An experimental study of passage-to-passage flow interactions in a single stage axial flow research turbine rotor

During the lifetime of a turbine stage, some of the blade tips may undergo changes due to mechanical rubbing with casing surface and also due to thermal oxidation. Understanding the effect these damaged blades have over the undamaged blades is essential to estimate the performance of the turbine stage in the operable tip clearance range. In this paper, the passage to passage aerodynamic interaction in a turbine stage is studied by modifying the tip gap of selected turbine blades and analyzing their effect on the neighboring blade passage flows. The experiments in this study are carried out in a single-stage low-speed axial turbine facility. All measurements are taken in the stationary frame of reference using a time-accurate differential dynamic pressure transducer mounted in a Kiel probe head. The experimental results from this study show that even with a significant increase on a selected blade's tip clearance, its effect on the AFTRF turbine flow is only confined to its neighboring blade passage. The disturbances due to the altered tip clearance of one passage are not measurably propagated to its neighboring turbine passages. The changes made in one of the blades in a turbine stage do not significantly alter the aerodynamic performance of other blades. This result is particularly important for large-scale turbine research rigs such as AFTRF where the unsteady total pressure field is mapped in a time-efficient and phase-locked manner.