The two-zone model for the design and flow analysis for centrifugal compressor impellers, based on the observation of the jet-wake exit flow pattern, was initialized in 1980’s to avoid modeling each individual loss. The two-zone model introduced four model parameters, diffusion ratio MR2, secondary mass fraction Msec_M, and deviations for the primary and secondary zones, δp and δs. This paper aims at developing a methodology to extract values for the model parameters from CFD and test data. Four methods have been developed or assessed in this paper. The first method identifies the primary zone on the exit plane by setting a meridional velocity threshold; the regions with the meridional velocity higher than the pre-set value are the primary zone. We came to the conclusion this method is not consistent with the two-zone model. The other three methods deal with the selection of multiple solutions to the two-zone model parameters by introducing different assumptions to meet the impeller efficiency and total-to-total pressure ratio exactly. The last one, reduced model, is recommended. It sets the secondary deviation to 0 and decrements the primary static pressure from the exit total pressure until the second unique solution is reached. The impeller performance map indicates that this solution has the second highest diffusion ratio, and the primary deviation and secondary mass fraction are the second highest too. An example design shows that the diffusion ratio can be affected by the blade profiling, and the impeller performance can be referred from the primary deviation and secondary mass fraction when the diffusion ratios are similar for different designs.

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