Experimental investigation of the unsteady flow in a centrifugal compressor stage

Experimental investigation of the unsteady flow in the radial gap and vaned diffuser of a centrifugal compressor stage was presented in this paper. Detailed instantaneous flow has been measured at different measuring positions using a hot-wire anemometer with the phase-locked ensemble-averaged technique. Different unsteady sources are distinguished by circumferentially averaged technique and "inverse spectral analysis," and the effect of different unsteady sources on the flow field and mechanism of the unsteady interaction were analyzed and explored. Results show that the subharmonic of the impeller blade passing frequency (BPF) is the dominant frequency of the unsteady flow in radial gap. The repercussion effect of vaned diffuser is smaller than the unsteadiness induced by impeller, with the same order of the magnitude. The fluctuation of the uncertain unsteady dimensionless velocity in radial gap is larger than that it has in the vaned diffuser; the magnitude of its fluctuation in the vaned diffuser only differs slightly. The unsteady effect of the impeller becomes larger at the measuring point near the convexity surface of diffuser vane and the shroud. The repercussion effect of vaned diffuser is very sensitive to the location of diffuser vane in radial gap.