Study On The Effect Of Blade Tip Slot On Aerodynamic Performance And Tip Vortex Of The Wind Turbine

Wind energy is representative in the field of new energy and is highly valued by various countries because of its large reserves and wide distribution.The aerodynamic performance of the wind turbine blade directly determines the wind energy efficiency,and then fundamentally determines the overall performance of the wind turbine.Therefore,improving the aerodynamic efficiency of wind turbine blades is currently an urgent problem to be solved.As the main area of aerodynamic force generation,the blade tip plays a vital role.Flow control technologies such as jets and various devices represented by tip winglets,flaps and vortex generators are widely used to improve the aerodynamic performance of blades and improve the wake vortex problem.The blade tip slots can improve the air flow around the blade tip and is an effective measure to improve the aerodynamic performance of the blade.In order to study the effect of blade tip slots on the aerodynamic performance of wind turbine and its control effect on blade tip vortex,NREL Phase Ⅵ wind turbine as a model selected in this paper to verify the feasibility of the numerical simulation method;Then,using the 1/8 scaled model as the research object,three annular slots from the leading edge to the tip surface of the blade are designed in the blade tip area;The IDDES numerical simulation method is used to analyze the blade efficiency and wake development at different speeds before and after the blade tip slots,and the influence of the blade tip slots on the blade tip vortex.The main work and research results are as follows:1.Taking the NREL Phase Ⅵ blade as the research object,the torque calculation and experimental values based on the numerical simulation methods of RANS,LES and IDDES are compared and analyzed to ensure the reliability of the numerical simulation method selected in this paper.The accuracy of IDDES method is slightly higher than that of RANS method and LES method through torque analysis under different wind speeds;Through the analysis of different cross-section pressure coefficients and normal force coefficients,the simulation results at low and medium wind speeds are basically consistent with the experimental results,which proves the reliability of the numerical method again;The comparative analysis of the threedimensional rotation effect of the blade under wind speeds of 7m/s and 10m/s shows that the combined effect of centrifugal force and Coriolis force leads to the threedimensional rotation effect of the blade.2.When the wind speed is 12m/s,the SST k-ω turbulence model is used to compare and analyze the output power and power growth rate of the wind turbine before and after the blade tip slots at different speeds.When the speed is 900 rpm,the power of the two wind turbines reaches the maximum;The power of the blade tip slots wind turbine increases from 600 rpm to 1700 rpm,but the power growth rate is smaller when the speed is lower than 900 rpm,and the power growth rate is larger when the speed is higher than 900 rpm;The blade tip slots causes the pressure difference between the suction surface and the pressure surface of the blade to increase,and the power of the wind turbine increases.The pressure surface of the blade is always in the state of adhesion flow,no flow separation occurs,and a greater degree of flow separation occurs on the suction surface;As the rotor speed increases,the tip speed ratio increases,the effective angle of attack decreases,the separation zone decreases,and the separation point moves back to the blade root;The blade tip slots weakens the flow separation phenomenon of the blade,the separation vortex of each section moves to the trailing edge,and the wake vortex at the tip of the blade falls off,indicating that the blade tip slots effectively inhibits the flow separation and reduces the strength of the separation vortex.3.The tip vortex’s influence on the blade is about 3% of the entire blade length;The closer to the blade tip,the greater influence of the blade tip vortex.The static pressure coefficient at the downstream vortex core is used to reflect the strength of the blade tip vortex.The static pressure coefficient of the vortex core decreases with the increase of the speed,the strength of the blade tip vortex increases and the attenuation speed becomes slower with the increase of the speed;The blade tip slots can reduce the strength of the blade tip vortex,accelerate the dissipation of the blade tip vortex and improve the quality of the downstream wind.The axial velocity in the wake plays a major role and has a greater impact on the wake structure;The air flow jetted from the annular slots has a significant inhibitory effect on the incoming flow,which can correspondingly reduce the axial velocity in the wake area,shorten the air flow propagation distance,reduce the impact on the downstream wind turbine,thereby increasing the efficiency and profitability of the entire wind farm.This paper studies the impact of the blade tip slots on the aerodynamic performance of wind turbines,reveals the power increase mechanism of the blade tip jets,shows the effect of the blade tip slots on the tip vortex control,and provides reference for the active control technology of wind turbines.