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

摘要

We present and discuss results on 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 6.4 × 10~5. Open-loop forcing experimental results are presented, wherein localized arc filament plasma actuators are shown to have two distinct effects on the irrotational near-field pressure, similar to their effects on the far-field acoustics reported earlier. At low forcing Strouhal numbers near the jet preferred mode, a large amplification in the pressure fluctuations is observed. At much higher forcing Strouhal numbers, an attenuation is observed in the pressure fluctuations over a broad range of excitation frequencies, especially in the axisymmetric mode of the pressure fluctuations. Previous experiments have shown that forcing the jet with these low and high Strouhal numbers results in jet mixing enhancement and far-field noise reduction, respectively. Two different gradient-free extremizing feedback control algorithms have been developed and implemented, each of which can perform online minimum seeking, as well as maximum seeking. Both methods demonstrate fast convergence to the optimum followed by steady operation. We also show that the far-field acoustic spectrum in steady-state operation of the closed-loop control is quite similar to that observed with optimal open-loop forcing.