采用弯叶片控制高负荷涡轮叶栅内附面层迁移的机理分析

Analysis of the Mechanism Governing the Migration of Boundary Layers in a Highly-loaded Turbine Cascade Controlled By Using Bowed Blades

对具有128.5°折转角的高负荷平面涡轮叶栅的内部流场进行了数值模拟。结合前期的实验结果,并利用拓扑学理论,详细分析了弯叶片对叶栅内附面层发展及旋涡运动的影响。结果表明,以通道涡为主的集中涡系在高负荷涡轮叶栅中部强烈掺混,使得中部的能量损失系数(0.56)明显高于端部(0.07),这是反弯叶片能改善此类叶栅整体气动性能的原因。对附面层迁移理论作了进一步讨论后指出,在高负荷涡轮叶栅内采用弯叶片减少二次流损失时应重点考察自由涡层的迁移。

Numerically simulated was the inner flow field in a highly-loaded plane turbine cascade with a turning angle of 128.5 degrees.In combination with the previous test results and by utilizing topological theory,the influence of bowed blades on the evolution of boundary layers and movement of vortices in the above-mentioned cascade was analyzed in detail.It has been found that the concentrated vortex system predominated by the passage vortices was drastically mixed and diluted in the middle portion of the highly-loaded turbine cascade and its energy loss coefficient(0.56) is conspicuously higher than that at both ends(0.07).This constitutes the underlying cause that negatively-bowed blades can improve the overall aerodynamic performance of a cascade.After a further discussion of boundary layer migration theory,it is noted that when the bowed blades are used in highly-loaded turbine cascades to reduce the secondary flow losses,the migration of free vortex layers should be investigated with focused attention.