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

降低未来喷气发动机的油耗可以通过提高压气机的压力比来实现，从而提高发动机的热效率。由于重量、长度和成本的限制，对于一定数量的级，直接的后果是级的气动载荷更高，压气机的稳定工作范围变小。叶片与端壁径向间隙内的泄漏流对压气机的气动稳定性有重要影响。与转子的套管处理类似，通过在旋转轮毂上使用称为轮毂处理的结构，可以在稳定性、总压和效率损失方面减少悬臂定子泄漏流的负面影响。仅在70 /80年代对单级低速压气机的轮毂处理进行了实验研究。在不考虑效率损失的情况下，证明了轮毂处理减少定子轮毂堵塞面积的能力。从那以后，这项技术就没有进一步的发展。该项目的目标是达到轮毂处理的知识水平，从而评估轮毂处理在实际压缩机中的技术应用潜力。为了完成这个项目，将研究轮毂处理方式的基本影响以及轮毂处理与压缩机之间的相互作用。在这些初步分析的基础上，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。第二个调查领域将是压缩机配置对轮毂处理功能的影响。有了这个方面，可以更精确地定位潜在的应用范围，并可以找到适用于不同压缩机的轮毂处理几何形状的标准。为了达到这些目标，将使用DLR-Code TRACE对两级亚音速高速压气机进行多次非定常计算。与之前的少数出版物不同，只关注非常基本设计的轮毂处理对定子流动的局部影响，而不考虑效率损失，在这个项目中，空气动力学优化的轮毂处理对多级压气机在总压比、稳定性和效率方面的影响将进行研究。本文不仅研究了轮毂处理对处理后的定子排性能的影响，还研究了轮毂处理对后续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.