Flow Analysis And Optimization Of A High Pressure Ratio Centrifugal Compressor

Centrifugal compressors are widely employed in middle and mall-sized aero-engines, micro turbines and turbochargers, and play a key role in national product and defense construction. In recent years, modern centrifugal compressors of high performance are required to meet the growing military and energy demands. Intensive researches on the complex flow structures in the centrifugal compressor channel are supposed to guide the design and development of centrifugal compressors with high pressure ratio, high efficiency and large mass flow. Detailed flow analysis and an optimal design of a high rotation speed and high pressure ratio centrifugal compressor are presented in this paper. Such a centrifugal compressor consists of a splitter impeller followed by two vaned diffusers, a radial one and an axial one. The main contents are listed as follows:1. Three-dimensional numerical analysis is carried out to investigate the flow field of the Eckardt impeller passage. The computed overall results and relative velocity/pressure distributions show good agreement with experimental tests originally conducted by Eckardt. And the predicted jet–wake structure in the impeller passage is also similar to the measured one.2. The detailed flow study in the impeller and the radial and axial diffusers is performed by the same calculation method at the design point. The results not only show that the loss productions mainly occur near the impeller shroud and near the hub and shroud of radial diffuser, but also explain the major factors affecting loss productions in such three regions.3. Jet-wake formation and development in the splitter impeller channel are interpreted and the wake is proved to be large-entropy and low-energy fluid gathering area. The effects of tip leakage flows and shock waves near leading edge on flow separation, circulation flow and wake are intensively investigated and the results indicate that tip leakage flows, shock waves, secondary vortex and their interactions dominate the internal flow structures, as well as the flow loss.4. A redesign of the impellor and the radial diffuser is undertaken without any change in meridional channel, based on the flow analysis of the original compressor. The optimized design turns out to be a great success with large aerodynamic performance development: the design mass flow increases by 8.2%, pressure ratio 5.0%and the isentropic efficiency 13.1%. The flow fluid in the previous three regions of high loss productions is greatly improved and the wake in the impeller channel is significantly weakened. In addition, the outlet flow of the impellor and the two diffusers becomes more uniform compared with the original one. The main and splitter blades loading distributions of the redesigned impeller are more rational and larger, while the radial diffuser obtains better pressure recovery and larger valid throat area.5. The significant influence of blade loading on tip leakage flow, the inducing impact of shock waves near the leading edge on the boundary layer separation as well as the impairing effects of strong leakage vortex on shock waves are deeply discussed by the comparison between the flow fields of the original compressors and the optimized one.