Probabilistic Mistuning Assessment Using Nominal and Geometry Based Mistuning Methods

Abstract

Two deterministic mistuning models utilizing component mode synthesis methods are used in a Monte Carlo simulation to generate mistuned response distributions for a geometrically perturbed Integrally Bladed Rotor. The first method, a frequency-perturbation approach with a nominal mode approximation used widely in academia and industry, assumes airfoil geometric perturbations alter only the corresponding modal stiffnesses while its mode shapes remain unaffected. The mistuned response is then predicted by a summation of the nominal modes. The second method, a geometric method utilizing non-nominal modes, makes no simplifying assumptions of the dynamic response due to airfoil geometric perturbations, but requires recalculation of each airfoil eigen-problem. A comparison of the statistical moments of the mistuned response distributions and prediction error is given for three different frequency ranges and engine order excitations. Further, the response distributions are used for a variety of design and testing scenarios to highlight impacts of the frequency-based approach inaccuracy. Results indicate the frequency-based method typically provides conservative response levels.