Nanosecond Pulse Dielectric Barrier Discharge Plasma Actuator Flow Contol Mechanisms And Application

Due to its simple structure,low power consumption,wide operating band,fast response,and could control flow at a higher velocity,nanosecond pulse dielectric barrier discharge plasma actuator is widely used for vortex and separation flow control.However,nanosecond pulse plasma flow control technology is multidisciplinary and with extreme time scales.Moreover,this type of actuators will produce multiple physical disturbances after discharge,such as force,Joule heat,and pressure waves,which causing its flow control mechanism is not clear.Experimental and numerical simulation studies were conducted in this article for further explore the mechanism of induced vortex by nanosecond pulse dielectric barrier discharge plasma actuator and the predominant disturbance factors in flow control.On this basis,the flow control application on a flying-wing aircraft is performed.Firstly,by conducting the Particle Image Velocimetry and infrared imaging tests on the ground condition,the macroscopic and time-averaged speed disturbances and heating effects of nanosecond pulse plasma actuator were studied.By conducting high-speed Schlieren experiment and numerical simulation methods,the transient compression wave structure and local heating effect produced by discharge were also obtained.Those researches achieved a complete understanding of the actuator characteristics.Secondly,the nanosecond pulse plasma actuator was used for flat plate boundary layer flow control.Transient disturbances on the boundary layer after actuator discharge were studied by numerical simulation method.The time-averaged boundary layer turbulences on the flat plate was obtained by using PIV and boundary layer probe.All these results showed that the plasma discharge inspires strong vorticty formation on the flat plate.And then,the mechanism of plasma discharge introduce vorticity was analysed by means of the vorticity transport equation.At the mean time,the mechanism of plasma discharge introduce vortex was analysed from the perspective of Richtmyer-Meshkov instability.Then,the nanosecond pulse plasma actuator was utilized on an airfoil.By ingenious design of the Schlieren apparatus,multiple physical effects of nanosecond pulse plasma actuator were separated,through comparative study methods,the predominant disturbing factor in flow control by nanosecond pulse plasma actuator was obtained.The results of smoke-wire,PIV test and numerical simulation showed that after plasma discharged,the density and pressure gradient caused fluid baroclinicity,which further induced vorticity increased and promoted vortex generation.The induced vortex were enlarged by the Kelvin-Helmholtz Instability in shear layer,and in turn,vortex promoted the internal and external flow of shear layers to mixing.Due to the complicated flow field structure when disturbanced the fluid flow by nanosecond pulse plasma actuator,the POD orthogonal mode decomposition method was used to extract the flow modes under flow control,and the dominant factor of flow change was accessed.Due to the importance of shear flow control in fluid mechanics and aerospace engineering,the excitation parameters that could impact on flow control efficiency were also researched in this article.Through a comparative study of pressure and PIV measurement,the optimal frequency of shear flow control is determined.The dimensionless forcing frequency is close to 1.The best forcing location in connection with flow conditions,which is the point prior to separation,but not far from.Finally,the nanosecond pulse dielectric barrier discharge plasma actuator was used to flow control on a flying wing aircraft,engaging in the application of aerodynamics and aerodynamic torque control.This article successfully realized the vortex and separated flow control,aerodynamic performance of the aircraft was also enhancement.This thesis in-depth research of the characteristics of nanosecond pulse dielectric barrier discharge plasma actuator,illustrated its mechanism of induced vortex and its dominant factors in flow control,clarified its flow control mechanism,this work is convenient for theory and practical application of plasma actuator in fluid machinery and aerospace applications.