Research at DLR towards airframe noise prediction and reduction

In the final approach phase airframe noise represents the ultimate aircraft noise barrier for future aircraft when equipped with quiet UHBR engines. This paper summarizes the results achieved at DLR in the development of methods and tools for airframe noise prediction and reduction. Numerous DLR internal, national and EC co-financed research projects were conducted to investigate the aerodynamic noise of wing high-lift devices and landing gears, which constitute the major airframe noise contributors. Experimental noise source studies where performed on both scaled 2D generic and complete high-lift wing models and on an A320 full-scale wing section as well as on full-scale landing gears. These tests aimed at the quantification of airframe noise levels, the identification of major aeroacoustic sources and the development of noise prediction schemes. The results from these experiments provided information on the noise generation mechanisms and radiation characteristics from slats and landing gears. Devices were developed, which promise an overall airframe noise reduction potential of up to 5 dB, relative to airframe noise levels of current aircraft. While such technologies already reach a high “technology readiness level” for landing gears, the development of noise reduction means for high-lift devices still remains in a research stage. For the development of low-noise high-lift devices for future aircraft by means of computational aeroacoustics, low-cost simulation codes were developed, validated and applied to a variety of 2D airframe noise problems.