Production and characterization of experimental low noise trailing edges made of cold rolled porous aluminum with special attention to the influence of cold rolling on the mechanical stability of the investigated materials

Abstract

In the framework of the CRC 880 “Fundamentals of high-lift for future civil air craft” methods for the reduction of aircraft noise are investigated. An important method for this noise reduction is the usage of porous material as low noise trailing edges. To improve the aeroacoustic properties of porous materials, an innovative rolling process was established by Tychsen et al. (Metals 8:598, 2018). Here, the rolling process is described as it is used as an important method for the production of samples. The influence of cold rolling on two different porous materials namely porous aluminum 80–110 (PA 80–110) and PA 120–150 is investigated. Important characteristics studied are the porosity, mechanical properties and the dependence of flow resistivity from the degree of deformation. The flow resistivity is of particular interest as the aeroacoustic performance is significantly influenced by it. The results are then compared to the findings for PA 200–250, which was investigated in Tychsen et al. (Metals 8:598, 2018). Lastly, experimental trailing edges made out of cold rolled porous aluminum with a gradient in thickness reduction are shown. The characterization of the aeroacoustic behavior is not part of this study. Reference is made to Rossignol et al. (Int J Aeroacoust 19:365–384, 2020), where trailing edges shown here are characterized aeroacoustically. The findings shown here demonstrate that different porous materials can be tailored by cold rolling without negative impact on the mechanical behavior. It is proven that the new rolling process is a versatile tool for the production of gradient porous material.

Investigation of the Porosity Gradient in Thickness Direction Formed by Cold Rolling in Porous Aluminum

“…This results in an irregular structure with open pores once the sodium-chloride particles are washed out (Figure 2). The material was used because it showed promising aeroacoustic behavior and good formability by rolling [1,17,18,21,31,32]. The open porosity of up to 60% pore volume fraction allows compaction in a wide range without completely preventing flow through the material (closed porosity).…”

“…It should be noted that the influence of a gradient of porosity in thickness direction on flow resistance has not yet been researched. Only in Tychsen et al [21] was the difference in thickness direction taken into account for the production of trailing edges. Usually, a material with a constant flow resistivity over the thickness is desired.…”

“…Concerning the gradient being favored by aeroacoustic simulations [19] a rolling process was used to set it within the porous material [16,21]. The rolling gap was changed during each rolling pass so that material was rolled in the form of a wedge.…”

“…A similar rolling process was first used for non-porous material, by Hauger [22]. The focus of investigations in [16,21] was on setting a flow resistivity gradient required in advance by aeroacoustic simulations. This goes hand in hand with a gradient in porosity.…”

“…This gradient in thickness direction may influence aeroacoustic efficiency of the material, since the flow resistivity is not constant over the thickness. This was taken into account for the fabrication of experimental trailing edges for wind tunnel tests [21].…”