Optimization of Hydrofoils for Horizontal Axis Marine Current Turbines Using Genetic Algorithm

Abstract

As fossil fuels near depletion and their detrimental side effects become prominent on ecosystems, the world is searching for renewable sources of energy. Tidal energy is an emerging and promising renewable energy resource. Tidal turbines can extract energy from the flowing water in a similar way as wind turbines extract energy from the wind. The upside with tidal turbines is that the density of water is approximately 800 times greater than that of air and a tidal turbine harnessing the same amount of power as a wind turbine can be considerably smaller in size. At the heart of the horizontal axis marine current turbines are carefully designed hydrofoil sections. While there is a growing need to have hydrofoils that provide good hydrodynamic and structural performances, the hydrofoils also have to avoid cavitation for safe operation. This study uses a genetic algorithm optimization code to develop hydrofoils which have the desired qualities mentioned above. The hydrofoil problem is parameterized using a composite Bezier curve with two Bezier segments and 11 control points. Appropriate curvature conditions are implemented and geometric constraints are enforced to maintain the hydrofoil thickness between 16 to 18%. XFOIL is used as the flow solver in this study. The hydrofoils are optimized at Reynolds number of 2 million and for angles between 4 to 10 degrees. The best foil from the results, named USPT4 is tested for performance with the CFD code ANSYS CFX. The CFX results are validated with experimental results in a wind tunnel at the same Reynolds number. The hydrofoil’s performance is also compared with a commonly used NACA foil.