Optimization of Airfoil Blend Limits With As-Manufactured Geometry Finite Element Models

A methodology is developed to maximize the size of airfoil blend repairs of airfoils and integrally bladed rotors while maintaining acceptable structural integrity criteria.  As-manufactured geometry of 1^st stage fan of an aerodynamic research rig is used to build a detailed finite element model of each airfoil.  The inherent blade-to blade variability in structural integrity criteria of the fan is shown for several modes for the purpose of defining an acceptable range of variation.   A parametric blend geometry definition and a mesh morphing algorithm are used with numerical optimization algorithms to maximize objective function values within constraint boundaries.  The mesh morphing algorithm modifies an existing nominal design model to the match a surface representation of the airfoil that that includes the parametric blend definition.  A variety of optimization algorithms are used to maximize the size of repairs while meeting multiple structural criteria.  Airfoil frequency crossing limits, mode shape deviations, modal force variation, smooth Goodman criteria, leading edge Goodman criteria, and mistuning amplification are all considered as constraints the optimization.  It is shown an optimal blend geometry can be found that is larger than traditional limits.  It is also found that the leading edge Goodman criteria is the limiting factor in the optimization.  Extending blend limits will allow engines to remain on-wing for extended periods and reduce sustainment costs.