Research On Passive Oscillating Hydrofoils For Tidal Current Energy Extraction Technology

With the consumption of fossil fuels and the aggravation of environmental pollution,more and more countries have motivated significant research efforts on clean and renewable energy sources in recent years, tidal current energy is well known example. Aiming at many problems and deficiencies of conventional rotating blades turbine, a passive oscillating hydrofoil energy extracting technology that imitates the tail swinging of fish to extract energy from flow field is presented in this paper. The feasibility of oscillating hydrofoil tidal current energy extraction is studied in this paper based on the obvious advantages exhibited by oscillating hydrofoil in shallow water sites, the main aspects studied are as follows:(1) Based on the comprehensive research status analysis of oscillating hydrofoil energy extraction device and the relevant influencing parameters at home and abroad, an oscillating hydrofoil energy extracting numerical simulation and experimental tests technology is introduced and studied. In the meanwhile, the theoretical analysis including the movement characteristics, energy extraction principle, oscillating hydrofoil energy extraction efficiency and power is presented and performed.(2) According to the overall scheme proposed, the structure of energy extraction device is designed and optimized. Then, concrete structure design and analysis of the key parts including oscillating hydrofoil, heaving motion energy extraction, hydrofoil pitching angle changing, mechanical energy transmission and conversion as well as supporting parts are completed. According to the requirements of the oscillating hydrofoil heaving and pitching sinusoidal motion rule with two degrees of freedom, the length and initial position of the key transmission parts are optimized and determined, and the reliability of optimization results are proved through dynamics simulation.(3) In order to study the force characteristics and energy extraction performance of oscillating hydrofoil in the flow field environment, an oscillating hydrofoil numerical simulation model is built by Fluent software, and the rationality verification of the model is also completed. Then the effect of heaving amplitude, pitching amplitude, tandem hydrofoils separation distance and reduced frequency on the energy extraction performance is analyzed,the relationship between the change of relevant parameters and energy extraction performance is determined. Moreover,the effect of wake vortex and hydrodynamic parameters at different reduced frequencies on energy extraction performance of the upstream hydrofoil and downstream hydrofoil is analyzed from the vortex formation and shedding structural features.(4) In order to validate the actual ability of oscillating hydrofoil energy extraction, the tidal current energy extraction experimental platform based on oscillating hydrofoil is built,on which a series of experiments are performed in the circulation water channel. Among them,the single hydrofoil and tandem hydrofoils energy extraction experiment at different reduced frequencies are carried out by changing generator loads, and the relationship between optimal energy extraction output of tandem hydrofoils and flow velocities are studied by changing flow velocities.