Time-resolved spectroscopic temperature measurements of an electric discharge generated in a supersonic flow

Abstract

Experiments using time-resolved emission spectroscopy are carried out to determine the temperature in a direct current (DC) electric discharge generated in a high-speed flow. The experiments are conducted in the STA shock tunnel at the French-German Research Institute of Saint-Louis (ISL) at a Mach number of 4.6 and at flow conditions corresponding to an altitude of 8 km. Nitrogen is used as test gas. The electric arc is generated on the surface of a wedge with a sharp leading edge. The electrodes of the DC plasma actuator are installed flush with the surface. During the discharge, the input power is regulated to a constant value of 10 kW. The B2Σ+ − X2Σ+ violet system of the CN molecule with the band head around λ = 388.34 nm is used for determining the vibrational and rotational temperatures in the positive column of the electric arc. In addition, copper atomic lines with the wavelength band between λ = 517 nm and λ = 525 nm are utilized to obtain the electronic-excitation temperature in the plasma. Thermal nonequilibrium is detected between the vibrational and rotational modes of the CN molecule in the outer layers of the positive column of the arc. The maximum electronic excitation temperature measured ranges during the experiment from 9,000 to 13,300 K leading to a mean value of 10,670 K.