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

降低未来喷气发动机的比油耗可以通过提高压气机的压比，从而提高发动机的热效率来实现。对于固定数量的级，由于重量、长度和成本的限制，直接后果是级的气动负荷更高，压缩机的稳定运行范围减小。叶片与端壁之间径向间隙的泄漏流动对压气机的气动稳定性有很大影响。与转子的机壳处理类似，可以想象，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动的负面影响。轮毂处理仅在70年代/80年代对单级低速压缩机进行了实验研究。在没有考虑效率损失的情况下，证明了轮毂处理能够减少定子轮毂处的堵塞面积。自那以后，这项技术一直没有进一步的发展。这个项目的目标是达到Hub处理的知识水平，从而能够评估Hub处理在真实压缩机中的技术应用的潜力。为了完成这个项目，我们将研究Hub处理方式的基本效果以及Hub处理方式与压缩机之间的相互作用。在这些初步分析的基础上，必须开发高效的Hub治疗几何结构，提供关于Hub治疗应用潜力的准确信息。第二个研究领域将是压缩机配置对轮毂处理功能的影响。在这一方面，可以更精确地定位潜在的应用范围，并可以找到在不同压缩机上适应Hub处理几何形状的标准。为了达到这些目标，将使用DLR-Code轨迹对一台两级亚音速高速压气机进行几次非定常计算。与以往的一些文献不同的是，本项目只关注基本设计的轮毂处理对静子流动的局部影响，而没有考虑效率损失，在本项目中，将从总压比、稳定性和效率的角度研究多级压气机的气动优化轮毂处理的影响。不仅要研究轮毂处理对处理后的定子排性能的影响，而且要研究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.