Improvement calculation accuracy of blade-shaft coupled torsional vibration by including axial shaft motion

Selected from various Eigen modes of blading, nodal diameter κ= 0 and κ= 1 are both related to shaft torsional and/or axial vibration and shaft bending vibrations respectively. In order to avoid the possibility of 2f (f=power system frequency) from torsional vibration resonance, ISO specifies the final calculation results considering the combination between κ= 0 blade and torsional shaft vibration. Previous study has reported a global method for blade-shaft torsional coupled vibration analysis governing both κ= 0 and κ= 1 in a systematic manner, and torsional coupled vibration analysis was completed. However, it is also known that coupling of blade-shaft axial vibration also influences the resonance of blade-shaft system, and it is highly requested to estimate resonance frequency accurately. Thus, a method for blade-shaft coupled vibration analysis in consideration of axial vibration coupling is proposed and its feasibility is investigated. A scale model of steam turbine is targeted as an example and calculated resonance frequencies are compared with experimental data and FEM data. As a result, the new method in consideration of axial vibration coupling is feasible tool to calculate resonance frequencies more precisely than previous method.