Influence of support structures on tidal turbine power output

A fully blade resolved CFD model with a RANS formulation using the k−ω SST turbulence model was used to study the tidal turbine performance in the presence of two support structures with cylindrical and elliptical cross-sections. The integrated rotor force coefficients were higher in the presence of the cylindrical support structure than the elliptical support due to the higher opposing thrust from the cylinder in the channel increasing the local flow velocity near the top half of the rotor. The angle of attack on the blade decreases as it approaches the support structure due to the reduction in stream-wise flow velocity just ahead of the support structure. This drop is higher for cylindrical support than the elliptical support due to its larger opposing thrust to the flow causing a larger drop in stream-wise velocity. The drop in the angle of attack due to the presence of support structures causes a significant drop in the blade sectional forces as it approaches the support structure. The presence of rotor also causes a drop in the forces on the support structure. The mean stream-wise force coefficients of the cylindrical and elliptical support structures are 0.21 and 0.12 respectively, which are much lower than if they were in open water without a rotor. In case of both the support structures, the stream-wise sectional forces behind the rotor swept area are lower than that in open-water whereas the mean cross-stream forces are higher. The thrust from the rotor and the support structure has a direct influence on the wake velocity. The velocity deficit just in-front of the support structure is 20% higher for the cylindrical support than the elliptical support due to its higher opposing thrust to the flow, and further downstream, the case with cylindrical support has higher velocity deficit followed by elliptical support and then the case with no support structure.