Experimental analysis of the influence of proximity to channel boundaries and blockage ratio on far field hydrodynamic effects and performance of rows of tidal turbines

Tidal energy is now the subject of an extensive amount of research. Several studies have demonstrated the significant potential contribution to low carbon electricity production which the tides are capable of. An inevitable transition in this technology is from single turbines to groups of turbines in suitable channels. This is necessary to help reduce the cost of generation, which are still considerably higher than established renewable technologies such as wind power, and also more conventional power generation sources such as coal. However much is still to be learned about the effects tidal technology have on their surrounding flow environment. Changing the specific position of a row of turbines with respect to flow boundaries and the level of blockage of a channel are two particular areas where large gaps in current knowledge have been identified.This work outlines the results of research carried out with the aim of filling some of these gaps in the knowledge. Experimental methods have been used to examine both the flow field and non-dimensional performance of tidal turbines when proximity to flow boundaries and blockage ratios are altered. Specific flow effects which have been examined include changes to the wake region of tidal turbine rows, the constraining of flow in certain localized regions of the flow domain and changes to volumetric flow rate distribution in split tidal channels.Results have demonstrated that changes to both the position and blockage ratio of a tidal turbine row in an open channel can cause considerable changes. Locating rows of turbines closer to flow boundaries, and increasing blockage ratio, results in increases to wake velocity deficit and turbulence intensity, and a simultaneous decrease in Reynolds shear stresses. In split tidal channels, it has been shown that locating towards the rear of a split in the direction of flow reduces the volumetric flow through impeded sub channels. This is significant in the context of previous research which has shown the imbalance in volumetric flow rate between sub channels to be directly related to the maximum extractable power of such channels. It is expected that the results of this research will ensure that tidal developers can make more informed choices when examining the optimum size and position of tidal turbine rows in any future tidal energy projects