Modified Extremum-Seeking Closed-Loop System for Jet Mixing Enhancement

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Modified Extremum-Seeking Closed-Loop System for Jet Mixing Enhancement

Fan, D. W

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 fe 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 fe/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 fe/f0 and hence a maximum K, the modified system achieves a contraction in the fluctuating fe, 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.