Self-adaptive flow control via frequency-modulated sweeping jets in a compressor cascade

This study experimentally investigates the flow control behavior of self-excited sweeping jet actuators (SSJA) with varying feedback channel lengths in a compressor cascade. Aerodynamic measurements, oil-flow visualization, and unsteady spectral analysis are combined to examine the role of jet frequency in separation control. The results show that SSJA significantly reduces total pressure loss under moderate-to-high positive incidence conditions, with the L = 7 mm case showing the best overall performance among the tested configurations and achieving a maximum reduction of 27.1%. In contrast, under negative incidence conditions, where the flow remains largely attached, the actuator exhibits limited influence without introducing additional losses. Flow-field analysis indicates that higher-frequency sweeping jets induce streamwise vortices, enhance momentum exchange between the freestream and the boundary layer, delay separation, and suppress dominant vortex structures. Spectral results show that the jet frequency varies with feedback channel length and driving pressure difference. Shorter channels generate higher-frequency jets and are associated with improved control effectiveness. Furthermore, the observed variation of dominant frequency and control effectiveness with incidence supports a potential self-adaptive interpretation of SSJA behavior. These findings support a frequency-related interpretation of SSJA flow control in the present compressor cascade and provide guidance for the design of efficient separation-control strategies under similar operating conditions.