| Summary: | 碩士 === 國立成功大學 === 航空太空工程學系 === 105 === Nowadays, renewable energy plays a crucial role in building a more sustainable life for the world by cutting back the energy consumption from traditional fossil fuel sources-the main cause of global warming. Beside the conventional kinds of renewable energy such as wind and solar, marine current energy has yet been significantly deployed although it has the greatest potential of energy. One of the recent technology for marine tidal current energy conversion is the utilization and adaptation of the conventional horizontal-axis turbine with the implementation of diffuser-augmented duct. This duct enables the turbine performance be raised a significant percentage. The main purpose of this research is to study the possibility and physics that can further enhance the hydrodynamic performance of the diffuser-augmented tidal turbine with a nozzle add-on device. Hydrodynamic performance assessment and model design is based on computational fluid dynamics (CFD) simulations. A comparison of the potential performance of the original ducted turbine and the modified models with nozzle add-on was also carried out.
The add-on nozzle is designed to create a converged channel surrounding the duct outlet in order to accelerate the outbound flow and create a pressure drop surrounding the duct outlet. Hence, it creates a larger pressure difference between the inlet and outlet flow of the system. Wider pressure difference will result in a greater mass flow entering the system leading to the improvement in power output. Moreover, the pressure difference also is bigger across the blade surface and generates bigger torque and power output. Parametric study of the design in various configurations, mainly the nozzle length and the nozzle inlet/outlet area ratios, have been conducted to understand the influence of the geometric parameters on the turbine performance. The results confirmed that the overall hydrodynamic efficiency of the diffuser-augmented turbine has been significantly improved. The maximum hydrodynamic efficiency improvement was found to be equal to 28.2% with the nozzle add-on device implemented.
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