Analysis of the flow control and noise reduction characteristics of aircraft high-lift devices utilizing oscillating jets

This study employed the canonical 30P30N three-element airfoil model to investigate the aerodynamic and aeroacoustic issues arising from flow separation over flaps at moderate angles of attack during aircraft take-off and landing. A multi-parameter optimization framework leveraging the Bayesian optimization was developed to advance an oscillating jet-based control strategy for lift enhancement, drag reduction, and noise reduction. Hybrid aeroacoustic simulations, coupling improved Delayed Detached Eddy Simulation (IDDES) with the Ffowcs Williams-Hawkings (FW-H) equation, were conducted to evaluate the aerodynamic and aeroacoustic performance and elucidate the underlying physical mechanisms responsible for the observed lift augmentation, drag reduction, and noise mitigation. Numerical results demonstrated that an oscillating jet with a frequency equal to the characteristic frequency and a momentum coefficient of (1.897%, 0.006%) significantly suppressesed flow separation over the trailing-edge flap of 30P30N at a Reynolds number of 1.7×10⁶, a Mach number of 0.17, and an angle of attack of 5.5°, yielding approximately an 8.24% increase in lift and an 8.00% decrease in drag. Furthermore, the overall sound pressure level (OASPL) of the aerodynamic noise was reduced by 1.27 dB. At the 30° observation direction, OASPL experienced the largest reduction by 2.88 dB. A more substantial reduction of 4.28 dB was observed for the far-field low-frequency noise at (270°, 5C). Notably, the tonal peak associated with shedding vortices was attenuated by 14.05 dB, while the high-frequency noise remained largely unaffected. Analyses revealed that the jet not only directly injected energy into the flow field but also introduced disturbances that generated spanwise vortices, promoting energy exchange between low-momentum fluid within the shear layer and high-momentum fluid in the freestream. This energy exchange process effectively weakened the boundary enstrophy flux at the flap trailing edge. Consequently, the interaction region between positive and negative values of the Lamb vector divergence was significantly reduced, resulting in suppressed acoustic source strength. The findings of this study provide a theoretical basis for designing aircraft with enhanced lift, reduced drag, and mitigated noise.