Effect of the Return-channel Geometric Parameters on the Performance of a Centrifugal Compressor with a High-flow Coefficient

The return-channel of a preceding stage in a multi-stage centrifugal compressor has a significant effect on the aerodynamic performance of the current and subsequent stages. However, due to the relatively complex nature of the return-channel configuration with many geometric parameters, no general design guidance is available in the literature. In this study, numerical methods are used to study the effects of different geometric parameters of a return-channel on the performance of a high-flow-coefficient centrifugal compressor. A multi-objective genetic algorithm is applied to optimize the return-channel. The effects of different geometric parameters on the performance are then studied using a sensitivity analysis method. Calculation results show that the residual vortex intensity at the outlet of the return-channel is affected by the geometric angles of the inlet and outlet of the return-channel blades. The flow uniformity at the stage outlet is primarily affected by the geometric angle of the blade outlet and the number of blades. The overall performance of the compressor stage is primarily affected by the geometric angle of the blade inlet and the lateral inclination angle of the cover plate. Calculation results for a two-stage compressor consisting of the optimized first stage and its following stage show that the outlet flow field of the first stage is more uniform than the original first stage. Additionally, at the design operating condition, the polytropic efficiency and pressure ratio of the entire unit increase by 1.07% and 4.07%, respectively. The polytropic efficiency and pressure ratio for the second stage increase by 2.34% and 3.51%, respectively. The impeller head coefficient increases by 7.33%. The theoretical analysis shows that for high-flow-coefficient centrifugal compressors, reducing the residual vortex intensity of the outlet flow field of the return-channel in a stage can significantly improve the off-design performance of the following stage.