The HEXENOR proposal aimed to study, design and manufacture three items ( short, mean, and long) each made of two innovative concepts, a quiet plug and a quiet diffuser which will be mounted on a turboshaft engine to reduce the noise radiated by the exhaust. A preliminary study was concerned with the capability of two materials a Ferritic stainless steel (low cost material) and TiAl alloy (light but fragile material) to satisfy the design constraints and the engine hard conditions. High cycle fatigue, thermo-mechanical and metallurgical characterisation tests were conducted before the design step. Also an academic work was achieved to determine an optimal configuration of a new quiet diffuser concept made of angular and axial cavities surrounding an internal perforated wall of the duct lined section.
This approach was based on the measurement with a flow duct facility developed during the Ducat European program without and with cold flow of the liner configurations efficiency for a higher order mode incident pressure vector and the development of an analytical model of the acoustic propagation through the lined barrel leading to the calculation of the attenuation of each configuration with and without flow. The choice of the optimal configuration to design the quiet diffuser was the result of a trade off between acoustic efficiency provided by the academic study, mass and cost specifications.
The main results achieved so far by WP2 were:
- The analytical model of the academic muffler is one of the main results of this project.
- The comparison between no flow theoretical and experimental results on the DUCAT facility has shown a very good agreement validating the analytical development taking into account higher order mode propagation in lined wall duct.
- The main goal of WP2 has been fulfilled as the liner characteristics of the three items have been defined for design in accordance with Turbomeca and other partners after a parametric study based on the no flow analytical calculation with the actual exhaust diffuser conditions.
Main works achieved:
All metallurgical, thermo-mechanical and fatigue tests on K44X steel and TiAl materials have been conducted. Also Gfe has carried out manufacturing technology evaluation of the TiAl alloy.
The main results were that K44X steel was satisfying the TM specifications. Concerning the TiAl alloy, A4 sheets of TiAl had been rolled with a 0.8mm thickness which also is satisfying the TM specifications.
A first version of the TiAl nozzle design had been released, as a CAD model in December, 2012, for TM design validation. The validation of the design solution was still pending. The delay in the design phase was mainly due to outstanding issues related to thermal dilatation stresses. Several design solutions had been proposed. The CFD simulations in WP4 hd been cancelled, in agreement with TM, to be replaced by existing measured data, but a structural and vibration analysis of the selected design solution will still be required.