Abstract

Conventional airfoil blend repair limits are established using nominal, design intent geometry. This convention does not explicitly consider inherent blade-to-blade structural response variations associated with geometric manufacturing deviations. In this work, we explore whether accounting for these variations leads to significant differences in blend depths and develop a novel approach to effectively predict blade-specific blend allowables. These blade-specific values maximize part repairability according to their proximity to defined structural integrity constraints. The methodology is demonstrated on as-manufactured geometry of an compressor rotor. Geometric point cloud data of this rotor is used to construct as-built finite element models of each airfoil. The effect of two large blends on these airfoils demonstrates the opportunity of blade-specific blend limits. A new approach to determine each airfoil's blend repair capacity is developed that uses sequential least squares quadratic programming and a parametric blended blade FEM that accounts for manufacturing geometry variations and variable blend geometry. A mesh morphing algorithm modifies a nominal geometry model to match the as-built airfoil surface and blend geometry. Numerical optimization maximizes blend depth values within frequency, mode shape, and high cycle fatigue (HCF) constraint boundaries. Large variations in blend depth allowables between blades are found and competing structural integrity criteria are responsible for their limits. It is also shown that, despite complex modal behavior caused by eigenvalue veering, the proposed optimization approach converges. The developed methodologies may be used to extend blend limits, enable continued operations, and reduce sustainment costs.

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