An Experimental Study of Using Vortex Generators As Tip Leakage Flow Interrupters in an Axial Flow Turbine Stage

Abstract

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.