Effect of the Axial Spacing between Rotor and Stator with Regard to the Indexing in an Axial Compressor

An experimental investigation was carried out to examine the influence of the axial spacing between rotor and stator. The test facility of the Swiss Federal Institute of Technology is made up of an inlet guide vane (IGV), a rotor and a stator. Temperature and aerodynamic measurements determined the characteristics of the compressor stage. Data were acquired over a range of flow coefficients for four different axial spacings. A refined measurement mesh was used for Pitot probe measurements in different sections of the compressor. As the compressor has a rather low aspect ratio of 1.21, the flow was governed by strong secondary flows. The interaction between the different secondary flows, especially the Influence of the IGV wake on the secondary flows in the stator, were detected by the detailed Pitot probe measurements. Shifting the stator axially changes the circumferential position of the IGV wake entering the stator. From this statement, the link between an axial variation of the distance between rotor and stator and the clocking between IGV and stator will be shown. Further Pitot measurement with different indexings between IGV and stator were performed. The Pitot measurements for the different axial spacings as for the different indexings brought to light strong interactions in the wall regions especially between the IGV wake and the clearances at the rotor tip and at the stator hub. The structure of the flow thus changes with the indexing and with the axial spacing.