Research On Flow Field And Structure Optimization Of Concentrated Wind Energy Turbine

The concentrated wind energy turbine is a kind of wind power generation system,which can drive rotors to rotate with the natural wind accelerated,rectified and homogenized by the concentrated wind energy device.Compared with the conventional horizontal axis wind turbine,it has many advantages,such as lower cut-in wind speed,smaller rotor diameters,higher wind energy utilization rate,lower noise,higher stability and security,etc.However,the popularization and application of this special type of wind turbines have been restricted by the core component of the concentrated wind energy turbine:concentrated wind energy device with disadvantages of high manufacturing and processing cost,installation and maintenance difficulties.The aim of the research was to improve the concentration efficiency of the concentrated wind energy device,reduce the cost per kilowatt hour of the electricity generated by concentrated wind energy turbines,improve the operation security and stability.The influence law of the concentrated wind energy device structure and geometric parameters on the internal flow field characteristics was investigated with the concentrated wind energy device as the research subject by means of the three-dimensional Computational Fluid Dynamics(CFD)method.And the performance of impellers with and without the concentrated wind energy device original model and optimization model was simulated and analyzed in this research.Main contributions are as follows:(1)Research on the influence rules of the axial section shape on the flow filed characteristics of concentrated wind energy deviceUnder the condition of parallel incoming flow with the wind shear,the influence law of the axial section shape on the flow field characteristics inside the concentrated wind energy device was studied.Based on the original model,eight concentrated wind energy device models with different axial section shapes(including five radially asymmetric structures)were designed respectively.The flow field characteristics simulation results show that:the flow velocities inside the radially symmetric concentrated wind energy devices with contractor generatrices being circlular arc are higher than other structures in this research.And concentrated wind energy devices with radially asymmetric structures have better rectifying and homogenization effects on the incoming flow with the velocity gradients in the flow field reduced.Considering the average flow velocities,velocity gradients,actual manufacturing and installation conditions comprehensively,the radially symmetric structure with the generatrices of the contractor being circular arc and the diffuser being linear is the optimum structure in eight models.The average flow velocity in it can be increased by 25.88%compared with the original model.(2)Research on the influence rules of different pressurization board configurations on the flow filed characteristics of concentrated wind energy deviceFlow field characteristics inside the concentrated wind energy device is closely related to the configuration of pressurization board.Concentrated wind energy device models with pressurization boards shaped as square,regular hexagon,regular octagon,regular dodecagon,regular octadecagon and roundness were designed respectively with the axial section optimum shape model as the example.The comparison study of these six pressurization board configurations’ influence on flow field characteristics of the concentrated wind energy device were conducted in wind shear.Results show that:considering the flow velocities and velocity gradients comprehensively,the concentrated wind energy device with circle pressurization board has the best flow field performance among these six models.The maximum velocity magnitude and maximum velocity along the X-axis of the internal flow field can be increased by 18.39%and 29.42%respectively compared with the original model.Average flow velocity on the impeller plane can be improved by 28.87%and the velocity gradient can be reduced by 35.45%.(3)The optimization design of the flanged diffuser geometric configurationThe circular flange structure added on the diffuser exit boundary can improve the suction effects of the concentrated wind energy device on the incoming wind and increase the internal flow velocity,thereby enhancing the output power of the wind turbine.With the circle pressurization board model as the research object,the concentrated wind energy device model with flanged diffuser was designed and established.And the numerical simulation was carried out to investigate the flanged diffuser geometric parameters’ effects on the internal flow field characteristics of the concentrated wind energy device in shear.The results show that:the flow velocities and the useable wind energy of the rotor swept area inside the concentrated wind energy device can be improved with the increase of the flange height.It can be concluded comprehensively that,the concentrated wind energy device with the flange of the height being 11/30 of the central cylinder diameter,the angle between the generatrix and diffuser outlet in anti-clockwise direction being 3° has better flow field performance.Compared with the model without the flange,the maximum flow velocity inside the optimal flanged diffuser model can be improved by 29.22%,average flow velocity along the X-axis on the impeller plane can be increased by 22.87%and the flow velocity gradient can be reduced by 36.80%.(4)Research on the influence of concentrated wind energy device on the impeller performanceBased on the Wilson correction model,the blade aerodynamic design was proceeded for the concentrated wind energy turbine.The impeller performance with and without the concentrated wind energy device before and after the optimization were simulated and analyzed under the condition of parallel uniform incoming flow.The conclusion is that under the condition of incoming wind speed ranging from 3m/s to lOm/s,the power of the impeller inside the concentrated wind energy device optimal model is 1.6 to 2.5 times of the impeller without the concentrated wind energy device.With the rated wind speed,the impeller power of the optimal model is 52.24%higher than the original model.The concentrated wind energy device structure optimization methods have been proposed from the numerical simulation research with the influence law of the concentrated wind energy device’s configuration on the internal flow field characteristics revealed.Research results can provide the foundation for the large-scale and industrialized application of the concentrated wind energy turbines with theoretical and practical significance.