Computational Study on Track Noise From Infinite Wing with Leading-Edge Krueger Flap

In this study, unsteady-flow simulations are performed around two settings of the leading-edge Krueger flap as well as a conventional slat designed for a natural laminar flow airfoil at JAXA. The objectives are to clarify the flowfield, noise sources, and their characteristics around the Krueger flaps compared to the conventional slat noise, and to show the potential of Krueger flaps in lowering the noise compared to the slat. The simulations are conducted for infinite wing configurations with a Krueger flap. The influence of Krueger track noise is investigated through simulations with and without a simplified Krueger track. Furthermore, a study is conducted to assess how the fidelity of the Krueger flap track affects noise levels. The comparison between the slat and Krueger flaps shows significantly less noise for the Krueger flaps, which are designed to have a smaller recirculation region of the shear layer from the cusp, resulting in a longer distance between the reattachment point and the trailing-edge. When the track is attached, the noise level increases significantly across all frequency ranges. However, the Krueger flap shows lower noise levels compared to the slat. Moreover, it is found that the fidelity of the Krueger flap track geometry affects noise levels by increasing high-frequency noise and decreasing low-frequency noise, but the overall change is not significant when compared to the noise level increase associated with the slat track. This study indicates the Krueger flap has promising potential to lower noise compared to the slat.