Research On Unsteady Aerodynamic Characteristics And Optimal Design Of Wind Turbine

Blade element momentum theory is used to design the wind turbine blade,which has simple calculation process and fast solution speed.But there is certain deviation between designed aerodynamic performance and the actual aerodynamic performance.The flow field around wind turbine is an unsteady flow field and affected by complex inflow such as the wind shear,wind gusts and atmospheric turbulence.In this paper,the flow field of Phase VI wind turbine blade was investigated using numerical simulation method.The results of the numerical simulation were compared with the NREL UAE wind tunnel experiments to verify the computational method.The investigation contents are listed as follows.The effects of uniform inflow,wind shear and gust on the aerodynamic characteristics of the wind turbine were investigated.The flow characteristics of the near wake of' wind turbine blade were quantitatively analyzed.In the uniform flow,the periodical changes of the torque were shown.The flow characteristics of near wake were strongly influenced by the rotating blades.There was a significant axial velocity deficit.This axial velocity deficit was gradually decreased as the air flows downstream.The axial interference factor,tangential interference factor and radial velocity were affected by wind shear coefficients at the region of the blade near wake,especially the radial velocity.Due to the vortex inductive effect,the axial velocity had a higher velocity gradient in the near wake region of the blade tip.The torque of wind turbine was basically consistent with the wind profile curve in the gust wind.The results show that the designed blade still failed to achieve the best aerodynamic performance.A set of local twist angle optirmization methods were established,which combined the surrogate model and the CFD method.A hybrid genetic pattern search was used to improve the accurate Kriging surrogate model.The geometry of WindPACT 1.5 MW wind turbine blade was optimized.It was found that the local twist angles of the section airfoil were reduced and the torque of the optimized wind turbine blade was improved by approximately 3.45%.The output power of the pre-bending blade was lost by the present pre-bending method.Based on Kriging surrogate model,the pre-bending method of wind turbine blade was proposed in this paper.The pre-bending blade was obtained by this pre-bending method and the output power of pre-bending blade was increased.The aerodynamic performance of the airfoil S809 with and without vortex generators was further investigated.The control mechanism of the vortex generators on the flow separation of the airfoil boundary layer was revealed from the momentum transferring and the vortex trajectory.The lift coefficient,drag coefficient,x-velocity gradient and vorticity were analyzed quantitatively and the chord position of the vortex generator was considered.When the vortex generators were arranged rationally at the front end of the suction surface,the lift coefficient of the airfoil could be effectively enhanced,the emergence of the phenomenon of stall was delayed and the stall angel of attack was increased.The stall angle of attack was increased from 14 degrees to 18 degrees when the vortex generators were installed at the 10%chord positions.The detached vortices were created by vortex generators.The high momentum fluid of the main region was involved into the boundary layer and the low momentum fluid of the boundary layer was involved into the main region by the detached vortices.The flow separation was thus controlled effectively by the vortex generators.The longitudinal vortices flowed downstream and gradually integrated into the airfoil boundary layer till the longitudinal vortices immerse into the boundary layer.The control mechanism of the double vortex generator arrangements was revealed.The lift coefficients were further improved at the higher angle of attack,and the stall angle of attack was increased further with the effects of double vortex generator arrangements.Finally,the vortex generators were applied to the stalled Phase ? wind turbine blade.The torque of wind turbine was basically unchanged by a reasonable arrangement of the vortex generators in a specified range of wind speed.