Noise reduction of a high-lift airfoil with a very long chord slat based on aerodynamic and aeroacoustic analysis

The leading-edge slat of high-lift devices is recognized as a dominant source of airframe noise. Realizing effective noise reduction while preserving aerodynamic performance remains a major challenge for high-lift design in civil aircraft. To address this issue, the present study investigates a multi-element airfoil with a very long chord slat (VLCS) through surrogate-based aerodynamic optimization, followed by high-fidelity aeroacoustic analysis and wind tunnel measurements. Compared with a conventional slat, the optimized VLCS exhibits a seamless leading-edge configuration at takeoff and a reduced deflection with an enlarged gap at landing, achieving improvements of 10.4% in takeoff lift-to-drag ratio and 7.8% in landing maximum lift coefficient. Far-field acoustic results indicate that noise reduction at takeoff is primarily associated with the suppression of broadband components, while at landing the dominant low-frequency tonal peaks are effectively attenuated, consistent with modified shear-layer dynamics within the slat cove near the trailing edge. These numerical findings are further confirmed by wind tunnel measurements, showing an overall noise reduction of ∼1 dB at takeoff and 3 dB at landing. The present results demonstrate the potential of the VLCS for integrated aerodynamic and aeroacoustic optimization of high-lift devices.