those uncertain factors is the effect of seabed friction causing vertical shear of the flow, which is difficult to study theoretically and requires 3-D CFD simulations. Also, little is known about the performance of multiple rows of marine turbines. Consequently, throughout this thesis, numerous arrangements of marine turbines (modelled as actuator disks) have been tested using ANSYS Fluent®, with the idea of assessing the effects of various parameters such as: intra-device spacing, number of rows and turbine resistance coefficient. These CFD simulations have been compared with existing theoretical models (two-scale actuator disk models) for the power extracted by the turbines with the aim of validating these theoretical models. Also, the results of CFD simulations have been analysed in detail to better understand the characteristics of flow past these turbine arrays.

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