Extremizing Feedback Control of a High-Speed and High Reynolds Number Jet

Abstract

We present results of the development and application of extremizing feedback control to high-speed and high Reynolds number axisymmetric jets. In particular, we demonstrate control authority on the near-field pressure of a Mach 0.9 jet with a Reynolds number based on jet diameter of 7.8 ◊ 10 5 . Open-loop forcing experiments are presented wherein localized arc filament plasma actuators are shown to have two distinct effects on the near-field pressure, similar to their effect on the far-field acoustics reported earlier. At low forcing Strouhal numbers (StDF’s) near the jet column mode instability, a large amplification in the pressure fluctuations is observed. At higher StDF’s (close to the initial shear layer instability) a broad attenuation is observed in the near-field pressure fluctuations, especially in the axisymmetric mode. Previous experiments have shown that forcing the jet with these low and high frequencies result in jet mixing enhancement and far-field noise reduction, respectively. Two different gradient-free extremizing feedback control algorithms have been implemented, each of which can perform online minimum-seeking as well as maximumseeking. Both methods demonstrate fast convergence to the optimum followed by steady operation.