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.
Typical turbomachinery aerothermal problems of practical interest are characterized by flow structures of wide-ranging scales, which interact with each other. Such multiscale interactions can be observed between the flow structures produced by surface roughness and by the bulk flow patterns. Moreover, additive manufacturing (AM) may sooner or later open a new chapter in the way components are designed by granting designers the ability to control the shape and patterns of surface roughness. As a result, surface finish, which so far has been treated largely as a stochastic trait, can be shifted to a set of design parameters that consist of repetitive, discrete micro-elements on a wall surface (“manufacturable roughness”). Considering this prospective capability, the question would arise regarding how surface microstructures can be incorporated in computational analyses during designing in the future. Semi-empirical methods for predicting aerothermal characteristics and the impact of manufacturable roughness could be used to minimize computational cost. However, the lack of element-to-element resolution may lead to erroneous predictions, as the interactions among the roughness micro-elements have been shown to be significant for adequate performance predictions (Kapsis and He, 2018, “Analysis of Aerothermal Characteristics of Surface Micro-Structures,” ASME J. Fluids Eng., 140(5), p. 051104). In this paper, a new multiscale approach based on the novel block spectral method (BSM) is adopted. This method aims to provide efficient resolution of the detailed local flow variation in space and time of the large-scale microstructures. This resolution is provided without resorting to modeling every single ones in detail, as a conventional large-scale computational fluid dynamics (CFD) simulation would demand, but still demonstrating similar time-accurate and time-averaged flow properties. The main emphasis of this work is to develop a parallelized solver of the method to enable tackling large problems. The work also includes a first of the kind verification and demonstration of the method for wall surfaces with a large number of microstructured elements.
A novel patterned-void structure is developed to improve the fatigue life compared to conventional circular cooling holes typically used in gas turbine components exposed to high temperatures. The distinctive S-shape of the voids and their specific arrangement enable manipulation of the structure's macroscopic stiffness and Poisson's ratio. An investigation of the isothermal and thermomechanical fatigue properties of the proposed structure is carried out in strain-controlled conditions. The testing is performed on tubular specimens machined from a Nickel-based superalloy commonly used in gas turbine combustion systems (Haynes 230 ™). The isothermal fatigue tests, performed at 300°C, 600°C and 800°C, demonstrated an increase in crack-initiation life of the proposed structure by a factor of up to 28 compared to the standard circular holes. The thermomechanical fatigue tests, performed across temperature ranges 300°C - 750°C and 300°C - 850°C, and using in-phase and out-of-phase strain ratios, demonstrated an increase in crack-initiation life by a factor of up to 16. The life after crack initiation (crack-propagation mode) was also shown to be longer for the proposed structure, which is attributed to a crack-arresting behavior inherent to the structure.
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