This paper presents a methodology for rapidly analyzing the effect of blending damaged compressor blades on structural integrity. Heavy duty gas turbine compressor blades are subjected to damage from numerous sources. Compressor blades are blended in the field to allow continued operation with minimal risk of failure. By constructing analysis models parametrically, blend limits may be rapidly and reliably established for an entire compressor.
Erosion from washing or fogging, foreign object impacts, icing, tip rubs, and clash can damage both stator vanes and blades. Replacement of blades and stator vanes is very costly. The blades on some engines cannot be removed without de-stacking the rotor. The high cost of replacement provides an incentive to determine blend limits that do not compromise mechanical integrity. Field service support of compressor hardware includes the evaluation of compressor damage and the determination of whether such damage can be blended out in situ. Compressors on F-class engines have more than 15 stages, so at least 30 different airfoils must be analyzed when stator vanes are included. One must consider damage in the tips as well as leading and trailing edges at numerous radii. The variation in sizes, locations, and combinations of blends coupled with the number of airfoils results in a intense analytical task. Field service must also support multiple design configurations that include original engine manufacturer (OEM) blades as well as more robust aftermarket designs.
By setting up parametric analysis models of each blade, PSM has been able to provide its field service support group with accurate blend limits and has created a tool with which nonstandard blends may be evaluated in nearly real-time. This paper presents a methodology which has been applied to an entire compressor. A pre-stressed large-displacement modal analysis was performed which includes contact effects and considers a wide range of operating speeds using the linear perturbation technique. Combinations of parametrically defined blends are analyzed automatically. The effects of the blends on the modal frequencies were evaluated against in-house criterion. Plots of vibratory stress capability were produced to highlight which airfoils and which portions of airfoils are vulnerable in case of damage. The parametric nature of the analysis allows the user to easily change the position size and shape of the blends. With this methodology PSM is able to rapidly evaluate blends of stator vanes and blades for whole compressors and provide reliable and timely guidance to our field service representatives.