The efficient inclusion of rotation-induced inertia effects in a shaft-blisk assembly model using zero-speed modes

A successful design of rotating shaft-bladed disk (“blisk”) assemblies requires the facility to reliably predict the resonance speeds, which must be avoided during operation to avoid failure. Rotation-induced inertia effects (centrifugal stiffening, spin softening, Coriolis forces and gyroscopic moments) can cause significant variation of the modal frequencies with speed. A review of the state-of-the-art highlights the need for a methodology that can efficiently include all rotation-induced inertia effects in a generic shaft-blisk system. The novel contribution of this paper is a methodology to include such effects in a generic shaft-blisk system, using zero-speed finite element (FE) modal data, without the need for additional FE analysis at each speed, or the derivation of equations from first principles. This contribution is motivated by the need to upgrade an existing blisk simulator designed to generate blade tip timing (BTT) data for the development and validation of BTT algorithms. Rotational effects are added as discretised “external” excitations to the modal equations, which remain based on the zero-speed modes. The method is progressively validated on six examples, using results from the literature and commercial FE rotordynamics software, to demonstrate its accuracy and high efficiency of computation for both Campbell diagrams and forced response.