| Near space and low earth orbit(altitude range: 30-300km)are of excellent value to national economy construction and national defense construction.Thus,both areas have always been a focus of attention and competition in various countries all over the world.The near space crafts and LEO satellites are the main tools for developing and utilizing resources in near space and low earth orbit.The research and development of propulsion system,which is closely related to the tools’ orbital work cycle,play an important part in the design of near space crafts and LEO satellites.Considering the airspace pressure conditions,this paper takes an electric propulsion system,which is based on a single dielectric barrier discharge along the surface as the plasma source with air as the working fluid,as the research object.The evaluation of its performance under low pressure,and a concept design of its air-intake device,are also carried out in this paper.According to the experimental research scheme and requirements of the electric thruster with a single dielectric barrier discharge along the surface,which should be in a low-pressure environment with variable parameters,a low-pressure test system is set up based on the laboratory vacuum chamber system.Then,the measurement scheme of the thruster’s parameters and performance is designed,including the discharge parameter measurement and thrust measurement as the core.Meanwhile,a series of test prototypes with different design parameters are designed and processed for the variable parameters test and study.Firstly,the basic performance of SDBD-based electric thrusters under low pressure is evaluated.The data of thrusters’ discharge voltage and discharge current is obtained,and the power consumption during discharge operation is calculated.The measurement scheme obtains the thrust and efficiency(thrust power ratio),which can be the representatives of the basic thrust performance parameters under low pressure.The results show that,under the pressure of 10-90 k Pa,the thrust levels of test prototypes are in the magnitude of 0.1-5m N,while the power consumption levels are in the magnitude of 10 W.Besides,the influence of operating parameters on the performance parameters of basic thrust is studied.Secondly,the variable parameters experiments are conducted to find the relevance and influence factors on the relationship between the pressure at which the thrust gets to peak and other parameters.Specifically,the influences of the thickness and material of dielectric,and the peak-peak value of the applied voltage are studied.The results show that the greater the thickness of the dielectric,the smaller the pressure at which the thrust reaches the optimal value.The greater the dielectric constant of the dielectric,the larger the pressure at which the thrust reaches the optimal value.The greater the peak-peak value of the applied voltage,the larger the pressure at which the thrust reaches the optimal value.In addition,the characteristic mechanism of thrust based on SDBD discharge under low pressure is explored.According to previous studies,the thrust model based on Townsend’s First Ionization Coefficient is proposed,which theoretically explains the phenomenon that the thrust non-monotonously changes with the pressure and has a peak value under low pressure.Meanwhile,the theoretical formula is deduced from the thrust model,and the relationship between the pressure at which the thrust reaches the optimal value and the applied voltage and the parameters of the dielectric is revealed.The qualitative analyses are consistent with the experimental results,and the quantitative analyses of the experimental data are also consistent with the theoretical formula.Finally,based on the basic demands and requirements of the existing air-breathing thrusters,the airintake device is introduced and analyzed.Taking the passive compression air-intake device as the research object,its parameters such as collection efficiency,aspect ratio,compression ratio and so on are carefully chosen and the device is eventually designed. |
