Amid growing concern over climate change and the resultant need to reduce CO2 emissions, as well as an ever-increasing global population with a rising demand for electricity, renewable energy sources have an important role to play in future electricity generation. One such source is tidal stream energy, which offers the potential for predictable electricity generation by harnessing the energy of the tide using arrays of underwater turbines.
This research explores the impact of hydrodynamic interactions between the blades of a tidal stream turbine and its support structure on turbine performance, as well as the hydrodynamic interaction of multiple turbines. Experiments were carried out using scale model turbines installed in experimental water channels, and a motorised drive system and encoder was used to record turbine performance.
Due to turbulence in the region upstream of the support structure, separation distance between the turbine blades and support structure was found to significantly influence performance. An optimal separation distance between the blades and support structure was found to allow maximum performance. The turbulent wake of an upstream turbine was also found to have a notable impact on downstream turbine performance, leading to a reduction in power output. This effect is governed by upstream and offset separation distance and support structure diameter. Particle Image Velocimetry was used to record downstream turbine velocity wakes, which were found be a complex amalgamation of turbine and support structure elements.
The testing of a turbine installed on four complex support structures produced large differences in power outputs, further highlighting the influence of support structure design on turbine performance, and confirming its importance to the design of tidal stream turbine arrays.