Research On Effect Of Surface Erosion Morphology On Aerodynamic Performance Of Wind Turbine Airfoil

Wind turbines have been affected by hail storms,sandstorms,and other erosions for a long time,resulting in damage to the surface of wind turbine blades and seriously affecting the safe and power output of wind turbines.In this paper,according to the S809 airfoil,the erosion features of the different depths and ranges of the leading edge surface are studied.The aim is to obtain the influence law of different erosion characteristics on the airfoil and its flow field.Under certain conditions,the process of airfoil erosion in dust particle environment was simulated.The CFD method was used to calculate and analyze the aerodynamic characteristics and flow field structure of the S809 airfoil with different erosion characteristics,and the influence mechanism of the leading edge erosion on the aerodynamic characteristics of the airfoil was studied.(1)SST k-? turbulence model was used for numerical calculation to study the influence of different leading edge delamination depths on the airfoil flow field and aerodynamic performance.The results show that the leading edge delamination changes the shape of the airfoil,causing the leading edge flow to become a step flow and the trailing edge separation zone to become larger and the separation point to move forward.With the deepening of the delamination depth and the increase of the angle of attack,the recirculation vortex of the leading edge and the trailing edge separation region converged.At the same angle of attack,the leading edge delamination has a greater influence on the pressure coefficient of the leading edge.When the angle of attack is less than 3°,the leading edge delamination has little effect on the lift and drag coefficient of the airfoil.When the angle of attack is more than 3°,the lift coefficient of the airfoil gradually decreases as the delamination degree deepens,and the drag coefficient gradually increases.Compared with smooth airfoil,the lift loss rate of the leading edge delamination airfoil is up to 55.08% and the maximum drag coefficient growth rate is 150.48%.(2)The pressure surface delamination airfoil and suction surface delamination airfoil with delamination depth of 3mm were established.The delamination changes the shape of the airfoil,flow through the leading edge of the pressure surface delamination airfoil is frontward-facing step flow,and flow through the leading edge of the suction surface delamination airfoil is backward-facing step flow.The recirculation vortex formed after the frontward-facing step causes the trailing edge flow to separate in advance,and the separation point moves forward.Compared with the smooth airfoil,both the pressure surface delamination and the suction surface delamination cause the early separation of the flow around airfoil trailing edge,and the greater the angle of attack,the more severe the flow separation.After delamination of the airfoil,under the circumstances of angle of attack is less than 8.2°,the lift coefficient and drag coefficient are closely to the values of smooth airfoil.After the angle of attack is greater than 8.2°,the lift coefficient decreases with increasing angle of attack,and the drag coefficient increases.The influence of the frontward-facing step flow is greater than that of backward-facing step flow.Therefore,the pressure surface delamination has a great influence on the aerodynamic performance of the airfoil.The delamination causes a sudden change in the profile of the airfoil surface,resulting in three phenomena in the surface pressure of the delamination airfoil.First,a partial pressure change occurs at the delamination location;second,the value of the pressure from leading edge to the maximum relative thickness decreases as the angle of attack increases,indicating the separation of the airfoil flow.Third,when the airfoil delamination occurred,the surface pressure from the leading edge to the maximum relative thickness fluctuates.(3)The gas-solid two-phase simulation was used to study the erosion process of sand particles on wind turbine airfoils.The airfoil at the blade radius of 99% of Phase VI wind turbine was selected as the research object.The angle of attack is 12.29°.Based on the gas-solid two-phase simulation of the smooth airfoil,the erosion depth was calculated from the distribution of the airfoil surface erosion rate and the airfoil shape was modified.Then,the gas-solid two-phase simulation of the modified airfoil was continually calculated under the same conditions,repeated the above steps.It was found that the erosion range of the pressure surface was from the leading edge to the 40% of string,the erosion range of the suction surface was within 10% of the string.The distribution of the erosion position at the leading edge is dense and gradually decreases along the chord line.After the deformation,the position of the airfoil erosion is progressively moving relative to the previous edge,and the erosion rate gradually increases with the increase of the number of deformations;the width of the airfoil erosion position gradually becomes narrower after the deformation,As the erosion time increases,the erosion rate gradually increases.The erosion process of the airfoil is as follows.After the airfoil erosions,the erosion position gradually moves forward based on the first erosion position,and gradually forms a densely distributed small pit.Next,the sand particles destroy the side wall of the small pit,making adjacent small pits become larger pits and then gradually form delamination.