Shadow method for measuring the electron density in a barrier discharge plasma on the Zhukovskii airfoil surface

Abstract

We have measured the electron temperature and density distributions in an ionized gas flow initiated by a high-frequency barrier discharge on the Zhukovskii airfoil surface by the method of photometry of shadow patterns for two probe radiation wavelength λ r = 0.675 μm and λ b = 0.425 μm. The investigation was carried out in air at atmospheric pressure. The maximum value of the electron density was N e 2.2⋅10 15 cm −3 with an insignificant change in the air temperature in the discharge gap.Introduction. Controlling the boundary layer and the character of the flow around various bodies at a dielectric barrier discharge on their surface is a topical direction of investigations in modern aerodynamics. The main tasks for researchers in this field are to increase the efficiency of actuators and develop a physical mechanism of influence of the barrier discharge on the flow characteristics. To attain these goals, experimental data on the electron density and temperature distribution, as well as on the averaged ionized gas temperature in the boundary layer, are needed.The results of investigating by optical methods the electron density of a dielectric barrier discharge plasma in stationary air are given in [1][2][3]. The measuring methods are based on the change in the optical density of the gas depending on the electron density. In measuring the refractive index by the laser beam deflection in passing through the discharge region, the maximum electron density in the dielectric barrier discharge plasma was equal to N e 10 13 -10 14 cm −3 [1]. The maximum value of N e obtained by photometering the shadow patterns for two probe radiation wavelengths was equal to N e 4.5⋅10 15 cm −3 [2, 3].The authors of [4] have established that the temperature of electrons in a filamentary glow discharge is almost pressure independent, whereas the electron density increases with decreasing ambient air pressure. Under diffusion glow conditions both characteristics increase with decreasing pressure.According to the data presented in [5], the average electron density in the barrier discharge plasma at a pressure of 1 atm and a discharge electrode gap of 1 mm is N e 10 14 -10 15 cm −3 . The gas temperature in the discharge gap on going from diffusion to filamented glow discharge conditions increases from 300 to 500 K [6].In [7,8], the results of experimental measurements of the electron density and temperature by the spectral methods are presented. The electron density and temperature in the barrier discharge initiated in helium at a pressure of 760 Torr a frequency 10 kHz, and a voltage on the discharge electrodes of 2-4 kV, measured by the spectral method, were equal to N e 10 11 cm −3 and T e 1 eV. In [8], the characteristics of an asymmetric aerodynamic actuator based on the surface dielectric barrier discharge were investigated. From the point of view of the simplified collisional-radiative model for the N 2 molecule, the authors made calculations of the averaged temperature and density of electrons using the measurement data for the rad...