多级轴流涡轮的变工况特性线分析

Analysis of Off-Design Characteristics of Multistage Turbines

选用第一级静叶出口折合速度cλ1和转子折合转速uλ两个自变量进行计算,获得了不同工况参数πT(压比)和λu(转速)下的涡轮级通用特性线网。对4种广泛使用的速度系数进行最小二乘法均值拟合,并将其应用于变工况计算模型之中。研究了3级涡轮变工况下的效率、流量以及功率等总体特性的变化规律,详细分析了涡轮各级的焓降分配、动叶进口的撞击损失以及流出余速损失所发生的变化。结果表明:各级对于工况变动的敏感程度不同,后几级在变工况下各参数变动的幅度比前几级剧烈;变工况下余速损失的变动尤为剧烈,其对级效率的影响甚大。因此,在变工况下,从各级所处的特定角度来考虑其性能的优化极为重要。

A general characteristics network of a turbine for different operational parameters πr （pressure ratio） and λu （dimensionless converted circumferential velocity） have been calculated, by taking the first stage stationary vances＇ dimensionless converted exit velocity λc1 , as well as λu as the two independent variables. An expression for the velocity coefficient model is obtained by the least square fitting method, making use of data, calculated by 4 widely used formulas. This mode is subsequently applied in the off-design calculation model, The overall off-design behaviour, including efficiency, flow rate and power delivered, of a 3 stage turbine is further being, studied, including a detailed analysis of the variations of enthalpy drop distribution among stages, of the impingement losses at the moving blades entry as well as of the leaving velocity losses, Results show that the sensitivity to off-design modes of operation is not the same for the different stages-parameter variations of following stages are more intense than those of preceding stage; especially pronounced being the change of leasing velocity loss, remarkably effecting stage efficiency, Therefore, it is of utmost importance for optimization to consider each stage by itself from the point of view of its specific operational condition, Figs 11 and refs 6.