Abstract: In order to illustrate the loss sources and enhance the aerodynamic performance of 1+1 counter-rotating turbines at off-design conditions，flow field analysis and blade profile improving method were presented through detailed numerical simulations. First，the comparison between the partly loaded flow fields of a counter-rotating turbine and a conventional two stage co-rotating turbine，which have the same design parameters，is implemented. It is found that，the boundary layer of the second vane in the co-rotating turbine separates on the suction side near the leading edge，whereas that in the counter-rotating turbine on the pressure side. Second，aiming at reducing the flow loss，a profile improving method for the pressure side of the second vane in this counter-rotating turbine is proposed，based on a theory of separation angle. This method helps to accelerate the flow on the pressure side near the leading edge and makes the second vane more adaptable to negative incidences. The redesigned vane significantly eliminates the flow separation on the pressure side near the leading edge at 14%，58% and 92% spans，and maintains a decent aerodynamic performance at positive incidence conditions. Finally，the simulation results show that the efficiencies at off-design conditions all increased and the efficiency at the design condition does not deteriorate. When the counter-rotating turbine runs at 70% and 50% design speed，the efficiencies of the low pressure stage are improved by 1.5% and 2.0%，respectively. Correspondingly，the efficiencies of the counter-rotating turbine at these two partly loaded conditions rise by 0.5% and 0.7%，respectively.

Key words: Counter-rotating turbine；Off-design conditions；Aerodynamic optimization

摘要： 为阐明1+1对转涡轮变工况性能损失的主要来源并提出改进方法，以1+1对转涡轮为例进行了部分载荷工况下的流场模拟、分析和优化。与相同设计参数的同转涡轮进行部分载荷工况流场对比，发现部分转速下同转涡轮在级间导叶吸力面前缘出现分离，而1+1对转涡轮在压力面前缘出现分离。针对此流动损失，为1+1对转涡轮级间导叶提出了一种基于分离角的压力面优化设计方法，提高了近前缘压力面的气流速度，增强了其对负攻角的适应性，基本消除了叶片14%、58%和92%叶高处压力面前缘的流动分离，在正攻角工况下亦保持了良好气动性能。数值验证了该涡轮的效率在全工况范围内明显提高，而设计点效率未受负面影响。其中，在对转涡轮70%和50%设计转速的两个工况点上，低压涡轮效率较优化前分别提升了1.5%和2.0%，涡轮总效率较优化前分别提升了0.5%和0.7%。

关键词: 1+1对转涡轮；变工况；优化设计