Most of previous researches of inlet turbulence effects on blade tip have been carried out for low speed situations. Recent work has indicated that for a transonic turbine tip, turbulent diffusion tends to have distinctively different impact on tip heat transfer than for its subsonic counterpart. It is hence of interest to examine how inlet turbulence flow conditioning would affect heat transfer characteristics for a transonic tip. This present work is aimed to identify and understand the effects of both inlet freestream turbulence and end-wall boundary layer on a transonic turbine blade tip aero-thermal performance. Spatially-resolved heat transfer data are obtained at aerodynamic conditions representative of a high-pressure turbine, using the transient infrared thermography technique with the Oxford High-Speed Linear Cascade research facility. With and without turbulence grids, the turbulence levels achieved are 7–9% and 1% respectively. On the blade tip surface, no apparent change in heat transfer was observed with high and low turbulence intensity levels investigated. On the blade suction surface, however, substantially different local heat transfer for the suction side near tip surface have been observed, indicating a strong local dependence of the local vortical flow on the freestream turbulence. These experimentally observed trends have also been confirmed by CFD predictions using Rolls-Royce HYDRA. Further CFD analysis suggests that the level of inflow turbulence alters the balance between the passage vortex associated secondary flow and the OverTL flow. Consequently, enhanced inertia of near wall fluid at a higher inflow turbulence weakens the cross-passage flow. As such, the weaker passage vortex leads the tip leakage vortex to move further into the mid passage, with the less spanwise coverage on the suction surface, as consistently indicated by the heat transfer signature. Different inlet end-wall boundary layer profiles are employed in the HYDRA numerical study. All CFD results indicate the inlet boundary layer thickness has little impact on the heat transfer over the tip surface as well as the pressure side near-tip surface. However, noticeable changes in heat transfer are observed for the suction side near-tip surface. Similar to the freestream turbulence effect, such changes are attributed to the interaction between the passage vortex and the OTL flow.

Recent work has indicated qualitatively different heat transfer characteristics between a transonic blade tip and a subsonic one. High resolution experimental data can be acquired for blade tip heat transfer research using a high speed linear cascade. While recognising an important role played by the cascade tests in validating computational models at the same conditions, some questions arise in relation to the effects of relative casing motion: 1) Does the relative casing movement change the main flow physics influencing the blade tip aerothermal performance? 2) Can a cascade set up with stationary casing wall rank different designs? 3) How do the effects of the casing motion depend on tip design configurations? A combined experimental and CFD study on several high pressure blade tip configurations is conducted to address these issues. Firstly, extensive experimental tests with aerodynamic loss and heat transfer measurement in a high speed linear cascade have been carried out for a squealer tip configuration at engine representative aerodynamic conditions. A systematic validation of the CFD solver (Rolls-Royce HYDRA) is presented, which serves as a basis for the computational analyses of the effects of the relative casing motion. Two tip configurations (squealer and flat tip) at three tip gaps (0.5%, 1.0%, 1.5% span) are analysed. The main aerodynamic impact of the casing motion is seen to promote the passage vortex, which consequently supresses the pitchwise reach of the tip leakage vortex. Inside the tip gap, the behaviour is dominated by the extra wall friction in relation of the inertia of the bulk fluid through the gap. As such, the moving casing effect is particularly strong for the flat tip at a small tip gap. For the large and medium tip gaps, both stationary and moving casing results are shown to consistently capture the trends in overall aerothermal performances. The present results confirm that even with relative casing motion, there is still a significant portion of transonic flow over a blade tip. For both the stationary and moving casing cases, the gap dependence of the over-tip heat transfer shows opposite trends for the transonic and subsonic regions respectively. The gap dependence of the blade tip heat transfer is shown to be clearly dependent on tip geometry configurations, as the bulk flow in a squealer cavity is subsonic regardless of the tip gap size, whilst the local flow state over a flat tip is much more responsive to the change of gap size.