Effects of Labyrinth Seal Variation on Multistage Axial Turbine Flow
Effects of Labyrinth Seal Variation on Multistage Axial Turbine Flow
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DOI：
10.1115/gt2003-38270
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发表时间：
2003
期刊：
影响因子：
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通讯作者：
J. Schlienger;A. Pfau;A. Kalfas;R. Abhari
中科院分区：
文献类型：
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作者：
J. Schlienger;A. Pfau;A. Kalfas;R. Abhari
增加总涡轮机效率的需要总是重新设计涡轮机级的驱动力。特别是，端壁区域的迷宫泄漏流有助于增加总损失的产生。为了评估这一机制，详细研究了迷宫密封几何形状变化对叶片性能的影响。在两级低速涡轮机装置上对两种不同的围带密封几何形状进行了试验研究。密封几何形状在再入腔的尺寸和形状上不同。基线密封设计有一个大的矩形再入腔容积，以耗散密封间隙后加速泄漏流的动能。替代密封设计的再入腔体积在尺寸上减小，并且使用环形插入件将花键形轮廓添加到端壁。这种改进改变了泄漏射流的气体路径，并改变了下游叶片排上的冲角。在涡轮机级内的各个平面上使用最先进的气动和快速响应压力探头进行测量。结果发现，插入物改善了端壁处的流动分布均匀性。定子通道内的测量结果揭示了叶尖通道涡流在叶片吸力侧形成的起源，已经在定子通道的入口处。这一结果不符合经典的二次流理论，后者认为通道涡在静叶通道内从压力侧迁移到吸力侧。在流动示意图中描述了转子轮毂和定子尖端处的二次流通道涡流的起源和形成。对泄漏流与主流场相互作用区流向涡和切向涡的产生进行了研究和讨论。第二种密封配置的测得的多变涡轮机总效率相对于基线情况降低了0.3%。泄漏气体通道的再进入气流角的变化减小了转子轮毂上的负冲角，并增大了定子尖端前缘处的负冲角。在第二种试验情况下，较小的空腔体积使二次流和混合损失在轮毂处减少，在叶尖处增加。因此，小间隙和再进入腔中的插入物的组合显示出对总涡轮机效率没有有益的影响。
The need to increase overall turbine efficiency is always a driving force for redesigning a turbine stage. In particular, the labyrinth leakage flows in the endwall regions contribute to an increase of the overall loss generation. In order to asses this mechanism, a detailed study of the effects of labyrinth seal geometry variation on the blade performance is presented. Two different shroud seal geometries have been experimentally investigated in a two stage low speed turbine facility. The seal geometries differ in the size and shape of the re-entry cavity. The baseline seal is designed with a large rectangular re-entry cavity volume in order to dissipate the kinetic energy of the accelerated leakage flow after the seal gap. The re-entry cavity volume of the alternative seal design is reduced in size and a spline shaped contour is added to the endwall using annular inserts. This modification alters the gas path of the leakage jet and changes the incidence angles on the downstream blade rows. The measurements are performed with state of the art pneumatic and fast response pressure probes at various planes within the turbine stage. It is found that the inserts improved the flow profile uniformity at the endwalls. The measurements within the stator passage reveal the origin of the tip passage vortex formation at the blade suction side, already at the inlet to the stator passage. This result does not conform to the classical secondary flow theory, which suggests that the passage vortex migrates from the pressure to the suction side within the stator passage. The origin and formation of the secondary flow passage vortices at rotor hub and stator tip is described in a flow schematic. The generation of streamwise and tangential vorticity at the interaction area of leakage and main flow field also is studied and discussed. The measured overall polytropic turbine efficiency for the second seal configuration, relative to the baseline case, is reduced by 0.3%. The change in the re-entry flow angle of the leakage gas path reduces the negative incidence angle on the rotor hub and increases it at the stator tip leading edge. The secondary flow and mixing loss is reduced at the hub and increased at the tip in the second test case with the smaller cavity volume. Hence, the combination of small clearances and inserts in the re-entry cavities shows no beneficial effect on the overall turbine efficiency.Copyright © 2003 by ASME