Numerical and experimental analysis of low-pressure steam turbine blades coupled with lacing wire

Many industrial steam turbine applications require the capability for variable speed operation in combination with high mass flow rates and high back pressure levels. Especially the low-pressure blading has to be designed carefully with respect to the mechanical integrity. An effective way to reduce blade vibration is the introduction of a simple lacing wire to couple the moving blades. In this paper, the structural behavior of blades coupled by a wire is verified by means of linear and nonlinear finite element method. Different modeling techniques for the coupling effects are presented and discussed. Special focus is put on the nonlinear effects of the contact between blade and wire to investigate the frictional damping performance of the system. The obtained numerical results are validated by strain gauge measurements on a full-scale test turbine under real steam conditions in an industrial steam turbine test rig. The experimental data show low blade vibration amplitudes in the whole operational range indicating a high damping performance of the investigated wire design. The calculation results from the forced response analysis including the frictional effects are in good agreement with the experimental data.