Design Study of Horizontal Axis Tidal Turbine Blade

A design study was conducted to understand the implications of bio-mimicking a curved caudal fin type horizontal axis tidal turbine blade design, using National Advisory Committee for Aeronautics (NACA) 0018 is presented. A method of transforming the traditional horizontal axis tidal turbine by defining a third order polynomial center line on which the symmetrical airfoils were stationed is also disclosed. Each of the airfoil characteristics: twist angle distribution, chord lengths, and a center line passing through the airfoil centers were automatically transformed to create the curved caudal fin-shaped blade; translating the spinal blade axis into percentage wise chord lengths, using NACA 0018 airfoil. A 3D mesh independency study of a straight blade horizontal axis tidal turbine modeled using computational fluid dynamics (CFD) was carried out. The grid convergence study was produced by employing two turbulence models, the standard k-ε model and shear stress transport (SST) in ANSYS CFX. Three parameters were investigated: mesh resolution, turbulence model, and power coefficient in the initial CFD, analysis. It was found that the mesh resolution and the turbulence model affect the power coefficient results. The power coefficients obtained from the standard k-ε model are 15% to 20% lower than the accuracy of the SST model. Further analysis was performed on both the designed blades using ANSYS CFX and SST turbulence model. The results between the straight blade designed according to literature and the caudal fin blade showed a maximum power coefficient of 0.4028%, and 0.5073% respectively for 2.5m/s inlet velocity.