Specification of Porous Materials for Low-Noise Trailing-Edge Applications

Abstract

Systematic testing of the microstructural and aeroacoustic properties of porous metals applicable as low-noise trailing-edge (TE) treatments has been initiated within the Collaborative Research Center SFB 880-Fundamentals of High-Lift for Future Civil Aircraft. Generic TE noise experiments were performed at Re = 0.8 × 10 6 to 1.2 × 10 6 in DLR's open-jet AWB facility. Complementary flow measurements in the closed test section MUB wind-tunnel of the TU Braunschweig served to quantify the induced aerodynamic effects. The presented database forms part of an ongoing cumulative effort, combining experimental and numerical methods, to gain a deeper understanding of the prevalent TE noise reduction mechanisms. For the large variety of porous materials tested herein a clear dependence of the achieved broadband noise reduction (reaching 2-6 dB at maximum) on the flow resistivity was identified. Basic design recommendations for material resistivity and pore sizes, the latter to minimize high-frequency self-noise contributions, were deduced for low-noise TE applications. An acoustic nearfield pressure release across the porous region, adversely coupled with a loss in lift performance for porous TE replacements, appears as the major noise-reduction requirement.

Modification of Porous Aluminum by Cold Rolling for Low-Noise Trailing Edge Applications

“…Further analysis of mechanical behavior (the damage behavior in particular), has neither been characterized for porous aluminum as received nor for cold-rolled material. Besides, it remains unclear how the findings can be used to address the shortcomings of porous materials for low-noise trailing edge applications noticed by Herr et al [6]. Information given in [7][8][9][10] that is relevant for this study is published for the first time in the context of a reviewed journal paper here.…”

“…The specific flow resistivity has a major influence on the reduction of trailing edge noise [4][5][6]. It is a main goal to produce material with specific flow resistivity similar to PA 80-110 which was used by Herr et al [6]. Thus, it is reasonable to use material with greater pores and low specific flow resistivity for cold rolling.…”

“…Being in approach for landing, a major part of noise is generated by the circulation of air along the airframe. The trailing edge of the wing is one of the main acoustic sources at the airframe, which can be diminished by using open porous materials in the trailing edge [4][5][6]. Herr et al [6] used different porous materials in an acoustic wind tunnel experiment, to analyze the effects of porous materials as trailing edges.…”

“…Thus, it is reasonable to use material with greater pores and low specific flow resistivity for cold rolling. The mechanical properties of the cold-rolled material are then compared to those of PA 80-110 as received (which was used by Herr et al [6]). In this study, PA 200-250 was selected for the rolling experiments.…”

“…It must be pointed out that due to cold rolling, porosity and pore size decrease and consequently specific flow resistivity increases. The specific flow resistivity has a major influence on the reduction of trailing edge noise [4][5][6]. It is a main goal to produce material with specific flow resistivity similar to PA 80-110 which was used by Herr et al [6].…”