Jet Engine Compressor Blade Refurbishment by Application of the Advanced Re-Contouring Process

In modern jet propulsion Systems the core engine has an essential influence on the total engine performance. Especially the high pressure compressor plays an important role in this scheme. Substantial factors here are losses due to tip clearance effects and aerodynamic airfoil quality. During flight Operation the airfoils are subject to wear and tear on the leading edge. These effects cause a shortening of the chord length and the leading edge profiles become deformed. This results in a deterioration of the engine efficiency performance level and a reduced stall margin. The paper deals with the re-contouring of the leading edges of compressor airfoils. Lufthansa Technik AG in cooperation with the Institute of Jet Propulsion and Turbomachinery (RWTH Aachen University) developed a new method for the profile definition for the blade refurbishment. The common procedure of smoothing out the leading edges manually on a wheel grinding machine can not provide a defined contour nor a reproducible result of the overhaul process. In order to achieve optimized flow conditions in the compressor blade rows, suitable leading edge contours have to be defined for the worn airfoils. In an iterative process the flow behavior of these redesigned profiles is checked by numerical flow simulations and the shape of the profiles is improved. The following machining of the new defined leading edge contours is achieved on a grinding station handled by an appropriately programmed robot. Within this Advanced Re-contouring Process (ARP) the worn blades are precision-measured and then provided with an aerodynamically optimized leading edge profile numerically newly developed under computer control. The application of this process enhances the performance and lowers the fuel consumption while prolonging the blades’ service life by 25%. The performance achievable with ARP has been confirmed both through a long term analysis and by a back-to-back comparison test on the engine test stand. For this purpose the stages 3 through 14 of a CF6-50 high pressure compressor were on the one hand fitted with conventionally overhauled blades and on the other with ARP-optimized blades of the same basic geometry. By installing the optimized blades the EGT margin could be increased by 3° to 4° C. This results in an prolongation of the on-wing time by more than 1000 hours.