汽轮机湿蒸汽级中凝结流动的三维数值分析

对一台凝汽式汽轮机低压末三级中的湿蒸汽自发凝结流动进行了三维数值分析,并与忽略自发凝结影响的流动计算结果进行了比较。结果表明,自发凝结流动中,湿蒸汽级组内焓降在各级之间的分配、各级反动度、级的工作压力范围、叶栅出口气流角和出口气流速度发生明显变化。各湿蒸汽级处于“变工况”运行状态,部分湿蒸汽级内流动状况显著变差,并导致叶片强度与振动方面安全性降低。除非平衡凝结损失外,凝结导致湿蒸汽透平级“变工况”运行是湿蒸汽级效率降低的重要原因。

THREE-DIMENSIONAL SIMULATION OF THE CONDENSING FLOW IN THE WET STEAM STAGES OF A STEAM TURBIN

The three-dimensional wet steam flow with spontaneous condensation in the three low pressure stages of an condensing steam turbine was numerically investigated and the results were compared with those in the superheated flow. It was indicated that the distribution of enthalpy drop, the reaction degree, the range of working pressure, the outflow velocity and flow angle in each wet steam stage obviously change due to the effects of spontaneous condensation. The re-distribution of flow parameters in condensing flow leads to 'off-design' condition for the turbine stages in actural operation, which results in additional efficiency loss and the negative effect on the blade safety. Besides the well-known non-equilibrium losses, the 'off-design' loss is an important factor leads to low efficiency of wet steam turbine.