Abstract Purge air is injected in cavities at hub of axial turbines to prevent hot mainstream gas ingestion into interstage gaps. This process induces additional losses for the turbine due to an interaction between purge and mainstream flow. To deal with this issue, this paper is devoted to the study of a low speed linear cascade with an upstream cavity at a Reynolds number representative of a low-pressure turbine using RANS and LES with inlet turbulence injection. Different rim seal geometries and purge flow rates are studied. Details about numerical methods and comparison with experiments can be found in a companion paper. The analysis here focuses on the loss generation based on the description of the flow and influence of the turbulence introduced in the companion paper. The measure of loss is based on an exergy analysis (i.e. energy in the purpose to generate work) that extends a more common measure of loss in gas turbines, entropy. The loss analysis is led for a baseline case by splitting the simulation domain in the contributions related to the boundary layers over the wetted surfaces and the remaining domain (i.e. the complementary of boundary layers domains) where secondary flows and related loss are likely to occur. The analysis shows the strong contribution of the blade suction side boundary layer, secondary vortices in the passage and wake at the trailing edge on the loss generation. The study of different purge flow rates shows increased secondary vortices energy and subsequent loss for higher purge flow rates. The rim seal geometry with axial overlapping promotes a delayed development of secondary vortices in the passage compared to simple axial gap promoting lower levels of loss.

中文翻译：

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具有上游腔的线性级联中的流动描述第 2 部分：评估使用火用公式产生的损失（草案）

摘要 在轴流式涡轮轮毂的空腔中注入吹扫空气，以防止热主流气体吸入级间间隙。由于吹扫和主流流之间的相互作用，该过程导致涡轮机的额外损失。为了解决这个问题，本文致力于研究具有上游腔的低速线性叶栅，雷诺数代表低压涡轮，使用 RANS 和 LES 并带有入口湍流注入。研究了不同的边缘密封几何形状和吹扫流速。有关数值方法的详细信息以及与实验的比较，可以在配套论文中找到。此处的分析侧重于基于对随附论文中介绍的湍流的流动和影响的描述的损失生成。损失的测量基于火用分析（即 用于产生功的能量），它扩展了燃气轮机中更常见的损失度量，即熵。通过将模拟域划分为与湿润表面上的边界层相关的贡献以及可能发生二次流和相关损失的剩余域（即边界层域的补充），从而针对基线情况进行损失分析。分析表明，叶片吸力侧边界层、通道中的次级涡流和后缘尾流对损失产生的贡献很大。对不同吹扫流速的研究表明，更高的吹扫流速会增加二次涡流能量和随后的损失。