A numerical performance analysis of a ducted, high-solidity tidal turbine in yawed flow conditions

Analysing the fluid dynamic performance of a bare rotor when succumb to yawed flow conditions has consistently presented a diminishment in mechanical power conversion efficacy. Introducing a duct along the rotor perimeter has been acknowledged to sustain performance, yet the causation behind this phenomenon is uncertain. This study puts forward an investigation into the hydrodynamic performance concerning a true-scale, ducted, high-solidity tidal turbine in yawed free-stream flows by utilising blade-resolved, unsteady computational fluid dynamics. Investigating the performance within an angular bearing range of 0o to 45o with the turbine axis, increases in mechanical rotational power and thrust are acknowledged within a limited range at distinct tip-speed ratio values. Through the multiple yaw iterations, the maximum attainment falls at an angle of 23.2o, resulting in a power increase of 3.44% to a peak power coefficient of 0.35 at a nominal tip-speed ratio of 2.00, together with an extension of power development along higher tip-speed ratios. In verification of the power increase, the outcomes are analysed by means of linear momentum theory; by utilising area-averaged values of static pressure acquired from annular radial surfaces fore and aft of the rotor, an analogous relationship with the blade-integrated outcomes is attained. The analysis concludes that, at higher tip-speed ratios, the pressure drop across the rotor increases at limited flow bearings, enhancing the resultant axial force loading upon the blades, hence providing further performance augmentation of the ducted, high-solidity tidal turbine.