Study On Energy Capturing Performance Of Turbine Blades Under Sub-low Speed Tidal Current

In recent years,with the development of the marine strategy and the vigorous development of the marine economy,the development and utilization of marine energy has received widespread attention.Turbine blades are a key component of tidal current capture.Their hydrodynamic research is mainly focused on high-velocity sea conditions,and the average velocity in most sea areas in China is less than 1m/s.NACA airfoil blades driven by differential lift force are limited in applicable conditions.Therefore,it is of great significance to study the tidal energy capture blades in lowvelocity sea waters.This paper is mainly based on the study of the ability of tidal energy capture blades in sub-low-velocity waters(usually the maximum tide is less than 1m/s and the maximum tide is less than 1.5m/s).According to the experiments,the energy capture effects of different types of blades at sub-low flow rates are compared and analyzed,and the power coefficient curve is drawn.Based on the curves,Savonius type blades are optimized and sea trial experiments are performed.The research work includes the following two aspects:First,on the basis of the traditional NACA blades,combined with the analysis of the influence of the flow impact resistance on the blades at the sub-low velocity,a new thin-walled blade is proposed,and the lift-impact composite hydrodynamic model of the horizontal axis blades suitable for the sub-low velocity current is established.Based on this model,according to the current velocity characteristics of the sea area of Yushan islands,which is the sea test area,optimization and modeling are carried out,and thinwalled horizontal axis airfoil blades and NACA airfoil comparison blades under the same conditions are developed for this sea area.At the same time,Savonius type vertical axis pure resistance blades with the same tip speed ratio are studied.The energy capturing characteristics of the three blades are tested by the integrated experimental system of the blades.According to the experimental results,the curves of velocity and power coefficient of different types of blades are drawn.Second,based on experimental results,based on computational fluid dynamics(CFD)simulations,the pressure field and velocity field of the horizontal axis thinwalled airfoil blades,horizontal axis NACA airfoil blades,and vertical axis Savonius type blades at sub-low velocity are analyzed.The mechanical and kinematic characteristics of the three types of blades are analyzed and discussed.The Savonius vertical axis blade with the best comprehensive performance at the incoming flow speed of 0.8m/s was further optimized.Overlap rate was used as the optimization parameter.Five different overlap rates from 0 to 0.3 were selected.The simulation was carried out under different kinds of blade tip speed ratios.And a total of 60 groups of simulations were performed to obtain the Savonius blade tip speed ratio and power coefficient curves.Aiming at the energy harvesting efficiency at a low flow rate,the vertical axis Savonius blade with the best comprehensive performance when the flow is 0.8m / s is further optimized.Using the overlap rate as the optimization parameter,five different overlap rates from 0 to 0.3 are selected.The simulation was performed under 12 different tip speed ratios from 0.4 to 1.3.A total of 60 sets of simulations were performed to obtain the Savonius-type blade tip speed ratio and power coefficient curves.Through comparative simulation analysis of different overlapping rates,it is found that the energy capturing effect is the best when the overlapping rate is 0.15.The research results are applied to the self-powered system of marine ranch in Xiangshan,Ningbo.Finally,the optimization results were verified experimentally.The power generation and power coefficients of the blades before and after optimization were studied on the offshore sea test area,which verified the excellent performance of the proposed design theory and airfoil in sub-low speed waters.This research will promote the research of turbines in the low-velocity waters in the future.