Entropy generation in the tip region of a high-pressure turbine

This research investigated loss mechanisms from tip-clearance flows in a high-pressure turbine. Unshrouded tips of turbine blades are subject to a pressure-driven flow phenomenon from the pressure to suction surface. This flow feature, known as the tip-clearance flow, is a major loss contributor in axial-flow turbines. Both experimental and computational data were acquired to study entropy generation. The experimental results were used to understand and interpret phase-locked averaged hot-wire measurements. The necessary assumptions to properly interpret phase-resolved data were discussed. The experimental and computational data were then used to understand the turbine stage flow-field. Metrics such as corrected mass flow rate, total-to-total pressure and temperature ratios, and various efficiencies were examined. The entropy transport equation was used to identify and quantify the loss-generating mechanisms. Loss generation was greatest in the latter half of the turbine rotor. The main loss-generating mechanism was turbulent viscous dissipation by the inner and outer shear layers of the tip-leakage jet. Losses by mean viscous dissipation were present near the suction-side blade surface and rotor blade tip. Redistribution of entropy generated from the aforementioned regions was mainly by turbulent entropy transport.