Turbine Tip and Shroud Heat Transfer and Loading: Part B — Comparisons Between Prediction and Experiment Including Unsteady Effects

Flowfield predictions in the tip regions of turbine blades have recently increased in fidelity, but additional data and greater collaboration between numerical and physical experimenters is required to make further improvements. This is particularly true as one moves to experiments and predictions of the full annulus, rotating conditions found in actual turbomachines. Toward this end, a recent set of experimental measurements obtained in a single-stage high pressure turbine at the US Air Force Turbine Research Facility (TRF) was complemented with true predictions of the tip flowfield undertaken at Pratt & Whitney. The TRF is a full scale rotating rig that operates at flow conditions that are non-dimensionally consistent with the true turbine environment. Both heat transfer and surface pressure measurements were obtained on the tip of the blade, along the shroud, and at 96.5% of the blade span providing significantly detailed information on the flowfield in the tip region. The experimental data was obtained at frequencies up to 100 kHz so that multiple data samples per vane and/or blade passing event were recorded. These measurements were complemented and extended with 3-D, Reynolds-Averaged Navier-Stokes (RANS) predictions that together revealed the true flow pattern and the overall heat load to the airfoil. Because of the greater spatial resolution of the predictions, they also revealed additional flowfield physics that was not captured by the experiment. Both steady state and time-resolved comparisons were then made between the predictions and the data to reveal the complex nature of the flowfield in the turbine tip-gap region. These comparisons will help to elucidate the fundamental physics involved in this highly complicated region of the turbine.