Active control of thermoacoustic fluctuations by nanosecond repetitively pulsed glow discharges

In this study, the use of nanosecond repetitively pulsed (NRP) glow discharges to mitigate thermoacoustic fluctuations was investigated. Two strategies in applying the discharges were compared: continuous forcing and closed-loop gated forcing. It was found that NRP glow discharges could mitigate thermoacoustic fluctuations in a wall-stabilized methane-air flame either by applying the discharges continuously or using a closed-loop control scheme. A parametric study was done to investigate the role of the forcing phase, the applied voltage (6.3–6.8 kV), the pulse repetition frequency (15–30 kHz), the duty cycle (24–50%), and the forcing frequency on the performance of the plasma actuator. The most effective control of the thermoacoustic fluctuations was obtained when using the closed-loop control scheme with an applied voltage of 6.8 kV, a forcing frequency matching the instability frequency, close to phase opposition with the instability, and a power input of 0.8% of the flame thermal power. It was also found that the duty cycle in the tested range did not have a significant effect on the performance of the scheme when the number of discharges per cycle was constant. Phase-locked imaging of the flame was employed and showed that the flame's base location, surface area, and surface area gradient oscillated over the thermoacoustic period. For the best discharge forcing, the oscillations in the flame's base location and surface area were suppressed making the flame temporally and spatially stable.