In order to investigate in detail the performance of steam turbine stages the Low Speed Test Rig at Politecnico di Milano has been adapted. The setup consists of a one and an half turbine stage with an inlet guide vane. Two kind of experimental approaches are planned in the project: the first, denominated “performance”, has been carried out by the OGTL department of GE Oil&Gas Florence while, at the same time, Politecnico di Milano performed detailed inter-stage measurements with steady probes and time resolved high response pressure probes. An axial steam turbine stage was tested under several operating conditions in terms of rotational speed, mass flow and inlet angle with the aim to provide the functional curves of the machine together with detailed flow-field measurements. In this paper, a detailed description of the inter-stage flow-field is presented for the most relevant operating condition. Then, a comparison between three different points at the same rotational speed (but different mass flow) is proposed. Finally, the effects of different axial gaps on the overall performance of the stage are discussed.

In particular, two different vane-rotor axial gaps have been tested by traversing pressure and temperature probes in three different axial planes. The first measurement plane is located at the first stator exit with the aim to provide details of the inlet swirl angle and 3D flow-field generated by the IGV. In the second plane, located at the rotor exit, the effect of different load conditions on the rotor performance and average flow-field is discussed. Finally, the measurements obtained in the third plane, placed at the second stator exit, are afterwards compared with the one obtained in the first plane, in order to evidence the influence of an unsteady inlet flow-field on the stator behaviour. The aim of the work is to provide very detailed aerodynamic measurements; this large amount of data will be used to validate the results of the CFD simulation carried out in the design stage. In this paper the preliminary findings of the steady flow-field will be presented as the basis for further analysis.

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