Aerodynamic Design And Optimization Of Low-speed Wind Turbines With Shroud And Lobed Ejectors

The 21 st century will be the century of the more rapid development of human civilization. In order to improve and protect the human survival environment, the human pursuit of energy is gradually shifting from the traditional fossil energy to the safe and reliable green energy. Low-speed wind energy is a form of renewable energy, which has not only huge reserves, but also a world-wide distribution. It is therefore of great significance to design wind turbines for efficie nt utilization of low-speed wind energy for changing the present energy structure. However, the low-speed wind energy also has the disadvantages of low-energy-grade, low energy density and high turbulivity level, so the new wind turbine must resolve the above problems well. Therefore, a one stage horizontal axis wind turbine with a shroud and lobed ejector by the idea of the turbofan engine nozzle ejector technology was proposed for the efficient utilization of low-speed wind energy by taking into consideration the effect of the shroud and lobed ejector in this paper, and the following several aspects of research work were presented:From the view of maximum available energy, the wind turbine stage model, wind turbine stage with the shroud effect model and wind turbine stage with shroud and ejector model were established. The calculation method of aerodynamic parameters at each position of the ejector wind turbine was given. The design parameters of wind turbine stage and shroud and lobed ejector are presented. Based on the one-dimensional design method of traditional turbine and the blade element momentum theory of traditional wind turbine, the pressure controlled vortex and blade element group quasi-three-dimensional design method, had been established for wind turbine stage with characteristics of the big radial enthalpy drop difference and very small diameter height ratio. The wind turbine stage blade was optimized basing on the genetic algorithm and quasi-threedimensional design method. The parameters of the three-dimensional profiles were corrected through CFD method. According to the working characteristics of wind ejector, the geometry calculation method of the wind lobe ejector with the same shroud effect was established, 3D modeling scheme was presented through the UG NX software.In order to select a suitable numerical method to predict the aerodynamic and ejector performance of wind turbine in the Low-speed wind flow field(Re=5.5×105), a low-speed annular cascade experiment with a similar Reynolds number and a PIV experiment of the lobed ejector with the same Reynolds number, were evaluated the RANS equation and four turbulivity models using the commercial software ANSYS CFX. RANS equation and SST turbulence model was most accurately predicted in the flow field of a turbine cascade and the internal and external flow field of the ejector.Power output performance of the wind turbine was studied on by using the above numerical method. The aerodynamic performance of blade cascades and mixing performance of the ejector in the inner and outer flow field at the design point were analyzed. The laws of the formation, development and dissipation of the streamwise and normal vortices behind the lobes, and the ejection mechanism of the internal and external mixing tube were described. It was found that the complex vortices in the flow field outside the wind turbine included streamwise vortices, normal vortices behind the lobes, and three large scale vortex rings. These vortices contributed the bypass flow to pump the low speed inner flow out of the turbine stage. The vacuum degree along the whole blade height, which improved the flow capacity of the turbine stage and the enthalpy drop of unit mass gas, is the fundamental reason of the new wind turbine for the effic ient utilization of the low-speed wind energy. It is proved that it is reasonable to design Lowspeed wind turbines using the ideas of the turbine stage and wind ejector.Before the aerodynamic and ejection performance optimization of the wind ejector, in order to analyze the influence of the outlet flow angle on the performance of the ejector under the different rotating speed in the same wind speed, and to further investigate on whether the optimal outlet flow angle exists for the best aerodynamic and ejection performce in the overall design scheme of the wind turbine stage design and wind ejector design or not, the effect of turbine outlet flow with the angle from 0 °to 30 ° along the axial direction on the performance of ejector was numerically researched. As the results shown, the overall vorticity level of streamwise vortices and nomal vortices gradually dropped. The total pressure loss of the injector of lobes was increased; When the angle is greater than 10°, the vortex structure in the outflow field gra dually became instability, and the performance of the air ejector is obviously decreased. Above research explained that the overall level of output power of wind turbine with shroud and lobed ejector was higher than the t raditional three-blade wind turbine with the shroud and lobed ejector. Also, it is proved that in the onedimensional and quasi-three-dimensional design proccess of the turbine stage, it should as far as possible to ensure that turbine stage actual exit flow along the axial direction to the outlet of the turbine stage.After finding that the geometric parameters were the main influencing factors of the ejection performance of the shroud and lobed ejector, a four-lobe-parameter(elevation angle, bow angle, axial length and lobed width) rapid design method was presented in the design of lobed ejector, and aerodynamic and ejection performance optimization work was carried on basing on the orthogonal design of linear regression, the steepest ascent method, the multivariate nonlinear regression analysis method and CFD method. The output power of the optimized wind turbine was increased from 6.14 to 7.45% as the inlet speed changes from 2~6m/s on the basis of the original, the massflow of the inner passage and ejection ratio increased 2%, and the wind energy utilization coefficient ranges from 0.711 to 0.776. The velocity-frequency data of the low-speed wind farms were used to evaluate the annual power generation of the optimized wind turbine. Compared with the traditional wind turbine with the same rotation radius, the optimized turbine can generate 3~4 times in the wind conditons, and has good adaptability in high turbulent flow field, high efficiency, low noise and environmental protection.