Numerical And Experiment Studies On A Novel Vertical-axis Tidal Current Energy Conversion Device

With the progress of society and economic development, more energy is an urgent need to all over the world. The need to source more energy from clean renewable energy resources is becoming increasingly important as evidence that energy crisis, climate change, all caused largely by human activity, continues to grow. Excessive consumption of traditional fossil energy consumption and the resulting environmental pollution has seriously affected the social progress, economic and industrial development. Many countries in the world have begun to study renewable energy sources such as ocean renewable energy and related energy research application. The tidal currents energy gradually becomes the research hotpot as its predictability, saving land resource and higher energy density in recent years.In the background of a15kw new type vertical-axis tidal current energy conversion device tested in sea trial, A novel concept of co-axis dual-rotors tidal current turbine is put forward. Several research work is arranged around this new type turbine such as:numerical and experiment study on single-rotor vertical axis turbine considering the3D effect of support arms; self-start performance of the new type turbine; Theoretical analysis and numerical simulation on fatigue response of main shaft. Main research contents are summarized as follows:(1) Based on the theory of helicopter rotor aerodynamics, the3D flow field of turbine with support arm and without support arm are simulated and discussed. The normal force coefficients and tangential force coefficients of turbine blade with support arm and without support arm have been calculated. Meanwhile the pressure distribution along the span of turbine blade with and without the support arm are computed with the variation of tip speed ratio. Based on modified Realizable k-s turbulence model and Navier-Stokes equation, the end plate effect of the vertical-axis tidal current turbine is3D hydrodynamic numerically simulated by commercial CFD software Fluent. Three kinds of different aerofoils support arms NACA0012、NACA0015、NACA4415and circle section support arm are simulated to compare the start-up performance, steady rotation speed and power conversion coefficient. In order to improve the self-start performance, a novel turbine called co-axis dual-rotors turbine is proposed and numerical simulation is carried out to quantitatively analyze the influence of different phase difference installation angle. Finally, the best installation Angle is given out by schemes optimization.(2) To intuitive understanding the performance of the vertical-axis turbine and facilitate the validation of numerical model, the laboratory experiment has been carried out using three different types of NACA aerofoil connecting arm and circle section connecting arm. Based on the experiment and numerical results, A prototype15kW co-axis dual rotors tidal current turbine are field test in DaXiao Changshan channel. A vertical-axis tidal current turbine with3.8m diameter and4m span blade were installed and velocity, rotation speed and power were measured. Before sea-trial a modified tidal current numerical model is proposed to get the tidal current field and estimate the reserves distribution of tidal current energy with Significant Influence Factor(SIF) method. And for the characteristic of reciprocating flow in the region of DaXiao Changshan channel, the method of average power conversion efficiency is introduced to estimate the performance of the turbine.(3) The main shaft is one of the most important components of vertical-axis tidal current turbine used to transmit torque generated from blade and withstand other cyclic loading. Firstly, a novel concept of stress correction method is developed to obtain the fatigue characteristic S-N curve of main shaft. Secondly, the rainflow counting method is adopted to describe the variable-amplitude high-cycle torque loading spectrum. Finally the classical linear cumulative damage Palmgren-Miner theory is utilized to estimate the fatigue damage coefficient. Due to the complexity of the main shaft load, failure modes can not be explicit expressed. So the reliability of the support vector machine (SVM) theory is proposed to apply to the main shaft structure, based on which the failure probability of the main shaft structure system reliability are analyzed and discussed.