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.
Highlights
The CRC 880 investigates methods for reducing aircraft noise
An elementary source mechanism lies at the trailing edge of the wing when the vortex structures of the turbulent boundary layer interact with the sharp trailing edge of the wing profile
Additional experimental trailing edges for aeroacoustic measurements in the acoustic wind tunnel of the DLR Braunschweig are shown. It is described how the porosity of the individual trailing edges was adjusted by the cold rolling process and which differences between the different materials and different rolling states can be recognized in computed tomography cross-sections
Summary
The CRC 880 investigates methods for reducing aircraft noise. By using increasingly quieter engines, the sound generated by the turbulent flow around the wings becomes more important, especially during landing. In the study shown here, the aim was to roll material with a gradient in thickness reduction in such a way that the requirements for a low noise trailing edge insert (compare [9, 14]) can be achieved. This rolling process was presented in [1] using a porous aluminum with a filter fineness in the range of 200-250 m (PA 200-250) with a pore size ranging from 0.63 to 3 mm. Rossignol et al are using a perforated sheet metal with a gradient in porosity and flow resistivity with an non-periodic designed structure, which is compared to the TEs (trailing edges) made out of porous aluminum
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