Experimental Evaluation of Service Exposed Nozzle Guide Vane Damage in a Rolls Royce A 250 Gas Turbine

Abstract

A unique methodology and test rig was designed to evaluate the degradation of damaged nozzle guide vanes (NGVs) in a transonic annular cascade in the short duration facility at the Royal Military College. A custom test section was designed which featured a novel rotating instrumentation suite. This permitted 360 deg multispan traverse measurements downstream from unmodified turbine NGV rings from a RollsRoyce/Allison A250 turboshaft engine. The downstream total pressure was measured at four spanwise locations on both an undamaged reference and a damaged test article. Three performance metrics were developed in an effort to determine characteristic signatures for common operational damage such as trailing edge bends or cracked trailing edges. The highest average losses were observed in the root area, while the lowest occurred closer to the NGV tips. The results from this study indicated that multiple spanwise traverses were required to detect localized trailing edge damage. Recommendations are made for future testing and to further develop performance metrics.