On the Noise Generation of Krueger Leading Edge Devices

Abstract

Krueger type leading edge devices are appropriate means to ensure the necessary high lift performance for laminar wing concepts that are currently under investigation in order to reduce the environmental impact of transport aircraft in terms of COx and NOx emissions. If at the same time community noise levels would increase due to the use of Krueger leading edge devices the effort to reduce the environmental impact of aircraft would be partly contradicted. In view of the above initial noise measurements on a 3-dimensional semi-span wind tunnel model were conducted in order to (i) characterize the noise generated by a Krueger device and (ii) to compare the airframe noise contribution of a Krueger device with a conventional slat under similar aerodynamic conditions. Two different Krueger designs were noise tested in the anechoic open test section of DNW’s low speed wind tunnel Braunschweig. The so called reference Krueger flap has a short chord, a steep deployment angle and a negative overlap while the configuration named optimized Krueger features a long chord, a shallower deployment angle and a positive overlap of the Krueger trailing edge over the wing leading edge. The aerodynamic and acoustic study reveale, that Krueger noise compares well to slat noise in terms of maximum noise levels and spectral shape. Furthermore Krueger generated noise dominates the high lift system related airframe noise component. This first outcome of this DLR-internal study demands first of all strong efforts to minimize Krueger noise right from the beginning. Second, it was demonstrated that a long chord Krueger with positive overlap and moderate deflection angle serves provides a significant up to 5 dB noise reductions compared to the reference Krueger and the conventional slat.