Auxetic behavior in low porosity metallic structures is demonstrated via a simple system of orthogonal elliptical voids. In this minimal 2D system, the Poisson's ratio can be effectively controlled by changing the aspect ratio of the voids. In this way, large negative values of Poisson's ratio can be achieved, indicating an effective strategy for designing auxetic structures with desired porosity.
Perforated liners, especially in combination with a bias flow, are very effective sound absorbers. When appplied to gas turbine combustors, they can suppress thermo-acoustic instabilities and thus allow the application of new combustion concepts concerning higher efficiency and lower emissions. While the successful application of such a damping concept has been shown, it is still not possible to accurately predict the damping performance of a given configuration. This paper provides a comprehensive database of high quality experimental data. Variations of geometric, fluid mechanic, and acoustic parameters have been studied, including realistic engine configurations. The results demonstrate each parameter influence on the damping performance. A low order thermo-acoustic model is used to simulate the test configurations numerically. The model shows a good agreement with the measurements for a wide range of geometries and Strouhal and bias flow Mach numbers.
Stringent environmental requirements are pushing the current development of aero gas turbine combustors towards lean combustion concepts with relatively small combustor volume. This approach has a detrimental effect on the high altitude relight capability of an aeronautical engine. But the ability to light up at a specific altitude is one of the certification requirements that an engine has to fulfil. To ensure the relight capability, extensive testing for new combustor developments is needed. These test set-ups are expensive as they have to be conducted at sub-atmospheric conditions. Thus, the use of a simple tool to evaluate the ignition tendency of a combustor at an early development stage is advantageous. The code SPINTHIR, developed by Cambridge University, is capable of calculating the ignition performance in turbulent spray flames in a simplified approach. It has been previously validated for different types of flames and applications. In order to adjust the code for lean burn combustors, a new function for a better resemblance of the turbulent spray dispersion has been introduced and the high sensitivity towards cell sizes has been balanced by modifying the ignition criteria. Finally, the results of the code have been compared in this work with recently obtained ignition test performed by Rolls-Royce. Thereby, the influence of varying combustor geometries on the lean ignition limit has been tested. In comparison with these tests, the code’s results show very good matches which verify the conducted changes and give further credence to the model.
Mechanical metamaterials have attracted great interest due their ability to attain material properties outside the bounds of those found in natural materials. Many promising mechanical metamaterials have been designed, fabricated, and tested, however, these metamaterials have not been subjected to the rigorous requirements needed to certify their use in demanding industrial applications that require multifunctional behavior. This paper details an auxetic multifunctional metamaterial that has been optimized to outperform conventional designs for cooling systems commonly used in the space, the transportation, the energy and the nuclear industry. Experimental tests performed to certify this material for use in gas turbines have shown that in comparison to conventional designs, the metamaterial increases structural life by orders of magnitude while also providing more efficient cooling and maintaining similar acoustic damping characteristics. This metamaterial offers an agile and economical solution for the realization of next generation components.
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