| Take off and landing performance is the key performance indicators of aircraft and determines the security,the flexibility,the economy,the comfort of aircraft.In order to improve the take off and landing performance of aircraft,the airplanes are usually equipped with high-lift systems,such as leading edge slats and Krueger flaps.Advantages of these devices include improvements in take off and landing performance,turn rates,glide range and payload.Meanwhile,these devices are becoming more complicated,expensive and clunky.Promoting the development of the advanced high-lift systems is the point for the reduction of take off distance,saving energy,improving the performance of taking off and landing,and achieving the object of―Green Aviation‖.The Slatless Wing has taken away the leading edge high-lift systems,such as leading edge slats and leading edge flap,reduced the aircraft weight,simplified the structure and saved power.How to compensate for the lift loss resulting from taking away the leading edge high-lift systems and suppress the flow separation around the flap is the critical factor for implementing the engineering application of Slatless Wing.As a significant branch of aerodynamics,the flow control technology can provide the important knowledge-base and supports for sloving the problems about Slatless Wing,correcting the shortcomings of the aircraft and promoting the development of the aircraft.Flow control using plasma actuators have gradually become the mainstream of the research field of flow control,due to the simple structure,quick response and easy installation.In order to slove the problem of Slatless Wing,the flow separation control over a supercritical wing was investigated with an asymmetric dielectric-barrier-discharge(DBD)plasma actuator and a symmetric DBD plasma actuator using force measurement,particle image velocimetry(PIV),tuft flow visualization and smoke flow visualization at different Reynolds number in the low speed wind tunnel.The control effects of the asymmetric DBD plasma actuator and the symmetric DBD plasma actuator were compared and the controlling mechanisms of the two plasma actuators were studied.The control effect of plasma actuator was enhanced at Reynolds number 2,000,000 based on this research.Firstly,the characteristics of DBD plasma actuator in still air was investigated using an oscilloscope and PIV system.(1)The results suggested that the length of exposed electrode is an important parameter which affect the consumed power of plasma actuator.Before the threshold,the consumed power of plasma actuator increases with the length of exposed electrode.The consumed power of plasma actuator changed little with the length of exposed electrode beyond the threshold.(2)The transient PIV results indicated that the induced flow filed of plasma actuator is the nonlinear and unsteady system and the area of high turbulence intensity and high turbulent kinetic energy are is close to the surface.(3)The body force is one of important standards to evaluate the control effect of plasma actuator.The PIV results suggested that the region of strong body force was concentrated around the wall.At the beginning,the body force was enhaced with the time.When the induced flow field reached steady state,the body force changed little with time.(4)Analysis of transient flow field induced by plasma actuator suggested that the starting vortex has the ablity of entraining high-momentum fluid into the near-wall region.The starting vortex moved away from the wall with time,the circulation generated by plasma actuator enhaced with time and the radius of vortex core increased with time.(5)The PIV results of the near-wall region indicated that the induced jet is a turbulent wall jet which had some coherent structure,including rolling up vortex and secondary vortex,when the plasma actuator was operated at higher voltage.And these coherent structures were related to a dominant frequency which promoting mixing.Secondly,in order to be close to the real conditions,the flow field generated by symmetrical plasma actuator under flow condition was investigated using PIV system.The results indicated that the breakdown time of upstream starting vortex which was in the opposite direction of incoming flow was extended and the disturbance ability of plasma actuator was enhanced under flow condition.Meanwhile,the life time of downstream starting vortex was reduced and the body force the near-wall region was increased.Thirdly,the experimental study was carried out to evaluate the effect of asymmetrical and symmetrical plasma actuators on flow separation control using force measurement,tufts flow visualization and PIV system in the 0.75 m30.75 m low speed wind tunnel.(1)The force measurement suggested that the flow separation is suppressed by plasma actuator which was mounted on the leading edge of the airfoil.The stall angle of attack was delayed and the maximum lif coefficient was increased when the plasma was actuated.The plasma actuator can achieve the function of leading edge slat and laid a foundation for solving the the problems about Slatless Wing.(2)Compared to the asymmetrical plasma actuator,the symmetrical plasma actuator has the better control effect at high Reynodls number due to the induced vortex.(3)Momentum injection was a major controlling mechanism of the asymmetrical plasma actuator.However,momentum injection was not a point for controlling mechanism of the symmetrical plasma actuator.The induced vortex generated by the the symmetrical plasma actuator which can achieve the effect of moving surface boundary layer control technology and entrain high-momentum fluid into the near-wall region is found to be the key for improving the aerodynamics performance of airfoil at high angle of attack.(4)The ratio of benefit to consumed power increased with the Reynolds number.Fourthly,the experiments of flow separation control over a three dimensional wing were conducted to examine the control effect of symmetrical plasma actuator using force measurement and PIV system in theΦ3.2 m low speed wind tunnel based on the experimental results of two dimensional airfoil.(1)The force measurement results indicated that the flow separation around the wing is suppressed by the symmetrical plasma actuator at Reynolds number 2310~6.The stall angle of attack was delayed by approximately 2 degree and the maximum lift coefficient was increased by approximately 8.9%.(2)The ratio of benefit to consumed power increased with the Reynolds number,which was similar to the two dimensional airfoil experiments.(3)The results of scale effect investigation suggested that the ratio of benefit to consumed power of big scale testing model was higher than the ratio of small scale testing model.It indicated that the flow separation control over a full size aircraft using symmetrical plasma actuator could be achieved.Finally,the Unmanned Aerial Vehicle(UAV)flight testing was carried out to evaluate the control effect of symmetrical plasma actuators using pressure and attitude angle measurement of UAV under realistic environment.It is implemented that power supply is wirelessly controlled by upgrading the circuit board of power supply and writing programs.The circuit board for pressure and attitude angle measurement was developed and the platform of flight testing was established.(1)The flow separation around one wing of UAV was suppressed by one symmetrical plasma actuator and the large roll angle of UAV was generated.(2)The flow separation around two wings of UAV is suppressed by two symmetrical plasma actuators and pressure peak on the suction surface of wing become stable.It indicated that the function of leading edge slat was achieved by symmetrical plasma actuators. |
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