Research On Plasma Wind Velocity Measurement Technology Based On AC Gas Discharge

Plasma wind velocity measurement technology based on AC gas discharge has high spatial resolution,high frequency response,no need of temperature compensation,high signal-to-noise ratio,easy calibration and other significant advantages.It is one of the most promising wind velocity measurement techniques in the study of supersonic flow field,and it has broad application prospect in aviation,aerospace,military,meteorology and other fields,at present,its theoretical and simulation studies are not yet mature.In this paper,AC(alternating current)plasma anemometer is taken as the research object,and the study of plasma wind velocity measurement technology is carried out from three aspects: numerical simulation,experiment and electrical modeling.Firstly,a new approach to build the numerical modeling of AC plasma anemometer is proposed.In the study,a two-dimensional gas flow field model between electrodes was established,and the two-dimensional plasma model based on PIC/MCC method was introduced,then,the coupling of them was completed,and the two-dimensional numerical simulation platform of the AC plasma anemometer is built.The numerical simulation platform can not only analyze the influence of gas flow velocity on ion density distribution,electron density distribution and potential from micro perspective,but also study the influence of discharge parameters on the performance of plasma anemometer from macro perspective.Then,a new experimental system of AC plasma anemometer is designed.Its feasibility is proved by the theoretical analysis.Subsequently,the equipment selection and design process of the experimental system are introduced in detail.The negative feedback coupled circuit module composed of resistor and capacitor in series is introduced into the system,which can suppress the positive feedback process of gas discharge and improve the stability of discharge system.In addition,the built system contains the high voltage power module,which can realize the air discharge mechanism that using the radio frequency maintains discharge after the high voltage lighting,thus a more stable radio frequency air discharge status can be obtained.The experimental result show that there is a good linear relationship between the effective value of load voltage and the wind velocity value,which can be applied to the wind velocity measurement.Finally,the idea of building an AC plasma anemometer electrical model is proposed.Based on the theoretical and experimental analysis,the equivalent circuit model is established,and its structure consists of three parts: the positive column region,the sheath and the diffusion region.The positive column region is equivalent to a resistor,and the sheath is equivalent to a parallel circuit consisting of a current source,a capacitor and an ideal diode,while the diffusion region is equivalent to a series circuit including a resistor and an inductor.The circuit models of the plasma anemometer without airflow and under airflow are established respectively according to the connection structure of each part.Finally,the feasibility and reliability of electrical modeling are verified by OrCAD circuit simulation.The established circuit model complements the shortages of numerical simulation from the electrical point of view,and takes full account of the circuit characteristics of the AC plasma anemometer.Therefore,it can be used as an electrical tool to study and optimize the plasma anemometer.