The unsteady and fully three-dimensional aerodynamics of HP turbines represent a relevant research branch for future aero-engine design. When stator-rotor interaction mechanisms and clocking effects are of concern, advanced measurement techniques as well as unsteady CFD codes are required. An extensive study on this topic was carried out in a one and a half stage transonic turbine operating at Graz University of Technology. Two steady and unsteady measurement techniques (Laser Doppler Velocimetry and a Fast Response Aerodynamic Pressure Probe) and an unsteady 3D CFD code were applied to the problem. In this paper, the 1st vane – rotor interaction is presented and discussed in detail to provide the basis for the analysis of the rotor – 2nd vane and the vane-vane interactions. The rotor-exit flowfield is mainly characterized by the wake, the hub passage vortex, the tip leakage vortex and the trailing edge shocks. All the flow structures except the tip leakage flow are strongly influenced by the first vane; in particular the main source of blade row interaction is the first vane trailing edge shock, that periodically alters the rotor trailing edge shock and the rotor hub passage vortex. The comparison with the CFD assesses the interpretation of the flow physics, and supports the identification of the first stator effects at the second stator inlet. A discussion on the stage performance is also provided.

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