大转角涡轮叶栅复合弯曲定性分析与应用验证

通过定性推导分析了复合弯曲对叶栅吸力面静压分布与端部周向迁移流体折转过程的影响，明确了复合弯曲对大转角高负荷平面涡轮叶栅流场的影响机制，并结合已有仿真结果进行了初步验证。复合弯曲是在反弯叶片吸力面端部进行局部正弯，令叶片压力面反弯、吸力面端部正弯结合叶身反弯的造型方式。研究表明，复合弯曲设计通过改变吸力面低能流体的展向迁移趋势与周向迁移流体的折转趋势抑制了叶栅二次流的发展。一方面，复合弯曲设计调节了叶展中部与叶栅端部附近吸力面逆压梯度与展向静压梯度分布，抑制了吸力面低能流体向脱落涡与壁角涡高损失区的迁移与堆积；另一方面，复合弯曲设计影响了周向迁移流体折转过程，抑制了周向迁移流体向叶栅端部的折转及其折转过程中与吸力面附近流体的掺混。因此，复合弯曲设计能够在常规反弯基础上进一步改善叶栅流场。 

Qualitative analysis and application validation of compound bowing design in turbine cascade with large turning angle

The influence of the compound bowing design was discussed based on theoretical analysis and verified by numerical simulations based on a highly-loaded linear turbine cascade with a large turning angle. The compound bowing design applied local positive bowing design near the endwall region on the suction surface of a negative bowed blade, so the blade presented negative bowed pressure surface and compound bowed suction surface. Generally, the study showed that the compound bowed suction surface could improve the flow field by adjusting the static pressure distribution on suction surface and the deflection of the cross flow. In detail, the negative bowed suction surface could suppress the development of the boundary layer and the shedding vortex near the mid-span, while the positive bowed suction surface could suppress the development of the boundary layer and the Corner Vortex near the endwall. Moreover, the positive bowed suction surface near the endwall could further suppress the passage vortex and the corner vortex by adjusting the deflection of the cross flow and reducing the interaction between the cross flow and boundary layer near the suction surface. As a result, it showed that the compound bowed cascade could lead to a loss coefficient reduction about 65.5% better than the negative bowed one in this study.