Characteristics of meso-pressure six-phase alternative current arc discharge plasma jet: Experiments

Abstract

During the re-entry process of a supersonic vehicle in near space, the interaction between the flying vehicle and surrounding air is violent due to the hypersonic relative speed.As a consequence, the shock-heated air in the vicinity of the vehicle surface is ionized.Thus, the formed plasma layer operates in strong collision, non-uniform and nonequilibrium states.One of the serious system operation problems resulting from this non-equilibrium plasma layer is the so-called communication blackout.Physical simulation of the near-space plasma environment in laboratory based on various plasma sources is a much lower cost method than the in-situ measurements in the vehicle re-entry process.In this paper, based on the ideas for designing the dual jet direct current arc plasma and the muti-phase alternating current discharge plasma, a physical design on the multi-phase alternating discharge apparatus is proposed for generating a large volume plasma arc-jet.And a multi-phase gas discharge plasma experimental platform-2015(MPX-2015) is established with the image recording/processing, electrical and optical emission spectroscopy measurement system in this laboratory. The preliminary experimental observations show that under a typical operating condition with a 500 Pa background pressure, a large volume plasma jet with a maximum diameter of 14.0 cm and a maximum length of 60.0 cm is obtained on this newly developed platform.The influences of the gas flow rate, the chamber pressure, the electrode gap spacing and the arc current on the characteristics of the plasma free jet and impinging jet are also studied.The experimental results show that within the parameter ranges studied in this paper, the chamber pressure has a very significant influence on the size of the plasma jet, i.e., both the diameter and length of the plasma free jet increase with chamber pressure decreasing, and a similar variation trend is also observed for the thickness and length of the plasma layer surrounding a bluff body.In addition, the size of the plasma layer also increases with the increase of the plasma working gas flowrate and the discharge current.These results are helpful in the more in-depth investigating of the aerodynamic heat effect and blackout issue of the re-entry process of supersonic vehicle in near space in future.In the future research, we will modify the structures of the plasma generators in order to obtain supersonic plasma arc-jets, and study both the quasi-steady and transient characteristics of the arc plasmas, as well as the strong interactions among the plasma jet, the surrounding air and the solid bluff body.