No abstract

No abstract

Rising numbers of flights and aircrafts cause increasing aircraft noise, resulting in the development of various approaches to change this trend. One approach is the application of metallic liners in the hot gas path of aero-engines. At temperatures of up to 600 °C only metallic or ceramic structures can be used. Due to fatigue loading and the notch effect of the pores, mechanical properties of porous metals are superior to the ones of ceramic structures. Consequently, cellular metals like metallic foams, sintered metals, or sintered metal felts are most promising materials. However, acoustic absorption depends highly on pore morphology and porosity. Therefore, both parameters must be characterized precisely to analyze the correlation between morphology and noise reduction performance. The objective of this study is to analyze the relationship between pore morphology and acoustic absorption performance. The absorber materials are characterized using image processing based on two dimensional microscopy images. The sound absorption properties are measured using an impedance tube. Finally, the correlation of acoustic behavior, pore morphology, and porosity is outlined.

Abstract:A new method to adjust the pore size in superalloy membranes is shown, utilizing controlled cooling from solution heat treatment of the solid superalloy. Hereby, the nucleation rate and, thus, the size of the γ'-precipitates can be varied to a large extent. This leads to a corresponding variation in the pore size once the membrane material is produced by directional coarsening of the γ'-phase to an interconnected network and subsequent selective extraction of the γ-phase. Furthermore, it was found that coherent and incoherent γ'-precipitates can be used alike to fabricate superalloy membranes, and yet, result in vastly different pore morphologies. The findings widen the application range of this novel material class.

Due to increasing air traffic and the extension of airports, many people are exposed to significant noise loads causing insomnia and other reactions, which impair health and productivity. [1,2] To change this development, various approaches have been developed to reduce airframe noise, jet noise, and engine noise. This work focuses on the approach to reduce noise by inserting open-celled metals in the hot gas path. Polymers are not able to bear the heat of around 614°C in this section of the aero engine and brittle ceramic structures would crack under the high fatigue loading. [3] Open-celled metals are metal sponges or sintered fiber felts which also resemble geometrically conventional passive absorbers.The most important material property in regard to acoustic absorption is the air flow resistivity J resulting from pore morphology and porosity. Depending on the production processes, e.g. sintering of metal fibers, metal flakes, or hollow spheres, coating of polymer foams, or powder metallurgy, the characteristic dimensions of the pores are usually in a range of 0.01 to 10 mm and the porosity in a range of 20-95%. [4][5][6][7] In this broad spectrum of materials, the air flow resistivity varies several orders of magnitude. To choose the correct material, it is necessary to characterize the different materials, measure, and simulate their acoustic absorption at room temperature. Finally, the simulation is adjusted by changing the properties of air meaning temperature and pressure to simulate the acoustic absorption at conditions of an aero engine. Note, that fluid flow effects are still neglected.