Research On Aerodynamic Performance Control Of Wind Turbine Airfoil With Leading-edge Protuberances

The complex operating environment of wind turbines leads to obvious flow separation on the surface of wind turbine blades,and flow separation leads to the phenomenon of aerodynamic stall occurs frequently.On the one hand,it seriously affects the aerodynamic performance of the wind turbine blades,and reduces the power generation efficiency of the wind turbine;on the other hand,due to the periodic separation of the vortex on the blade surface,it causes vibration during the blade operation,which seriously affects the stability of the wind turbine operation.As the core component of blade aerodynamic performance,the wind turbine airfoil needs an effective flow control method to suppress the flow separation on the surface of the wind turbine airfoil,and improve the aerodynamic performance of the wind turbine airfoil.As a novel passive control method,the leading-edge protuberances can effectively suppress flow separation,improve stall characteristics,and improve the overall aerodynamic performance of the airfoil.In this paper,the leading-edge protuberances are applied to the wind turbine airfoil,and the effect of the leading-edge protuberances on the static and dynamic aerodynamic performance of the wind turbine airfoil is analyzed through the combination of aerodynamic and flow field experiments and numerical calculation.Furthermore,the average and fluctuation characteristics of the wind turbine airfoil with leading-edge protuberances are analyzed.In addition,the mechanism of flow separation control is studied by constructing a modeling method for the flow field characteristics of the airfoil with leading-edge protuberances.Firstly,through aerodynamic experiments,it is found that the leading-edge protuberances can effectively improve the static aerodynamic performance of the wind turbine airfoil,and improve the aerodynamic stall characteristics.On this basis,a sensitivity analysis of the surface roughness for the airfoil with leading-edge protuberances is carried out,and the surface roughness has a greater impact on the aerodynamic performance of the wind turbine airfoil.The static aerodynamic performance of the wind turbine airfoil affected by the surface roughness is seriously deteriorated.The airfoil produces lower lift and higher drag and torque,and the aerodynamic fluctuation value increases significantly.When affected by the surface roughness,the method of leading-edge protuberances improves the aerodynamic fluctuation characteristics of the wind turbine airfoil in the stall region,and at the same time,it also improves the average aerodynamic characteristics of the wind turbine airfoil.Secondly,through the development of the leading edge transition technology,the similarity of aerodynamic changes under different Reynolds numbers is established.The aerodynamic and flow field experiments are used to analyze the control effect of the leading-edge protuberances on the flow separation and the improvement of aerodynamic performance for the static wind turbine airfoil under natural inflow conditions.Through experimental research,it is found that in the stall region,the stall characteristics of the airfoil with leading-edge protuberances are more gentle,and the leading-edge protuberances effectively improves the average aerodynamic performance of the wind turbine airfoil in the post-stall region of high angle of attack.The aerodynamic performance of the wind turbine airfoil is affected by the flow separation of the airfoil suction surface,and the leading-edge protuberances in the post-stall region effectively suppress the occurrence of flow separation.Correspondingly,the airfoil with the leading-edge protuberances maintains better aerodynamic performance in the post-stall region.In addition,the leading-edge protuberances effectively reduce the shedding energy of the separation vortex in the boundary layer,which helps to reduce the turbulence intensity of the velocity field of the boundary layer,thereby reducing the aerodynamic fluctuation of the wind turbine airfoil.On this basis,the aerodynamic experiments are used to further analyze the improvement effect of the leading-edge protuberances on the dynamic aerodynamic average and fluctuation characteristics of the wind turbine airfoil under natural inflow conditions.Studies have shown that the leading-edge protuberances effectively suppresse the dynamic aerodynamic hysteresis effect,reduce the strength of dynamic stall,and suppresse the formation of secondary dynamic stall vortex,which also effectively reduce the maximum lift coefficient,the change value of lift coefficient,and the value of negative aerodynamic damping.At the same time,the leading-edge protuberances can reduce the dynamic aerodynamic fluctuation of the wind turbine airfoil,and improve the stability of the dynamic aerodynamic force.Moreover,with the increasing of the dynamic pitching frequency,the improvement of the dynamic aerodynamic average and fluctuation characteristics of the leading-edge protuberances gradually noticeable.Finally,in order to incorporate the flow control mechanism of the leading-edge protuberances into the design of wind turbine blades,it is necessary to establish a quantitative relationship between the structural parameters of the protuberances and the flow field characteristics.In this paper,a theoretical model of the influence law of the leading-edge protuberances on the flow field is proposed.Through modeling analysis,it is found that the calculation results of aerodynamic and flow field for themodeled airfoil and the solid airfoil with leading-edge protuberances maintain a good consistency.Moreover,in the low angle of attack area,due to the greater degree of flow separation at the trough position,the aerodynamic characteristics of the airfoil with leading-edge protuberances are reduced.On the contrary,in the post-stall region with high angle of attack,the leading-edge protuberances effectively suppresse flow separation and improve the aerodynamic performance of the airfoil in the high separation region.The protuberance structure generates additional force on the flow field,which causes a pressure gradient between the suction surface and the pressure surface,and the pressure gradient causes a significant flow vortex on the airfoil suction surface.When the pressure gradient on both sides of the protuberance structure is higher,a higher-strength flow vortex is generated,which causes the airfoil suction surface to generate a lower pressure area.In this case,the flow on the airfoil surface is in an attached state,which effectively suppresses the occurrence of flow separation.In summary,the method of leading-edge protuberances is applied to the wind turbine airfoil in this paper.Through the aerodynamic and flow field experiments,the effect of the leading-edge protuberances on improving the aerodynamic performance of the wind turbine airfoil under different working conditions is studied in depth.Combined with the numerical calculation method,a theoretical model of the influence of the leading-edge protuberances on the characteristics of the flow field is proposed to further reveal the flow separation control mechanism.It provides an important foundation for the optimization design and practical engineering application of the flow control method of the leading-edge protuberances on wind turbine blades.