Improved Rotor Design With Combined 3D-2D Probabilistic Approach

Abstract

Availability and flexibility, largely in terms of start-up times, are becoming paramount for today’s steam turbine operation. Thus, precise knowledge of the stresses components experience and their lifetime consumption in transient regimes is vital for safe turbine operation. A typical lifetime-driving feature is low cycle fatigue in rotor grooves that is caused by rotor-blade root interaction and thermo-mechanical stresses. In the course of a previous project at Technische Universität Dresden [1, 2] a 2D axisymmetric, transient thermo-mechanical model of an intermediate pressure steam turbine rotor had been developed for probabilistic analysis. Thereby, the blade root compound’s stiffness and the twisting of rhomboid blade roots in circumferential grooves, both of which cannot be modelled directly in 2D, were found to be key drivers for uncertainties in lifetime calculation. To overcome these limitations, a 3D four-stage, fifteen-blade mechanical model for further analysis was created. The present work introduces this 3D model. It is then employed in a probabilistic sensitivity study to further refine the understanding of the influence of unknown or uncertain boundary conditions on the stresses that drive lifetime consumption. These results for stationary and exemplary transient operation are fed back into fine-tuning the existing 2D model in order to match the 3D calculated stresses. With its far lower computational effort the improved 2D model is well-suited for efficient future probabilistic analysis for robustness estimation and design space exploration.