Research On Flow Mechanism Of Plasma Actuation And Its Control Effect

Plasma flow control is a new type of active flow control technology that converts the energy of an electric field into the momentum or heat of the gas molecule of boundary layer,thereby,suppressing flow separation,reducing turbulent boundary layer resistance,and controlling shock-boundary layer interaction as the active flow control technology.Due to its short response time,no moving parts,and frequency bandwidth,plasma flow control has become a key research direction in the field of aerodynamics and plasma physics.In order to explore the basic characteristics of plasma actuation and its mechanism for improving the aerodynamic characteristics of the flow,the velocity field,pressure field and density field of the plasma induced flow field are studied in depth,and the calculation of the complete plasma actuation bodyforce is established.At the same time,a numerical simulation model of plasma aerodynamic actuation based on electrostatic force field was developed.The characteristics and control mechanism of improvement in aerodynamic performance by plasma actuation was studied,focus on drag reduction of turbulent boundary and separation control in high-speed flow.The research content and innovations of this paper mainly include the following six aspects:1.The dielectric barrier discharge induced flow field structure of the plasma actuator plate model was measured and analyzed in a static atmosphere using a two-dimensional PIV system and a high-speed PIV system.The inducing mechanism of plasma flow field by continuous discharge and pulse discharge was studied.The plasma induced body force distribution is calculated by the velocity field measurement results of the two-dimensional PIV system.The variation trend of the induced flow field under different peak-to-peak voltages and different carrier frequencies is studied.The plasma control electrical parameters are optimized and the mathematical model of plasma actuation is established.For the pulse discharge mode of duty cycle,based on the measurement results of high-speed PIV,the evolution law of plate-induced flow field vortex structure with different duty cycles and different discharge frequencies is studied.2.In order to study the pressure field of plasma induced flow field,an accurate pressure measurement system for equal fluid induced flow field and a complete and reliable measurement method were designed and developed.The problem that the pressure gradient of the flow field induced by the plasma actuator in the static atmosphere is too small to accurate measurement have been solved.The measurement results and the simulation results of the pressure field distribution are compared to verified the reliability of the pressure field measurement results of the experiment.At the same time,the influence of the pressure term on the body force induced by the plasma actuator is studied.The measured pressure field data is taken as the source term and substituted into the Navier-Stokes equation to calculate the body force distribution,revealing the body force and pressure term have a close relationship.3.The high-speed schlieren technique is used to study the time-series and spatial structure of the near-wall density field of aerodynamically actuated plasma under static atmosphere.The experimental results show that the initiation,development and dissipation of the induced vortex is an unsteady start-up process.In the pulse discharge mode,the flow propagates in the form of intermittent pulses.The continuous discharge mode cannot produce a closed induced vortex,and the flow is turbulent.At the same time,the peak-to-peak voltage and duty cycle are the key parameters affecting the initial position and maximum velocity of the induced vortex.As the duty cycle increases,the initial velocity of the induced vortex is pushed back,and the maximum velocity of the induced vortex is positively correlated with the voltage.The pulse frequency is the dominant factor determining the frequency of induced vortex generation.The generation frequency of the induced vortex is strictly consistent with the pulse frequency.The speed step change caused by pulse discharge is the formation mechanism of the induced vortex.The switching instant of the actuator discharge and vacancy is the vortex core.At the moment of growth,the duty cycle determines the spatial structure and propulsion mode of the induced vortex.4.Based on the combination of phenomenological simulation method and physical principle to solve the plasma fluid equations method,a body force model based on electrostatic force field is established.By solving the potential equation and charge density equation of plasma,the plasma actuation effect is taken as the body force source term is introduced into the flow control equation to achieve a relatively accurate numerical simulation of plasma flow control.According to the body force model,the simulation calculations of the plate wall jet and the airfoil flow induced by the DBD plasma actuation are carried out respectively,and compared with the experimental results,the reliability of the body force calculation model is verified.5.In the low-speed wind tunnel experiment,plasma flow control technology was applied and a new measure of drag reduction in the turbulent boundary layer was tried.A smooth plate model suitable for the low-speed wind tunnel was designed and processed.A set of bidirectional discharge DBD plasma actuators was arranged on the model.The velocity distribution of the turbulent boundary layer was measured by a constant temperature hot wire anemometer.The friction velocity of the turbulent boundary layer was fitted based on the Spalding formula,and the frictional drag of the wall was quantitatively calculated.The test results show that,in the presence of plasma actuation,a velocity defect occurs at both measurement locations downstream of the selected acuator compared to the velocity profile without plasma actuation.This shows that DBD plasma actuation can successfully reduce the frictional drag in the turbulent boundary layer at the wall downstream of the acuator.At the same time,the result analysis also shows that the drag reduction effect caused by the reverse discharge actuation is slightly better than the drag reduction caused by the forward discharge actuation,and in the local region of the turbulent boundary layer of the flat model with DBD plasma actuator,the drag reduction efficiency can be reached about 8%.6.By conducting plasma flow control experiments in NF-6 continuous high-speed wind tunnel,an experimental method of plasma flow control technology in high-speed wind tunnel was explored.The flow control characteristics of high-speed flow airfoil flow around different Mach numbers,different flow types,different plasma electrical parameters and different control power sources were studied.The experimental results and control mechanism were analyzed in depth.The experimental results show that in the subsonic region,the plasma excitation can increase the airfoil lift and reduce the airfoil drag,delay the airfoil's stall angle of attack and the drag divergence angle of attack,and achieve effective control of the airfoil flow separation,among which AC power supply effectively controls the flow separation in Mach number 0.6.