| The retrofit design of steam turbine is optimizing the aerodynamic characters and structure of a steam turbine on the basis of original model to increase efficiency and save the cost for specific operating conditions and the mechanical structure.In this thesis the performance of original turbine for the design working conditions and off-design working conditions is calculated in the first. The results showed that the two pressure levels with partial air intake structure of the prototype do not have enough power output due to the small axial dimensions and circumferential space. And the loss is too large. Meanwhile, the span wise of last rotor is 166 mm, which results in the smaller area of the outlet. The Mach number of the outlet for the last rotor reaches 1.4, which makes it difficult to design the profile of this rotor. Above all, the power output is not enough for the p rototype model.After making sure the main problem, the revised design is carried out with increasing the height of the blade and decreasing the internal diameter. Then the height of the first stage reaches 19 mm and the pressure stages are changed to be full-arc admission. With revising the profile of every stage, the height of the last and second last blades is improved, which makes the supersonic flow disappear in this two stages.The homogenization cavity behind the regulating stage can provide enough space to make sure the circumferential flow can be more homogenetic and expedite. The results shows that the retrofit model have better flow condition and enough power output.In the end, the off-design conditions of 75%~120% are calculated to research the performance of the retrofit unit. In comparison to the design condition, the parameters between neighboring stages of the off-design conditions can also vary in reasonable range. There is no full-stage supersonic flow for the retrofit unit and the velocity ratio of each stage is varied in a small range near the design condition. |
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