Abstract
A high-load mixed-flow compressor with an extremely high inlet hub/tip ratio (0.889) is designed and analyzed for replacing the rear stages of a multistage high pressure axial compressor. The effects of blade number, splitter blades and dimensionless geometric parameters on the impeller performance are investigated by an improved loss model. A full-surface parameterization control method is adopted for blade optimizations of the mixed-flow impeller and the tandem stator. As a retrofit design of the multistage axial compressor, an unconventional type of axial-co-mixed-flow combined compressor scheme is proposed and discussed. Further, in order to minimize the axial dimension and maximize the load, this paper also proposed preliminary designs of the twin-stage mixed-flow compressor and the twin-stage counter-rotating mixed-flow compressor respectively equipped with the high hub/tip ratio mixed-flow compressor. The results indicate that the mixed-flow impeller configuration with 42 principal blades and splitter blades with a fifth of principal blade length has the maximum efficiency at design flow rate. Blade height/pitch ratio is a considerable parameter which demonstrates the interaction among hub/tip ratio, aspect ratio and solidity especially for high hub/tip ratio cascade designs. The mixed-flow compressor can greatly improve the load capacity of the high pressure compressor with slight impact on efficiency and surge margin. At low rotate speed, the mixed-flow impeller can maintain relatively high efficiency level and even carry a higher proportion of the load, while the tandem stator limits the overall efficiency improvement. Besides, structures with no return channel of the three unconventional combined compressors are beneficial to the reduction of dimension and cost, which shows the potential application prospects of high hub/tip ratio mixed-flow compressors.
