E xp erim en tal Evaluation of S ervice-Exposed Nozzle G uide Vane D am ag e in a R olls Royce A -250 Gas TurbineA unique methodology and test rig was designed to evaluate the degradation o f 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 Rolls-Royce!Allison A-250 turbo shaft engine. The downstream total pressure was measured at four spanwise locations on both an undamaged reference and a damaged test article. Three peiformance metrics were developed in an effort to determine characteristic signatures fo r common opera tional 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 fo r future testing and to further develop performance metrics.Off-Design NGV Conditions. Service-exposed damage in gas turbines can often be visually identified. Figure 1 shows the three Contributed by the Turbomachinery Committee of ASME for publication in the Journal of E ngineering for G as T urbines and Power. Manuscript

Effect of laser welding parameters such as power, out-of-focus length, speed, diameter of feeding wire and feeding speed on weld properties are studied. The process parameters and their respective and interactive effects on the final responses have been investigated simultaneously by minimizing the number of experimental runs. The results, indicating the interlateral relationship between laser process parameters and responses, have been used to optimize the laser parameters, to predict the responses and to increase the process robustness. Two millimetre thick plates of AA6061 were welded in fillet configuration using a cw/Nd:Y AG laser and AA5356 wire as the filler metal. Two different experiment-designing methods were used and compared to find the most efficient way to optimize laser welding. The Taguchi method that allows a multicriteria optimization, using orthogonal arrays, was used to reduce the number of trials necessary to cover the whole functional process parameters window. The same kind of optimization was then carried out with E.M. method in a more interactive way allowing a dynamic construction of the feasible domain throughout the data collection. The weld properties of interest were weld fillet size, penetration depth, concavity size and HAZ dimensions.

This paper addresses the issue of aerodynamic performance of a novel 3D leading edge modification to a reference vane. An analysis of tubercles found in nature and some engineering applications was used to synthesize new leading edge geometry. Three variations of the reference low pressure turbine vane were obtained by changing the characteristic parameters of the tubercles. Shock structure, surface flow visualization and total pressure measurements were made through experiments in a cascade rig, as well as through computational fluid dynamics. The tests were carried out at design zero incidence and off-design ±10-deg and ±5-deg incidences. The performance of the new 3D leading edge geometries was compared against the reference vane. Some leading edge tubercle configurations were effective at decreasing total pressure losses at positive inlet incidence angles. Numerical results supplemented experimental results.

A unique methodology and test rig was designed to evaluate the degradation of damaged Nozzle Guide Vanes 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° multi-span traverse measurements downstream of unmodified turbine NGV rings from a Rolls-Royce/Allison A-250 turbo-shaft engine. Downstream total pressure was measured at four span-wise 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 span-wise traverses were required to detect localized trailing edge damage. Recommendations have been made for future tests, for test rigs and for ideas to develop performance metrics.

An experimental program which investigated the surface temperature distribution of a contemporary gas turbine combustion liner is presented. An array of 65 embedded surface mounted thermocouples was installed on a Rolls Royce/Allison T56 combustion liner and exposed to combustion conditions in the Combustion Chamber Sector Rig (CCSR) at the Royal Military College of Canada. The CCSR was operated at two test points to simulate idle and cruise modes of operation. Corresponding exhaust temperature measurements were taken in the test combustion chamber exhaust plane with a sweeping thermocouple rake. These efforts were the latest in a multi-year program to investigate the impact of service wear related geometric deformations of combustion liners and damaged/fouled fuel nozzles on the exit temperature profile from typical combustion chambers. It has been previously ascertained that real-world geometric anomalies in the T56 combustion chambers, particularly in the transitional zone, can modify the exhaust temperature profile to a sufficient degree so as to risk hot section damage due to excessive heat exposure. The collection and analysis of surface temperature data represents a useful extension of the knowledge base of the T56 combustion system within the context of the overall program and is paramount to upcoming numerical modelling efforts aimed at assessing hot section damage risks.