FAST SIMULATION OF DYNAMIC BEHAVIOUR OF HEAVY DUTY GAS TURBINES FOR QUALITY IMPROVEMENT AND REDUCED DESIGN CYCLE TIME

摘要

ALSTOM has made big improvements in simulating the dynamic behaviour of the GT (rotor, bearings and structural parts), in terms of displacements and forces by developing a 2 stage approach comprising a simplified physical model and detailed calculations using finite elements condensed into a matrix super element (substructuring). The models from each have been validated against frequency measurements. The simplified approach provides a fast overview in terms of sensitivity analysis of basic physical influences. It accurately reflects the generic dynamic behaviour of both rotor and structure. Reducing the FE-calculation time by a factor of 10 has enabled the influence of small or large modifications to individual part designs on the dynamic behaviour of the GT to be understood to the highest level of detailed design features. Calculated frequency results from modal and forced response calculations are compared to measurements within a 2% margin. In particular the focus is on the improvements in the quality of the finite element modelling with more detailed features and more accurate identification of eigenfrequencies and coupled modes. Validation work comprises the modal analysis of single parts and subassemblies as well as matching mode shapes and frequencies of complete gas turbine. Models are used to evaluate design improvements prior to engine testing or implementation in field engines in order to comply with prescribed exclusion zones, to be introduced as early as the concept stage as well as providing project teams with overviews for planning and decision making. Future developments to include Modal Assurance Criteria and rapid post-processing will further reduce design cycle time and improve quality in terms of the consistency and repeatability with regard to mode shape recognition.