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On decoupled and fully-coupled methods for blade forced response prediction

Moffatt, S.; He, L.

Authors

S. Moffatt

L. He



Abstract

Two highly efficient fully-coupled methods of predicting the resonant forced response of turbomachinery blades have been developed with the intention of increased computational efficiency over a decoupled method. The flow and structural equations are solved simultaneously, based on the frequency-domain nonlinear harmonic method and the modal reduction technique. By combining the aerodynamic forcing and damping calculations into a single analysis, the coupled solution at a single excitation frequency is approximately half that of the decoupled method. Significant flow–structure coupling effects were discovered, leading to a study into the impact of frequency shift on the fully-coupled solution. A case study on the NASA Rotor 67 transonic aero fan rotor shows a significant reduction in vibration amplitude for the fully-coupled solution due to the resonant frequency shift, caused by the aerodynamic added mass effect. Prompting the development of a novel resonance-tracking algorithm to solve the additional degree-of-freedom in resonant frequency, the increase in computational efficiency in the fully-coupled method is lost due to the need for multiple solutions. A study into the added mass effect and the implications on the coupled solution is undertaken and an evaluation is made between the use of decoupled and fully-coupled forced response systems. It is shown that the decoupled method can accurately predict the resonant vibration level from a single calculation at the natural frequency and is insensitive to frequency shift for lightly damped cases.

Citation

Moffatt, S., & He, L. (2005). On decoupled and fully-coupled methods for blade forced response prediction. Journal of Fluids and Structures, 20(2), 217-234. https://doi.org/10.1016/j.jfluidstructs.2004.10.012

Journal Article Type Article
Publication Date 2005-02
Deposit Date Feb 16, 2007
Journal Journal of Fluids and Structures
Print ISSN 0889-9746
Publisher Elsevier
Peer Reviewed Peer Reviewed
Volume 20
Issue 2
Pages 217-234
DOI https://doi.org/10.1016/j.jfluidstructs.2004.10.012
Keywords Turbomachinery, Flows.