The effect of tidal flow directionality on tidal turbine performance characteristics

With many Tidal Energy Conversion (TEC) devices at full scale prototype stage there are two distinct design groups for Horizontal Axis Tidal Turbines (HATTs). Devices with a yaw mechanism allowing the turbine to always face into the flow, and devices with blades that can rotate through 180° to harness a strongly bi-directional flow. As marine turbine technology verges on the realm of economic viability this paper reveals the performance of Cardiff University's concept tidal turbine with its support structure either upstream or downstream and with various proximities between the rotating plane of the turbine and its support stanchion. Through the use of validated Computational Fluid Dynamics (CFD) modelling this work shows the optimal proximity between rotor plane and stanchion as well as establishing, in the given context, the use of a yaw mechanism to be superior to a bi-directional system from a performance perspective

Kinetic energy extraction of a tidal stream turbine and its sensitivity to structural stiffness attenuation

© 2015 The Authors. The hydrodynamic forces imparted on a tidal turbine rotor, whilst causing it to rotate and hence generate power, will also cause the blades to deform. This deformation will affect the turbine's performance if not included in the early design phase and could lead to a decrease in power output and a reduction in operational life. Conversely, designing blades to allow them to deform slightly may reduce localised stress and therefore prolong the life of the blades and allow the blades to deform in to their optimum operational state. The aim of this paper is to better understand the kinetic energy extraction by varying the material modulus of a turbine blade. Shaft torque/power, blade tip displacement, and axial thrust results are presented for 2, 3 and 4 bladed rotor configurations at peak power extraction. For the rotor design studied the FSI model data show that there is a low sensitivity to blade deformation for the 2, 3 and 4 bladed rotors. However, the results reveal that the 3 bladed rotor displayed maximum hydrodynamic performance as a rigid structure which then decreased as the blade deformed. The 2 and 4 bladed rotor configurations elucidated a slight increase in hydrodynamic performance with deflection

Influence of a velocity profile & support structure on tidal stream turbine performance

With tidal turbine technology in its infancy prototype devices are likely to be positioned at locations where both the local marine environment and vessel navigation are favourable. However, as marine turbine technology develops toward economic viability there is a propensity for undesirable interactions with local shipping, higher turbulence levels and velocity shear through the water column to occur. The latter high shear could result from positioning the turbine lower in the water column, perhaps due to local shipping requirements. This paper helps to elucidate the performance of the tidal turbine and in particular the blade forces during rotation within a high shear velocity profile. A velocity profile from ADCP measurements was used as an inlet boundary for CFD analysis. The work shows that the presence of a suitably positioned stanchion downstream of the turbine will result in reduced performance characteristics over a complete rotation. However, the amplitude of the characteristics, in particular, the axial loading increases which would require careful design considerations