Vertical Axis Wind Turbine With Self-adapting Darg-lift Conversion And The Study On Its Dynamic Characteristics

In recent years, due to increasing environmental pollution, the surge in energydemand and sustained reduction in fossil fuels, the focus on renewable energyimproved significantly. Among these energy, wind energy was cheaper and thefastest-growing renewable energy. So people had done a lot of work to study how toeffectively take advantage of this energy, and the wind turbine was the mostimportant form. Wind turbines could be divided into horizontal axis windturbine(HAWT) and vertical axis wind turbines(VAWT). Compared with HAWT,VAWT had such advantages like independence of wind direction, easy maintenanceand simple blades structure, and received more and more attention. VAWTs weremainly divided into resistance type wind turbines, lift type wind turbines andcombined wind turbines. These types of VAWTS had some problems. In order tosolve the problems of VAWT, this paper integrated the advantages of resistance typewind turbine and lift type wind turbine, and proposed a vertical axis wind turbinewith self-adapting drag-lift conversion (VAWT-SDLC). The wind turbineovercomed the shortcomings of resistance type wind turbine and lift type windturbine. The dynamic characteristics of the wind turbine were experimentally andtheoretically studied, and the working mode judgment model and aerodynamicperformance prediction model were also established.Firstly the VAWT-SDLC prototype and its aerodynamic performance testdevice were developed. The prototype was mainly composed of blades, supportarms and bearings. The obvious feature was that each group of blades wascomposed of the moving blade and stationary blade. Moving blades could open andclose according to the wind speed and the rotational speed, and automatic conversethe operating mode of the wind machine. The test device included wind tunnel,wind turbine and test system. The test system could collect speed and torque of thewind turbine, and the output signal could be displayed through the PC. Thedevelopment of prototype and test device provided an experimental platform for thestudy of the aerodynamic performance of the wind turbine.The VAWT-SDLC was different from traditional VAWT. In the resistancemode, the moving blades would be opened in the downwind side, and closed in theupwind side. There was no existing aerodynamic model which was entirely suitablefor this wind turbine. Based on double-multiple streamtube model, the performanceprediction model of VAWT-SDLC in drag mode was established. Then, throughcomparison of theory calculated and experimental results of the prototype in wind tunnel, it was found that theoretical results agreed well with the experimental data.The aerodynamics model in resistance model was proved feasible on theperformance prediction of VAWT-SDLC. The model provided a theoretical basisfor the engineering application of VAWT-SDLC.The self-starting was the basic characteristics of the wind turbine, and it wasalso an important index to measure the performance of the wind turbine. In the firstthe self-starting performance of the VAWT-SDLC prototype was experimentallyresearched in the wind tunnel. Compared to the static self-starting performance ofDarrieus straight-bladed wind turbine with the same geometric parameters, theperformance of VAWT-SDLC was obvious better than that of Darrieus wind turbine.The impact of the number of blades, diameter and wind speed on the stati c anddynamic self-starting performance of VAWT-SDLC was studied through windtunnel experiments. The static self-starting performance increased with the increasein the number of blades. The increase of the diameter had some impact on the staticself-starting performance under different azimuth, but had little effect on theaverage self-starting performance. At low wind speeds, the increases of the windspeeds reduced the static self-starting performance. But at higher wind speeds, therewas little effect. The increase of blades would reduce the dynamic self-startingperformance. When the diameter is bigger, the dynamic self-starting performancewas better. At low wind speed, the increase of wind speed improved the dynamicself-starting performance. At high wind speeds, wind speed had little effect.The largest difference between existing vertical axis wind turbine and VAWT-SDLC was that VAWT-SDLC could automatically complete the conversion processbetween drag mode and lift mode according to the different working conditions.Based on multi-streamtube model, the operating mode judgment model of theturbine was established. And the model was validated by the results of wind tunnelexperiments. The impact of number of blades, diameter and wind speed onoperating mode conversion was studied through wind tunnel experiments. It wasfound that under constant wind speed, the increase in the number of the bladewould bring conversion forward. The increase of diameter would make theconversion delayed. Through experiment between3m/s and10m/s wind speed, itwas found that the wind speed had little impact on the tip speed for conversion, butgreat impact on the ability to achieve conversion.The output characteristics of VAWT-SDLC in resistance mode were studiedthrough wind tunnel experiment. Comparing the power output characteristics ofVAWT-SDLC and Darrieus straight-bladed wind turbine with2,3and4blades,0.7m diameter in wind speed of6m/s, it was proved that the output characteristic of all VAWT-SDLC was better than that of Darrieus wind turbine.The effect of blade number, diameter and flow velocity on the output characteristicsof VAWT-SDLC were investigated in detail. It was found in all experiments thatdynamic torque coefficient of wind turbines decreased with the increase of tipspeed ratio. Power firstly increased, then decreased with the increase of tip speedratio. In the3blade number, the dynamic output characteristics of4blades windturbine were optimum. The output characteristic of wind turbine increased with theincrease of the diameter. The output performance of the wind turbine increased withthe increase of wind speed. While the wind speed had small influence on the tipspeed ratio at which wind turbine achieved maximum power.