Flow Characterization And Aerodynamics Control Of A Sawtooth Plasma Actuator With Multiple Electrodes

As a kind of renewable energy,wind energy accounts for an increasing proportion of new energy in the world.As the main equipment for collecting wind energy,the performance of wind turbines restricts the development of the entire wind power industry.How to improve the power generation efficiency of wind turbines has become a global focus of research and development.Improving the aerodynamic performance of wind turbine blades is an important technical way to improve the efficiency of power generation.When flow separation occurs,the aerodynamic performance of wind turbine will deteriorate sharply.Based on this issue,an experimental study on active control of flow separation of wind turbine blades by using a dielectric barrier discharge plasma exciter was carried out.Five sawtooth plasma actuator（SPA）configurations with multiple encapsualated electrodes（A-E）,each with different electrode numbers or electrical circuits are proposed.The objective of the present work is threefold.First,the plasma-induced flow velocity,thrust,and vorticity of SPAs are examined.Second,the plasma-induced flow topology is investigated for gaining a rudimentary understanding of the underlying mechanism responsible for the flow velocity and vorticity improvement through careful examination of oil flow visualization images.Third,the enhanced aerodynamic performance of a NACA4412 airfoil by the optimum SPA configuration is investigated and the underlying physics is explored.It is found that configuration C,which is consists of three encapsulated electrodes driven by+V_dc and one exposed electrode powered by alternating current（ac）voltage V_ac,outperforms others,achieving the maximumω_x and u of650 s^-1 and 6.83 m/s,respectively.Further,under the same P,the maximum u of this configuration is 26.5%higher than that of the“traditional”SPA with only one encapsulated electrodes and one exposed electrode.In addition,the C has better efficiency in improving the aerodynamic performance of the airfoil.When Re=1.0×10⁵,the steady actuation of C delays the stall angle of attack of NACA4412 airfoil by 4°and increases the maximum time-average lift coefficient C_Lmaxby 8.1%.The optimal unsteady actuation parameters,F⁺（=f_bc/U_∞,where f_b is the modulation frequency,c and U_∞are the wing chord length and free flow velocity respectively）and the duty cycle DC are 1.4 and 7%.Under the optimal unsteady actuation,the stall angle is delayed to 22°.Whenα=22°,the time-average lift coefficient C_L is increased by 101%,and the power consumption can be saved by93%compared with the steady excitation.In contrast to steady mode actuation,which produces the wall-normal velocity fluctuations that trigger the formation of the spanwise vortical structure,the optimum unsteady mode actuation periodically produces the spanwise vortical structures above the suction surface.These structures travel from the leading-to the trailing-edge of the airfoil,forming a low-pressure region above the airfoil,thus augmenting C_L.