This paper presents the experimental and numerical evaluation and comparison of the different flow fields downstream of a turbine center frame duct and a low-pressure turbine stage, generated by varying the inlet flow conditions to the turbine center frame duct. The measurements were carried out in an engine-representative two-stage two-spool test turbine facility at the Institute for Thermal Turbomachinery and Machine Dynamics at Graz University of Technology. The rig consists of a high-pressure (HPT) and a low-pressure (LPT) turbine stage, connected via a turbine center frame (TCF) with non-turning struts. Four individual high-pressure turbine purge flow rates and two low-pressure turbine purge flow rates were varied to achieve different engine-relevant TCF and LPT inlet flow conditions. The experimental data was acquired by means of five-hole-probe area traverses upstream and downstream of the TCF, and downstream of the LPT. A steady RANS simulation taking all purge flows in account was used for comparison and additional insight are gained from a numerical variation of the HPT and LPT purge flow rates.

The focus of this study is on the impact of the variations in TCF inlet conditions on the secondary flow generation through the TCF duct and the carry-over effects on the exit flow field and performance of the LPT stage. Existing work is limited by either investigating multi-stage LPT configurations with generally very few measurements behind the first stage or by not including relevant HPT secondary flow structures in setting up the LPT inflow conditions. This work addresses both of these shortcomings and presents new insight into the TCF and LPT aerodynamic behavior at varying the HPT and LPT purge flows. The results demonstrate the importance of the HPT flow structures and their evolution through the TCF duct for setting up the LPT inflow conditions, and ultimately for assessing the performance of the first LPT stage.

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