| The development of wind power is an important means for China to further promote the revolution of energy production and consumption and to promote the prevention and control of air pollution.In the past ten years,thanks to the rich wind resources,policy guidance and technology promotion,China’s wind power installed capacity has achieved rapid growth.In order to capture more wind resource and reduce the unit cost of wind turbines,the large-scale wind turbine has become a major trend in the development of wind power technology.However,the accompanying problems such as increased blade size,enhanced aeroelastic characteristics and multi-scale flow will result in the blade being in a more complex and severe load environment,which seriously threaten the safety of the blade structure.When the wind condition is complicated,with the blade aeroelastic deformation,the blade angle of attack is prone to increase and then flow separates with the separation vortex falling off,making the blade force more complicated and reducing blade aerodynamic efficiency.In order to improve the ability of the blade to cope with complex wind conditions and loads and improve blade aerodynamic efficiency,it is necessary to adopt advanced and effective flow control methods to meet the requirements of blade aerodynamic load reduction and flow separation control.In view of the development potential of the flexible trailing edge flap(TEF)control method and the adaptive flap(AF)control method,based on the study of domestic and foreign research results,and combining with shortage of the research on flow control methods and the needs of development,this paper uses numerical simulation to systematically studied the effect of these flow control methods on load reduction and flow separation control.The main research contents are as follows:1.Using the S809 airfoil as the base airfoil,the computational fluid dynamics(CFD)method based on Reynolds time average(RANS)is used to study the static and dynamic flow control effects of the TEF under different flow conditions.The results show that the TEF has a strong static regulation ability on airfoil lift coefficient in attached flow condition.However,with the emergence of flow separation,the lift regulation ability of TEF is reduced,and the ability to regulate the drag coefficient is enhanced.When the flow separation is severe,the deflection of the TEF to the airfoil suction surface can slow down the flow separation,and the lift and drag coefficient is both reduced,which has a certain load shedding effect.2.To study the load reduction ability of the TEF under complex load conditions,based on the actual flow characteristics of the airfoil in the horizontal axis wind turbine blade,and using the force of the airfoil in the blade flapping direction as the control signal,the closed-loop load control model of the TEF under the unsteady flow is established combining with the CFD method.The results show that under the three unsteady inflows,the TEF significantly slow down the force fluctuation of the airfoil compared to the base airfoil.In addition,for the flow control system established in this paper,when the proportional constant and the delay time are too large,the control system will be unstable,and the flapping speed will reach a certain value without further improving the control effect.3.Different from the characteristics of the TEF to slow down the flow separation with the lift and drag both reduced,the AF can increase the airfoil lift coefficient and reduce the drag coefficient when the flow separation is palliated,so the aerodynamic efficiency of the blade can be improved by the AF at the same time.This paper uses RANS method to analyze the control effect of the AF on flow separation from three aspects: airfoil aerodynamic coefficient,separation area size and airfoil surface pressure distribution.The results show that the flap reduces the pressure upstream by reducing the backflow of the separation zone,thereby promoting the flow attachment.Meanwhile,the downstream pressure is also increased,so that the pressure of the airfoil pressure surface is increased synchronously,thereby enhancing the lift.In addition,the study found that there are certain rules for the flap flow control effect and the flap lifting angle.By further analyzing the relationship between the aerodynamic moment of the AF,the lifting angle and control effect,it is found that for a certain angle of attack,with the lifting of the flap,the control effect is gradually improved,and the aerodynamic moment of the flap is gradually increased.After the optimal control effect is achieved,the aerodynamic moment of the flap begins to decrease.With the best control effect as the standard,the influence of the flap position,the flap length and the number of flaps on the control effect was carried out.The results show that under the premise that the hinge point does not affect the flow attachment,the closer the flap is to the separation point,the better the delay in flow separated,but when the flap length is enough to prevent the reflow,the smaller the length,the better the effect.In addition,the double flaps have the best performance in delaying flow separation,and the role of the two flaps will vary primary and secondary depending on the degree of separation.4.When the flap works in the optimal position,it will be subjected to a certain aerodynamic moment.For this reason,this paper proposes to balance the aerodynamic moment of the flap to make the AF works in the optimal position by applying a linear external moment similar to the spring action at the hinge point of the flap.In addition,based on the variation of the surface pressure on the AF during the flap lifting,a method based on synthetic torque control is proposed to keep the AF operates the optimal position.In order to verify the feasibility of the above two improved methods,based on two different flow separation processes,the flow control effect of the flap constrained by external torque is studied.The results show that the method of external spring torque is prone to failure when the flow separation is large,and the synthetic torque control method performs well overall,and completely prevents the lifting of the AF when the flow separation is small,avoiding the adverse effects of flap lifting on the aerodynamic performance of the airfoil.5.In order to study the flow separation control effect of the AF more comprehensively and credibly,the AF dynamic flow control research is carried out by using the DES model which can more realistically provide the generation and shedding of the vortex during the flow separation process and fluid-solid coupling(FSI)method.Firstly,the flow separation characteristics of the 2D and 3D base airfoil and flap airfoil are compared.The base airfoil flow field results show that,compared with the 2D flow separation,as the span increases,the vortex shedding strength decreases and the vortex shedding position is delayed.Meanwhile,the fluctuation of lift and drag coefficient is weakened.Although the results of 2D and 3D flow fields differ in the vortex shedding strength for base airfoil,the flap airfoil flow field results show that,the flow control effects of the AF in 2D and 3D DES results have certain similarities,that is,the lift coefficients are both increased and the drag coefficients are both reduced,with the similar surface pressure distribution consistent with the 2D RANS results.6.After the feasibility of using the 2D DES method to study the control effects of the AF is clarified,a more comprehensive study of the dynamic flow control effects of the flaps was carried out.The dynamic characteristics of the AF include the influence of the AF on the dynamic evolution of the separated flow field and the dynamic motion of the AF.The results show that: the flow control effect of AF is mainly reflected in increasing the average value of the lift coefficient,reducing the average value of the drag coefficient,increasing the fluctuating frequency and reducing the fluctuation.The moment of inertia and motion damping have little effect on the flap control effect,but have a great influence on the flap motion characteristics.The influence of increasing the moment of inertia is mainly caused by the weakening of the high-frequency component of the flap motion and the increase of the low-frequency component,but the fluctuation range of the flap is not changed as a whole.The effect of increasing the motion damping is mainly reflected in the simultaneous reduction of the high-frequency component and the low-frequency component of the flap motion,and the reduction of the overall motion range of the flap,and the fluctuation is more stable. |
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