Design and Simulation of a Horizontal-Axis Tidal Turbine (HATT) Blades for Tropical Site Conditions using Reynolds-Averaged Navier-Stokes - Blade Element Momentum Theory (RANS-BEMT)

Ocean Renewable Energy (ORE), particularly the tidal energy, has seen increasing interests in the development of renewable energy in the Philippines. Currently, the proposed and operational tidal stream turbine blade designs are intended for areas of higher tidal flow velocities (> 4 m/s). However, the Philippines is situated in the tropical region where tidal stream flows are characterized by low flow velocities (< 2 m/s). Using the existing blade designs on tropical site conditions may result in lower efficiency and uneconomical results. This study tackles the design and simulation of Horizontal-Axis Tidal Turbine (HATT) blades for the tropical site conditions such as those found in the Philippines. A coupled Reynolds Average Navier-Stokes (RANS) and Blade Element Momentum Theory (BEMT) is used to design a notional HATT blade and evaluate its performance. RANS-BEMT approach allows the study of the tidal turbine blades’ interaction with the surrounding fluid as it considers the turbulence through RANS simulation and surface pressure distribution along the blades to check the design for cavitation in the hydrodynamic analysis.This study starts with the characterization of the potential sites for tidal energy extraction. The Davao Gulf in Davao del Sur, Philippines is one of the potential areas for tidal in-stream technology that remains unexplored. Conducting a numerical hydrodynamic modeling and resource assessment of tidal stream potential in Davao Gulf will quantify the amount of resource available in the region and pinpoints the areas that are most suitable for tidal in-stream turbine deployment. To demonstrate this process, the Davao Gulf’s hydrodynamic model is simulated using TELEMAC-2D to determine the Probability Distribution Function (PDF) of the tidal stream velocities from a potential installation site. The simulated site’s hydrodynamic model is then validated by comparing its predicted values with the in-situ data available. The free surface of the hydrodynamic model obtained in this study has RMSE and Pearson’s R values of 0.119 m and 0.989, respectively, which indicates a very high accuracy and correlation against the in-situ measured data. As for the site’s selection criteria, the potential site must have depths ranging from 30 to 50 m that can accommodate a 10 m diameter HATT and where the mean spring tide velocity is the highest. From these given criteria, the coordinate (6.958, 125.715) is chosen as the potential site for a HATT installation. The selected location shows a maximum flow velocity of 1.6 m/s and the most frequent velocity of 0.65 m/s.In designing the HATT blade, the NACA 63815 hydrofoil is used for blade profile due to its high lift to drag ratio compared to other candidate hydrofoils. An open-source BEMT code is utilized in calculating the turbine blade geometry, such as chord and twist distributions of the chosen hydrofoil across the blade span. Then, its 3D model is simulated in ANSYS Fluent to calculate its performance curves and hydrodynamic loads at different flow velocities. The simulation shows that the HATT has a maximum power coefficient of 0.36 at a Tip Speed Ratio (TSR) of 6.2, as well as a very low likelihood of cavitating. The turbine’s power performance curve and the selected site’s PDF are then used to calculate the estimated Annual Energy Production (AEP) of the notional HATT for the chosen location, estimated at 32,000 kWh/yr.