The flow leaking through the gap between rotor blade tips and casing surface in a turbine stage is an important source of energy loss. The current study uses a new concept named as Tip Leakage Interrupters (TLI) to mitigate some of the adverse effects of the tip leakage flows and improve the efficiency of an axial turbine stage. The TLIs are a system of vortex generators attached onto the suction side of the turbine blade tip. The TLI design was developed in a proof of concept effort and they operate by inducing controlled vortical structures originating from strategically shaped/oriented multiple and sub-miniature vortex generators. These induced vortical structures, when properly interact with the tip leakage vortex reduce the damaging aerodynamic effects of the leakage flow. The TLIs in this investigation were mounted near the suction side corner of turbine blade tips rotating in a single-stage cold-flow turbine facility. In this investigation, three different parameters such as the mounting location of TLI on the airfoil tip region, the number of TLIs mounted and the specific orientation of TLI were varied. The TLI mounted near the minimum pressure point on the suction side of the blade generated the largest vortical structure that is counter rotating to the leakage vortex system and hence had the greatest effect in reducing the strength of the leakage vortex. Adding more TLIs on the blade suction surface was found to improve the tip leakage mitigation effort. The study showed that changing the specific orientation of the TLI with respect to the incoming flow drastically changes the rotational direction of the vortex it generates and its nature of interaction with the leakage vortex.

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.