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A zonal approach for the prediction of the far-field radiation from flows in lined ducts is investigated. The approach combines a high-order computational aeroacoustics scheme with the recently developed acoustic intensity-based method for the calculation of far-field radiations. The advantage over the application of an acoustic analogy is the usage of an open control surface for the acoustic input. The capability of the current hybrid approach was validated on the basis of two benchmark cases. One considers the sound radiation from a two-dimensional semi-infinite duct in which a small fraction of the walls close to outlet nozzle is fined. The second problem concerns the sound radiation from a bypass enginelike annular duet with lined and hardwalled configurations of the infinite centerbody and sheared flow conditions. A broadband time-domain impedance boundary condition based on the extended Helmholtz resonator model and the Ingard-Myers boundary condition is implemented in the computational aeroacoustic code to model the acoustic linings. Although mesh refinement may improve the solutions, the good agreements of analytical solutions and numerical results, in particular for the radiation characteristics, verify this approach as an accurate and efficient prediction tool. DOI: 10.2514/1.J050478

Currently, there are a lot of research activities dealing with gamma titanium aluminide (γ-TiAl) alloys as new materials for low pressure turbine (LPT) blades. Even though the scatter in mechanical properties of such intermetallic alloys is more distinctive as in conventional metallic alloys, stochastic investigations on γ- TiAl alloys are very rare. For this reason, we analyzed the scatter in static and dynamic mechanical properties of the cast alloy Ti- 48Al-2Cr-2Nb. It was found that this alloy shows a size effect in strength which is less pronounced than the size effect of brittle materials. A weakest-link approach is enhanced for describing a scalable size effect under multiaxial stress states and implemented in a post processing tool for reliability analysis of real components. The presented approach is a first applicable reliability model for semi-brittle materials. The developed reliability tool was integrated into a multidisciplinary optimization of the geometry of a LPT blade. Some processes of the optimization were distributed in a wide area network, so that specialized tools for each discipline could be employed. The optimization results show that it is possible to increase the aerodynamic efficiency and the structural mechanics reliability at the same time, while ensuring the blade can be manufactured in an investment casting process. [ABSTRACT FROM AUTHOR]