| With the progress of the times and technological development,energy consumption is growing exponentially,and the environmental pollution caused by fossil energy consumption is becoming more and more serious.In this context,countries all over the world have increased their research on renewable energy,and wind energy has been favored by all countries for its wide distribution and high economical advantages.Wind turbines,as machinery for converting wind energy,are divided into horizontal axis wind turbines and vertical axis wind turbines.Horizontal axis wind turbines are more widely used than vertical axis wind turbines,but there are disadvantages such as high manufacturing cost,difficult to repair and maintain,and complicated yaw control.Vertical axis wind turbines have received a lot of attention in recent years because of their low center of gravity,low noise,no yaw,low vibration and easy maintenance.However,during the operation of vertical axis wind turbines,the angle of attack of each blade changes periodically with the azimuth angle,resulting in periodic fluctuations in its torque and power,which in turn affects the quality of power generation.Therefore it is particularly important to use an effective flow control method to reduce the power fluctuations of vertical axis wind turbines without reducing the average power.Microtab,a miniature airfoil installed near the trailing edge of the airfoil,can effectively control the airfoil lift.However,the static Microtab cannot cope with the periodic motion of the vertical axis wind turbine blade,making the control ineffective in some flow cases.In order to reduce the power fluctuation of vertical axis wind turbine,this paper studies the control effect of Microtab on static and dynamic airfoil aerodynamic force,and then proposes a Microtab control strategy to reduce the pitch airfoil aerodynamic force fluctuation;it studies the influence law of Microtab on the torque characteristics of vertical axis wind turbine,and proposes a Microtab control strategy that can photosmooth the torque characteristics of vertical axis wind turbine The detailed work and conclusions are as follows:1.The numerical model of the airfoil and the unit is established based on the H-type three-blade vertical axis wind turbine,and the reliability of the parameters such as grid distribution,turbulence model,computational convergence and time step is verified,which provides a reliable numerical model for the dynamic flow control of the airfoil and the vertical axis wind turbine.2.In order to determine the control strategy of Microtab in dynamic flow control,the chordal installation position and control height of Microtab on the airfoil lift drag are studied based on the static airfoil model.The results show that the optimal control position of Microtab is at 95% C of the trailing edge of the airfoil,and the lift coefficient of the airfoil increases with the increasing control height when the control height is in the range of 0～2.0% C and the angle of attack of the airfoil is in front of the stall angle of attack,and the height of Microtab is at 1.0 ～1.5%C,the lift-to-drag ratio is increased the most.3.In order to investigate the effect of Microtab on the aerodynamic performance of the airfoil when the angle of attack changes periodically,the control mechanism of three static Microtab(upper surface,lower surface,and both surfaces)on the aerodynamic force of the pitching airfoil was firstly investigated,and it was found that the arrangement of Microtab on the pressure surface of the airfoil could effectively increase the lift and lift-to-drag ratio of the pitching airfoil and improve the aerodynamic performance of the airfoil to a greater extent.On the contrary,the Microtab on the suction side of the airfoil can reduce the lift and lift-to-drag ratio of the pitching airfoil.In the case of the same flow state and control height,the magnitude of the pressure surface control to raise the lift is larger than that of the suction surface control to reduce the lift;the control effect of dynamic Microtab on the pitching airfoil aerodynamics is studied,and the results show that the dynamic Microtab can effectively control the lift fluctuation of the pitching airfoil.4.To study the Microtab active control strategy that can reduce the power fluctuation of vertical axis wind turbine,firstly,numerical simulations of the uncontrolled unit were conducted to analyze the overall and single blade torque characteristics of the wind turbine.Secondly,the control mechanism of two types of Microtab(inner and outer surface)on wind turbine aerodynamic force is investigated,and it is found that Microtab inner surface control decreases the torque when the blade is located on the windward side;Microtab outer surface control increases the torque when the blade is located on the windward side;Microtab outer surface control decreases the torque.Then,the Microtab control strategy of reducing the blade torque at 90 ± 40 ° azimuth and increasing the blade torque at 270 ± 40 ° azimuth is proposed with the goal of reducing the torque fluctuation,and the results show that the control strategy can reduce the torque fluctuation of the vertical axis wind turbine,but the control effect is limited.Finally,the Microtab control strategy is carried out for the full range of angles to reduce the unit torque of the vertical axis wind turbine in the range of 0～20 °,75～135 °,185～255 ° and 315～360 ° azimuths;and to increase the unit torque of the vertical axis wind turbine in the range of 20～75 °,135～185 ° and 255～315 ° azimuths.The torque fluctuation is further reduced compared with the previous control strategy,which improves the stability of vertical axis wind turbine operation and power generation quality. |
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