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

Abstract

Noise reduction of aircrafts during take-off and landing has become an important part of research in aviation. The circulation of air around the airframe is a major source of noise during landing. This includes noise generated at the trailing edge. Open porous materials, such as porous aluminum, are investigated for the reduction of this noise. In this study, cold rolling is used to enhance the structure of porous aluminum in matters of aeroacoustics and mechanical properties. An important parameter characterizing the acoustic behavior is flow resistivity which is measured using the alternating airflow method. The flow resistivity is highly dependent upon the pore structure which is analyzed using three-dimensional computer tomography (CT). Additionally, CT combined with discontinuous tensile testing is used to study the influence of cold rolling on the damage behavior of porous aluminum. Besides the damage behavior, mechanical parameters have been determined to identify reasonable degrees of deformation. A cold rolling technique to produce material with a gradient in porosity is described and experimental porous trailing edges for measurements in an acoustic wind tunnel are shown. The findings of this study show that cold rolling is a promising way to customize porous aluminum for low-noise trailing edge applications.

Numerical investigation of porous materials for trailing edge noise reduction

“…These parameters are determined at TU Braunschweig as a cooperation within the SFB 880. 25 While the porosity as a geometric quantity is calculated based on CT scans of the material, the permeability is determined by measuring flow resistance through by an alternating flow at 1 Hz, as defined in the standard specification DIN EN 29053. The Forchheimer coefficient can not be determined by the experimental material characterization and is therefore neglected.…”

“…Therefore, material scans can be used to obtain the necessary information about the inner structure. 25,34 In this approach, no approximation of the flow inside the pores is needed. However, due to the small pore sizes of about 1 mm and less, the numerical effort becomes too high to consider a vast variety of materials.…”

“…This similarity suggests that also for the present setup graded porous materials could be beneficial in terms of the achievable noise reduction. To evaluate the effect of such a material with locally varying permeability and porosity, the cold rolled version of the PA200-250 is applied 25 that provides a low permeability at the intersection and a high permeability at the trailing edge. The evaluated porosity and permeability from the experimental material characterization are shown in Figure 10.…”

“…CT scans of exemplary porous trailing edges with different pore sizes and additional cold rolling process with varying infeed as provided by the Institute for Materials at TU Braunschweig. 25 (a) PA80-110. (b) PA200-250.…”

Design, Experimental and Numerical Characterization of 3D-Printed Porous Absorbers

“…Within the Collaborative Research Center (CRC) 880 at TU Braunschweig, several investigations have been conducted to reduce the aeroacoustic noise at the trailing edge by manufacturing the trailing edge of porous material. Basic design recommendations for this application are given in [12] and a manufacturing process for trailing edges with spatially varying material parameters is presented in [13]. In [14,15], numerical investigations are carried out that investigate the influence of porous liners that are placed on the outer skin of an aircraft on the structure borne sound energy flow into the airframe under an aeroacoustic load.…”