Abstract: Flow separation and secondary flow in the S-duct of an aircraft engine cause severe pressure loss and airflow distortion at the outlet, lowering engine performance. Herein, a serial two-electrode plasma synthetic jet (PSJ) actuator array is used to actively control the flow field in the duct and improve its characteristics. The results show that the PSJ significantly increases the wall pressure recovery coefficient, suppresses flow separation, and improves the outlet pressure distortion. The primary and secondary orders of the influencing factors are as follows: control position>jet momentum coefficient>excitation frequency>jet configuration. The best jet control position is near the separation location, and the best jet configuration is the ‘Λ’ configuration. The higher the jet momentum coefficient and excitation frequency, the better the flow control. The wall pressure coefficient increases by up to 127.8%, and the outlet steady pressure distortion index decreases by 9.15%. The control mechanism is the direct energy injection into the flow boundary layer through a high-speed jet and the indirect control effect of the induced streamwise vortex. On the one hand, the PSJ suppresses flow separation by improving the ability of the boundary layer to resist the inverse pressure gradient. On the other hand, it reduces pressure distortion by decreasing the intensity of the secondary flow and weakening the backflow. This study thus provides a new technology for the active control of the flow-field characteristics in an S-duct and has significance for guiding the application of synthetic jet technology in S-ducts.

Key words: S-duct; Flow control; Plasma synthetic jet (PSJ); Flow separation; Pressure distortion

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