Analysis tools for the unsteady interactions in a counter-rotating two-spool turbine rig

Counter-rotating turbines represent the state of the art of actual and future aero-engines, built for a considerable reduction of weight and fuel consumption. However, in the open literature there is a limited number of experimental and computational research about the unsteady interactions in such complex configurations. The paper presents an experimental investigation on the two-spool counter-rotating transonic turbine at Graz University of Technology. The rig was designed in cooperation with MTU Aero Engines and Volvo Aero and considerable efforts were put on the adjustment of all relevant model parameters. The test setup consists of a high pressure (HP) stage, a diffusing mid turbine frame with turning struts and a shrouded low pressure (LP) rotor.A two-sensor fast response aerodynamic pressure probe (2S-FRAPP) has been employed to provide time-resolved aerodynamic area traverses downstream of the LP turbine. Structures at the blade passing frequency of each rotor are resolved by the use of the shaft encoders. Furthermore, a newly developed phase averaging procedure is introduced to take into account the combined rotor–rotor interactions. Different reconstructions of the time resolved flow field are then presented in the paper, where a detailed description of the post-processing tools and their interpretation is provided.

► Unsteady measurements were performed in a two-spool counter-rotating turbine.
► An “ad hoc” phase average procedure has been developed for the data analysis.
► The technique successfully maintains the frequency contents of the original signal.
► The different sources of unsteadiness are isolated, identified and analyzed.