Abstract
This paper describes the design of a fixed pitch horizontal axis tidal turbine for use in a DeltaStream device. The DeltaStream unit consists of three turbines each mounted on a swivelling nacelle atop a pylon which is located at the vertex of a delta shaped freestanding structure. The tidal turbine has to be designed so that the total thrust on the assembly is less than the frictional forces opposing any motion. This leads to a design requirement where the power-thrust ratio is a maximum for the turbine. This is especially difficult with a fixed pitch turbine where it is required to maximise the power over the tidal cycles for a maximum possible thrust. The turbine blades were designed using design methods more commonly used in turbomachinery rather than the Blade Element Method (BEM) used in wind turbines. The design was then assessed by CFD using CFX over a range of tip speed ratios to generate a set of non-dimensional characteristics which could be used, together with a tidal probability distribution from EMEC, to generate average powers and peak loads. The unsteady loads were assessed by estimating the level of the mean unsteady velocity and how the rotor would respond in a one-dimensional manner. Site specific data could then be applied to obtain more realistic loads.