TIP-SHAPING FOR HP TURBINE BLADE AERO-THERMAL PERFORMANCE MANAGEMENT

A large portion of the over-tip leakage flow is often transonic for a typical high pressure (HP) turbine blade. It has been observed that the tip heat transfer is noticeably lower in a high speed flow tip region than in a low speed region. The present study therefore investigates the feasibility of controlling blade heat transfer by tip shaping to locally accelerate the flow to a transonic regime. The results show that a significant heat load reduction can be achieved by the local flow acceleration. Such over-tip-shaping provides a great potential as an effective means to control heat load distribution (and hence thermal stress) over the blade tip surface. The feasibility of the concept and flow physics have been demonstrated in detail by CFD analyses, with and without the effect of moving casing. The experimental results obtained from a high speed linear cascade facility have also been presented. In addition, the proposed tip-shaping concept may also provide a potential for promoting choking inside the tip gap as a way to control the over-tip leakage mass flow.