![]() ![]() Studies have shown that while flaps can lead to increased lift after stalling, they did not propose a generally applicable optimal flap structure. Altman and Allemand 22 carried out research on three airfoils with different cambers of NACA-0012, USA-28, and Eppler-423 through low-speed wind tunnel experiments and discussed the change of lift after three airfoils are added with the same structure flap. 21 combined numerical and experimental methods to study the effect of adding a self-activating movable flap on the HQ17 airfoil under unsteady conditions. Bramesfeld and Maughmer 20 found through low-speed wind tunnel experiments that installing a movable flap on the upper surface of the S824 airfoil has a significant effect on increasing the lift than that of the clean airfoil the lift can be increased by about 20%. 19 explored the physical mechanism of NACA0020 airfoil with flap in unsteady flow, studies have shown that flap can improve the dynamic stall characteristics of airfoils and can delay stall while increasing dynamic lift. In order to verify the aerodynamic performance of an airfoil with a flap at large AOA and the influence of the structural parameters of a flap on the aerodynamic performance of the airfoil, scholars at home and abroad have carried out research using experimental and numerical methods. Therefore, the use of “popped-up-feather-type” high-lift devices (passive flaps) on the suction side of the airfoil can counteract the negative aerodynamic effects associated with the dynamic stall in the presence of large-AOA inflow and a sharp deterioration of airfoil aerodynamic performance. It has been found that hidden feathers on the upper surface of the birds’ wings are slightly popped to mitigate the adverse effects of airflow separation for improved flight efficiency in the process of takeoff and landing or gusts ( Fig. In recent years, the flight characteristics of birds have attracted the attention of researchers. 10–12 For the flow separation problem existing in the flow around the airfoil under large α, the passive control technology based on the bionics principle has received special attention. The passive flow control does not need to introduce external energy and optimizes the flow field structure by changing the boundary conditions of airfoil surface flow, such as flap, 3,4 vortex generators, 5,6 suction surface grooves, 7–9 and surface flexible structures. Flow separation control technology mainly includes active and passive schemes. 1,2 Flow separation affects the lift–drag characteristics of an airfoil, increases the flow energy loss, and causes severe aerodynamic fluctuations on the airfoil surface, thereby limiting the safe and efficient operation of the wind turbine. When the angle of attack (AOA) increases to the stall value, separation vortices formed on the airfoil suction surface hinder the kinetic energy exchange between the mainstream flow and the airfoil boundary layer due to the influence of the fluid viscosity and the flow reverse pressure gradient. Flow separation is common in the flow around airfoils for wind turbine blade airfoils. Wind turbine blades are the main energy conversion components in wind energy infrastructure, and their design directly determines the efficiency of wind turbines to obtain wind energy. The airfoil with optimal flap leads to a smaller separation vortex and wake vortex, therefore delaying the dynamic stall effect.Īs one of the main clean and renewable resources, wind energy plays a positive role in adjusting the energy consumption structure and promoting ecological civilization. The calculation results show that the optimal flap obtained by RSM increases the pressure difference between the suction and the pressure surfaces at large AOA, suppresses flow separation on the suction surface, and delays the stall AOA. The clean airfoil and the airfoil with optimal flap are compared and analyzed from the static and dynamic aerodynamic characteristics by numerical simulation. Multivariate quadratic polynomials are used to carry out equation regression analysis on the combined results of 17 sample schemes, and the mathematical surrogate model between the flap structure parameters and the airfoil lift–drag ratio and the optimal design parameter combination of the flap structure are obtained. The lift–drag ratio of an airfoil is taken as the optimization response target, and the Box–Behnken design is adopted to design the experiment scheme for H, D, and θ. The response surface methodology (RSM) optimization of H, D, and θ is conducted. A self-popped up flap is added to the airfoil (S809) suction surface to improve aerodynamic performance under large angle of attack (AOA) inspired by the slightly popped up feathers on the trailing edge of a bird’s wing. ![]()
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