Research On The Influence Of Overlap Ratio And Wind Gathering Hood On Aerodynamic Performance Of Three-blade Savonius Wind Turbine

Wind energy,as one of the new energy sources,has attracted much attention in recent years,and the market has been expanding yearly.While wind turbines are developing towards large-scale,attention has also been paid to small off-grid wind turbines,wind water pumps,wind heating and other systems for rural and remote areas.As a typical representative of drag-type vertical axis wind turbine,Savonius wind turbine has the characteristics of simple structure,low cost,low speed but large torque coefficient,can be well applied to the above scenarios.However,it can be further optimized by structural optimization and addition of wind gathering device owing to its large starting moment fluctuation and the reverse torque present in partial azimuth angles.Three-blade Savonius wind turbine was taken as the research object in this study to improve the starting stability and improve the starting torque.Wind tunnel test and numerical simulation methods are used to explore the influence of blade overlap ratio and gathering hood on the performance of the wind turbine.The definition of overlap ratio and net overlap ratio of Savonius wind turbine with three blades were proposed based on the structural characteristics of the wind turbine,and nine groups of different wind turbine models were established,covering the net overlap ratio from 0 to 0.36(overlap ratio from 0.14 to 0.50).The effects of overlap ratio on static start-up performance and dynamic performance of wind turbines at different Reynolds numbers were studied by wind tunnel test and numerical simulation.The results show that the reverse starting torque of the wind turbine disappears when the net overlap ratio is greater than 0.06.The average starting moment of wind turbine could be improved while the net overlap ratio ranges from 0.06 to 0.36,with a maximum increase of 147.06%.The start-up stability of wind turbine could be improved while the net overlap ratio ranges from 0.01 to 0.21 and 0.31 to 0.36,with a maximum increase of 42.75%.In terms of dynamic performance,the output power of the wind turbine could be improved while the net overlap ratio ranges from 0.06 to 0.11.The 0.06 net overlap ratio wind turbine with the best start-up stability,improved average torque and the largest output power was selected as the research object.The air gathering end plate,solid air gathering hood and hollow air gathering hood with different structural parameters were designed respectively.The influence of the structure and size of different types of hoods on the aerodynamic performance of wind turbines was investigated.The results show that all three types of hoods have the function of gathering air and diverting flow.The inclination angle of the hood has no obvious effect on the air gathering capacity.The air gathering capacity is affected by the size of the air gathering hood.The wind gathering function can be fully exploited while the diameter of the downside is 1.3 times of the diameter of the wind wheel and the height is 60% of the height of the wind wheel.The dynamic performance of wind turbine could be improved by the setting of end plate,but it would reduce the starting torque in azimuth angle ranging from 50° to 110°.In terms of static starting performance,the average starting torque coefficient of no end plate wind turbine with hollow gathering hood has the largest improvement,which is 48.21% higher than that of end plate wind turbine without gathering hood,52.24% higher than that of no end plate wind turbine without gathering hood.In terms of dynamic performance,the output performance of end plate wind turbine with solid gathering hood has the largest improvement,which is 22.71% higher than that of end plate wind turbine without gathering hood,14.74% higher than that of no end plate wind turbine without gathering hood.This study provides a reference for the research on the structural parameters of Savonius wind turbine and a new idea for the research on the wind collection and diversion device applied to Savonius wind turbine.At the same time,it provides a theoretical basis for the application of Savonius wind turbine in small off-grid wind power generation and wind heating scenarios.