Numerical simulation on the unsteady flow in a centrifugal compressor is performed, and compared with the experimental data. The influence of the impeller-diffuser interaction on the flowfields is discussed, and the reasons for the losses are also explored. Results show that qualitative and quite fair quantitative agreements are achieved between the predicted and measured flowfields. The influence of the impeller wake on the convexity surface of diffuser is great. The potential repercussion of the diffuser on the suction surface of the impeller is much larger than on the pressure surface. Effect of the unsteady interaction is strongest in the radial gap. The unsteady flow itself may compensate for the loss generated in stage, and the stage efficiency is inversely proportional to the entropy production.
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