Research On Energy Extraction Characteristics For The Blade Position-variable Tidal Current Turbine

The blade position-variable tidal current turbine is a brand new device that utilizes tidal current as the main energy source.This article is aimed at improving the efficiency of tidal current turbine,which the numerical simulation and simulation experiments are carried out to analyze the operation of the blade position-variable tidal current turbine under various operating conditions.In addition,the basic operation rule and hydrodynamic performance of such new pattern water turbine.The working principle of the blade position-variable tidal current turbine is introduced.Meantime,the force condition and movement of blades in turbine running are analyzed.Two important parameters of tip speed ratio and effective blade opening length are proposed,and the main factors that influence the hydrodynamic performance are discussed preliminarily.A numerical simulation of the hydrodynamic performance of the turbine is carried out by a two-way fluid-structure interaction simulation method.Through the similarity analysis,the conversion relation between the prototype and the model is determined.The moving boundary problem is dealt with by the method of moving mesh while the numerical simulation model of tidal current turbine hydrodynamics is set up.For the turbine with different flow velocity and different resistance moment,the numerical simulation of the operation condition has basically mastered the basic law that the tidal current turbine efficiency changes with the tip speed ratio.Starting with the analysis of the parameters of tidal current turbine impeller,the law of opening and closing of the turbine during turbine running was studied,and the basic characteristics of tidal current turbine running were obtained.Through the comprehensive analysis of the simulation results,the optimum tip velocity,the highest efficiency and other hydrodynamic performance parameters are collected as well.A simulation experiment on the blade position-variable tidal current turbine is carried out.Taking the coefficient of energy as the main research object and the tip speed ratio as the key variable parameter,a scheme of a new type of turbine simulating by circulating water tank has been established,while vast experimental data have been gathered during the experiment.Through the comparative analysis of the experimental images,an inevitable connection between the blade opening and closing position and the tip speed ratio has been found.It is found that due to the special action of the linkage mechanism,at least one blade of the turbine is kept opening in the downstream,also at least one of the blades is in a fully closed state in the countercurrent zone.By analyzing and processing the experimental data,the law of tidal current turbine’s efficiency changing with the tip speed ratio under positive and reverse flow conditions is studied,and the parameters such as the optimal tip velocity ratio and the maximum energy efficiency of the turbine are obtained.On the other hand,the different characteristics of tidal current turbine’s efficiency in positive and reverse flow were learned as well.The fluid-solid interaction numerical simulation method was used to study the influence of the change of cross-sectional area on tidal current turbine’s energy efficiency,a more accurate prediction of turbine energy efficiency can be achieved via establishing a relationship between fluid velocity in the vane and flow velocity in distance.At the same time,the circulation tank is used to simulate the increase of the turbine efficiency after the shroud is added.It is found that the three-section flow diversion structure plays an obvious role in improving the energy efficiency of the blade position-variable tidal current turbine.The optimal design of the new type of turbine shroud is carried out.With the purpose of improving the capacity of the turbine,and combined with the movement characteristics of blade position-variable tidal current turbine to determine the use of three-stage diversion structure as a new type of energy diversion dome of the basic structure.For the first time,the design scheme of airfoil with concave aerofoil is put forward.The numerical simulation is used to study the growth effect of different NAC A aerofoil structures,and compared with the growth effect of circular arc structure,so as to confirm the selection of NACA airfoil structure of diffuser concave speed growth segment.Finally,through the simulation and optimization of the hydrodynamic performance of the dome,the optimal structural design parameters and optimal installation parameters of the three-stage NACA airfoil concentrating dome are obtained.Intensive study has conducted on the thorough research to the law of motion and the hydrodynamic performance of the blade position-variable tidal current turbine by means of numerical simulation and simulation experiment.The design parameters of the new type of diversion structure are optimized.The results are of great significance for the follow-up research and engineering application of the blade position-variable tidal current turbine.