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

• Applicant: Professor Dr.-Ing. Peter Jeschke
• Subject Area: Hydraulic and Turbo Engines and Piston Engines
• Term: from 2014 to 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 247436028

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.

• DFG Programme: Research Grants