Lutz Völker

Experimental and Numerical Investigation of the Nonlinear Vibrational Behavior of Steam Turbine Last Stage Blades With Friction Bolt Damping Elements

Low-pressure last stage blades of industrial steam turbines are subjected to high dynamic loading. Especially in variable speed applications resonant blade vibration cannot be avoided. Thus, the aim of the blade layout is to reach a robust design that can cover high vibrational amplitudes while still keeping good efficiency. An effective way to keep vibration amplitudes low is the introduction of friction damping elements to the blades. In this paper the structural behavior of a low-pressure last stage blade coupled by friction bolt damping elements is described by means of linear and nonlinear Finite Element Method. Special focus is put on the nonlinear effects of the contact between blade and damping element to investigate the frictional damping performance of the system. The obtained numerical results are validated by strain gauge and tip timing measurements in a full scale test turbine under real steam conditions at the Institute of Thermal Turbomachinery and Machinery Laboratory of the University of Stuttgart.Copyright

Numerical investigation of the impact of part-span connectors on aero-thermodynamics in a low pressure industrial steam turbine

A numerical study on the flow in a three stage low pressure industrial steam turbine with conical friction bolts in the last stage and lacing wires in the penultimate stage is presented and analyzed. Structured high-resolution hexahedral meshes are used for all three stages and the meshing methodology is shown for the rotor with friction bolts and blade reinforcements. Modern three-dimensional CFD with a non-equilibrium wet steam model is used to examine the aero-thermodynamic effects of the part-span connectors. A performance assessment of the coupled blades at part load, design and overload condition is presented and compared with measurement data from an industrial steam turbine test rig. Detailed flow field analyses and a comparison of blade loading between configurations with and without part-span connectors are presented in this paper. The results show significant interaction of the cross flow vortex along the part-span connector with the blade passage flow causing aerodynamic losses. This is the first time that part-span connectors are being analyzed using a non-equilibrium wet steam model. It is shown that additional wetness losses are induced by these elements.Copyright

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.