| Summary: | Performance advantages from blockage are not currently accounted for in tidal turbine rotor and array design. Experiments have been performed to study the impact on performance of two identical rotors designed for, and operating in, high local blockage, when deployed in a large cross-section (low global blockage) tank. Tests were carried out on a single, and then two side-by-side, rotors in order to study the influence that local blockage has on the constructive interference between the rotors. This paper presents the impact that the second rotor has on the mean power and thrust coefficients. It is shown that at the design point, the power coefficient increases by 20% for a less than 10% increase in thrust. By operating the two turbines at different speeds it is shown that a further increase in power (up to 12%) can be achieved for one turbine by operating the neighbouring rotor at 1.5 times the thrust, which itself results in a reduction in power of the higher thrust turbine. At the design point flow is shown to accelerate significantly between and downstream of the two rotors, with similar though less extreme observations in the bypass regions. The results for performance and flow patterns follow trends that are observed in the literature for both theoretical and numerical studies, paving the way for industry to benefit from constructive interference in next generation turbine design.
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