Parametric study of high-frequency characteristics of plasma synthetic jet actuator

A major issue of plasma synthetic jet actuator (PSJA) is the severe performance deterioration at high working frequency. In this study, experiments and numerical simulation are combined together to investigate the influence of thermal conductivity, throat length (L_th) and discharge duration (T_d) on the high-frequency characteristics of PSJA. Results show that the variation of the actuator thermal conductivity and discharge duration will not alter the saturation frequency of the actuator, whereas decreasing the throat length results in an increase of the saturation frequency. For a short-duration capacitive discharge of 1.7 μs, a clear shock wave is issued from the orifice, followed by a weak jet. As a comparison, when the discharge duration is increased up to 202.6 μs, a strong jet column is formed and no obvious shock wave can be visualized. Based on numerical simulation results, it becomes clear that the long-duration pulse-DC discharge is able to heat the cavity gas to a much higher temperature (3141 K) than capacitive discharge, greatly improving the conversion efficiency of the arc discharge energy to the internal energy of the cavity gas. In addition, high-speed Schlieren imaging is deployed to study the performance degradation mechanism of PSJA at high working frequency. Monitor of the exit jet grayscale indicates that as long as the saturation frequency is exceeded, the actuator becomes unstable due to insufficient refresh time. The higher the discharge frequency, the more frequently the phenomenon of 'misfires' will occur, which explains well the decaying jet total pressure at above saturation frequency.