The influence of solidity on the performance characteristics of a tidal stream turbine

The performance characteristics of a tidal stream turbine are critical when assessing its economical viability. The solidity of the rotor, which is a function of the blade chord length and the number of blades, will affect the performance characteristics, from both a power output and a structural loading viewpoint. This paper investigates the influence of solidity on the performance characteristics of a horizontal axis tidal turbine using experimentally validated CFD models. The solidity was varied by altering the number of blades in the numerical models. Increasing the solidity was found to increase the peak Cθ and peak Cp and reduce the λ at which these occur. Ct was found to be approximately the same at peak Cp which was assumed to be the normal operating condition. At λ above peak Cp, near freewheeling, Ct continued to increase for the 2 bladed turbine, remained approximately constant for the 3 bladed turbine and decreased for the 4 bladed turbine, indicating that higher solidity rotors would have to withstand lower loads in the event of a failure. In addition, the thrust per blade was shown to increase with a reduction in the number of blades.