Design and simulation of a bidirectional underwater open-center micro tidal turbine for harvesting tidal energy

Abstract

Costal and Island regions of Bangladesh require reliable, predictable, and locally adaptable renewable energy solutions. Sandwip and similar coastal locations experience repeated tidal motion, which makes tidal Stream Energy a promising option for decentralized electricity generation. This thesis presents the design, hydrodynamic simulation, and electrical output evaluation of a bidirectional micro tidal stream turbine intended for low-to-moderate tidal current applications. The proposed turbine uses a ducted, open-centered annular geometry with a six-blade rotor. The open-centered rotor allows flow to pass through the central region while the blades extract energy from the surrounding annular flow region. A curved ducted housing is used to guide the incoming tidal current and support the practical turbine assembly. The turbine was first designed in SolidWorks. Two CAD representations were considered: a practical assembly including support base, stator housing, coil slots, rotor-magnet concept, and duct structure; and a simplified no-base geometry used for ANSYS Fluent simulation. The CFD model was analyzed for tidal velocities from 0.4 m/s to 2.4 m/s at a fixed tip-speed ratio of 3. The CFD dataset produced turbine efficiency values mostly between approximately 50% and 56%, The mechanical outputs were then used in a simplified MATLAB/Simulink electrical model. In the third term, the turbine torque and angular speed are applied to a permanent magnet synchronous machine (PMSM) generator, which is directly connected to a balanced 15 ohm three-phase resistive load. Phase RMS voltage, phase RMS current, three-phase load power, load energy, electrical frequency, and mechanical-to-load efficiency were calculated for each operating point. At 2.1 m/s, the system produced about 3362.83W mechanical shaft power and delivered about 528.7W load power. A 21-point power-velocity lookup table was also used with a 24.84-hour tidal velocity profile to estimate energy output over one lunar tidal day. The integrated energy output was approximately 6.675 kWh per lunar tidal day, 193.48 kWh per 30 days, and 2.354 MWh per year