The need for steam turbines to operate under low load conditions has increased due to diversified power generation, especially for industrial steam turbines. While, operating at low load conditions may cause strong and non-synchronous unsteadiness and a high blade dynamic loading for the last stage. Full annulus model should be used to investigate the circumferential asymmetric unsteadiness. Currently, rarely full annulus model has been applied to both aerodynamic and structural analysis numerically due to the high computational cost. In this paper, an unsteady aerodynamic and structural interactive analysis method of real industrial steam turbine using full annulus model under low load conditions is presented. In the structural analysis, the finite element analysis (FEA) procedure to calculate the dynamic stress is rearranged. Therefore, the blade dynamic stresses that is currently not computationally feasible can be estimated with limited computational resources. Consequently, the computational cost of the aerodynamic and structural interactive analysis method is substantially reduced. The aerodynamic results indicate typical unsteady phenomenon, a big separation region behind the last rotor and tip vortex between last stator and rotor. The tip vortex is the main cause to the pressure fluctuation on blade surfaces. The structural analysis results show a reasonable dynamic stress trend of last stage blades at different volume flows and the highest vibration from aerodynamic excitations is at about 25 percent of design flow.


Aerodynamic and Structural Numerical Investigation of Full Annulus Last Stage of Steam Turbine Under Low Load Conditions

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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