Aeroacoustics evaluation and mechanism of Krueger flap

Noise generated by high-lift devices is a major contributor to aircraft noise during approach and landing. Most published research on high-lift device noise focuses on slat configurations, with noise reduction measures applied to mitigate slat noise, such as droop nose devices or long-chord slat devices. Another alternative for laminar-flow wing technology is the Krueger leading-edge flap. In this study, numerical simulations were conducted to analyze the flow field, noise sources, and detailed characteristics around a high-lift Krueger flap configuration, including both a baseline configuration with a Krueger storage cavity and a configuration without the cavity. Far-field noise propagation was calculated using the Ffowcs Williams-Hawkings equation. The results indicate that the baseline configuration with the cavity exhibited strong tonal noise at low frequencies, while the cavity's influence on the Krueger flap noise was primarily in the form of broadband noise within the mid-to-high frequency range. The impact of angle-of-attack variations on overall noise was also studied, revealing that changes in the angle of attack significantly affected the flow field around the Krueger flap and its slot region. However, the impact of the cavity on the downstream flow field and noise is not significant. Notably, a substantial reduction in Krueger flap noise was observed at specific angles of attack, which is a factor that is essential in the study of noise associated with actual aircraft.