Investigation On The Characteristics And Mechanism Of Separation Flow Control Using Plasma Actuation

With the rapid development of automatic control,electronic information,artificial intelligence,composite materials,and other technical fields,active flow control technology has become an important means to expand and improve the aerodynamic performance of aircraft in the non-design state.Surface Dielectric Barrier Discharge(SDBD)is a fast-growing branch of active flow control technology.It is rapidly studied due to its simple structure,fast response time,low energy consumption and good robustness.It is widely used in the study of various flow phenomena.At high angles of attack,the aerodynamic performance of the aircraft is inseparable from its surface separation and flows.Existing studies have shown that active flow control technology has obvious effects in the suppression and utilization of separation flow,Thus,it becomes an important means to improving the aerodynamic performance at high angles of attack.In this paper,the separation flow characteristics and flow control mechanism under the excitation of SDBD plasma are studied.The conical forebody and flying wing layout are taken as the research object,The wind tunnel experimental technology is used as the specific research method.The alternating current(Alternating Current,AC-)and nanosecond pulse(NS-)plasma are used for separation control.The results confirm the effectiveness of the plasma actuator in separation controls.Meanwhile,the mechanism of the plasma flow control is given.It provides a reliable technical basis and mechanism reference for the practical application of the plasma flow control technology.Firstly,the characteristics of AC-SDBD and NS-SDBD plasma actuation are compared in the static atmosphere.The induced physics fields of two kinds of plasma actuation are analyzed and the flow control mechanism is concluded.The optimization of AC-SDBD and NS-SDBD plasma actuation is further studied.The results show that the AC-SDBD plasma actuation effects the flow by the induced near-wall jet on the covered electrode side.By applying the thick dielectric barrier,the induced flow and thrust are significantly improved.The certain law is satisfied with the thrust varies with the input voltage in the logarithmic space.The duty-cycle cycle plasma actuation can adjust the induced vortex size and vorticity by changing the duty-cycle ratio.The NS-SDBD plasma actuation relies on the transient thermal effect generated by the rapid increase of input voltage in separation control.The thermal effect appears as a combined compression wave at the microsecond time scale and starts the vortex process at the millisecond time scale.Meanwhile,the electromagnetic problem of NS-SDBD plasma actuation is solved by using reliable shielding methods.Thirdly,a pair of AC-SDBD plasma actuation is applied to control the asymmetric vortex flow field over the conical forebody at high angles of attack.The effective flow control speed is 42m/s with the Reynolds number based on the diameter of core base of 3.09×10~5.The induced thermal effect at microsecond and second-time scale is directional,focusing on the covered electrode side.comparing the control results of plasma actuation in different layouts,the control mechanism of separation vortex is concluded.The actuation position should be set between the azimuth angle of 80°and 90°.Once the flow starts to accelerate,becoming to separate,the small perturbation induced by NS-SDBD plasma actuation will not effectively control the asymmetric vortex flow field.Finally,the NS-SDBD plasma actuation arranged at the leading edge of the wing is used to control the longitudinal aerodynamic characteristics of the flying wing.The effective control wind speed is 30 m/s.Through the full-length plasma actuation,the maximum lift coefficient is increased by 7.5%,the pitching moment coefficient is reduced by 11.6%,and the stall angle of attack is delayed by 3°.Comparing the plasma actuation of different layouts,the flow control mechanism is concluded,At the small angle of attack,the separation first appears in front of the wing,on the outer side of the edge.As the angle of attack increases,the separation point gradually moves upward to the inner side of the forward edge.Under the premise of not considering the control efficiency of the actuator,the control effect of the full extension excitation is the best.