Thermodynamic Characterization of High-Speed and High-Enthalpy Plasma Flows

Abstract

This contribution proposes a description of selected experimental activities conducted in aerospace sciences and dedicated to generate experimental data to assess atmospheric entry plasma models. In order to provide comprehensive set of experimental data, high enthalpy shock tube facilities have been developed to generate plasma representative of entry plasma for broad range of trajectory entry conditions. The shock-heated plasma is obtained through adiabatic compression and the resulting post-shock plasma flow exhibits thermodynamic state analogous to actual entry plasma. However, significant insight can be obtained through experiments conducted also with non-equilibrium plasma flows obtained with other methods. The typical methodologies adopted to provide experimental data of interest to enhance entry plasma modeling are sketched for four distinct non-equilibrium plasma kinds produced respectively by four specific ground facilities. The contribution firstly will consider experimental campaigns conducted with a high enthalpy shock tube in order to document in absolute radiance the radiative signature in the UV spectral range of an Earth entry plasma. Then, the investigations of the interaction between a shock wave and an electrical discharge will be described. These investigations were performed to identify the role of the internal degrees of freedom of molecular gases on the propagation of the shock. Also, the contribution covers investigations devoted to the thermodynamic state characterizations by means of spectroscopic diagnostics in the cases of the non-equilibrium plasmas flows generated by plasma wind tunnels. The examination of the Saha-Boltzmann equilibrium is proposed in the case of a subsonic plasma flow. And at last, the characterization methods of air supersonic plasma jet are presented and the 2D distributions of the subsequently measured plasma properties are documented for a straight comparisons with non-equilibrium plasma jet computations.