Component-Mode Reduced-Order Models for Geometric Mistuning of Integrally Bladed Rotors

Two methods that explicitly model airfoil geometry surface deviations for mistuning prediction in integrally bladed rotors are developed by performing a modal analysis on different degrees of freedom of a parent reduced-order model. The parent reduced-order model is formulated with Craig-Bampton component-mode synthesis in cyclic symmetry coordinates for an integrally bladed rotor with a tuned disk and airfoil geometric deviations. The first method performs an eigenanalysis on the constraint-mode degrees of freedom that provides a truncated set of interface modes, whereas the second method includes the disk fixed-interface normal mode in the eigenanalysis to yield a truncated set of ancillary modes. Both methods can use tuned or mistuned modes, where the tuned modes have the computational benefit of being computed in cyclic symmetry coordinates. Furthermore, the tuned modes only need to be calculated once, which offers significant computational savings for subsequent mistuning studies. Each geometric mistuning method relies upon the use of geometrically mistuned airfoil modes in the component-mode framework to provide a very accurate reduced-order model. Free and forced response results are compared to both the full finite-element model solutions and a traditional frequency-based approach used widely in academia and the gas-turbine industry. It is shown that the developed methods provide highly accurate results with a significant reduction in solution time compared to the full finite-element model and parent reduced-order model.