Computational Study on Noise From Natural Laminar Flow Infinite Wing With Krueger Flap and Comparison to Slat Noise

In this study, unsteady-flow simulations are performed around a leading-edge Krueger flap and a conventional slat designed for a natural laminar flow airfoil at JAXA. The study aims to explore the noise reduction potential of the Krueger flaps by clarifying their flowfield, noise sources, and characteristics. The simulations are performed for infinite wing configurations, and the effect of their track noise is also investigated. The flowfields around the designed Krueger flap are found to be similar to those around the slat. However, the designed Krueger flap shows significantly less noise, particularly in the lower frequency range, at all the directivity angles, achieving a smaller re-circulation region in the cove and locating the reattachment point of shear layer further upstream of the trailing-edge for low noise performance. When the track is attached, the noise level increases significantly across all frequency ranges and directivities. However, the Krueger flap shows lower noise levels compared to the slat. Moreover, it is found that the thickness of the Krueger flap track does not contribute significantly to the noise level when compared to the slat track. This study indicates the Krueger flap has a promising potential to lower noise compared to the slat.