Study of the effect of glow discharges near a M = 3 bow shock

This paper aims at investigating the effect of discharges generated near steady bow shocks and their possible use for localized heat deposition leading to drag reduction. We report the observation of steady discharges generated in front of a blunted model in a M = 3 supersonic flow. The test model is designed as a pair of coaxial electrodes, and set up in the ONERA R1Ch M = 3 blowdown wind tunnel. A high voltage power supply is used to generate negative discharges. A corona regime, a glow regime, and a filamentary arc regime are observed. The negative corona regime consists of Trichel pulses dissipating less than 200 mW of electrical power. The glow discharge absorbs powers up to 0.5 kW. It displays a strong light emission in the vicinity of the shock front, followed by a darker region downstream of the shock. The drag coefficient is measured and shows no measurable change when a glow discharge is switched on. To explain this and further investigate the effect of localized heat deposition at the shock front, modified Rankine-Hugoniot jump relations are computed, taking into account a volumetric heat source. This allows one to compute a fair estimate of the drag coefficient and shows that drag reduction by localized heating in the shock front is possible. However, it also shows that in our experiment, the plasma thermal power is too small to appreciably reduce the drag, possibly because of the role of the electron impact excitation of N 2 vibrations, whose fairly long relaxation time could shift downstream the effective gas heating. More generally, the model shows that power-efficient plasma-induced drag reduction requires high plasma heating efficiency.