The paper discusses the time-averaged flow of a new concept turbine transition duct placed in a two-stage counter-rotating test turbine located at the Institute for Thermal Turbomachinery and Machine Dynamics of Graz University of Technology.

As a possible architecture for the turbine transition duct of future engines, the structural vanes carrying the bearing loadings can be integrated with the first low pressure vane row in one aerodynamically optimized wide-chord vane. Such architecture is also called Turning Mid Turbine Frame (TMTF).

In order to increase the flow uniformity and to decrease the unsteady content of the flow at the inlet of the LP rotor, a baseline TMTF was redesigned embedding two splitter vanes into the strut passage. The discussion on the flow field is based on numerical results obtained by a CFD code and validated by aerodynamic measurements.

The flow structures moving from the outlet of the transonic high pressure stage are observed propagating towards the low pressure stage. In particular the splitter vanes are seen playing a major role in suppressing the big structures generated by the struts. On the other hand new losses are introduced by the splitter structures. Such structures play a decisive role in the overall component performance and therefore their effect should be properly understood in the design phase.

This work provides a deep insight into the flow physics of TMTF designed with an embedded concept for next generation aero-engines. This configuration is seen to be a promising architecture in order to compact the engine size while keeping the components performance high.

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