Tip-Shroud Cutbacks in a Low-Pressure Gas Turbine Stage

摘要

This paper presents an experimental and computational study of tip-shroud modifications in a low-pressure gas turbine. Partial shrouds are a viable option to reduce the static stresses in high-speed stages compared to full shrouds while still benefiting from superior aerodynamic efficiency compared to unshrouded blades. Three different tip-shroud platform cutbacks have been tested experimentally in a low-aspect-ratio 1.5-stage low-pressure axial turbine and are compared to a full-shroud baseline. A detailed analysis of the fluid dynamics is carried out to provide a starting point for shroud optimizations. The leading- and trailing-edge platforms are cut back separately to isolate the effect of each modification. The final rotor then features a combined partial shroud on both leading and trailing edge, with the same material reduction as the shroud leading-edge cutback. The time-resolved flowfield and pressure measurements are accompanied by three-dimensional, unsteady Reynolds-averaged Navier-Stokes simulations, which provide insight into the over-tip leakage flows and their interaction with the mam flow both at cavity inlet and outlet The aerodynamic losses with the trailing-edge cutback are reduced compared to the baseline, but the resulting underturning from the interaction with the shroud exit cavity makes it inferior in terms of efficiency compared to the leading-edge cutback. The isolated shroud leading-edge cutback shows the best tradeoff between stress reduction and aerodynamic efficiency penalty (0.7%).