Numerical modelling for characteristics of the meso-pressure six-phase alternative current arc discharge plasma jet

Abstract

In the re-entry process of hypersonic vehicle in near space,the violent interaction between the vehicle and the surrounding air will ionize the air and leaves a complex environment in the vicinity of the vehicle surface.Both the flow field and the communication between the vehicle and the controlling center on the earth are significantly affected by the generated plasma layers.This will result in serious system operation problems such as the communication blackout or radio blackout.Numerical modelling is one of the most widely used methods to investigate such complicated physical-chemical processes involving coupled magneto-hydrodynamics,heat transfer,dissociation,ionization,excitation and their reverse processes.Due to the strong collision,non-uniform and non-equilibrium characteristics of the plasma layers formed in the vicinity of the vehicle surface,a self-consistent physical-mathematical model,as well as a database for the transport properties of non-equilibrium plasmas,describing the non-equilibrium features of plasmas is one of the pre-requisites for numerical simulations.This paper focuses on the non-equilibrium plasmas produced near the bluff body surface in the re-entry process of hypersonic vehicles in near space,and a new non-equilibrium plasma model which has been developed previously by our group is employed for conducting two-dimensional (2D) simulations on the characteristics of the non-equilibrium argon plasma jets based on the multiphase gas discharge plasma experimental platform-2015(MPX-2015) established in our laboratory.The modelling is conducted under two different flow conditions, i.e.,the sub-sonic flow condition and the super-sonic flow condition.Under the sub-sonic flow condition,the 2D nonequilibrium modeling results are consistent well with the experimental measurements which validates the reliability of the non-equilibrium physical-mathematical model,as well as the developed computer codes in this study.The modeling results under the super-sonic flow conditions show that the spatial uniformity of the plasma layer surrounding the bluff body,as well as the total heat flux to the bluff body surface from plasmas,decreases significantly with the increase of the plasma jet velocity;while the local electron number density increases in the vicinity of the head of the bluff body, the thickness of the plasma layer surrounding the bluff body first decreases,and then increases.These modelling results provide a theoretical guidance for conducting experimental studies under a super-sonic flow condition on MPX-2015. In the future research,we will extend the physical-mathematical model to investigate of the transient,non-equilibrium features of the air discharge plasmas,and the complicated interactions between the plasma jet and the surrounding air, and/or the downstream bluff body under different operating conditions.Simultaneously,we will also try to develop the in-situ experimental methods to obtain the spatiotemporal distributions of the temperature,velocity and species concentrations in the plasma layer,and conduct a comparison between modelling results and measured data.