Fundamental Numerical Investigation of Hub Treatments for Cantilevered Stators in Axial Compressors

未来喷气发动机的燃料消耗率的降低可以通过达到更高的压缩机压力比和更高的发动机热效率来实现。对于恒定数量的级，由于重量、长度和成本限制，直接结果是级的更高的空气动力学负载和压缩机的稳定操作范围的减小。压气机叶片与端壁径向间隙中的泄漏流对压气机的气动稳定性有重要影响。与转子的壳体处理类似，可以考虑使用旋转轮毂上的结构（称为轮毂处理）来减少悬臂式定子在稳定性、总压和效率损失方面的泄漏流的负面影响。对于单级低速压气机，轮毂处理仅在70年代/80年代进行了实验研究。证明了轮毂处理减少定子轮毂堵塞面积的能力，但没有考虑效率损失。该项目的目标是达到轮毂处理的知识水平，从而能够评估轮毂处理在真实的压缩机中的技术应用潜力。为了完成本项目，将研究轮毂处理的操作模式的基本影响以及轮毂处理与压缩机之间的相互作用。基于这些初步分析，必须开发有效的轮毂处理几何形状，提供有关轮毂处理应用潜力的准确信息。第二个调查领域是压缩机配置对轮毂处理功能的影响。有了这一点，可以更精确地确定潜在的应用范围，并找到在不同压气机上采用轮毂处理几何形状的准则。为了达到这些目标，将对一个两级亚音速高速压气机用DLR-TRACE程序进行几次非定常计算。与之前的几篇出版物不同的是，本项目仅关注设计非常基本的轮毂处理对定子流的局部影响，而不考虑效率损失，本项目将研究多级压气机中气动优化轮毂处理对总压比、稳定性和效率的影响。本文不仅研究了轮毂处理对处理后静叶排性能的影响，而且还研究了轮毂处理对后级和压气机性能的影响。

The reduction of the specific fuel consumption for future jet engines can be achieved by reaching higher pressure ratios of the compressor and therefore higher thermal efficiencies of the engine. For a constant number of stages due to weight, length and costs constraints direct consequences are a higher aerodynamic loading of the stages and a decrease of the stable operating range of the compressor. The leakage flows in the radial clearances between the blades and the endwalls have a major influence on the aerodynamic stability of a compressor. Similar to Casing Treatments for the rotors it is conceivable to reduce the negative effects of leakage flows for cantilevered stators in terms of stability-, total pressure- and efficiency losses, with the use of structures on the rotating hub, called Hub Treatments. Hub Treatments were only experimentally investigated in the 70s/80s for single stage low speed compressors. The capacity of Hub Treatment decreasing the blockage area at the stator hub was demonstrated, but without a consideration of the efficiency losses. There has since been no further development of this technology.The objective of this project is to reach a level of knowledge of Hub Treatments enabling to evaluate the potential of Hub Treatments for a technical application in a real compressor. To accomplish this project the basic effects of the mode of operation of Hub Treatments as well as the interaction between the Hub Treatment and the compressor will be investigated. Based on these first analyses, efficient Hub Treatment geometries have to be developed, providing accurate information about the potential of application of Hub Treatments. A second field of investigation will be the influence of the compressor configuration on the Hub Treatment functionality. With this aspect the potential range of application could be located more precisely and criteria for adapting Hub Treatment geometries at different compressors could be found. To reach these objectives, several unsteady calculations with the DLR-Code TRACE will be conducted for a two stages subsonic high speed compressor. In differentiation with the few previous publications, focusing only on the local influence of very basically designed Hub Treatments on the stator flow and without a consideration of efficiency penalties, in this project the impact of aerodynamically optimized Hub Treatments in a multistage compressor in terms of total pressure ratio, stability and efficiency will be investigated. Not only the influence of the Hub Treatments on the performance of the treated stator row but also on the performance of the following stage and the compressor will be studied.