Modified extremum-seeking closed-loop system for jet mixing enhancement

A modified extremum-seeking closed-loop control system is proposed for jet mixing enhancement. The system introduces a variable perturbation component that may act to adjust adaptively the searching range of the optimal control signal. The actuator is a single pulsed minijet injected radially into the main jet before its issue. The excitation frequency f_e for the minjet is controlled by an electromagnetic valve. The open-loop control measurements indicate that, given the duty cycle and the mass flow rate ratio of the minijet to the main jet, the decay rate K of jet centerline mean velocity, which provides a measure for jet mixing, displays a maximum at the optimum frequency ratio f_e/f₀ = 0.5, where f₀ is the preferred-mode frequency of the main jet. Comparison is made between the modified and classical systems. Although both may find automatically the optimal f_e/f₀ and hence a maximum K, the modified system achieves a contraction in the fluctuating f_e, when the control target is reached, by 70%, and subsequently an increase in K by 12%. The new system further exhibits a better robustness than the classical.