| Under the pressures of the urgent need for conventional energy and the deterioration of the global ecological environment,wind energy has been paid more and more attention as an effective clean energy.Absorbing wind energy through wind turbines and using it to generate electricity is the most widely used way to utilize wind energy.How to make more effective use of wind energy and improve the utilization rate of wind energy of wind turbines is the focus of researchers’ attention.In this paper,a curved shape wind gathering device installed at the upper and lower of the rotor was designed to improve the aerodynamic performance of the straight-bladed vertical axis wind turbine(SB-VAWT).The wind gathering device could improve the inlet velocity and the pressure distribution of the blade along the wingspan direction,reduce the flow energy loss at the tip of the blade to improve aerodynamics characteristics of SB-VAWT.In this study,numerical simulations and wind tunnel tests were used to explore the key control factors of curve conduction,and three parts of research were mainly carried out:1)By using the B-spline curve generation method,the curve shape of the wind gathering device was constructed by cubic fourth-order B-spline curve,and the main structure parameters of the wind gathering device were corresponded to the control point of the B-spline curve.Different curve shapes were formed by the combination of each control point in different positions through the quadratic orthogonal rotation combination design method.Taking the average starting moment as the goal,the influence of the wind gathering device with different structure parameters on the starting characteristics of SB-VAWTs were calculated by three-dimensional numerical simulation,and the better curve structure parameters of the wind gathering device were found.Taking the radius ratio of upper and lower surfaces,inlet angle and outlet angle as the test factors,a better combination of curve parameters was obtained,the parameter combination is that radius ratio of upper and lower disk surfaces is 1.9,the inlet angle is 16 degrees and outlet angle is 4 degrees.At this point,the maximum starting moment of SB-VAWT could be increased by 14.8%.2)The whole flow field characteristics of SB-VAWT with and without wind gathering wind device were compared,as well as the pressure and velocity distribution of flow field on different blade element sections.The optimization effect of wind gathering device on different blade element sections was analyzed from the force variation and streamline direction,and the improvement mechanism of wind gathering device on the aerodynamic characteristics of SB-VAWT was revealed.The results showed that the improvement of the flow field in theSB-VAWT with wind gathering device was different in different planes,the improvement of the flow field at the tip plane was more obvious,the aerodynamic force at the tip of the blade was increased.The radial shear force on wind turbine blades was reduced,so that the force of the blade along the wingspan direction was balanced,and the starting moment of the wind turbine was increased.3)The model of wind gathering device with a better curve obtained in the calculation was made,and the wind tunnel tests were carried out on the starting characteristics,rotational speed characteristics and output power characteristics of SB-VAWTs with and without wind gathering device under different wind speeds to confirm the effectiveness of the wind gathering device to improve the aerodynamic characteristics of the SB-VAWT.The results showed that the wind gathering device could improve the output power characteristics of SB-VAWT.At low wind speed,It mainly affected the output power at high tip speed ratio,expanded the range of tip speed ratio for high output power.At high wind speed,it mainly affected the output power at low tip speed ratio,so that the rotor can also output higher effective power at low rotational speed.The wind gathering device could reduce the minimum self-starting wind speed required to enable it to output effective power at low wind speed.The higher the wind speed,the shorter the time for the gathering wind turbine to reach the stable speed,and higher the rotational speed.However,the improved effect of the wind gathering device will decrease with the increase of wind speed.In this study,the B-spline curve construction was applied to the study of the structural parameters of the wind gathering device of the SB-VAWT,at the same time,the parameter combination design method used in this paper provided an effective method for designing SB-VAWT with similar multistructural parameters.The numerical simulation and wind tunnel test were carried out to confirm the effectiveness of the proposed device with curved shape in improving the starting characteristics,rotational speed characteristics and output power characteristics of SB-VAWT.It provided a theoretical basis for the development of more compact and economical wind gathering devices.It has reference value for the application of the SB-VAWT in the low wind speed area. |
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