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首页> 外文期刊>International Journal of Heat and Fluid Flow >Vortex dynamics mechanisms of separated boundary layer in a highly loaded low pressure turbine cascade
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Vortex dynamics mechanisms of separated boundary layer in a highly loaded low pressure turbine cascade

机译：高负载低压汽轮机级联中分离边界层的涡流动力学机制

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This paper investigates the vortex dynamics in the suction-side boundary layer on an aero-engine low pressure turbine blade at two different Reynolds numbers at which short and long laminar separation bubbles occur. Different vortical patterns are observed and investigated through large eddy simulation (LES). The results show that at the higher Reynolds number, streamwise streaks exist upstream of separation line. These streaks initiate spanwise undulation in the form of vortex tubes, which roll-up and shed from the shear layer due to the Kelvin-Helmholtz instability. The vortex tubes alternately pair together and eventually distort and break down to small-scale turbulence structures near the mean reattachment location and convert into a fully turbulent boundary layer. At the lower Reynolds number, streamwise streaks are strong and the separated flow is unable to reattach to the blade surface immediately after transition to turbulence. Therefore, bursting of short bubbles into long bubbles can occur, and vortex tubes have larger diameters and cover a part of the blade span. In this case vortex pairing does not occur and vortex shedding process is promoted mainly by flapping phenomenon. Moreover, the results of dynamic mode decomposition (DMD) analysis show a breathing motion as a source of unsteadiness in the separation location, which is accompanied by the flapping phenomenon.
机译：本文在两个不同的雷诺数的空气发动机低压涡轮机叶片上调查吸入侧边界层的涡流动力学，在其发生短和长层间分离气泡。通过大型涡流模拟（LES）观察和研究不同的涡旋模式。结果表明，在较高的雷诺数，流动条纹存在于分离线的上游。这些条纹以涡流管的形式发起血管生效，由于Kelvin-Helmholtz不稳定性，从剪切层卷起和脱落。涡旋管交替地将其配对并最终扭曲并分解为平均重新附点位置附近的小规模湍流结构，并转换成完全湍流的边界层。在较低的雷诺数，流动条纹强，并且在过渡到湍流之后，分离的流动不能立即重新连接到叶片表面。因此，可能发生短气泡的短气泡，并且涡流管具有较大的直径并覆盖叶片跨度的一部分。在这种情况下，涡旋配对不会发生，并且主要通过拍打现象来促进涡旋脱落过程。此外，动态模式分解（DMD）分析的结果显示了作为分离位置中不稳定的源的呼吸运动，其伴随着扑振现象。

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