The numerical simulation was performed with a non-equilibrium condensing flow model to investigate the influences of the redesigned last stage turbine on the aerodynamic performance of the last stage, and the overall aerodynamic performance and condensation characteristics of the low pressure cylinder of a 300 MW steam turbine. The computation for the isolated last stage turbine shows that the flow capacity, power output and efficiency are obviously improved, and the leaving velocity loss is clearly reduced after redesign. The analyses of the low pressure cylinder were conducted when the redesigned last stage turbine was placed in its right place in the multi-stage environment The results show that the power output and efficiency of the low pressure cylinder rise by 0. 53% and 0. 47%, respectively. The improvement of the low pressure cylinder performance is attributed to the significant decrease in the leaving velocity loss. The redesign can affect the enthalpy drop in the penultimate stage turbine as well as the aerodynamic performance of the last stage turbine. The supercooling degree drops by 3-5 K in the spanwise direction, and the nucleation region and the nucleation rate also decrease in the final rotor passage. The change of the condensation characteristics of the rest stages due to the redesign can be neglected. These results imply that the last stage can be isolated from the multi-stage turbine and optimized separately in the redesign process of a low pressure cylinder.%采用湿蒸汽非平衡凝结流动模型对某300 MW汽轮机末级透平改型的气动性能及低压缸总体气动和湿蒸汽凝结特性进行了对比研究,末级透平的单独计算结果表明:改型后末级透平的通流能力、功率和效率均有明显提高,余速损失明显降低.改型后的未级透平置于低压缸多级透平环境中的计算结果表明:低压缸的功率和效率分别提高了0.53％和0.47％,末级余速损失降低是低压缸性能提高的主要因素；末级透平改型不仅会影响末级的气动性能,而且会影响次末级的总焓降；改型后末级动叶沿叶高的过冷度降低了3～5 K,成核范围和成核率均明显减小,其余各级凝结特性的改变可以忽略；在低压透平改型中,末级可以独立对待,单独优化.
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