UNSTEADY FLOW EFFECTS ON STEAM TURBINE LAST STAGE BLADES AT VERY LOW LOAD OPERATING CONDITION

Unsteady aerodynamic and structural interactive analysis method for design and development of highly efficient low pressure last stage blades and results of its main application on very low load conditions are reported in this paper. Main features of this method are the enhanced analysis scope including very low load conditions and validations using measured data of real steam turbines including very low load conditions as well. Our schemes for this project were introducing boundary conditions from measured data in real steam turbines, full annulus all blade unsteady aerodynamic analysis and large scale parallel computing for unsteady structural analysis. The aerodynamic analysis results indicate that one root cause of the relatively large blade vibration at low load conditions seems to be a tip vortex induced by the blade windage. A modified method that introduced accurate structural analysis boundary condition data from aerodynamic analysis results is demonstrated. The structural analysis of a six-blade group with lacing wire dumping structure was performed.