Experimental Study of a Double Arc Nitrogen Plasma: Static and Dynamic Behavior

摘要: In the frame of studies devoted to reentry simulations, we have devised and tested an original double arc plasma torch which provides a long-time highly stable low-pressure supersonic nitrogen jet. The arcs are investigated at both anode levels by means spectroscopic diagnostics. They not attached on walls single local roots as it is generally case atmospheric pressure. first chamber, totally dissociated ionized, measured electron density temperature close those derived from local-thermal-equilibrium calculation. also within second chamber exit where flow abruptly released. results allow examine validity thermodynamic equilibrium criteria in nonstandard conditions encountered plasma. purpose estimating jet specific enthalpy energetic efficiency, Mach number measurements performed axis using pitot probe they compared fluent numerical simulation results. dynamic behavior analyzed classical tools such fast Fourier transform, correlation functions Wigner distribution. temporal series exhibit two main characteristic frequencies: At low frequency, electric generators yield very reproducible 150-Hz oscillations, whereas firing gives birth sharp 6.7-kHz peak ascribed generation acoustic waves region attachment. value this frequency that depends neither supplied power nor mass rate interpreted assuming acts Helmholtz oscillator